Download - in June 1973
THE GEOLOGY OP THE MERCUR GOLD CAMP, UTAH
b y
E d w i n M i c h a e l G u e n t h e r
A t h e s i s s u b m i t t e d t o t h e f a c u l t y o f t h e U n i v e r s i t y o f U t a h i n p a r t i a l f u l f i l l m e n t o f t h e r e q u i r e m e n t s
f o r t h e d e g r e e o f
M a s t e r o f S c i e n c e
i n
E c o n o m i c G e o l o g y
D e p a r t m e n t o f G e o l o g i c a l a n d G e o p h y s i c a l S c i e n c e s
U n i v e r s i t y o f U t a h
J u n e 1 9 7 3
THI! GEOLOGY OF THI! MERCUR GOLD CAMP. UTAH
by
Edwin Michael Guenther
A thesis s ubmitted to the faculty of the Universlty of Utah in partial fulfIllment of the requirements
for the degree of
Master of SOience
in
Economic Geology
Department of GeologIcal and Geophysical SCiences
Univers lty of Utah
June 1973
THE GEOLOGY OF THE MERCUR GOLD CAMP, UTAH
b y
E d w i n M i c h a e l G u e n t h e r
C o p y r i g h t © 1 9 7 3 E d w i n M i c h a e l G u e n t h e r
No p a r t o f t h i s b o o k m a y b e r e p r o d u c e d b y a n y m e c h a n i c a l , p h o t o g r a p h i c , o r e l e c t r o n i c p r o c e s s f o r p u b l i c o r p r i v a t e u s e w i t h o u t w r i t t e n p e r m i s s i o n f r o m t h e a u t h o r .
THE GEOLOGY OF THE MERCUR GOLD CAMP, UTAH
by
Edwin Michael Guenther
cOPyright~1973 Edwin Michael Guenther
No pa rt of this book may be reproduced by any mechan ical , photographic. or electronic process for public or priva te use without written permission from the autho r .
This thesis for the
Master of Scienoe Degree
by
EdN1n n.lchael Guenther
UNIVERSITY OF UTAH LIBRARIES
AC KNO iJU: LG 11E NT S
The fol1cHing thesis �ms originated, researched.
arid I=0.1d for by the author. 1'he author was hindered in
h1s re��8:'cl, effr)Tts by 'i:he lack of availabl1i ty of
instruments and the lack of funds.
I would lite to the.nk Dre M.L. Jensen, Dro .. T . H .
Goodwin, and Prof. M.P. Erickson for critically reading
the manuscript and making suggestions for improving it.
I would also like to thank Dr. M.L • . Jensen for letting
the author conduct som� sulfur isotope analyses and
making constructive criticisMS on ln�erpretatlon of the
sulfur isotope data. I would l�ke to thank the U.S.
Bureau of Mines for some carbon assays of samples. The
author who has worked with Great Northern Re sou rc e
Development would like to thank them for graclcusly
allowlL� the gratuitous publication of information
valued at $275.000 in this thesis at the University of
Utahe Pursuant to the wishes of Great Northern Resource
Development the author is unfortunately restl'1cted
from present1ng all observat1ons or conclusions that
were reached d.uring the investigation of th0 area.
,
CONTENTS
P a g e
A b s t r a c t . . . • . . • • .X
I n t r o d u c t i o n . . 1
A . G e o l o g i c M a p p i n g . . 2
L • I/O C L l u i O » » 4 « * t » f i « « » » « # » » » t « » i » » # # » « » » » « « e » » J ;
C . A n a l y t i c a l P r o c e d u r e s » , . 3
D . B r i e f H i s t o r y o f M i n i n g A c t i v i t i e s
i n t h e A r e a . 5
S t r a t i g r a p h y . *9
S t r u c t u r e
A , B r e c c i a P i p e s . , , . s . . l 6
B . J o i n t P a t t e r n s . . . . 1 9
I n t r u s i v e H o c k s • . . . . . 2 4
A . K e r s a n t i t e . . . . . . . . . . . . . . . . . . 2 4
B . B i r d ' s - e y e P o r p h y r y . . . . . . 2 4
C , E a g l e H i l l R h y o l i t e 0 2 5
1 . S t r u c t u r a l R e l a t i o n s • 2 6
2 . P e t r o l o g y , 2 8
A l t e r a t i o n o f t h e S e d i m e n t a r y R o c k s . . . . . . . . . . . . . . 3 1
A . S i 1 v e r L e d g e • « • • • • • • • • . . . 3 2
B . G o l d L e d g e . 3 6
C • W e a t h e r i n g * . . . . • • • • • • • • • . • • • • . . . . • 4 0
CONTENTS
Page
A bs tr9.c t •. Co •••• A ••••••••••••••••••• ., •••••••••• CII .... x
IntroGuct:lr.n. 1 _ • • • • • • • • • • • • • • • • • e , • • • • • • • • • ~ • • • e ~
A. Geologie • eo. • • • ~ • • ~ • • • ~ • • • • • • ~ • • .2
B. I/oc·9.tlon ••••••••••••• ~ •••••••••• " ••••••••• 3
c. Analytje.al Procedures. . . . . ~ . . . . . . . . . . . . . ~ .3
D. Brief History of Mining Activities
in the i_rea ............•.•....•..........• 5
Stratigra.phy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . •• 9
Structure ••.••••••••••••••••••• < •••••••••••• ~ •••• 12
Breccia Pipes •• . . . . . . . . . . . . . . . . . . . . . . . ~ . .16
D. Joint Patterns. . . . . . . . . . . . . . . . . . . . . . . . . . • 19
Intrusiva Rocks ••• • • • • • • • • • • • ~ • • • • • • • • c • • • • • • • • • • 24
Kersantite • • • • • • • • • • • • ~ • • • • • • • • • • • Q - • • • • .. 24
B. Bird's-eye Porphyry. . ~ . . . . . . . . . . . . . . . . ~ . .. 24
c. Eagle Hill Rhyolite ••••• · . ~ . . . . . . . . . . ~ ~ . 1 • f)truc tural Rela.tions. · . . . . . ~ . . . . . . . . . • 26
2" Pe t 1'0 loe;y •••••••••••• · . . . . . . . . . . . . . . . • 28
Altera.tion of the Sedimentary Rocks. • • • • • • • • • • • 0 • )1
A. Ledge. o « 0 • • • • • • • • • • • • 0 • • • • • • • • • • • .)2
B. Gold Ledge. e _ • • • • • • • • • • • • • • • • • • • ~ • • • • • • • • )6
c. • • ~ • • • • • • • ~ • • • ~ c ~ ~ ~ • • • • _ • . . • 40
P a g e
A l t e r a t i o n o f t h e E a g l e H i l l I n t r u s i v e • . . , . . 4 3
T h e G o l d D s p o s i t s . . . . . . . 4 8
E l e m e n t a l A n a l y s e s o f R o c k S a m p l e s 5 ^
I m p l i c a t i o n s o f C a r b o n a n d O r g a n i c C o m p o u n d s . . . . . 5 6
S u l f u r I s o t o p i c D a t a . . « . > . » • • • . • • • • • • • • • • . 6 3
S u m m a r y a n d R e c o m m e n d a t i o n s , „ . * . . • • 7 3
S e l e c t e d R e f e r e n c e s • • • . • • • • • • • • • • • • • • • • • . • » 7 6
V i t a , . . . . 8 0
v i
PClge
.t.,lt;er::;.tion of the E~Lc;le lUll Intrusi~e •....... ... 4)
Tt~·: Golfl :;3r.l;slts ................... oe~ •• c ••••• 9 ••• 48
Elemental Analyses of Reck Samples ••• o.~ ••• # ••••• 52
IL.pllcations of C8:z.'bon Si.i1G. Organic Co~poun~3 ..... 056
StL!.fur Da.ta- ••• Oq ....
Su:nmary and Reco7!llnend8tions.
• • • • • • h • • • • • • 0 ~ • ~ • • ... 63
.73 ~ . ~ . • • . . . . . . . . . . . .6. Selected References •••••••••••••••••••••••••••••• 76
V 1 ta .... e ........ It •• f' •• 0, •••• & • II , • o!# •••••••• ~ ....... 19 .80
vi
ILLUSTRATIONS
P a g e
F i g u r e 1 . — I n d e x m a p s h o w i n g l o c a t i o n o f
l i s j u i i r j U t a n • • • . • • . • • • . . * • . • • • . • . . , • - • - • • . * • #4
2 , — V i e w o f H e r c u r f r o m E a g l e H i l l . . . . . . . . . 6
3 . . — V i « w o f M e r c u r f r o m S u n r i s e H i l l . , 6
4 . — G e o l o g i c m a p o f M e r c u r , U t a h . . . . 1 3
5 . — C o l l a p s e b r e c c i a G e y s e r - M a r i o n m i n e . , , 1 6
6 , — - S a c r a m e n t o m i n e v i e w . . . . . . . 1 ?
? . — C l o s e - u p o f b r e c c i a . . « , . . . . 1 ?
8 , - - C o n t o u r d i a g r a m o f j o i n t d i s t r i b u t i o n , 2 0
9 . — P l o t o f s t r i k e d i r e c t i o n s * * . , , 2 1
1 0 , — P l o t o f f a u l t s t r i k e d i r e c t i o n s 2 1
1 1 * — I n d e x m a p o f i g n e o u s r o c k s l o c a t i o n . • . 2 5
1 2 . - ~ C l o s e » u p o f M e r c u r j a s p e r o i d t y p e s . . . . 3 4
1 3 . — P h o t o m i c r o g r a p h o f a n h e d r a l j a s p e r o i d , 3 5
1 4 . - - P h o t o m i c r o g r a p h o f t y p i c a l j a s p e r o l d . . 3 5
1 5 . — P h o t o m i c r o g r a p h o f g o l d o r e s e q u e n c e . . 3 9
1 6 . — P h o t o s h o w i n g r e l a t i o n s h i p s b e t w e e n
w e a t h e r e d a n d u n w e a t h e r e d o r e . , . » . , « , . , 4 2
ILLUSTaAT IO~JS
P.s.ge
Figure 1.--In1ez ~ap showing lecation of
1-19j'·8ur:- Uta:l •. ., ........ o. $. (t a" ••• & W 9 •••• 4
2o--View of Mercur from Eagle Hlll ••••••••• 6
3. --V_,~.··.··.T of· ~.A_rcu·.-.~. f-o~ Sun~{~· q4J~1 6 _ • 1 ~ ..1.. ~.AU .... ..4. .. )0 '_ ...... ..l.. ~. .., •••••
4.--Geologlc map of Mercur. Utah •••••••••• 13
5.--Collapsb breccia Geyder-Marion mine ••• 16
6 .. --Sacr&mento mine v~.e~l ••••••••••••••••• e17
7c--Close~up of brece1a •••••••••••••• 9 •••• 17
8.--Contour diagram of Joint distribution.20
9.--Plot of strike dlrec~~ons ••••• Q ••• ~.~.21
10.--Plot of fault strike d1rections ••••••• 21
11~ao~Index map of 19neous rocks lccation .... 25
12.--Close-up of Nereur j3spero1d types~ ••• 34
13~--Photo~lcrograph of anhedral jasperoid.35
14.--Photomlcrograph of typ1cal jasperoid •• 35
15.--Photomlcrcgraph of gold ore sequence •• 39
l6.--·Photo showJ.ng relationshtps between
weathered and unweathered ore ••••••••• 42
P a g e
F i g u r e 1 9 . - - I n f r a r e d s p e c t r a o f NaOH o r g a n i c
e x t r a c t i o n s * • . . . . . . . . . . . • . 6 0
2 0 I n f r a r e d s p e c t r a o f NH^Ac o r g a n i c
e x t r a c t i o n s - 6 1
2 1 . — M a p s h o w i n g s u l f u r i s o t o p e s a m p l e
c o l l e c t i o n s i t e s , t . . . . . . . . 6 5
2 2 . — R e a c t i o n s i n a f u m a r o l i c c o n d u i t . . . . * 6 8
v i i l
Page
Fi gure 19 .--Infra r ed ::;pectra of taOH organ ic
extract1ons • • •• • ••••••• ~ • • • c •••• • •• •• 60
20 .--Infrared spect r a of NH4AC organic
ex t r o.c ti ons •. •••• •• ••••.••• • •••••• ••• 61
21. --Nap showing s ulfur i sotope s umple
collec t1on s1tes • . •• •• •• •• •• 8 • • ••• • •• 6S
22.--Reac tions in a fumarollc conduit ... . .. 68
"1111
TABLES
P a g e
1 . A t o m i c a b s o r p t i o n v a l u e s 4 5
2 . Q u a l i t a t i v e e m i s s i o n s p e c t r o g r a p h s a n a l y s e s . . 5 3
3 * S e m i - q u a n t i t a t i v e e m i s s i o n s p e c t r o g r a p h l c
a n a l y s e s . . A . . . . . . . . . . . . . . . * . . . . . . . . . * . . * . . » . . . » 5^*
4 . S u l f u r i s o t o p i c d a t a . . 6 6
»
TAELES
Page
1. At o51ic llbso rptlon val ues •• • ••••••••••••••••••• 45
2. Qualitative em i ssion spectrogr aphic ar~lyses •• 5J
3. Seml -qu~ntltatlve emission spectrog raphic
a nalyses ......... .. .... . ~ .... .. . ... ... 0 " ..................... . 54
4. Sulfur i s otopic data •••••••. • •• •• •••••••• • •••• 66
ABSTRACT
The g o l d d e p o s i t s a t M e r c u r , U t a h , a r e t y p i c a l
e p i t h e r m a l d e p o s i t s . O r e d e p o s i t i o n p r o b a b l y o c c u r r e d
a t d e p t h s o f 1 , Q 0 0 f e e t o r l e s s w i t h l o w t e m p e r a t u r e s O Q
r a n g i n g f r o m 2 0 0 + t o 1 0 0 0 , T h e m o s t p r o m i n e n t t y p e
o f m e t a s o m a t i s m a s s o c i a t e d w i t h t h e g o l d d e p o s i t s i s
s i l i c i f i c a t l o n a c c o m p a n i e d b y s e r i c i t i z a t l o n . S u l f u r
i s o t o p i c d a t a f o r t h e d e p o s i t s h a v e a m e a n v a l u e o f
o f + 7 . 9 p e r m i l a n d h a v e a s p r e a d o f v a l u e s w h i c h c o r r e l a t e
w i t h s u l f u r i s o t o p i c d a t a f o r h o t s p r i n g d e p o s i t s .
M e r c u r i s o f i n t e r e s t s t r u c t u r a l l y b e c a u s e o f t h e
o c c u r r e n c e o f t w o b r e c c e a p i p e s b e l i e v e d t o h a v e
o r i g i n a t e d a s e x p l o s i v e e v e n t s .
O r g a n i c e x t r a c t i o n a n d a n a l y s i s b y i n f r a r e d
s p e c t r o s c o p y o f c a r b o n - r i c h s a m p l e s f r o m M e r c u r , U t a h ,
a n d C a r l i n a n d G e t c h e l l M i n e , N e v a d a , s h o w t h e p r e s e n c e
o f a l k a n e a n d c a r b o n y l g r o u p s . T h e c a r b o n p r e s e n t i n
a l l t h r e e a r e a s i s b e l i e v e d t o b e t h e r e s u l t o f
r e d u c t i o n o f h y d r o c a r b o n s t o c a r b o n b y t h e c h e m i c a l
c o n d i t i o n s t h a t o n c e e x i s t e d i n t h e h y d r o t h e r m a l a r e a s .
'\
ABSTRACT
The gold teposits at M~rcur, Utah, ar~ typical
epithermal deposits. Ore deposition proba"oly occurred
at d,..;pths 0;.' 1.000 feet or less with low terr:p~ratures
.... 0 0 r ranging fran ~OO + to 100 C. 'he most prominent type
of metasomatism associated with the gold deposits 1s
siliclfic~tion accompanied by sericitization. Sulfur
isotopic d9.t-a fOT the deposits ha.ve a. mean value of <5 s31•
of +7.9 permil and have a spread of values which cOl'relates
with sulfv.r isotopic data for hct; spring deposits.
lJlercur 1s of interest struc{;urally b~cause of the
occurre!me of two breccea pipsE believed to have
originated as explosive events.
Org~nic extraction a.nd analysis by infra.red
spectroscopy of carbon-rich samples from Mercur, Utah,
and Carlirl and Getchell Mine, Nevada, shDw the preset'!ce
of alkane and carbonyl groups. The carbon present in
all three areas is believed to be the result of
reduction of hydrocarbons to carbon by the chemical
conditions that once existed in the hydrot.hermaJ. areas.
INTRODUCTION
T h e f i r s t c o m p r e h e n s i v e w o r k o n t h e M e r c u r a r e a
w a s d o n e b y S p u r r ( 1 8 9 4 - 9 5 ) w h e n t h e d i s t r i c t w a s s t i l l
i n i t s i n f a n c y a s a g o l d p r o d u c e r . T h e a u t h o r i s
i n d e b t e d t o h i s d e s c r i p t i o n s o f t h e m i n e l o c a t i o n s ,
w o r k i n g s , a n d g e o l o g i c s e t t i n g s — e s p e c i a l l y r e g a r d i n g
t h e p r e s e n c e o f c a r b o n , S p u r r a l s o g a v e t h e f i r s t
d e t a i l e d a c c o u n t o f t h e h y d r o t h e r m a l a l t e r a t i o n o f t h e
b e d r o c k a s s o c i a t e d w i t h t h e d e p o s i t s . Some o f h i s
i n t e r p r e t a t i o n s a s t o a l t e r a t i o n w e r e l a t e r d i s c r e d i t e d
b y B u t l e r ( 1 9 2 0 , p , 3 9 0 ) who f o u n d t h a t w h a t S p u r r h a d
c a l l e d a l t e r e d i n t r u s i v e s i l l s w e r e i n r e a l i t y a l t e r e d
l i m e s t o n e o r s h a l e l a y e r s .
T h e f i r s t c o m p r e h e n s i v e s t u d y o f t h e g e o l o g y
a n d o r e d e p o s i t s o f t h e s o u t h e r n O q u i r r h M o u n t a i n s w a s
d o n e b y G i l l u l y ( 1 9 3 2 ) d u r i n g t h e s u m m e r s o f 1 9 2 6
a n d 1 9 2 7 , b u t h e d i d n o t d o a d e t a i l e d s t u d y o f t h e
o r e d e p o s i t s o f t h e M e r c u r a r e a b e c a u s e h e s t a t e s
t h a t t h e m i n e s w e r e i n a c c e s s i b l e a t t h e t i m e o f h i s
I n v e s t i g a t i o n . H i s d i s c u s s i o n o f t h e a l t e r a t i o n o f t h e
i g n e o u s r o c k s a n d o f t h e s e d i m e n t a r y r o c k s o f t h e a r e a
h a s b e e n m o s t h e l p f u l t o t h e a u t h o r i n d e l i n e a t i n g
w h a t h a d b e e n d o n e i n t h i s a r e a .
R i g b y a n d B i s s e l l ( 1 9 5 9 ) o f B r i g h a m Y o u n g U n i v e r s i t y
w e r e t h e n e x t i n v e s t i g a t o r s t o c o n d u c t r e s e a r c h i n t h e
INTRODUCTION
The first comprehensive work on the Mercur area
was done by Spurr (1894-95) when the district was still
in its infancy as a gold producer. The author is
indebted to his descriptions of the mine locations,
workings, and ~eologic settings--especially reg~rding
the presence of carbon. Spurr also gave the first
detailed account of the hydrothermal alteration of the
bedrock associated with the deposits. Some of his
interpretations as to alteration were later discredited
by Butler (1920, p. 390) who found that what Spurr had
called altered intrusive sills were in reality altered
limestone or shale layers.
The first comprehensive study of the geology
and ore deposits of the southern Oquirrh Mountains was
done by Gilluly (1932) during the summers of 1926
qnd 1927. but he did not do a detailed study of the
ore deposits of the Mercur area because he states
that the mines were inaccessible at the time of his
investigation. His discussion of the alteration of the
igneous rocks and of the sedimentary rocks of the area
has been most helpful to the author in delineating
what had been done in this area.
Rigby and Bissell (1959) of Brigham Young University
were the next investigators to conduct research in the
2
a r e a . I n 1 9 5 5 • t h e y s u p e r v i s e d a g e o l o g i c s u m m e r f i e l d
c a m p d u r i n g w h i c h t h e a r e a w a s r e m a p p e d a t a s c a l e o f
1 : 1 2 , 0 0 0 f o r t h e f i r s t t i m e s i n c e G i l l u l y ( 1 9 3 2 ) h a d
m a p p e d t h e a r e a . T h e l a t t e r 1 s m a p w a s m a d e b y p l a n e t a b l e
a n d o p e n - s i g h t a l i d a d e o n a t o p o g r a p h i c b - i s e w i t h a
s c a l e o f 1 : 3 1 , 2 5 0 ( G i l l u l y , 1 9 3 2 , p . 4 ) . T h e a u t h o r ,
d u r i n g a r e c o n n a i s a n c e e x a m i n a t i o n o f t h e a r e a i n t h e
s u m m e r o f 1 9 7 1 » o b s e r v e d s u f f i c i e n t p r e v i o u s l y o v e r l o o k e d
s t r u c t u r a l f e a t u r e s , a l t e r a t i o n p a t t e r n s , a n d s t r a t i g r a p h i c
f i e l d r e l a t i o n s w h i c h , b e c a u s e o f t h e i r i m p o r t a n c e t o t h e
e c o n o m i c g e o l o g y o f t h e a r e a , l e d t h e a u t h o r t o u n d e r t a k e
t h i s s t u d y .
G e o l o g i c M a p p i n g
G e o l o g i c m a p p i n g o f t h e M e r c u r a r e a a t a s c a l e
o f 1 : 6 , 0 0 0 w a s u n d e r t a k e n b y t h e a u t h o r d u r i n g t h e
s u m m e r 1 9 7 2 . T h e g e o l o g y w a s p l o t t e d on. a t o p o g r a p h i c
b a s e m a p w h i c h w a s m a d e b y p h o t o g r a p h i c a l l y e n l a r g i n g
t h e U . S . G e o l o g i c a l S u r v e y ' s M e r c u r , U t a h , 1 5 m i n u t e
t o p o g r a p h i c q u a d r a n g l e . A e r i a l p h o t o g r a p h s w e r e u s e d f o r
p r e l i m i n a r y s t u d y o f t h e a r e a . T h e s c a l e o f t h e i n c l u d e d
g e o l o g i c m a p ( F i g . 4 ) w a s d e c r e a s e d f r o m t h e o r i g i n a l
t o r e d u c e t h e c o s t o f d u p l i c a t i o n ,
S i l i c i f i c a t i o n i n t h e g o l d o r e s e q u e n c e w a s n o t
m a p p e d b e c a u s e o f t h e d i f f i c u l t y o f t r a c i n g t h e
2
~rea. In 1955. they supervised a geologie summer field
c~mp during which the area w~s remapped at a scale of
1:12.000 for the first time since Gilluly (1932) had
mapped the area. The latter's map was made by plane table
qnd open-sight alidade on a topographic b'lse wi th A
scale of 1:31.250 (Gilluly. 1932. p. 4). The author,
during a reconnaisance examination of the ~rea in the
summer of 1971. observed sufficient previously overlooked
structural features, alteration patterns, and stratigraphic
field relations which, because of their importance to the
economic geology of the area. led the author to undertake
this study.
Geologic Mapping
Geologic mapping of the Mercur area at a scale
of 1:6,000 was undertaken by the author during the
summer 1972. The geology was plotted on a topographic
base map which was made by photographically enlarging
the U.S. Geological Survey's Mercur, Ut~h. 15 minute
topographic quadrangle.
preliminary study of the
Aerial photographs were used for
area. The scale of the included
geologic map (Fig. 4) was decreased from the original
to reduce the cost of duplication.
Silicification in the gold ore sequence was not
mapped because of the difficulty of tracing the
3
a l t e r a t i o n z o n e s , J a s p e r o i d w a s m a p p e d b e c a u s e i t
r e p r e s e n t e d e a s i l y m a p a b l e a r e a s .
L o c a t i o n
M e r c u r , U t a h , i s l o c a t e d a t t h e h e a d o f M e r c u r
C a n y o n ( f o r m e r l y L e w i s t o n C a n y o n ) i n t h e s o u t h e r n
p a r t o f t h e O q u i r r h M o u n t a i n s a b o u t 7 0 m i l e s b y r o a d
s o u t h e a s t o f S a l t L a k e C i t y ( F i g . 1 ) .
T h e t e r r a i n o f t h e s u r r o u n d i n g h i l l s i s o n e o f
m o d e r a t e r e l i e f . T h e m a x i m u m r e l i e f b e t w e e n t h e
g h o s t t o w n o f M e r c u r a n d E a g l e H i l l i s a b o u t 1 , 3 0 0 f e e t .
A n a l y t i c a l P r o c e d u r e s
T h e a u t h o r , d u r i n g t h e c o u r s e o f t h e p r e s e n t
i n v e s t i g a t i o n , u s e d s e v e r a l i n s t r u m e n t a l t e c h n i q u e s
t o g a i n i n f o r m a t i o n n e e d e d t o s o l v e t h e g e o l o g i c p r o b l e m s .
X - r a y d i f f r a c t i o n a n d f l u o r e s c e n c e t e c h n i q u e s w e r e u s e d
f o r m i n e r a l d e t e r m i n a t i o n s . A t o m i c a b s o r p t i o n a n d
e m i s s i o n s p e c t r o s c o p y t e c h n i q u e s w e r e u s e d f o r e l e m e n t a l
d e t e r m i n a t i o n s . I n f r a r e d s p e c t r o s c o p i c a n d g a s
c h r o m a t o g r a p h i c t e c h n i q u e s w e r e a p p l i e d t o t h e p r o b l e m
o f o r g a n i c i d e n t i f i c a t i o n o f c a r b o n a c e o u s s a m p l e s .
S e v e r a l p o l i s h e d s e c t i o n s w e r e p r e p a r e d f o r s t u d y
o f t h e o p a q u e m i n e r a l s o f t h e o r e s e q u e n c e . T h i n s e c t i o n
s t u d i e s w e r e u n d e r t a k e n t o e x a m i n e t h e m i n e r a l s u i t e
p r e s e n t , f o r r o c k i d e n t i f i c a t i o n , a n d f o r s t u d y o f
alteration zones. Jasperoid was mapped because it
represented easily mapable areas.
Location
Mercur, Utah, is loc~ted at the head of Mercur
Canyon (formerly Lewiston Canyon) in the southern
part of the Oquirrh Mountains about 70 miles by road
southe'-lst of Salt Lake City (Fig. 1).
The terrain of the surrounding hills is one of
moderate relief. The maximum relief between the
)
ghost town of Mercur and Eagle Hill is about 1,)00 feet.
Analytical Procedures
The author, during the course of the present
investigation, used several instrumental techniques
to gain information needed to solve the geologic problems.
X-ray diffraction and fluorescence techniques were used
for mineral determinations. Atomic absorption and
emission spectroscopy techniques were used for elemental
determinations. Infrared spectroscopic and gas
chromatographic techniques were applied to the problem
of organic identification of carbonaceous samples.
Several polished sections were prepared for study
of the opaque minerals of the ore sequence. Thin section
studies were undertaken to examine the mineral suite
present, for rock identification, and for study of
4
Great Salt Lake U T A H
Scale 0 50 miles I—II—I K3
UTAH
. Solt Lake City
O---:=-:::::::;::;===.-, , \
I
r •
, \
Tooel. Co. \
Stockton
rJ
~~H L.\e :0. , )
Figure 1. Index map s howing the locatlon of Mercur . Ut a h. (small bar 1n inset re pre s ent s one mile)
4
5
m i n e r a l h a b i t s ( t e x t u r e s ) .
B r i e f H i s t o r y o f M i n i n g A c t i v i t i e s i n t h e A r e a
S i l v e r w a s d i s c o v e r e d i n I 8 6 9 a t L e w i s t o n , t h e f o r m e r
n a m e o f M e r c u r , b u t t h e o r e p o c k e t s p r o v e d s p o t t y a n d
w e r e s o o n e x h a u s t e d . T h e d i s t r i c t w a s o r g a n i z e d o n A p r i l
1 6 , 1 8 7 0 , a s t h e Camp F l o y d d i s t r i c t . T h e e a r l y m i n e s
i n c l u d e d t h e C a r r i e S t e e l e , S p a r r o w h a w k , L a s t C h a n c e ,
S i l v e r C l o u d , M a r i o n , a n d M o r m o n C h i e f w i t h t h e C a r r i e
S t e e l e a n d S p a r r o w h a w k m i n e s b e i n g t h e b i g g e s t p r o d u c e r s .
T h e l o c a t i o n o f t h e S p a r r o w h a w k i s s h o w n o n F i g u r e s 2
a n d J, A f t e r s e v e r a l y e a r s o f s i l v e r p r o d u c t i o n , t h e
t o w n w a s d e s e r t e d i n 1 8 8 0 a n d t h e n a m e o f L e w i s t o n w a s
g i v e n t o a n o t h e r t o w n i n C a c h e C o u n t y , U t a h .
I n 1 8 7 9 » A r i e P i n e d o r e n a m e d t h e s i t e M e r c u r a f t e r
h i s d i s c o v e r y o f m e r c u r y i n t h e a r e a , b u t h i s d i s c o v e r y
D r o v e d u n e c o n o m i c a l . W i t h t h e d i s c o v e r y o f g o l d i n t h e
a r e a i n 1 8 8 3 » p r o s p e c t i n g w a s a g a i n r e s u m e d b u t t h e p o o r
e x t r a c t i o n o f t h e g o l d f r o m t h e m i l l e d o r e w a s d i s c o u r a g i n g .
I n I 8 9 O , a c a r l o a d o f o r e w a s s e n t t o D e n v e r , C o l o r a d o ,
f o r t r e a t m e n t b y t h e n e w l y d e v e l o p e d M c A r t h u r - F o r r e s t
c y a n i d e p r o c e s s . T h e r e s u l t s f r o m t h e t e s t p r o v e d
e n c o u r a g i n g a n d t h e f i r s t c y a n i d e p l a n t i n t h e U n i t e d
S t a t e s w a s c o n s t r u c t e d a t M a n n i n g , U t a h , n e a r M e r c u r
( G i l l u l y , 1 9 3 2 , p . 1 2 3 ) .
5
miner81 hqbits (textures).
Brief History of Mining Activities in the Area
Silver W<3.S d.iscovered in 1869 at Lewiston, the for-,er
name of Mercur, but the ore pockets proved spotty and
were soon exhausted. The district was organized on April
16, 1870, as the Camp Floyd district. The early mines
included the Carrie Steele. Sparrowhawk, Last Chance,
Silver Cloud, Marion. and Mormon Chief with the Carrie
Steele and Sparrowhawk mines being the biggest producers.
The loc<3.tion of the Sparrowhawk is shown on Figures 2
and 3. After several years of silver production, the
town was deserted in 1880 and the name of Lewiston was
given to another town in Cache County, Utah.
In 1879, Arie Pinedo renamed the site Mercur after
his discovery of mercury in the area. but his discovery
nroved uneconomical. With the discovery of gold in the
area in 1883. prospecting was again resumed but the poor
extraction of the gold from the milled ore was discouraging.
In 1890. a carload of ore was sent to Denver, Colorado,
for tre~tment by the newly developed McArthur-Forrest
cyanide process. The results from the test proved
encouraging and the first cyanide plant in the United
States was constructed at Manning, Utah, near Mercur
(Gilluly, 1932. p. 123).
6
F i g u r e 2 . P a n o r a m i c v i e w o f M e r c u r , U t a h f r o m E a g l e H i l l . ( 1 ) M e r c u r H i l l , ( 2 ) S p a r r o w h a w k m i n e , ( 3 ) G e y s e r -M a r i o n m i n e , ( 4 ) B r i c k y a r d m i n e , ( 5 ) I n g e r s o l l s h a f t , ( 6 ) G o l d e n G a t e m i n e a n d m i l l s i t e , ( ? ) E d ' s H i l l , ( 8 ) L e w i s t o n P e a k
( 1 ) S p a r r o w h a w k m i n e , ( 2 ) I n g e r s o l l s h a f t , ( 3 ) G e y s e r - M a r i o n m i n e , ( 4 ) M e r c u r H i l l m i n e , ( 5 ) G o l d e n G a t e m i n e a n d m i l l s i t e , ( 6 ) E d ' s H i l l
6
Figure 2. Panoramic view of Mercur, Utah from Eagle Hlli. (1) Mercur H1ll, (2) Sparrowhawk m1ne, () GeyserMarlon m1ne, (~) Br1ckyard m1ne, (5) Ingersoll shaft, 6) Golden Gate m1ne and m1ll s1te, (7) Ed's H Lew1ston Peak
Pigure). Panoramic view of Mercur. Hlli. (1) Sparrowhawk m1ne, (2) Ingersoll shaft, (3) Geyser- Marlon mine, (4) Mercur Hill mine, ( 5) Golden Gate m1ne and m1ll s1te, (6) Ed's H1ll
7
T h e m a i n g o l d p r o d u c t i o n i n t h e d i s t r i c t c a m e f r o m
o n l y a f e w ^ i n e s . ( G e y s e r - M a r i o n , S a c r a m e n t o , M e r c u r
H i l l , B r i c k y a r d , a n d G o l d e n G a t e ) a l l n e a r t h e t o w n
o f M e r c u r , T h e G e y s e r a n d M a r i o n m i n e s w e r e J o i n e d i n
1 8 9 7 t o f o r m t h e G e y s e r - M a r i o n m i n e . T h e G o l d e n G a t e
m i l l w a s c o n s t r u c t e d i n I 8 9 8 a n d i n 1 8 9 9 t h e M e r c u r
M i n e s G o . c o m b i n e d w i t h t h e M e r c u r G o l d M i n i n g a n d
M i l l i n g C o . w h i c h r e s u l t e d i n t h e o r e s f r o m t h e M e r c u r
H i l l a n d t h e G o l d e n G a t e m i n e s b e i n g m i l l e d a t t h e G o l d e n
G a t e m i l l . I n 1 9 1 3 , t h e C o n s o l i d a t e d M e r c u r G o l d M i n e s
C o . , w h i c h a c c o u n t e d f o r m o s t o f t h e g o l d p r o d u c t i o n i n
t h e d i s t r i c t , c e a s e d m i n i n g o p e r a t i o n s b e c a u s e o f t h e
f a i l i n g o r e g r a d e . T h e t o w n o f M e r c u r s o o n d w i n d l e d a l t h o u g h
t h e G e y s e r - M a r i o n a n d S a c r a m e n t o m i n e s o p e r a t e d f o r s e v e r a l
y e a r s t h e r e a f t e r ( F r a n k l i n a n d M i l l e r , 1 9 3 8 , p . 2 - 4 ) .
T h e S a c r a m e n t o m i n e w a s t h e o n l y m i n e i n t h e a r e a t o y i e l d
c i n n a b a r a n d g o l d a n d p r o d u c e d a r e p o r t e d 3 # 5 3 8 f l a s k s
o f m e r c u r y ( H o w a r d , 1 9 * 3 . P» 1 3 ) -
I n 1 9 3 3 t h e S n y d e r M i n e s C o . b e g a n w o r k i n g t h e
t a i l i n g s d u m p s t o t h e s o u t h o f M e r c u r a t t h e o l d t o w n
s i t e o f M a n n i n g . A t a b o u t t h e s a m e t i m e , t h e m i n e s
a t M e r c u r w e r e r e - o p e n e d b y t h e S n y d e r M i n e s C o . w i t h
t h e o r e s f i r s t b e i n g s h i p p e d t o M a n n i n g f o r m i l l i n g .
L a t e r , i n 1 9 3 7 , t h e m i l l i n g o p e r a t i o n s w e r e s h i f t e d t o
M e r c u r ( F r a n k l i n a n d M i l l e r , 1 9 3 8 , p . 5 ) . T h e y m i n e d t h e
e a s i l y w o r k a b l e l o w - g r a d e s u r f a c e o r e s i n q u a r r i e s o n
?
The main ~old production in the district came from
only a few~ines, (Geyser-Marion, Sacramento, Mercur
Hill, Brickyqrd, and Golden Gate) all neqr the town
of Mercur. The Geyser and Marion mines were joined in
1897 to form the Geyser-Marion mine. The Go1den Gate
mill was constructed in 1898 and in 1899 the Mercur
Mines Co. combined with the Mercur Gold Mining qnd
Milling Co. which resulted in the ores from the Mercur
Hill and the Golden Gate mines being milled at the Golden
Gate mill. In 1913, the Consolidated Mercur Gold Mines
Co., which accounted for most of the gold production in
the district, ceased mining operations because of the
fqiling ore grade. The town of Mercur soon dwindled although
the Geyser-Marinn and Sacramento mines operated for several
yeqrs thereafter (Franklin and Miller, 1938, p. 2-4).
The Sacramento mine was the only mine in the area to yield
cinnabar and gold and produced a reported 3.538 flasks
of mercury (Howqrd, 1913. p. 13).
In 1933 the Snyder Mines Co. began working the
tailings dumps to the south of Mercur at the old town
site of Manning. At about the same time, the mines
at Mercur were re-opened by the Snyder Mines Co. with
the ores first being shipped to Manning for milling.
Later, in 1937, the milling operations were shifted to
Mercur (Franklin and Miller. 1938. p. 5). They mined the
e8sily workable low-grade surface ores in quarries on
8
a l e a s e b a s i s ( F r a n k l i n a n d M i l l e r , 1 9 3 8 , p . 5 ) • T h e y
a l s o w o r k e d t h e r e m a i n i n g o r e i n t h e G o l d e n G a t e m i n e
t h r o u g h t h e I n g e r s o l l s h a f t ( F i g . 2 ) . T h e m i n e s w e r e
a g a i n s h u t d o w n i n 1 9 ^ 2 b e c a u s e o f a g o v e r n m e n t a l d e c r e e
c l o s i n g g o l d m i n e s .
T h e M e r c u r Dome G o l d M i n i n g C o . f o r m e d i n 1 9 3 7
m i n e d f r o m a n a r e a j u s t w e s t o f M e r c u r o f f t h e i n c l u d e d
g e o l o g i c m a p ( F i g , 4 ) . T h e B u r e a u o f M i n e s r e p o r t e d t h e
p r e s e n c e o f v a n a d i u m i n a c a r b o n a c e o u s s h a l e h o r i z o n
i n t h i s m i n e ( K i n g a n d W i l s o n , 1 9 ^ 9 . P . 1 ) .
T h e m i n e s t o t h e s o u t h a t S u n s h i n e i n c l u d e d t h e
O v e r l a n d a n d t h e S u n s h i n e , T h e g o l d o r e m i n e d a t S u n s h i n e
r e p o r t e d l y w a s s i m i l a r t o t h e o r e s f r o m M e r c u r . J a s p e r o i d ,
s i m i l a r t o t h a t a t M e r c u r , i s p r e s e n t .
T h e t w o l a r g e s t m i n e s i n t h e W e s t D i p c a m p w e r e
t h e N o r m a a n d t h e L a C i g a l e . T h e g o l d o r e h e r e a l s o w a s
r e p o r t e d l y s i m i l a r t o t h e o r e s f r o m M e r c u r , b u t t h e c a m p
h a d o n l y l i m i t e d p r o d u c t i o n .
P r o c t o r ( i n B i s s e l l , 1 9 5 9 # P . 2 1 4 ) s t a t e s t h a t
o v e r $ 2 5 * 5 0 0 , 0 0 0 I n m e t a l v a l u e s h a v e b e e n m i n e d a t M e r c u r .
I n I 9 6 9 * N e w m o n t E x p l o r a t i o n L t d . u n d e r t o o k e x p l o r a t o r y
d r i l l i n g f o r g o l d m i n e r a l i z a t i o n a r o u n d t h e o l d m i n e s o f
M e r c u r . T h e r e s u l t s o f t h e d r i l l i n g w e r e v e r y d i s c o u r a g i n g
a n d N e w m o n t h a s g i v e n m o s t o f t h e d r i l l c o r e a n d c u t t i n g s
t o t h e U t a h G e o l o g i c a l a n d M l n e r a l o g i c a l S u r v e y ' s c o r e
l i b r a r y .
8
a lease bqsis (Franklin and Miller. 1938, p. 5). They
also worked the remaining ore in the Golden Gate mine
through the Ingersoll shaft (Fig. 2). The mines were
again shut down in 1942 because of a governmental decree
closing gold mines.
The Mercur Dome Gold Mining Co. formed in 1937
mined from an area just west of Mercur off the included
geologic map (Fig. 4). The Bureau of Mines reported the
presence of vanadium in a carbonaceous shale horizon
in this mine (King and Wilson, 1949. p. 1).
The mines to the south at Sunshine included the
Overland and the Sunshine. The gold ore mined at Sunshine
reportedly was similar to the ores from Mercur. Jasperoid,
similar to that at Mercur. is present.
The two largest mines in the West Dip camp were
the Norma and the La Cigale. The gold ore here also was
reportedly similar to the ores from Mercur, but the camp
had only limited production.
Proctor (lU Bissell. 1959. p. 214) states that
over $25,500,000 in metal values have been mined at Mercur.
In 1969, Newmont Exploration Ltd. undertook exploratory
drilling for gold mineralization around the old mines of
Mercur. The results of the drilling were very discouraging
and Newmont has ~iven most of the drill core and cuttings
to the Utah Geological and Mineralogical Survey's core
library.
STRATIGRAPHY
T h e Humbug F o r m a t i o n a n d t h e G r e a t B l u e L i m e s t o n e
a r e t h e t w o s t r a t i g r a p h i c u n i t s i n t h e m a p a r e a . B o t h
h a v e b e e n d e s c r i b e d p r e v i o u s l y b y G i l l u l y ( 1 9 3 2 ) a n d b y
B l s s e l l ( 1 9 5 9 ) .
T h e c o n t a c t b e t w e e n t h e Humbug a n d t h e o v e r l y i n g
G r e a t B l u e L i m e s t o n e i s a r b i t r a r i l y p l a c e d " a t t h e
t o p o f t h e h i g h e s t o r t h o q u a r t z i t e , q u a r t z i t i c s a n d s t o n e , o r
c a l c a r e n i t e o f s i g n i f i c a n c e i n t h e H u m b u g 1 ' ( B i s s e l l , 1 9 5 9 ,
p . 5 6 ) . G d l l u l y h a s c a l l e d t h e o r t h o q u a r t z i t e s l e n t i c u l a r
a n d t h i s a u t h o r v e r i f i e d t h i s w h e n m a p p i n g t h e c o n t a c t
b e t w e e n t h e Humbug a n d t h e G r e a t B l u e . G i l l u l y e s t i m a t e s
t h a t o r t h o q u a r t z i t e s c o m p r i s e J0% o f t h e Humbug ( 1 9 3 2 ,
p . 2 8 ) . T h e m e a s u r e d t h i c k n e s s o f t h e Humbug v a r i e s f r o m
6 3 5 t o 6 4 5 f e e t f o r t h e u n i t i n t h e i m m e d i a t e a r e a ( G i l l u l y ,
1 9 3 2 , p . 2 8 ; B i s s e l l , 1 9 5 9 . p . 5 * 0 . T h e a g e o f t h e
f o r m a t i o n i s U p p e r M i s s i s s i p p i a n .
T h e G r e a t B l u e L i m e s t o n e , n a m e d b y S p u r r , i s t h e u n i t
f r o m w h i c h a l l t h e g o l d h a s b e e n m i n e d a t M e r c u r , I t
h a s b e e n d i v i d e d i n t o t h r e e m a p a b l e u n i t s : t h e L o w e r
G r e a t B l u e w h i c h i s U p p e r M i s s i s s i p p i a n , t h e L o n g T r a i l
S h a l e , a n d t h e U p p e r G r e a t B l u e w h i c h i s L o w e r
P e n n s y l v a n i a n , T h e " g o l d l e d g e " c o m p r i s e s s o m e o f t h e
b e d s a b o v e t h e L o n g T r a i l S h a l e , t h e L o n g T r a i l S h a l e ,
a n d b e d s o f t h e L o w e r G r e a t B l u e b e l o w t h e L o n g T r a i l
STRATIGRAPHY
The Humbug Formation and the Great Blue Limestone
9re the two stratigraphic units in the map area. Both
hqve been described previously by Gilluly (1932) and by
Bissell (1959).
The contact between the Humbug and the overlying
Great Blue Limestone is arbitrarily placed -at the
top of the highest orthoquartzite, quartzitic sandstone, or
calcarenite of significance in the Humbug- (Bissell, 1959.
p. 56). ~illuly has called the orthoquartzites lenticular
and this author verified this when mapping the contact
between the Humbug and the Great Blue. Gilluly estimates
that orthoquartzites comprise 30% of the Humbug (1932.
p.28). The measured thickness of the Humbug varies from
635 to 645 feet for the unit in the immediate area (Gilluly,
1932, p. 28; Bissell, 1959. p. 54). The age of the
formation is Upper Mississippian.
The Great Blue Limestone, named by Spurr, is the unit
from which all the gold has been mined 3t Mercur. It
has been divided into three mapable units: the Lower
Great Blue which is Upper Mississippian, the Long Trail
Shale, and the Upper Great Blue which is Lower
Pennsylvanian. The -gold ledge- comprises some of the
beds above the Long Trail Shale. the Long Trail Shale,
and beds of the Lower Great Blue below the Long Trail
1 0
S h a l e . T h e " s i l v e r l e d g e * i s I n t h e L o w e r G r e a t B l u e
b e l o w t h e " g o l d l e d g e . " T h e t o t a l t h i c k n e s s o f t h e
f o r m a t i o n i s a b o u t 3 . 6 0 0 f e e t a c c o r d i n g t o G i l l u l y
( 1 9 3 2 , p . 2 9 ) — t h e L o w e r G r e a t B l u e b e i n g a b o u t 5 0 0
f e e t t h i c k a n d t h e Long T r a i l S h a l e b e i n g a b o u t 1 0 0 f e e t
t h i c k . T h e U p p e r G r e a t B l u e h a s b e e n d e s c r i b e d a s
m o n o t o n o u s , t h i c k t o m a s s i v e l i m e s t o n e b e d s . I n t h e
L o w e r G r e a t B l u e , t h i n o r t h o q u a r t z i t e a n d s a n d s t o n e l a y e r s
c a n b e f o u n d a b o v e t h e Humbug c o n t a c t i n t h e M e r c u r a r e a .
A t s e v e r a l l o c a t i o n s i n M e r c u r , o n l y t h i n s a n d s t o n e
l a y e r s w e r e f o u n d w h e r e t h e c o n t a c t s h o u l d h a v e b e e n
b e t w e e n t h e G r e a t B l u e a n d t h e H u m b u g . T h e s e c t i o n
a b o v e t h e L o n g T r a i l S h a l e c o n t a i n s i n t e r b e d d e d s i l t s t o n e ,
s h a l e , a n d l i m e s t o n e b e d s a s d o e s t h e s e c t i o n b e l o w t h e
L o n g T r a i l S h a l e , The L o n g T r a i l S h a l e c a n b e r e c o g n i z e d
b y t h e f a c t t h a t s i l t s t o n e a n d s h a l e b e d s t h i c k e n t o
b e t w e e n 5 - 1 0 f e e t i n t h e u n i t w h e r e a s s h a l e a n d s i l t s t o n e
b e d s a b o v e a n d b e l o w a r e u s u a l l y l e s s t h a n t w o f e e t t h i c k .
B i s s e l l ( 1 9 5 9 . P . 5 7 ) h a s s t a t e d t h a t t h e L o n g T r a i l S h a l e
w a s e s p e c i a l l y h e l p f u l i n d e l i n e a t i n g s t r u c t u r e s i n t h e
m a p p e d a r e a b u t t h e u n i t i s n o t e a s i l y r e c o g n i z a b l e i n
t h e f i e l d b e c a u s e i t i s a n e a s i l y e r o d e d u n i t . On t h e
m a p b y B i s s e l l a n d R i g b y t h e u n i t w a s m a p p e d b e t w e e n
v a l l e y s , g u l l i e s , a n d i o w s p o t s b e t w e e n h i l l s w h i c h o n e
m i g h t e x p e c t t o b e d u e t o t h e w e a t h e r i n g o f a s h a l e
s e q u e n c e b u t c l o s e e x a m i n a t i o n s h o w s t h e u n i t i s n o t
10
Sh9le. The ·silver ledge· is in the Lower Great Blue
below the ·gold ledge.· The total thickness of the
formation is about 3,600 feet according to Gilluly
(1932, p. 29) --the Lower Great B-lue being about 500
feet thick and the Long Trail Shale being about 100 feet
thick. The Upper Great l!1ue has been described as
monotonous, thick to massive limestone beds. In the
Lower Gre~t Blue, thin orthoquartzite and sandstone layers
can be found above the Humbug contact in the Mercur area.
At several locations in Mercur, only thin sandstone
layers were found where the contact should have been
between the Gre~t Blue and the Humbug. The section
above the Long Trail Shale contains interbedded siltstone,
shale, and limestone beds as does the section below the
Long Trail Shale. The Long Trail Shale can be recognized
by the fact that siltstone and shale beds thicken to
between 5-10 feet in the unit whereas shale and siltstone
beds above and below are usually less than two feet thick.
Bissell (1959, p. 57) has stated that the Long Trail Shale
was especially helpful in delineating structures in the
mapped area but the unit is not easily recognizable in
the field because it is an easily eroded unit. On the
map by Bissell and Rigby the unit was mapped between
valleys, gullies, and iow spots between hills which one
might expect to be due to the weathering of a shale
sequence but close examination shows the unit is not
1 1
e x a c t l y w h e r e t h e y m a p p e d i t o r i n s o m e c a s e s i s n o t
p r e s e n t a t a l l .
A l l u v i u m c o n s i s t i n g o f s t r e a m g r a v e l a n d v a l l e y f i l l
c o v e r s a p r e v i o u s l y d e v e l o p e d e r o s i o n s u r f a c e . T h e g r a v e l
t o t h e s o u t h o f t h e B r i c k y a r d m i n e s h o w s s t r a t i f i c a t i o n ,
b u t t h e g r a v e l i n t h e g r a b e n w e s t o f t h e B r i c k y a r d s h o w s
n o s t r a t i f i c a t i o n a n d c o n s i s t s o f J u m b l e d r o c k f r a g m e n t s .
T h e t h i c k n e s s o f t h e a l l u v i u m v a r i e s , b u t i s c o m m o n l y
5 - 3 0 f e e t t h i c k . A w e l l - d e v e l o p e d t h i c k s o i l o c c u r s t o
t h e e a s t a n d s o u t h - e a s t o f t h e M e r c u r H i l l m i n e .
T h e a l l u v i u m i s p r e s e n t l y b e i n g e r o d e d a w a y s l o w l y ,
p o s s i b l y d u e t o u p l i f t o f t h e a r e a a n d / o r t h e c h a n g e o f
c l i m a t i c c o n d i t i o n s s i n c e t h e l a s t g l a c i a l p e r i o d .
exactly where they mapped it or in some cases is not
present at all.
11
Alluvium consisting of stream gravel snd valley fill
cov~rs a previously developed erosion surface. The gravel
to the south of the Brickyard mine shows stratification,
but the gravel in the graben west of the Brickyard shows
no stratification and consists of jumbled rock fragments.
The thickness of the alluvium varies. but is commonly
5-30 feet thick. A well-developed thick soil occurs to
the east and south-east of the Mercur Hill mine.
The alluvium is presently being eroded away slowly.
possibly due to uplift of the area and/or the change of
climatic conditions since the last glacial period.
STRUCTURE
T h e s t r u c t u r a l e l e m e n t s i n t h e M e r c u r a r e a i n c l u d e
f o l d s , f a u l t s , j o i n t s , b r e c c i a p i p e s , a n d a n i g n e o u s
i n t r u s i o n . B o t h r e g i o n a l a n d l o c a l f o l d s o c c u r i n t h e
a r e a w i t h t h e s m a l l f o l d s n e a r t h e i n t r u s i o n a p p a r e n t l y
b e i n g r e l a t e d t o t h e i g n e o u s i n t r u s i o n . M o s t o f t h e
f a u l t s a r e s m a l l w i t h d i s p l a c e m e n t s l e s s t h a n 5 0 f e e t .
M e r c u r i s o n t h e e a s t f l a n k o f t h e O p h i r a n t i c l i n e ,
a b r o a d , a s y m m e t r i c a l s t r u c t u r e o f L a r a m i d e a g e . T h e
g e n e r a l s t r i k e o f t h e e a s t l i m b o f t h e a n t i c l i n e s h o w n
i n t h e n o r t h e r n p a r t o f t h e m a p ( F i g . 4 ) i s a b o u t N 30°W
a n d t h e s t r i k e o f t h e a n t i c l i n a l a x i s , t a k e n f r o m B i s s e l l
a n d R i g b y ' s m a p ( 1 9 5 9 t p l a t e 1 ) , i s a b o u t N 2 0 ° W . I n t h e
s o u t h e r n p a r t o f t h e m a p a r e a a r o u n d t h e E a g l e H i l l
I n t r u s i v e , d i p a n d s t r i k e o f t h e b e d s d e v i a t e f r o m t h e
t r e n d o f t h e O p h i r a n t i c l i n e . T h e s e c h a n g e s , o v e r l o o k e d
b y p r e v i o u s i n v e s t i g a t o r s , s e e m t o i n d i c a t e a f o r c e f u l
e m p l a c e m e n t o f t h e i n t r u s i v e a f t e r r e g i o n a l f o l d i n g .
S e c o n d a r y f o l d i n g o n t h e n o r t h s i d e o f t h e i n t r u s i v e
f o r m s a s m a l l s y n c l i n e . A s m a l l a n t i c l i n e a l s o o c c u r s
t o t h e s o u t h o f t h e m a p a r e a o n t h e s o u t h - w e s t r i d g e o f
E a g l e H i l l . B o t h s t r u c t u r e s d e v i a t e f r o m t h e a x i a l t r e n d
o f t h e O p h i r a n t i c l i n e . One s m a l l s y n c l i n e o c c u r s o n t h e
h i l l t o t h e e a s t o f t h e G o l d e n G a t e m i n e . I t s a x i a l p l a n e
n e a r l y p a r a l l e l s t h e l a r g e r s t r u c t u r a l f e a t u r e o f t h e a r e a
STRUCTURE
The structural elements in the Mercur area include
folds, faults, joints, breccia pipes, and an igneous
intrusion. Both regional and local folds occur in the
area with the small folds near the intrusion apparently
being related to the igneous intrusion. Most of the
faults are small with displacements less than 50 feet.
Mprcur is on the east flank of the Ophir anticline,
a broad, asymmetrical structure of Laramide age. The
general strike of the east limb of the anticline shown
in the northern part of the map (Fig. 4) is about N JOoW
and the strike of the anticlinal axis, taken from Bissell
and Rigby's map (1959, plate 1), is about N 200 W. In the
southern part of the map area around the Eagle Hill
intrusive, dip and strike of the beds deviate from the
trend of the Ophir anticline. These changes, overlooked
by previous investigators, seem to indicate a forceful
emplacement of the intrusive after regional foldingo
Secondary folding on the north side of the intrusive
forms a small sync line. A small anticline also occurs
to the south of the map area on the south-west rldge of
Eagle Hill. Both structures deviate from the axial trend
of the Ophir anticline. One small syncline occurs on the
hill to the east of the Golden Gate mine. Its axial plane
nearly parallels the larger structural feature of the area--
1 3
F i g u r e 4 , G e o l o g i c m a p o f M e r c u r , U t a h , Figure 4.
1)
GEOLOGIC MAP OF MERCUR, UTAH
EXPLANATION
Alluvial deposits Stre-lll !;ravel and vall",! fill
Eagl. Hill Rhyolite rntrulHv ... hiterhyollteWJ.th
50m",o"artz,al'lJll-dine. andbiotitephenocry"tB
Mgbu
~~~t' Mgbl
Great Blue Llm •• lane
Mgbu,uFP"rwember; thick to llmestonebeds
Mgt!:ie~~:!~E:~~3 ~~~ ~e 6~1~;~~~P5, Hgl.1.1" .... r .. elllb<lT; thick to
,""ssivelJ.meston.ebeds
Humbu" Formation
JOlperold
Silicifi.d rock.
Explosive breccia
Geologie map of Mercur, Utah.
.. .. " z ::: c :::> o
Breccia
Kaolinized and Silicified Intrulive
Contad I/;J.shedwttereapproximatelylocaled;
dottecl..h .. reconc""led
~----............ . Fault, shawing dip
Dashed .. bereapproXl:matclylocatedj dotted .. here conc~aled. ~id~pthro- sJ.de; D, do.ntbrQft
~ .. Strike and dip of bed,
.,~
Vertical and Inclined shafts
Portal of adi'
Prospect
(if) Mine dump
Scale
0E"'='=="'='~3::==':;O.OO feet
.~"",=,====="",=,==="",=,===3o.5 km
N
1 Topo!':l'aphic baBe modi tied rrom
tb .. 1968 USGS Mercur, Ut"""
topo!':l'apblcauadraJI..II:1e
14
t h e O p h i r a n t i c l i n e . I t i s b e l i e v e d t o h a v e r e s u l t e d
f r o m f u r t h e r c o m p r e s s i o n o f t h e a r e a f o l l o w i n g t h e
f o r m a t i o n o f t h e O p h i r a n t i c l i n e .
T h e E a g l e H i l l i n t r u s i v e d e f i n i t e l y c u t s t h e G r e a t
B l u e L i m e s t o n e s e q u e n c e a n d a p p a r e n t l y h a s c a u s e d s o m e
d r a g f o l d s n e a r i t . I t a p p e a r s t o b e a l a r g e i n t r u s i v e
d i k e t h a t c o u l d o n c e h a v e s e r v e d a s a c o n d u i t f o r a
f i s s u r e e r u p t i o n . T h e t r e n d o f t h e i n t r u s i v e i s N 75°W
i n t h e m a p a r e a w i t h t h e g e n e r a l t r e n d o f f t h e m a p t o
t h e w e s t b e i n g a b o u t N 9 0 ° W ,
N o r m a l , r e v e r s e , a n d s t r i k e - s l i p f a u l t s o c c u r i n t h e
m a p a r e a . A l l f a u l t s o b s e r v e d i n t h e g o l d o r e s e q u e n c e
d i s p l a c e t h e a l t e r e d r o c k a n d a p p e a r t o h a v e f o r m e d
a f t e r s i l i c i f i c a t i o n , a l t h o u g h t h e r e c o u l d h a v e b e e n
r e n e w e d m o v e m e n t a f t e r s i l i c i f i c a t i o n . M o s t o f t h e
f a u l t s a p p e a r t o b e n o r m a l , b u t s e v e r a l o f t h e l o w - a n g l e
f a u l t s a p p e a r t o b e r e v e r s e , S p u r r ( 1 8 9 4 - 9 5 ) m e n t i o n e d
t h a t s o m e o f t h e g o l d d e p o s i t s o c c u r a l o n g s m a l l f a u l t s .
Some o f t h e f a u l t s s h o w s e v e r a l p e r i o d s o f d i s p l a c e m e n t .
S l i c k e n s i d e s o n a l o w - a n g l e f a u l t a b o v e t h e f a u l t e d
b l o c k o f j a s p e r o i d n e a r t h e c e n t r a l p a r t o f t h e G e y s e r -
M a r i o n m i n e s h o w a p r o m i n e n t r e v e r s e d i r e c t i o n o f m o v e m e n t ,
b u t m o v e m e n t p r o b a b l y o c c u r r e d i n b o t h d i r e c t i o n s . T h i s
l o w - a n g l e f a u l t i s c u t a n d o f f s e t a f e w i n c h e s b y a h i g h
a n g l e f a u l t . Two s m a l l f a u l t s w h i c h o c c u r o n o p p o s i t e
s i d e s o f t h e b r e c c i a i n t h e S a c r a m e n t o m i n e a r e a c l e a r l y
14
the Ophir anticline. It is believed to have resulted
from further compression of the area following the
form~tion of the Ophir anticline.
The Eagle Hill intrusive definitely cuts the Great
Blue Limestone sequence and apparently has caused some
drag folds near it. It appears to be a large intrusive
dike that could once have served as a conduit for a
fissure eruption. The trend of the intrusive is N 750 W
in the map area with the general trend off the map to
o the west being about N 90 w.
Normal, reverse, and strike-slip faults occur in the
map area. All faults observed in the gold ore sequence
displace the altered rock and appear to have formed
after silicification, although there could have been
renewed movement after silicification. Most of the
faults appear to be normal, but several of the low-angle
faults appeqr to be reverse. Spurr (1894-95) mentioned
that some of the gold deposits occur along small faults.
Some of the faults show several periods of displacemento
Slickensides on a low-angle fault above the faulted
block of jasperoid near the central part of the Geyser-
Marion mine show a prominent reverse direction of movement,
but movement probably occurred in both directions. This
low-angle fault is cut and offset a few inches by a high
angle fault. Two small faults which occur on opposite
sides of the breccia in the Sacramento mine area clearly
1 5
e x t e n d a s h o r t d i s t a n c e i n t o t h e i n t r u s i v e . T h e o n e o n
t h e s o u t h s i d e o f t h e p i p e h a s a r e d h e m a t i t e - s t a i n e d
f r a c t u r e z o n e w h i c h i s m o r e s i l i c i f l e d t h a n n o r m a l
f o r t h i s p a r t o f t h e a l t e r e d i n t r u s i v e . T h e f a u l t o n
t h e n o r t h s i d e o f t h e p i p e h a s a l a r g e r v e r t i c a l
d i s p l a c e m e n t t h a n t h e o n e o n t h e s o u t h s i d e .
T h e b r e c c i a t h a t o c c u r s n e a r t h e c e n t e r o f t h e o l d
t o w n o f M e r c u r o n t h e SE s i d e o f t h e G e y s e r - M a r i o n
m i n e o c c u r s a p p r o x i m a t e l y a t t h e i n t e r s e c t i o n o f t w o
f a u l t s ( P i g . 5 ) • One o f t h e f a u l t s a p p e a r s t o e x t e n d
d o w n f r o m t h e g r a b e n w h i c h f o r m s t h e w e s t e r n b o u n d a r y o f
t h e B r i c k y a r d m i n e * T h e b r e c c i a i s n o t s i l i c i f l e d
a n d t h e r e f o r e p r o b a b l y f o r m e d a f t e r t h e h y d r o t h e r m a l
a c t i v i t y i n t h e a r e a . T h e b r e c c i a w a s m i n e d f o r g o l d
b u t t h e u n a l t e r e d s e d i m e n t a r y s e q u e n c e i n c o n t a c t w i t h
t h e b r e c c i a w a s n o t m i n e d w h i c h s u g g e s t s t h a t m i n e r a l i z e d
m a t e r i a l w a s o n t h e d o w n f a u l t e d s i d e o r f e l l i n t o a n
o p e n a r e a . T h e m a t e r i a l a b u t t i n g t h e f a u l t n e a r t h e
B r i c k y a r d m i n e a p p e a r s t o b e u n s o r t e d a l l u v i u m , w h e r e a s
t h e m a t e r i a l b e l o w t h e G e y s e r - M a r i o n m i n e i s a b r e c c i a .
T h e b r e c c i a c o u l d h a v e r e s u l t e d f r o m e x t e n s i o n o f t h e
f a u l t z o n e a n d r e p e a t e d u p a n d d o w n m o v e m e n t o f t h e
f a u l t , o r f r o m t h e f o r m a t i o n o f a s o l u t i o n c a v e i n t h e
f a u l t z o n e a n d c o l l a p s e o f t h e r o o f .
15
extend a short distance into the intrusive. The one on \
the south side of the pipe has a red hematite-stained
fracture zone which is more silicified than normal
for this part of the altered intrusive. The fault on
the north side of the pipe has a larger vertical
displacement than the one on the south side.
The breccia that occurs near the center of the old
town of Mercur on the SE side of the Geyser-Marion
mine occurs approximately at the intersection of two
faults (Fig. 5). One of the faults appears to extend
down from the graben which forms the western boundary of
the Brickyard mine. The breccia is not silicified
and therefore probably formed after the hydrothermal
activity in the area. The breccia was mined for gold
but the unaltered sedimentary sequence in contact with
the breccia was not mined which suggests that mineralized
material was on the down faulted side or fell into an
open area. The material abutting the fault near the
Brickyard mine appears to be unsorted alluvium, whereas
the material below the Geyser-Marion mine is a breccia.
The breccia could have resulted from extension of the
fault zone and repeated up and down movement of the
fault, or from the formation of a solution cave in the
fault zone and collapse of the roof.
16
F i g u r e 5» C o l l a p s e b r e c c i a o n e a s t s i d e o f t h e G e y s e r -M a r i o n m i n e s h o w i n g o l d m i n e w o r k i n g s .
B r e c c i a P i p e s
O n e o f t h e m o s t n o t i c e a b l e b r e c c i a s i n t h e M e r c u r
a r e a o c c u r s a t t h e S a c r a m e n t o m i n e ( F i g . 6 ) . I t a p p e a r s
t o b e a n e x p l o s i v e b r e c c i a p i p e t h a t r e s u l t e d f r o m a
r e l e a s e o f b u i l t - u p g a s p r e s s u r e . T h e p i p e o c c u r s
a t t h e c o n t a c t b e t w e e n t h e i n t r u s i v e a n d t h e G r e a t B l u e
L i m e s t o n e . T h e b r e c c i a s h o w s a c r u d e z o n a t i o n o f b r e c c i a
f r a g m e n t s . On b o t h e d g e s o f t h e e x p o s e d p i p e , t h e
b r e c c i a i s c o m p o s e d o f a n g u l a r f r a g m e n t s o f 1 - 5 c m ,
a v e r a g e s i z e i n a r e d , f i n e - g r a i n e d , s i l i c i f i e d ( q u a r t z
a n d c h a l c e d o n y ) g r o u n d m a s s ( F i g , 7 ) » I n t h e c e n t r a l p o r t i o n
o f t h e p i p e , t h e b r e c c i a i s c o m p o s e d o f m o s t l y a n g u l a r
f r a g m e n t s a n d b l o c k s i n a r e d , f i n e - g r a i n e d s i l i c i f i e d
( q u a r t z a n d c h a l c e d o n y ) g r o u n d m a s s . A l a r g e m a s s o f
s i l i c i f i e d r o c k o c c u r s a t t h e b a s e o f t h e p i p e e x p o s u r e
16
Figure 5. Collapse breccia on east side of the GeyserMarion mine showing old mine workings.
Brecc ia Pipes
One of the most noticeable breccias in the Mercur
area occurs at the Sacramento mine (Fig. 6). It appears
to be an explosive breccia pipe that resulted from a
release of built-up gas pressure. The pipe occurs
at the contqct between the intrusive and the Great Blue
Limestone. The breccia shows a crude zonation of breccia
frq~ments. On both edges of the exposed pipe, the
breccia is composed of angular fragments of 1-5 cm.
average size in a red, fine-grained, silicified (quartz
and chalcedony) groundmass (Fig. 7). In the central portion
of the pipe, the breccia is composed of mostly angular
fragments and blocks in a red, fine-grained silicified
(quartz and chalcedony) groundmass. A large mass of
silicified rock occurs at the base of the pipe exposure
F i g u r e 6 . V i e w o f S a c r a m e n t o m i n e a r e a M e r c u r , U t a h . ( 1 ) a l t e r e d E a g l e H i l l r h y o l i t e , ( 2 ) S a c r a m e n t o b r e c c i a p i p e , ( 3 ) c a r b o n - r i c h a r e a , ( 4 ) o l d b u i l d i n g s a n d a d i t l o c a t i o n s f o r t h e S a c r a m e n t o m i n e
F i g u r e 7 . C l o s e - u p o f t y p i c a l b r e c c i a f o u n d n e a r t h e e d g e o f t h e S a c r a m e n t o b r e c c i a p i p e .
Figure 6. View of Sacramento mine area Mercur, Utah. (l) altered Eagle HlII rhyollte, (2) Sacramento breccIa pIpe, (J) c .. rbon-rich are .. , (4) old bu ildings a nd adit locations for the Sacramento mine
Flgure 7, edge
Close-up of typical breccia found of the Sac ramento breccia pipe.
nea r the
17
1 8
a n d s i m i l a r f r a g m e n t s o c c u r i n t h e g r o u n d m a s s a b o v e .
T h e m a s s c o n t a i n s r a r e q u a r t z p h e n o c r y s t s w h i c h s u g g e s t
t h a t t h i s r o c k i s a n i n t r u s i v e t h a t i n v a d e d t h e b r e c c i a
a f t e r p i p e f o r m a t i o n . T h e l a r g e m a s s c o u l d a l s o r e p r e s e n t
a l a r g e b l o c k o f a l t e r e d i n t r u s i v e i n c l u d e d i n t h e
b r e c c i a . T h e e n t i r e p i p e h a s b e e n a l t e r e d t o a s i l i c e o u s
s i n t e r w h i c h a d d s t o t h e d i f f i c u l t y o f i d e n t i f y i n g t h e
l l t h o l o g y o f t h e r o c k f r a g m e n t s . A h i g h a n g l e f a u l t
o f s m a l l d i s p l a c e m e n t c u t s t h e p i p e . T h i s f a u l t m i g h t
b e d u e t o s t r e s s e s d i r e c t e d u p w a r d s a n d s i d e w a r d s c a u s e d
b y r e n e w e d p o s t - c o n s o l i d a t i o n m o v e m e n t o f t h e i n t r u s i v e
a f t e r p i p e f o r m a t i o n . A n a r r o w h i g h l y f r a c t u r e d ,
s l l c k e n s i d e d z o n e w a s o b s e r v e d i n t h e m i n e d a r e a a r o u n d
t h e p i p e .
T h e o n l y p r e v i o u s d e s c r i p t i o n o f t h i s a r e a i s g i v e n
b y L e n z l ( 1 9 7 1 , p . 2 ) .
To t h e s o u t h , a b o v e M e r c u r , a r e s e v e r a l o p e n c u t s a l o n g t h e m o u n t a i n w i t h o n e v e r y l a r g e o p e n s l o p e t h a t e x p o s e s t h e c o n t a c t o f i n t r u s i v e r h y o l i t e w i t h t h e l i m e s t o n e c o u n t r y r o c k . T h e l i m e s t o n e h a s b e e n a l t e r e d t o a l i g h t v i o l e t a n d r e d c o l o r n e a r t h e i n t r u s i v e , o t h e r w i s e t h e a l t e r a t i o n a p p e a r s a s l i g h t b u f f , s i l i c i f i e d l i m e s t o n e o r l i g h t - g r a y - t o w h i t e s i l i c i f i e d s h a l e s .
I n c o n t r a s t , t h e e x p o s u r e a p p e a r s t o b e a h i g h l y b r e c c i a t e d
z o n e a n d n o t a c o n t a c t z o n e o f v i o l e t t o r e d a l t e r e d l i m e s t o n e .
O n e o t h e r e x p l o s i v e b r e c c i a p i p e o c c u r s w a s t o f t h e
S a c r a m e n t o b r e c c i a p i p e . T h e M e r c u r S o u t h b r e c c i a p i p e
i s s i m i l a r t o t h e S a c r a m e n t o b r e c c i a p i p e e x c e p t t h a t
1~
and similar fragments occur in the groundmass above.
~he mass contains rare quartz phenocrysts which suggest
that this rock is an intrusive that invaded the breccia
after pipe formation. The large mass could also represent
a lRrge block of altered intrusive included in the
breccia. ~he entire pipe has been altered to a siliceous
sinter which adds to the difficulty of identifying the
lithology of the rock fragments. A high angle fault
of small displacement cuts the pipe. This fault might
be due to stresses directed upwards and sidewards caused
by renewed post-consolidation movement of the intrusive
after pipe formation. A narrow highly fractured,
slickensided zone was observed in the mined area around
the pipe.
The only previous description of this area is given
by Lenzi (1971. p. 2).
To the south. above Mercur, are several open cuts along the mountain with one very large open slope that exposes the contact of intrusive rhyolite with the limestone country rock. The limestone has been altered to a light violet and red color near the intrusive. otherwise the ~lteration appears as light buff, silicified limestone or light-gray-to white silicified shales o
In contrast, the exposure appears to be a highly brecciated
zone and not a contact zone of violet to red altered limestor.e.
One other explosive breccia pipe occurs wast of the
Sacramento breccia pipe. The Mercur South breccia pipe
is similar to the Sacramento breccia pipe except that
1 9
i t l a c k s t h e r e d c o l o r o f t h e g r o u n d m a s s . T h e r e i s a
r a d i a t i n g f a u l t p a t t e r n o n t h e s o u t h s i d e o f t h e p i p e
b u t n o z o n a t i o n o f t h e b r e c c i a i s e v i d e n t f r o m t h e
o u t c r o p e x p o s u r e . T h e r o c k f r a g m e n t s a n d g r o u n d m a s s
i n t h e p i p e a r e s i l i c i f i e d t o a s i l i c e o u s s i n t e r . O n e
r o c k f r a g m e n t f r o m t h i s p i p e w h i c h w a s b e l i e v e d t o b e
a n i n t r u s i v e f r a g m e n t w h e n a n a l y z e d b y X - r a y d i f f r a c t i o n
s h o w e d t h e p r e s e n c e o f q u a r t z a n d s a n i d i n e .
F e a t u r e s s u g g e s t i n g i n c i p i e n t b r e c c i a p i p e f o r m a t i o n
o c c u r t o t h e e a s t o f t h e M e r c u r S o u t h p i p e . H e r e s l i g h t
s i l i c i f i c a t i o n s i m i l a r t o t h a t o f t h e o t h e r t w o p i p e s
o c c u r s a t t h e i n t e r s e c t i o n o f t w o f a u l t s . J u m b l e d
s t r a t a e x p o s e d t o t h e e a s t i n a r o a d c u t ( n o t s h o w n o n
F i g . 4 ) m i g h t b e d u e t o f a u l t i n g , s l u m p , o r p o s s i b l y
b r e c c i a p i p e f o r m a t i o n p r o c e s s e s .
J o i n t P a t t e r n s
To d e t e r m i n e p a s t s t r e s s e s i n t h e a r e a , 1 2 9 j o i n t
a t t i t u d e s w e r e m e a s u r e d i n t h e M e r c u r a r e a p r i m a r i l y
i n t h e G e y s e r - M a r i o n a n d M e r c u r H i l l a r e a s a n d w e r e
c o n t o u r e d t o g i v e F i g u r e 8 . F i g u r e 9 s h o w s t h e p l o t
o f t h e s t r i k e d i r e c t i o n s o f t h e 1 2 9 j o i n t s u s e d f o r
F i g u r e 8 ; F i g u r e 1 0 s h o w s t h e p l o t o f t h e s t r i k e d i r e c t i o n s
o f ? 1 f a u l t s o n t h e i n c l u d e d g e o l o g i c m a p ( F i g . 4 ) .
F i g u r e 1 0 s h o w s a g e n e r a l N 6 0 ° E s t r i k e o f m a n y o f
t h e f a u l t s ; t h e s t r i k e s o f t h e j o i n t s h a v e a c o n c e n t r a t i o n
19
it lacks the red color of the groundmass. There is a
radiating fault pattern on the south side of the pipe
but no zonation of the breccia is evident from the
outcrop exposure. The rock fragments and groundmass
in the pipe are silicified to a siliceous sinter. One
rock fragment from this pipe which was believed to be
an intrusive fragment when analyzed by X-ray diffraction
showed the presence of quartz and sanidine.
Features suggesting incipient breccia pipe formation
occur to the east of the Mercur South pipe. Here slight
silicification similar to that of the other two pipes
occurs at the intersection of two faults. Jumbled
strata exposed to the east in a road cut (not shown on
Fig. 4) might be due to faulting, slump, or possibly
breccia pipe formation processes.
Joint Patterns
To determine past stresses in the area, 129 joint
attitudes were measured in the Mercur area primarily
in the Geyser-Marion and Mercur Hill areas and were
contoured to give Figure 8. Figure 9 shows the plot
of the strike directions of the 129 joints used for
Figure 8; Figure 10 shows the plot of the strike directions
of 71 faults on the included geologic map (Fig. 4). o
Figure 10 shows a general N 60 E strike of many of
the faults; the strikes of the joints have a concentration
F i g u r e 8 . C o n t o u r d i a g r a m ( l o w e r h e m i s p h e r e p r o j e c t i o n ) o f j o i n t d e n s i t y o f 1 2 9 j o i n t s i n t h e M e r c u r , U t a h a r e a .
20
N
w E
s
F1gure 8. Contour dlagram (lower hemisphere project1on) of jo1nt dens1ty of 129 jo1nts 1n the Mercur. Ut ah area.
2 1
N 0
F i g u r e 9 . P l o t o f s t r i k e d i r e c t i o n s o f 1 2 9 j o i n t s .
F i g u r e 1 0 . P l o t o f s t r i k e d i r e c t i o n s o f ?1 f a u l t s a t M e r c u r , U t a h .
N o
W 90 L..-..-----~~~22~:.::.L---_.l90 E
Figure 9. Plot of strike directions of 129 joints.
N o
W 90 L-_____ -=:::::SWI~~~L_ ___ __.J 90 E
Figure 10. Plot of strike directions of 71 faults at Mercur. Utah.
21
2 2
a t a b o u t N 5 0 ° E w h i c h i s i n c o m p a r a t i v e a g r e e m e n t w i t h
t h e f a u l t d i r e c t i o n s . T h i s d i r e c t i o n i s a p p r o x i m a t e l y
p e r p e n d i c u l a r t o t h e a x i a l p l a n e o f t h e O p h i r a n t i c l i n e
w h i c h w o u l d m a k e t h i s t h e p r o b a b l e t e n s i o n d i r e c t i o n .
T h i s d i r e c t i o n i s v e r y s i m i l a r t o t h e t r e n d o f t h e l i n e
c o n n e c t i n g t h e t w o b r e c c i a p i p e s (N 5 5 ° B ) w h i c h m i g h t
I n d i c a t e a s t r u c t u r a l c o n t r o l f o r t h e i r f o r m a t i o n .
Two f a u l t s s h o w e x t e n s i o n in t h e M e r c u r M i l m i n e a r e a
b u t o n l y o n e c o r r e l a t e s w i t h t h e t e n s i o n d i r e c t i o n .
T h i s m i g h t i n d i c a t e t h a t o t h e r s t r e s s f i e l d s e x i s t e d
• o
i n t h e p a s t . T h e N 4 0 W m i n o r c o n c e n t r a t i o n o n t h e
f a u l t p l o t i s b e l i e v e d t o b e t h e r e l e a s e j o i n t a n d f a u l t
d i r e c t i o n . T h e N 2 5 ° E a n d N 8 0 ° B d i r e c t i o n s a r e b e l i e v e d
t o b e t h e s h e a r d i r e c t i o n s . T h e t r e n d o f t h e i n t r u s i v e
i s a b o u t N 7 5 ° W i n t h e m a p a r e a w i t h t h e g e n e r a l t r e n d
t o t h e w e s t o f t h e m a p a r e a b e i n g a b o u t B-W w h i c h i s
s i m i l a r t o o n e o f t h e s h e a r d i r e c t i o n s . H o w e v e r , i t
i s n o t c l e a r t h a t t h e i n t r u s i v e c a m e i n a l o n g t h e s h e a r
d i r e c t i o n .
T h e g e n e r a l s e q u e n c e o f e v e n t s f o r t h i s a r e a i s
b e l i e v e d t o h a v e s t a r t e d w i t h c o m p r e s s i o n t o f o r m t h e
O p h i r a n t i c l i n e w i t h s o m e f a u l t i n g . G i l l u l y ( 1 9 3 2 , p . 9 1 )
b e l i e v e d t h e c o m p r e s s i o n o c c u r r e d i n L a t e C r e t a c e o u s
o r e a r l y T e r t i a r y t i m e . T h e i n t r u s i o n o f t h e E a g l e H i l l
r h y o l i t e f o l l o w e d t h e f o r m a t i o n o f t h e a n t i c l i n e a n d
d i s r u p t e d t h e g e n e r a l a n t i c l i n a l t r e n d s , b u t o c c u r r e d
22
at about N 500 E which is in comparative agreement with
the fault directions. This direction is approximately
perpendicular to the axial plane. of the Ophir anticline
which would make this the probable tension direction.
This direction is verI similar to the trend of the line
connecting the two breccia pipes (5' 550 B) which might
indicate a structural control for their formation.
Two faults show extension in- the Mercur lfill mine area
but only one correlates with the tension direction.
This might indicate that other stress fields existed o in the past. The N 40 V minor concentration on the
fault plot is believed to be the release joint and fault
direction. The N 250 E and N 80°8 directions are believed
to be the shear directions. The trend of the intrusive
is about N 7SoV in the map Iirea with the general trend
to the west of the map area being about B-V which is
similar to one of the shear directions. However, it
is not clear that the intrusive came in along the shear
direction.
The general sequence of events for this area is
believed to have started with compression to form the
Ophir anticline with some faulting. ~illull (1932, p. 91)
believed the compression occurred in Late Cretaceous
or early Tertiary time. The intrusion of the Eagle Hill
rhyolite followed the formation of the anticline and
disrupted the general anticlinal trends, but occurred
2 3
w h i l e t h e a r e a w a s s t i l l i n c o m p r e s s i o n . F u r t h e r
c o m p r e s s i o n o f t h e a r e a c a u s e d n e w a n d r e n e w e d f a u l t i n g .
T h i s s e q u e n c e i s s i m i l a r t o t h a t g i v e n b y G i l l u l y
e x c e p t t h a t t h e a u t h o r b e l i e v e s t h e a r e a w a s i n a
c o n t i n u a l s t a t e o f c o m p r e s s i o n d u r i n g t h e s e q u e n c e o f
e v e n t s . B e c a u s e o n l y o n e s e t o f s t r e s s d i r e c t i o n s i s
r e a d i l y a p p a r e n t t h i s w o u l d t e n d t o i n d i c a t e o n e
m a j o r s t r e s s f i e l d . G i l l u l y ( 1 9 3 2 , p . 9 1 ) b e l i e v e d t h a t
t h e i g n e o u s i n t r u s i o n s o c c u r r e d i n E o c e n e t i m e . M o o r e
( 1 9 7 3 . p . 9 9 ) g i v e s a b i o t i t e K - A r a g e d a t e o f 3 1 . 6 + 0 . 9
m . y . ( O l i g o c e n e ) f o r t h e E a g l e H i l l r h y o l i t e i n t h e
S a c r a m e n t o m i n e a r e a a t M e r c u r .
23
while the area was still in compression. Further
compression of the area caused new and renewed faulting.
This sequence is similar to that given by Gilluly
except that the author believes the area was in a
continual state of compression during the sequence of
events. Because only one set of stress directions is
readily apparent this would tend to indicate one
major stress field. Gilluly (1932, p. 91) believed that
the igneous intrusions occurred in Eocene time. Moore
(1973. p. 99) gives a biotite K-Ar age date of 31.6 ± 0.9
m.y. (Oligocene) for the Eagle Hill rhyolite in the
Sacr~mento mine area at Mercur.
I N T R U S I V E R O C K S
F i g u r e 1 1 s h o w s t h e g e n e r a l d i s t r i b u t i o n o f i n t r u s i v e
I g n e o u s r o c k s i n t h e s o u t h e r n O q u i r r h M o u n t a i n s ( G i l l u l y ,
1 9 3 2 , p l a t e 1 3 , p . 9 7 ) . T h e v a r i e t i e s o f i g n e o u s
r o c k s I n c l u d e r h y o l i t e p o r p h y r y ( E a g l e H i l l r h y o l i t e ) ,
l a m p r o p h y r e ( k e r s a n t i t e ) , a n d g r a n o d i o r i t e p o r p h y r y
( B i r d ' s - e y e p o r p h y r y ) ,
K e r s a n t i t e
G i l l u l y ( 1 9 3 2 , p . 6 3 ) f o u n d f o u r l a m p r o p h y r e
( k e r s a n t i t e ) d i k e s o u t c r o p p i n g i n O p h i r C a n y o n , T h e
a u t h o r h a s c o l l e c t e d s o m e o f t h e l a m p r o p h y r e f r o m t h e
e a s t s i d e o f H a r t m a n n G u l c h a n d h a s f o u n d s m a l l a m o u n t s
o f p y r i t e p r e s e n t i n t h e r o c k . I t i s a l t e r e d a s G i l l u l y
( 1 9 3 2 , p . 6 4 ) h a s s t a t e d .
B i r d ' s - e y e P o r p h y r y
T h e B i r d ' s - e y e p o r p h y r y , n a m e d b y S p u r r ( 1 8 9 4 - 9 5 ,
p . 3 7 9 ) # o u t c r o p s o n P o r p h y r y H i l l , P o r p h y r y K n o b , a n d
L i o n H i l l . G i l l u l y ( 1 9 3 2 , p . 5 0 ) c l a s s i f i e d i t a s a
g r a n o d i o r i t e p o r p h y r y . T h e a u t h o r h a s e x a m i n e d e x p o s u r e s
o f i t o n P o r p h y r y K n o b a n d P o r p h y r y H i l l . T h e g r o u n d m a s s
o f t h e B i r d ' s - e y e p o r p h y r y o n P o r p h y r y K n o b i s n o t i c e a b l y
p r o p y l i t i z e d a n d w e a t h e r e d . G i l l u l y ( 1 9 3 2 , p . 4 9 ) f o u n d
i t t o c o n t a i n p h e n o c r y s t s o f p l a g i o c l a s e ( A b ^ Q - A n ^ Q ) ,
b a r r e l s h a p e d , h e x a g o n a l b l o t l t e t a b l e t s , h o r n b l e n d e ,
iNTRUSIVE ROCKS
Figure 11 shows the general distribution of intrusive
igneous rocks in the southern Oquirrh Mountains (Gilluly,
1932. plate 13. p. 97). The varieties of igneous
rocks include rhyolite porphyry (Eagle Hill rhyolite).
lamprophyre (kersantite), and granodiorite porphyry
(Bird's-eye porphyry).
Kersantite
Gilluly (1932. p. 63) found four lamprophyre
(kers~ntite) dikes outcropping in Ophir Canyon. The
author has collected some of the lamprophyre from the
e'3.st side of Hartmann Gulch and has found small amounts
of pyrite present in the rock. It is altered as Gilluly
(1932. p. 64) has stated.
Bird's-eye Porphyry
The B'ird' s-eye porphyr;r. named by Spurr (1894-95,
p. 379). outcrops on Porphyry Hill, Porphyry Knob, and
Lion Hill. Gllluly (1932, p. 50) classified it as a
granodiorite porphyry. The author has examined exposures
of it on Porphyry Knob and Porphyry Hill. The groundmass
of the Bird's-eye porphyry on Porphyry Knob is noticeably
propylitlzed and weathered. Gilluly (1932, p. 49) found
it to contain phenocrysts of plagioclase (Ab60-An40)'
barrel shaped. hexagonal biotite tablets, hornblende.
2 5
F i g u r e 1 1 . I n d e x m a p s h o w i n g t h e g e n e r a l d i s t r i b u t i o n o f i g n e o u s r o c k s i n t h e s o u t h e r n O q u i r r h M o u n t a i n s .
... O~)I ( .n)lOn
!
N
1 Sel l.
.;..~~~~'===",;2 .. li n
•
! ,,-/
( i ., '
\ \
"-,
I'tinnt
I
Figure 11. Index map showing the general distribution of igneous rocks in the southern Oquirrh Mountains.
2 6
m i n o r o r t h o c l a s e , a n d q u a r t z .
E a g l e H i l l R h y o l i t e
T h e E a g l e H i l l r h y o l i t e w a s n a m e d b y S p u r r ( 1 8 9 4 - 9 5 ,
p . 3 7 7 ) f o r t h e r h y o l i t e p o r p h y r y t h a t c r o p s o u t o n
t h e n o r t h s i d e o f E a g l e H i l l . T h e i n t r u s i v e r h y o l i t e
p o r p h y r i e s a t O p h i r a n d M e r c u r h a v e b e e n g i v e n t h e s a m e
n a m e a n d a r e s o m e w h a t s i m i l a r m i n e r a l o g i c a l l y • A l l
o u t c r o p s o f t h e r h y o l i t e e x a m i n e d w e r e i n t r u s i v e i n
c h a r a c t e r *
S t r u c t u r a l R e l a t i o n s
E x p o s u r e s o f E a g l e H i l l r h y o l i t e w e r e e x a m i n e d i n
t h e O p h i r a r e a i n D r y C a n y o n a n d o n t h e n o r t h s i d e o f
O p h i r C a n y o n . T h e r h y o l i t e p o r p h y r y h a s t h e f o r m o f a
d i k e i n O p h i r C a n y o n a n d h a s a n a r r o w c o n t a c t z o n e . I n
t h e D r y C a n y o n a r e a a b o v e O p h i r s e v e r a l i n t r u s i v e m a s s e s
o f r h y o l i t e o c c u r . G i l l u l y ( 1 9 3 2 , p . 5 8 ) d e s c r i b e d
s e v e r a l o u t c r o p s o f r h y o l i t e b r e c c i a i n t h e D r y C a n y o n
a r e a . T h e a u t h o r e x a m i n e d t h e o n e a b o v e t h e H i d d e n
T r e a s u r e m i n e .
Two s m a l l o u t c r o p s o f r h y o l i t e p o r p h y r y w h i c h h a v e
b e e n p r e v i o u s l y o v e r l o o k e d o c c u r NNE o f t h e o l d
t o w n s i t e o f W e s t M e r c u r . T h e s o u t h e r n m o s t o f t h e s e
o u t c r o p s o f r h y o l i t e e x h i b i t s c h a r a c t e r i s t i c s o f b o t h a
s i l l a n d a d i k e . An a d i t b l a s t e d i n t o t h e i n t r u s i v e
26
minor orthoclase, and quartz.
Eagle Hill Rhyolite
The Eagle Hill rhyolite Was named by Spurr (1894-95.
p. 377) for the rhyolite porphyry that crops out on
the north side of Eagle Hill. The intrusive rhyolite
porphyries at Ophir and Mercur have been given the same
name and are somewhat similar mineralogically. All
outcrops of the rhyolite examined were intrusive in
character.
Structural Relations
Exposures of Eagle Hill rhyolite were examined in
the Ophir area in Dry Canyon and on the north side of
Ophir Canyon. The rhyolite porphyry has the form of a
dike in Ophir Canyon and has a narrow contact zone. In
the Dry Canyon area above Ophir several intrusive masses
of rhyolite occur. Gilluly (1932, p. 58) described .-
several outcrops of rhyolite breccia in the Dry Canyon
area. The author examined the one above the Hidden
Treasure mine.
Two small outcrops of rhyolite porphyry which have
been previously overlooked occur NNE of the old
townsite of West Mercur. The southernmost of these
outcrops of rhyolite exhibits characteristics of both a
sill and a dike. An adit blasted into the intrusive
e x p o s e s a g o u g e z o n e a t t h e c o n t a c t b e t w e e n t h e l i m e s t o n e
a n d t h e i n t r u s i v e . P i e c e s o f b r e c c i a c o n t a i n i n g l i m e s t o n e
a n d i n t r u s i v e c a n b e f o u n d o n t h e o u t c r o p a n d a p p e a r t o
b e a n i n t r u s i v e b r e c c i a . T h e i n t r u s i v e i s b e l i e v e d t o
h a v e b e e n e m p l a c e d a s a v i s c o u s , d r y m a g m a . A l i g n m e n t
o f b i o t i t e f l a k e s i s a p p a r e n t w h i c h s u g g e s t s i n j e c t i o n
o f a v i s c o u s m a g m a .
T h e n o r t h e r n o f t h e t w o o u t c r o p s i s b e s t e x p o s e d
i n a n e x p l o r a t i o n p i t a n d i s a b r e c c i a o f l i m e s t o n e
a n d r h y o l i t e f r a g m e n t s . T h e b r e c c i a I s b e l i e v e d a l s o
t o b e a n i n t r u s i v e b r e c c i a . T h e l a c k o f h y d r o t h e r m a l
a l t e r a t i o n o f t h e l i m e s t o n e o r t h e i n t r u s i v e f r a g m e n t s
a n d t h e s m a l l c o n t a c t z o n e i s i n d i c a t i v e o f a h o t , d r y
m a g m a . T h e s e e x p o s u r e s a r e i m p o r t a n t b e c a u s e t h e y
a r e b e l i e v e d t o r e p r e s e n t a r e l a t i v e l y u n a l t e r e d e x p o s u r e
o f i n t r u s i v e s i m i l a r t o t h a t e x p o s e d o n t h e n o r t h s i d e o f
E a g l e H i l l .
T h e r h y o l i t e t h a t o u t c r o p s a t t h e m o u t h o f M e r c u r
C a n y o n h a s t h e f o r m o f a d i k e .
T h e s t r u c t u r a l c h a r a c t e r f o r t h e E a g l e H i l l r h y o l i t e
o n t h e n o r t h s i d e o f E a g l e H i l l i s a l a r g e d i k e w h i c h
h a s b e e n f o r c i b l y i n j e c t e d . I n m o s t p l a c e s o n l y a
n a r r o w c o n t a c t z o n e e x i s t s b u t i n s e v e r a l p l a c e s
s i l i c i f i e d z o n e s r a n g i n g u p t o s e v e r a l t e n s o f f e e t o c c u r .
I n t h e q u a r r i e d a r e a a t t h e S a c r a m e n t o m i n e , m i n i n g
o p e r a t i o n s e x p o s e d t h e c o n t a c t z o n e w h i c h i s c o n v e x o u t w a r d .
27
exposes a ~ouge zone at the contact between the limestone
and the intrusive. Pieces of breccia containing limestone
and intrusive can be found on the outcrop and appeqr to
be an intrusive breccia. The intrusive is believed to
have been emplaced as a viscous, dry magma. Alignment
of biotite flakes is apparent which suggests injection
of a viscous magma.
The northern of the two outcrops is best exposed
in an exploration pit and is a breccia of limestone
and rhyolite fragments. The breccia is believed also
to be an intrusive breccia. The lack of hydrothermal
alteration of the limestone or the intrusive fragments
and the small contact zone is indicative of a hot, dry
magma. These exposures are important because they
are believed to represent a relatively unaltered exposure
of intrusive similar to that exposed on the north side of
Eagle Hill.
~he rhyolite that outcrops at the mouth of Mercur
Canyon has the form of a dike.
The structural character for the Eagle Hill rhyolite
on the north side of Eagle Hill is a large dike which
has been forcibly injected. In most places only a
narrow contact zone exists but in several places
silicified zones ranging up to several tens of feet occur.
In the quarried area at the Sacramento mine, mining
operations exposed the contact zone which is convex outward.
2 8
P e t r o l o g y
T h e r h y o l i t e e x a m i n e d i n t h e O p h i r a r e a i s a p o r p h y r y
c o n t a i n i n g a b o u t 7 - 1 0 # v i s i b l e q u a r t z p h e n o c r y s t s . Q u a r t z ,
s a n i d i n e , o l i g o c l a s e , s e r i c i t e , a p a t i t e , c a l c i t e , a n d
o p a q u e s a r e v i s i b l e i n t h i n s e c t i o n . T h e g r o u n d m a s s i s
a p h a n i t i c , K - f e l d s p a r s t a i n i n g s h o w e d t h e g r o u n d m a s s t o
c o n s i s t o f s a n i d i n e a n d q u a r t z . T h e s a n i d i n e a n d
p l a g i o c l a s e b l e n d w i t h t h e w h i t e g r o u n d m a s s i n h a n d s p e c i m e n .
No b i o t i t e w a s s e e n i n t h e e x p o s u r e s o r i n t h i n s e c t i o n .
No m a g n e t i t e w a s s e e n b y t h e a u t h o r a l t h o u g h i t w a s
d e s c r i b e d b y G i l l u l y ( 1 9 3 2 , p . 5 9 ) . P y r i t e i s p r e s e n t .
S a n i d i n e o c c u r s a s p h e n o c r y s t s a n d i s t h e d o m i n a n t
f e l d s p a r p r e s e n t . O l i g o c l a s e i s m o r e a b u n d a n t i n t h e
i n t r u s i v e a t O p h i r t h a n i n t h e r h y o l i t e a t M e r c u r ,
a l t h o u g h o n l y a f e w t h i n s e c t i o n s o f t h e r h y o l i t e a t
O p h i r w e r e s t u d i e d .
T h e W e s t M e r c u r i n t r u s i v e c o n t a i n s a b u n d a n t b i o t i t e
a n d q u a r t z p h e n o c r y s t s w h i c h c o m p r i s e a b o u t 7 - 1 0 $ o f t h e
r o c k . Q u a r t z , s a n i d i n e , o l i g o c l a s e , b i o t i t e , s e r i c i t e ,
a n d c a l c i t e a r e v i s i b l e i n t h i n s e c t i o n . Q u a r t z , s a n i d i n e ,
a n d b i o t i t e a r e t h e m o s t a b u n d a n t m i n e r a l s — c a l c i t e i s
a l s o a b u n d a n t . T h e g r o u n d m a s s i s a p h a n i t i c .
I n t h e d i k e a t t h e m o u t h o f M e r c u r C a n y o n , q u a r t z ,
s a n i d i n e , p l a g i o c l a s e , c a l c i t e , a n d s e r i c i t e a r e v i s i b l e
i n t h i n s e c t i o n . T h e g r o u n d m a s s i s a p h a n i t i c . S m a l l
28
Petrology
The rhyolite examined in the Ophir ~rea is a porphyry
cont~inlng about 7-10% visible quartz phenocrysts. Quartz,
s~nidine, oligocl~se, sericite, apatite, calcite, ~nd
opaques qre visible in thin section. The groundmass is
aphanitic. K-feldspar staining showed the groundmass to
consist of sanidine and quartz. The sanidine and
plagioclase blend with the white groundrnass in hand specimen.·
No biotite was seen in the exposures or in thin section.
No m~gnetite was seen by the author although it was
described by Gilluly (1932, p. 59). Pyrite is present.
Sanidine occurs as phenocrysts and is the dominant
feldspar present. Oligoclase is more abundant in the
intrusive at Ophir than in the rhyolite at Mprcur,
although only a few thin sections of the rhyolite at
Ophir were studied.
The West Mercur intrusive contains abundant biotite
and quartz phenocrysts which comprise about 7-10% of the
rock. Quartz, sanidine, oligoclase, biotite, sericite,
and c~lcite are visible in thin section. Quartz, sanidine,
and biotite are the most abundant minerals--calcite is
also abundant. The groundmass is aphgnitic.
In the dike at the mouth of Mercur Canyon, quartz,
sanidine, pla~ioclase, calcite, and sericite are visible
in thin section. The groundmass is aphanitic. Small
2 9
s p h e r u l i t e s o f w h a t a r e e i t h e r q u a r t z o r k a o l i n i t e
a r e p r e s e n t . Q u a r t z a n d s a n i d i n e a r e t h e t w o m o s t
a b u n d a n t m i n e r a l s p r e s e n t — c a l c i t e i s l o c a l l y a b u n d a n t .
K a o l i n i t e w a s i d e n t i f i e d b y X - r a y d i f f r a c t i o n . Some
b i o t i t e w a s f o u n d o n s t u d y o f t h e o u t c r o p e x p o s u r e . S m a l l
a m o u n t s o f p y r i t e a r e v i s i b l e i n p o l i s h e d s e c t i o n .
I n t h e E a g l e H i l l r h y o l i t e a t M e r c u r , q u a r t z , s a n i d i n e ,
o l i g o c l a s e , b i o t i t e , s e r i c i t e , c a l c i t e , a n d o p a q u e s a r e
v i s i b l e i n t h i n s e c t i o n . T h e o p a q u e s i n t h i n s e c t i o n
i n r e f l e c t e d l i g h t a p p e a r t o b e p y r i t e . K a o l i n i t e
i s p r e s e n t i n s m a l l a m o u n t s t h r o u g h o u t t h e i n t r u s i v e
a n d i s a b u n d a n t i n t h e i n t r u s i v e n e a r t h e S a c r a m e n t o
b r e c c i a p i p e . I t w a s i d e n t i f i e d b y X - r a y d i f f r a c t i o n .
S c a t t e r e d s m a l l a m o u n t s o f i l l i t e , a l s o i d e n t i f i e d
b y X - r a y d i f f r a c t i o n , a p p e a r t o b e p r e s e n t i n t h e i n t r u s i v e .
C a l c i t e , w h i c h i s p r o b a b l y h y d r o t h e r m a l , i s a b u n d a n t
l o c a l l y i n t h e i n t r u s i v e w h e r e t h e r e i s a d e c r e a s e i n
p h e n o c r y s t c o n t e n t . C a l c i t e r e p l a c e s s a n i d i n e a n d
p l a g i o c l a s e p h e n o c r y s t s a s i s e v i d e n t i n t h i n s e c t i o n s .
T h e s i z e o f p l a g i o c l a s e c r y s t a l s v a r i e s f r o m p h e n o c r y s t s
t o m i c r o l i t e s . Some o f t h e p h e n o c r y s t s h a v e r i m s o f
q u a r t z . A g g r e g a t e s o f p h e n o c r y s t s - ( g l o m e r o p h y r i t l c
t e x t u r e ) o c c u r r a n d o m l y i n t h e i n t r u s i v e . I n t e r g r o w t h s
o f q u a r t z a n d f e l d s p a r o c c u r i n t h e p h e n o c r y s t a g g r e g a t e s
o r o c c u r a s s i n g l e p h e n o c r y s t s i n t h e g r o u n d m a s s .
T h e E a g l e H i l l r h y o l i t e w h i c h o u t c r o p s a t W e s t
29
spherulites of what ~re either quartz or kaolinite
are present. Quartz and sanidine are the two most
abundant minerals present--calcite is locally abundant.
Kaolinite was identified by X-ray diffraction. Some
biotite was found on study of the outcrop exposure. Small
amounts of pyrite are visible in polished section.
In the Eagle Hill rhyolite at Mercur, quartz. sanidine,
oligoclase, biotite, sericite. calcite, and opaques are
visible in thin section. The opaques in thin section
in reflected light appear to be pyrite. haolinite
is present in small amounts throughout the intrusive
and is abundant in the intrusive near the Sacramento
breccia pipe. It was identified by X-ray diffraction.
Scattered small amounts of illite, also identified
by X-ray diffraction, appear to be present in the intrusive.
Calcite, which is probably hydrothermal, is abundant
locally in the intrusive where there is a decrease in
phenocryst content. Calcite replaces sanidine and
plagioclase phenocrysts as is evident in thin sections.
The size of plagioclase crystals varies from phenocrysts
to microlites. Some of the" phenocrysts have rims of
quartz. A~gregates of phenocrysts. (glomerophyritic
texture) occur randomly in the intrusive. Intergrowths
of quartz and feldspar occur in the phenocryst aggregates
or occur as single phenocrysts in the groundmass.
The Eagle Hill rhyolite which outcrops at West
3 0
M e r c u r , M e r c u r , a n d O p h i r , i f i t d o e s c o m e f r o m o n e l a r g e
p l u t o n , p r o b a b l y u n d e r w e n t d i f f e r e n t i a t i o n . T h e d e p o s i t s
a t O p h i r a r e t y p i c a l m e s o t h e r m a l d e p o s i t s , w h e r e a s
t h e d e p o s i t s a t M e r c u r a r e e p i t h e r m a l . R o c k a l t e r a t i o n ,
r e p r e s e n t e d b y j a s p e r o i d , i s d i s t r i b u t e d b e t w e e n O p h i r
a n d M e r c u r ( G i l l u l y , 1 9 3 2 , p . 9 7 ) . T h i s a l t e r a t i o n c o u l d
r e p r e s e n t s i l i c a f r o m h y d r o t h e r m a l s o l u t i o n s c o m i n g f r o m
a p l u t o n a t d e p t h . O n e o f t h e d i s t i n g u i s h i n g f i e l d
c h a r a c t e r i s t i c s b e t w e e n t h e i n t r u s i v e s a t O p h i r a n d
M e r c u r i s t h a t t h e E a g l e H i l l r h y o l i t e c o n t a i n s m o r e b i o t i t e
a t M e r c u r t h a n a t O p h i r , M o o r e ( 1 9 7 3 t p . 1 0 0 ) s u g g e s t s
t h a t d i f f e r e n t i a t i o n f r o m a l a r g e m o n z o n i t i c p a r e n t m a s s
u n d e r l y i n g t h e O q u i r r h M o u n t a i n s g a v e r i s e t o t h e r h y o l i t e s
a t O p h i r a n d M e r c u r , U t a h .
30
Mercur, Mercur, and Ophir, if it does come from one lqrge
pluton, prob9bly underwent differentiation. The deposits
at Ophir are typic~l mesothermal deposits, whereas
the deposits ~t Mercur are epitherm91. Rock 91terqtion,
represented by jasperoid. is distributed between Ophir
and Mercur (Gilluly, 1932, p. 97). This alteration could
represent silica from hydrothermal solutions coming from
a pluton at depth. One of the distinguishing field
characteristics between the intrusives at Ophir and
Mercur is that the Eagle Hill rhyolite contains more biotite
at Mercur than at Ophir. Moore (1973, p. 100) suggests
that differentiation from a large monzonitic parent mass
underlying the Oquirrh Mountains gave rise to the rhyolites
a.t Ophir and JVlercur, Utah.
ALTERATION OF THE SEDIMENTARY ROCKS
T h e m o s t p r o m i n e n t t y p e o f m e t a m o r p h i s m o f t h e
s e d i m e n t a r y r o c k s i n t h e M e r c u r a r e a i s s i l i c i f i c a t i o n .
T h e s i l v e r l e d g e f r o m w h i c h s i l v e r w a s m i n e d i n t h e
e a r l y d a y s o f t h e c a m p i s a t y p i c a l j a s p e r o i d o f i n t e r g r o w n
q u a r t z g r a i n s a n d w h e r e m a s s i v e h a s l i t t l e a p p a r e n t
p e r m e a b i l i t y . T h e b r e c c i a t i o n o f t h e t y p i c a l j a s p e r o i d
c o u l d h a v e o c c u r r e d a f t e r o r e d e p o s i t i o n . T h e g o l d
l e d g e i s v a r i a b l e i n m a k e - u p a s t o d e g r e e a n d t y p e o f
a l t e r a t i o n . C e r t a i n l a y e r s h a v e b e e n h i g h l y s i l i c i f i e d
a n d o t h e r l a y e r s h a v e q u a r t z , s e r i c i t e , i l l i t e , a n d
c a l c i t e a d d e d , b u t p e r m e a b i l i t y s t i l l e x i s t s i n m o s t o f
t h e g o l d l e d g e w h e r e s i l i c i f i c a t i o n h a s n o t b e e n i n t e n s e .
T h e l a c k o f p e r m e a b i l i t y i n t h e m o r e m a s s i v e p o r t i o n s o f
t h e s i l v e r l e d g e c o u l d e x p l a i n w h y t w o d i f f e r e n t t y p e s
o f e l e m e n t a l d e p o s i t s o c c u r . T h a t i s , t h e g o l d b e a r i n g
s o l u t i o n s d i d n o t h a v e a c c e s s t o t h e s i l v e r l e d g e b e c a u s e
o f l a c k o f p e r m e a b i l i t y . T h u s t h e s i l v e r d e p o s i t e d i n
t h e s i l v e r l e d g e w h i c h h a s a h i g h e r t e m p e r a t u r e m i n e r a l
a s s e m b l a g e t h a n t h e g o l d l e d g e m a y b e e a r l i e r t h a n g o l d
d e p o s i t i o n . S p u r r ( 1 8 9 4 - 9 5 , p . 3 9 3 ) m e n t i o n e d t h a t
s m a l l a m o u n t s o f g o l d o c c u r i n t h e s i l v e r l e d g e ; a n d
l o w c o n c e n t r a t i o n s o f s i l v e r w e r e f o u n d b y t h e a u t h o r
i n t h e g o l d l e d g e .
ALTERATION OF THE SEDIMENTARY HOCKS
The most prominent type of metamorphism of the
sedimentary rocks in the Mercur area is silicification.
The silver ledge from which silver was mined in the
early days of the camp is a typical jasperoid of intergrown
quartz grains and where massive has little apparent
permeability. The brecciation of the typical jasperoid
could h~ve occurred after ore deposition. The gold
ledge is variable in make-up as to degree and type of
alteration. Certain layers have been highly silicified
qnd othpr layers have quartz, sericite, illite, and
calcite added. but permeability still exists inmost of
the gold ledge where silicification has not been intense.
The lack of permeability in the more massive portions of
the silver ledge could explain why two different types
of elemental deposits occur. That is. the gold bearing
solutions did not have access to the silver ledge because
of lack of permeability. Thus the silver deposited in
the silver ledge which has a higher temperature mineral
assemblage than the gold ledge may be earlier tha-n gold
deposition. Spurr (1894-95. p. 393) mentioned that
small amounts of ~old occur in the silver ledge; and
low concentrations of silver were found by the author
in the gold ledge.
32
S i l v e r L e d g e
G i l l u l y ( 1 9 3 2 , p . 9 7 - 1 0 1 ) m a d e a t h o r o u g h i n v e s t i g a t i o n
o f t h e j a s p e r o i d s i n t h e a r e a . He r e p o r t s t h a t a l l t h e
j a s p e r o i d s h a v e a t h o r o u g h l y b r e c c i a t e d c h a r a c t e r a n d i n
p l a c e s c o n t a i n s o m e l a m i n a t e d f r a g m e n t s r e s e m b l i n g b e d d i n g
j u m b l e d a t a l l a n g l e s . I n s o m e a r e a s , t h e j a s p e r o i d
a p p e a r s m a s s i v e a n d n o t t h o r o u g h l y b r e c c i a t e d — t h i s
c o n d i t i o n i s m o r e c o m m o n t h a n o n e i s l e d t o b e l i e v e f r o m
h i s r e p o r t . T h e j a s p e r o i d n e a r t h e o l d C a r r i e S t e e l e
w o r k i n g s c l e a r l y t r a n s g r e s s e s b e d d i n g .
G i l l u l y f o u n d t w o t y p e s o f j a s p e r o i d i n t h e a r e a o f
t h e s o u t h e r n O q u i r r h M o u n t a i n s . O n e t h a t i s :
a n a g g r e g a t e o f a n h e d r a l q u a r t z c r y s t a l s , a l l v e r y m i n u t e , u s u a l l y l e s s t h a n 0 . 0 3 m i l l i m e t e r i n d i a m e t e r , c o n t a i n i n g s m a l l q u a n t i t i e s o f a p a t i t e a n d z i r c o n a n d r a t h e r l a r g e q u a n t i t i e s o f b l u e - g r e e n , s t r o n g l y p l e o c h r o i c t o u r m a l i n e , m u s c o v i t e p l a t e s , a n d c a l o i t e c r y s t a l s . . . A s e c o n d v a r i e t y h a s t h e t e x t u r e k n o w n a s t h e ' t y p i c a l j a s p e r o i d 1 t e x t u r e . I t c o n s i s t s o f i n t e r g r o w n q u a r t z g r a i n s w i t h a s t r o n g t e n d e n c y t o e u h e d r a l f o r m s , s o t h a t i n t h i n s e c t i o n m o s t o f t h e g r a i n s a p p e a r b o u n d e d b y s t r a i g h t l i n e s , a n d n u m e r o u s h e x a g o n a l a n d p r i s m a t i c c r y s t a l o u t l i n e s a r e p r e s e n t . . . T o u r m a l i n e , s e r i c i t e , c a r b o n a t e , c a r b o n , e p i d o t e , a p a t i t e , a n d z i r c o n w e r e a l l r e c o g n i z e d i n t h i s v a r i e t y o f j a s p e r o i d a s w e l l a s i n t h e a n h e d r a l v a r i e t y . T h e s e e u h e d r a l q u a r t z g r a i n s a v e r a g e p r o b a b l y 0 . 1 5 t o 0 . 2 m i l l i m e t e r I n d i a m e t e r , a l t h o u g h l o c a l l y t h e a v e r a g e g r a i n m a y b e a b o u t 0 . 5 t o 0 . 7 m i l l i m e t e r . ( 1 9 3 2 , p . 9 8 )
G i l l u l y ( 1 9 3 2 , p . 9 9 ) d e s c r i b e d p l a c e s w h e r e t h e
t w o t y p e s b l e n d t o g e t h e r a n d r e p o r t s t h e b o u n d a r y
b e t w e e n t h e t w o a s b e i n g w a v y . T h e a u t h o r h a s f o u n d o n e
l o c a t i o n i n t h e G e y s e r - M a r i o n m i n e a r e a w h e r e t h i s i s
32
Silver Ledge
Gl11uly (1932, p. 97-101) made a thorough investigation
of the jasperoids in the area. He reports that all the
jasperoids have a thoroughly brecciated character qnd in
places contc:tin some laminat/!d fragments resembling bedd ing
jumbled at all angles. In some areas, the jasperoid
appears massive and not thoroughly brecciated--this
condition is more common than one is led to believe from
his report. The jasperoid near the old Carrie Steele
workings clearly transgresses bedding.
Gilluly found two types of jasperoid in the 9rea of
the southern Oquirrh Mountalns. One that iSI
an aggregate of anhedral quartz crystals, all very minute, usually less than 0.03 milllmeter in diameter, containing small quantities of apatite and zircon and rather large quantities of blue-green, stron~ly pleochroic tourmaline, muscovite plates, and caloite crystals ••• A second variety has the texture known as the 'typical jasperold' texture. It consists of int~rgrown quartz grains with a strong tendency to euhedral forms, so that in thin section most of the grains appear bounded by straight lines, and numerous hexagonal and prismatic crystal outlines are present ••• Tourmaline, sericite, carbonate, carbon, epidote, apatite, and zircon were all recognized in this variety of jasperoid as well as in the anhedral variety. These euhedral quartz grains average probably 0015 to 0.2 millimeter in diameter, although locally the avprage grain may be about 0.5 to 0.7 millimeter. (1932, p. 98)
Gilluly (1932, p. 99) described places where the
two types blend together and reports the boundary
between the two as being wavy. The author has found one
location in the Geyser-Marlon mine area where this is
3 3
c l e a r l y s h o w n ( F i g . 1 2 ) . F i g u r e 1 3 i s a p h o t o m i c r o g r a p h
o f t h e r o c k t y p e r e p r e s e n t e d b y BM-1 o n F i g u r e 12 w h i c h
i s s i m i l a r t o G i l l u l y 1 s a n h e d r a l v a r i e t y o f j a s p e r o i d
a n d c o u l d b e c a l l e d a s i l i c e o u s s i n t e r . Some o f t h e
q u a r t z g r a i n s a r e l a r g e r t h a n t h e t y p e r e p o r t e d a n d s o m e
s h o w a t e n d e n c y t o e u h e d r a l f o r m . F i g u r e 14 i s a
p h o t o m i c r o g r a p h o f t h e r o c k t y p e r e p r e s e n t e d b y BM-2 o n
F i g u r e 12 w h i c h i s s i m i l a r t o G i l l u l y ' s d e s c r i b e d
" t y p i c a l j a s p e r o i d . " T h e " t y p i c a l j a s p e r o i d " i s t h e
d o m i n a n t v a r i e t y o f j a s p e r o i d p r e s e n t . T h e q u a r t z g r a i n s
i n t h i n s e c t i o n h a v e w a v y e x t i n c t i o n s h o w i n g t h a t t h e y
h a v e b e e n s u b j e c t e d t o a s t r e s s f i e l d . G i l l u l y ( 1 9 3 2 ,
p . 1 0 0 ) b e l i e v e s t h a t t h e b r e c c i a t e d c h a r a c t e r o f t h e
j a s p e r o i d i s d u e t o c o n t r a c t i o n o f t h e c o l l o i d a l - s i l i c a
g e l w h i c h r e p l a c e d t h e o r i g i n a l l i m e s t o n e w h e n i t
c r y s t a l l i z e d . T h e s t r e s s o f c o n t r a c t i o n o f t h e s i l i c a
g e l m a s s c o u l d h a v e c a u s e d t h e d e f o r m a t i o n o f t h e
c r y s t a l l o g r a p h i c e l e m e n t s .
C e l c i t e i s p r e s e n t i n b o t h t y p e s o f J a s p e r o i d b u t
t h e a n h e d r a l v a r i e t y c o n t a i n s m o r e c a l c i t e i n t h e
G e y s e r - M a r i o n m i n e a r e a t h a n t h e " t y p i c a l j a s p e r o i d "
t y p e . T h e c a l c i t e i n t h e a n h e d r a l v a r i e t y m a y b e
u n r e p l a c e d l i m e s t o n e a s i n t h e e u h e d r a l v a r i e t y . Some
c a l c i t e m a y b e h y p o g e n e a s G i l l u l y ( 1 9 3 2 , p . 9 9 ) b e l i e v e s ,
b u t n o t a l l . T h e " t y p i c a l j a s p e r o i d " i s b e l i e v e d t o
r e p r e s e n t a g r e a t e r a m o u n t o f s i l i c i f i c a t i o n t h a n t h e
33
clearly shown (Fig. 12). Figure 13 is a photomicrograph
of the rock type repres~nted by BM-l on Figure 12 which
is similar to Gilluly's anhedral variety of jasperoid
and could be called a siliceous sinter. Some of the
quartz grain~ are larger than the type reported ~nd some
show a tendency to euhedral form. Figure 14 is a
photomicrograph of the rock type represented by BM-2 on
Figure 12 which is similar to Gilluly's described
. "typical jasperoid.- The -typical jasperoid- is the
dominant v8riety of jasperoid present. The quartz grains
in thin section have wavy extinction showing that they
have been subjected to a stress field. Gilluly (1932,
p. 100) believes that the brecciated character of the
jasperoid is due to contraction of the colloidal-silica
gel which replaced the original limestone when it
crystallized. The stress of contraction of the silica
gel mass could have caused the deformation of the
crystallographic elements.
C91cite is present in both types of jasperoid but
the 3nhedral variety contains more calcite in the
Geys~r-Marion mine area than the -typical jasperoid"
type. The calcite in the anhedral variety may be
unreplaced limestone as in the euhedral v~riety. Some
c~lcite may be hypogene as Gilluly (1932, p. 99) believes,
but not all. The "typical jasperoid" is bplieved to
represent a greater amount of silicification than the
3 4
F i g u r e 1 2 . A n h e d r a l v a r i e t y ( B M - 1 ) i n c o n t a c t w i t h t h e " t y p i c a l v a r i e t y * ( B M - 2 ) v a r i e t y o f j a s p e r o i d i n t h e G e y s e r - M a r i o n a r e a ,
o t h e r t y p e a n d t h u s r e p r e s e n t s a f u r t h e r s t a g e o f
c r y s t a l d e v e l o p m e n t ,
G i l l u l y ( 1 9 3 2 , p . 9 9 ) r e f e r s t o t h e c a r b o n f o u n d i n
t h e j a s p e r o i d s a s a h y p o g e n e m i n e r a l . T h i s i s p r o b a b l y
o p e n t o q u e s t i o n s i n c e t h e l i m e s t o n e t h e q u a r t z r e p l a c e d
p r o b a b l y c o n t a i n e d c a r b o n a c e o u s m a t e r i a l a s d o e s s o m e o f
t h e u n r e p l a c e d l i m e s t o n e i n . t h e s e q u e n c e .
T h e d i s t r i b u t i o n o f j a s p e r o i d f r o m L i o n H i l l , w h i c h
i s s o u t h o f O p h i r , t o M e r c u r i s o f i n t e r e s t b e c a u s e i t
m i g h t l e a d t o s o m e u n d e r s t a n d i n g o f t h e i g n e o u s h i s t o r y
o f t h e a r e a . A l t h o u g h G i l l u l y h a s s t a t e d t h a t t h e r e i s
n o d i r e c t r e l a t i o n b e t w e e n t h e j a s p e r o i d s a n d t h e i n t r u s i v e s
i n t h e a r e a b e t w e e n L i o n H i l l a n d M e r c u r ( 1 9 3 2 , p . 9 8 ) .
34
Figure 12. Anhedral variety (BM - i) 1n cont~ct with the -typical variety· (BM- 2) variety of jasperold 1n the Geyser-Marion are~ .
other type and thus represents a further stage of
cryst~ l development.
G111uly (1 932. p. 99) refers to the ca rbon found 1n
the jasperolds ~s a hypogene mineral. Thi s 1s probably
open to question since the limestone the quartz replaced
probably contained carbonaceous matprial as does some of
the unreplaced 11mestone . ln . the sequence.
The dlstrlbutlon of jasperold from Llon H1H, whlch
1s south of Ophir. to Mereur 1s of interest because it
might lead to some understanding of the igneous hi s t ory
of the a res. Al tho ugh Gl11uly has stated that there 1s
no direct relat Io n between the jasperolds and the intrusives
ln the a rea between Llon Hl11 and Mercur (1 932 . p. 98) ,
F i g u r e 1 3 . P h o t o m i c r o g r a p h o f t h e a n h e d r a l v a r i e t y o f j a s p e r o i d ( B M - 1 ) . c r o s s e d - n i c o l s . 4 7 X
Figure 1). Photomicrograph of the anhedral variety of jasperoid (BM-i) . crossed-nicols. 47X
Figure 14. Photomicrograph of (BM-2). crossed-nlcols.
-typical 47X
jasperoid-
35
3 6
G o l d L e d g e
M e t a m o r p h i s m o f t h e g o l d l e d g e v a r i e s a c c o r d i n g
t o t h e p a r t o f t h e s e d i m e n t a r y s e q u e n c e m i n e r a l i z e d
a n d c l o s e n e s s t o t h e S a c r a m e n t o b r e c c i a p i p e . T h e m a i n
t y p e o f a d d i t i v e m e t a m o r p h i s m i s s i l i c i f i c a t i o n a l t h o u g h
l o c a l l y , a l o n g w i t h t h e s i l i c a , s e r i c i t e , i l l i t e , a n d
c a l c i t e h a v e b e e n d e p o s i t e d . I l l i t e i s a b u n d a n t i n t h e
a l t e r e d c l a y a n d c a r b o n r i c h a r e a n e a r t h e S a c r a m e n t o
b r e c c i a p i p e .
M e t a m o r p h i s m o f t h e L o n g T r a i l S h a l e i n t h e M e r c u r
a r e a i s l a r g e l y a s i l i c i f i c a t i o n p r o c e s s . T h e q u a r t z
g r a i n s o f t h e s i l i c i f i e d r o c k s a r e a n h e d r a l , r e s e m b l i n g
t h e a n h e d r a l v a r i e t y o f J a s p e r o i d , y e t t h e r o c k i s
d i f f e r e n t f r o m t h e p r e v i o u s l y d i s c u s s e d t y p e , w h i c h i s
s i m i l a r t o a s i l i c e o u s s i n t e r , a n d c o n t a i n s i l l i t e . T h e
q u a r t z p r e s e n t i s p r o b a b l y r e c r y s t a l l i z e d q u a r t z f r o m
t h e s h a l e a n d s i l t s t o n e s e q u e n c e ; a d d i t i o n o f q u a r t z b y
h y d r o t h e r m a l s o l u t i o n s i s v e r y p r o b a b l e . T h e r o c k h a s t h e
a p p e a r a n c e o f a s i l t s t o n e e x c e p t t h a t i t l a c k s b e d d i n g .
T h e p y r i t e a n d a r s e n o p y r i t e p r e s e n t a r e i n v i s i b l e t o t h e
e y e a n d i m p a r t a d e g r e e o f f a l s e b e d d i n g t o t h e r o c k i n
t h i n s e c t i o n .
A l t e r a t i o n o f t h e L o n g T r a i l S h a l e , i n t h e M e r c u r
H i l l m i n e a r e a i s s i m i l a r t o t h a t i n t h e B r i c k y a r d m i n e
a r e a . C e r t a i n l a y e r s , w h i c h w e r e p r o b a b l y l i m e s t o n e l a y e r
b e f o r e s i l i c i f i c a t i o n , a r e h i g h l y s i l i c i f i e d a n d r e p r e s e n t
Gold Ledge
Metqmorphism of the gold ledge varies according
to the part of the sedimentary sequence mineralized
36
and closeness to the Sacramento breccia pipe. The main
type of additive metamorphism is silicification although
locally, along with the silica, sericite, illite, qnd
calcite have been deposited. Illite is abundant in the
altered clay and carbon rich area near the Sacrgmento
brecc ia pipe.
Metamorphism of the Long Trail Shale in the Mercur
area is largely a silicification process. The quartz
gr8ins of the silicified rocks are anhedral, resembling
the anhedr~l variety of jasperoid, yet the rock is
different from the previously discussed type, which is
similar to a siliceous sinter, and contains illite. The
quartz present is probably recrystallized quartz from
the shale and siltstone sequence; addition of quartz by
hydrothermal solutions is very probable. The rock has the
appearance of a siltstone except that it lacks bedding.
The pyrite and arsenopyrite present are invisible to the
eye and impart a degree of :false bedding to the rock in
thin section.
Alteration of the Long Trail Shale, in the Mercur
Hill mine area is similar to that in the Brickyard mine
area. Certain layers, which were probably limestone layers
before silicification, are highly silicified and represent
3 7
a j a s p e r o i d .
Some o f t h e b e d s b e l o w t h e L o n g T r a i l S h a l e
s e q u e n c e i n t h e G e y s e r - M a r i o n m i n e s h o w g r a i n s i z e
g r a d a t i o n s a n d b e d d i n g s t r o n g l y r e m i n i s c e n t o f a
s i l t s t o n e i n t h i n s e c t i o n . T h e s e b e d s a r e o n l y s l i g h t l y
a l t e r e d a l t h o u g h t h e y a r e a d j a c e n t t o h i g h l y s i l i c i f i e d
u n i t s . T h e b e d s b e l o w t h e L o n g T r a i l S h a l e i n t h e M e r c u r
H i l l m i n e a r e a a r e s i l i c i f i e d a n d i n p l a c e s a r e s e r i c i t i c i z e d .
Wha t i s m o s t n o t i c e a b l e a b o u t t h e o r e s e q u e n c e h e r e i s
t h e i n t e r l a y e r i n g o f a l t e r e d , s l i g h t l y a l t e r e d , a n d
u n a l t e r e d b e d s i n t h e o r e s e q u e n c e . R e m n a n t b e d d i n g i s
v i s i b l e i n t h e a l t e r e d b e d s w h i c h i s o n e c h a r a c t e r i s t i c
t h a t i s l a c k i n g i n t h e s i l v e r l e d g e o r t h e " t y p i c a l
j a s p e r o i d . " T h e h i g h l y a l t e r e d b e d s a r e b e l i e v e d t o
r e p r e s e n t b e d s t h a t o n c e h a d h i g h e r p e r m e a b i l i t y t h a n
t h e o t h e r b e d s a n d t h u s c o u l d s e r v e a s c h a n n e l w a y s
f o r s o l u t i o n s . Some o f t h e f o s s i l s i n t h e a l t e r e d g o l d
s e q u e n c e w h i c h h a s b e e n s i l i c i f i e d a n d s e r i c i t i z e d a p p e a r
t o h a v e b e e n u n a l t e r e d d u r i n g t h e a l t e r a t i o n p r o c e s s e s
a n d c o n t a i n u n r e p l a c e d c a l c i t e .
I n o n e o f t h e q u a r r y a r e a s i n t h e M e r c u r H i l l m i n e
o n e s i d e o f a f a u l t i n t h e a r e a i s h i g h l y s i l i c i f i e d t o
j a s p e r o i d w h e r e a s t h e o t h e r , s i d e h a s b e e n l e s s s i l i c i f i e d
a n d h a s v e i n l e t s o f s e r i c i t e p a r a l l e l t o r e m n a n t b e d d i n g
p l a n e s . V e i n l e t s o f c a l c i t e c r o s s - c u t q u a r t z a n d s e r i c i t e
i n t e r g r o w t h s i n t h i n s e c t i o n w i t h t h e c a l c i t e p r o b a b l y
37
a jasperoid.
Some of the beds below the Long Trail Shale
sequence in the Geyser-Marion mine show grain size
gradations and bedding strongly reminiscent of a
siltstone in thin section. These beds are only slightly
altered although they are adjacent to highly silicified
units. The beds below the Long Trail Shale in the Mercur
Hill mine area are silicified and in places are sericiticized.
What is most noticeable about the ore sequence here is
the interlayering of altered. slightly altered, and
unaltered beds in the ore sequence. Remnant bedding is
visible in the altered beds which is one characteristic
that is lacking in the silver lecig.e or the "typical
jasperoid." The highly altered beds are believed to
represent beds that once had higher permeability than
the other beds and thus could serve as channelways
for solutions. Some of the fossils in the altered gold
sequence which has been silicified and sericitized appear
to have been unaltered during the alteration processes
and cont~in unreplaced calcite.
In one of the quarry areas in the Mercur Hill mine
one side of a fault in the area is highly silicified to
jasperoid whereas the other, side has been less silicified
and has veinlets of sericit(~ parallel to remnant bedding
planes. Veinlets of calcite cross-cut quartz and sericite
intergrowths in thin section with the calcite probably
3 8
b e i n g h y d r o t h e r m a l i n o r i g i n . S e v e r a l g e n e r a t i o n s o f
p y r i t e a r e e v i d e n t w i t h t h e l a t e r p y r i t e m o r e a n h e d r a l
i n f o r m ( P i g . 1 5 ) . T h e d i f f e r i n g a l t e r a t i o n t y p e s o n
e i t h e r s i d e o f t h e f a u l t a r e b e l i e v e d t o b e d u e t o f a u l t
r e l a t i o n s a n d t o t h e e f f e c t o f h y d r o t h e r m a l s o l u t i o n s
o n d i f f e r i n g r o c k t y p e s a n d d i f f e r i n g s e d i m e n t a r y s e q u e n c e s
w h i c h h a d b e d s o f h i g h e r p e r m e a b i l i t y .
Some f l u o r i t e w a s f o u n d i n a c o m p a r a t i v e l y u n a l t e r e d
s e q u e n c e a t t h e t o p o f M e r c u r H i l l .
T h e s e d i m e n t a r y s e q u e n c e n e a r t h e S a c r a m e n t o b r e c c i a
p i p e i s b e l i e v e d t o r e p r e s e n t e i t h e r t h e L o n g T r a i l
S h a l e s e q u e n c e o r b e d s b e l o w i t . a n d i s c h a r a c t e r i z e d
l o c a l l y b y b e d s h a v i n g l a r g e a m o u n t s o f i l l i t e . P y r i t e
i s p r e s e n t i n v a r y i n g a m o u n t s . T h e a r e a a r o u n d t h e b r e c c i a
p i p e i s o f i n t e r e s t b e c a u s e o f t h e d i f f e r e n t
a l t e r a t i o n t y p e s i n w h i c h c a r b o n i s p r e s e n t . O n e s a m p l e
a s s a y e d f o r c a r b o n n e a r n u m b e r 3 o n F i g u r e 6 h a d 4 , 2 $
c a r b o n p r e s e n t . H y d r o c a r b o n s a r e c l e a r l y v i s i b l e i n
t h i n s e c t i o n f r o m r o c k s a m p l e s t h a t s h o w c a r b o n a s s o c i a t e d
w i t h c l a y m i n e r a l s t h a t p r o b a b l y f o r m e d i n s m a l l s o l u t i o n
c h a n n e l w a y s b e t w e e n f r a c t u r e s . I n t h e a r e a o f n u m b e r 3
o n F i g u r e 6 t h e a l t e r a t i o n v a r i e s f r o m a s i l i c e o u s
s i n t e r w i t h i n t e r s t i t i a l c a r b o n t o a n i l l i t e - q u a r t z
r o c k w i t h c a r b o n . I t i s q u e s t i o n a b l e i f a n y o f t h e
c a r b o n - r i c h a r e a i s a l t e r e d i n t r u s i v e , b u t t h e n e a r n e s s
o f t h e i n t r u s i v e t o t h e c a r b o n - r i c h a r e a i s s u g g e s t i v e .
38
being hydrothermal in origin. Several generations of
pyrite are evident with the later pyrite more qnhedrql
in form (Fig. 15). The differing alteration types on
either side of the fault are believed to be due to fault
relations and to the effect of hydrothermal solutions
on differing rock types and differing sedimentary sequences
which had beds of higher permeability.
Some fluorite was found in a comparatively unaltered
sequence at the top of Mercur Hill.
The sedimentary sequence near the Sacramento breccia
pipe is believed to represent either the Long Trail
Sh~le sequence or beds below it, and is characterized
locally by beds having large amounts of illite. Pyrite
is present in varying amounts. The area around the breccia
pipe is of interest because of the different
alteration types in which carbon is present. One sample
assayed for carbon near number J on Figure 6 had 4.2%
carbon present. Hydrocarbons are clearly visible in
thin section from rock samples that show carbon associated
with clay minerals that probably formed in small solution
channelways between fractures. In the area of number 3
on Figure 6 the alteration varies from a siliceous
sinter with interstitial carbon to an illite-quartz
rock with c~rbon. It is questionable if any of the
carbon-rich are~ is altered intrusive, but the nearness
of the intrusive to the carbon-rich area is suggestive.
3 9
F i g u r e 1 5 - P h o t o m i c r o g r a p h o f a l t e r e d g o l d o r e s e q u e n c e f r o m t h e M e r c u r H i l l m i n e s h o w i n g a c a l c i t e v e i n l e t w i t h p y r i t e i n t h e c e n t e r w h i c h w a s d e f o r m e d b y t h e l a t e r g r o w t h o f a p y r i t e c r y s t a l , t r a n s m i t t e d l i g h t , 4 7 X c a , c a l c i t e ; p y , p y r i t e ; q t z + s e r , q u a r t z a n d s e r i c i t e l n t e r g r o w t h ; j , j a r o s i t e s t a i n
S m a l l n o d u l e s t h a t m i g h t b e m o r e s i l i c e o u s t h a n t h e
s u r r o u n d i n g r o c k c a n b e f o u n d i n t h e c a r b o n - r i c h a r e a a n d
c o n t a i n t h i n f i l m s o f p y r i t e a l o n g f r a c t u r e s .
Wavy e x t i n c t i o n o f t h e q u a r t z g r a i n s a n d t h e l a r g e
a m o u n t o f s l i c k e n s i d e d f r a g m e n t s i n t h e c a r b o n - r i c h z o n e
m i g h t r e p r e s e n t t h e s h o c k m e t a m o r p h i c e f f e c t s t o t h e
s u r r o u n d i n g r o c k s w h e n t h e S a c r a m e n t o b r e c c i a p i p e w a s
f o r m e d . Some o f t h e f r a g m e n t s i n t h e c a r b o n - r i c h z o n e
r e s e m b l e p h y l l i t e i n h a n d s p e c i m e n b e c a u s e o f t h e t h o r o u g h l y
s l i c k e n s i d e d n a t u r e o f t h e r o c k a n d t h e h i g h c o n t e n t o f
c l a y m i n e r a l s p r e s e n t .
No n o t i c e a b l e h y d r o t h e r m a l a l t e r a t i o n w a s e v i d e n t i n
t h e l i m e s t o n e b e d s a b o v e t h e g o l d l e d g e o n t h e h i l l b e h i n d
39
Figure 15. Photomicrograph of altered gold ore sequence from the Mercur Hill mine showing a calcite velnlet with pyrite 1n the center which was deformed by the later growth of a pyrite crystal. transm1tted 11ght. 47X ca, calcite; py, pyrite; qtz + ser, quartz and serlctte Intergrowth; j, jaroslte stain
Small nodules that might be more siliceous than the
surrounding rock oan be found 1n the carbon-rich area and
contain thin films of pyrite along fractures.
Wavy extinction of the quartz grains and the large
amount of slickensided fragments 1n the carbon-rich zone
might represent the shock metamorphic effects to the
surrounding rocks when the Sacramento breccia pipe was
formed. Some of the fragments 1n the carbon-rich zone
resemble phyll i te in hand specimen because of the thoroughly
slickens ided nature of the rock and the high content of
clay minerals present.
No noticeable hydrothermal alteration was evident in
the 11mestone beds above the gold ledge on the h111 beh1nd
4 0
t h e G o l d e n G a t e m i l l s i t e . A l t e r a t i o n a s s o c i a t e d w i t h
w i t h t h e g o l d o r e s e q u e n c e s e e m s t o b e r e s t r i c t e d t o
t h e m o r e p e r m e a b l e u n i t s a n d d o e s n o t v e r t i c a l l y
t r a n s c e n d b e d d i n g n o t i c e a b l y . T h i s w o u l d s e e m t o i n d i c a t e
t h a t i f o n e w e r e t o l o o k f o r o t h e r a l t e r a t i o n a s s o c i a t e d
w i t h g o l d m i n e r a l i z a t i o n , o n e m u s t f i n d a n a c t u a l
a l t e r e d o u t c r o p .
W e a t h e r i n g
W e a t h e r i n g o f t h e s i l v e r l e d g e o r m o r e c h a r a c t e r i s t i c a l l y
o f t h e " t y p i c a l j a s p e r o i d " i s t y p i f i e d b y a l t e r a t i o n
o f s u l f i d e m i n e r a l s t o s u l f a t e s , c a r b o n a t e s , o r o x i d e s ,
S t i b n i t e t h a t w a s o n c e p r e s e n t a l t e r s t o s t i b i c o n i t e
a n d s u l f u r . C o p p e r - b e a r i n g s u l f i d e s a l t e r t o a z u r i t e a n d
m a l a c h i t e . A z u r i t e a n d m a l a c h i t e c a n b e f o u n d o n t h e
o l d d u m p s t o t h e w e s t o f t h e o l d C a r r i e S t e e l e m i n e .
Some a z u r i t e a n d m a l a c h i t e w a s f o u n d n e a r t h e o l d S i l v e r
C l o u d m i n e . J a r o s i t e , m a l a c h i t e , a n d a b l u e - g r e e n a l u n i t e
a r e f o u n d i n t h e q u a r r y a r e a s o f t h e o l d S p a r r o w h a w k m i n e .
W e a t h e r i n g o f t h e g o l d l e d g e i s t y p i f i e d b y t h e
a l t e r a t i o n o f s u l f i d e m i n e r a l s t o s u l f a t e s o r o x i d e s .
G y p s u m i s f o u n d i n m a n y o f t h e o x i d i z e d a r e a s . I n t h e
p r o t e c t e d a r e a s u n d e r g r o u n d h a l o t r i c h i t e i s l o c a l l y
a b u n d a n t a n d i s u s u a l l y f o u n d i n t h e o x i d i z e d z o n e s .
I t t a k e s t h e f o r m o f s t a l a c t i t e s , h e l i c t i t e s , n e e d l e s , o r
f i b r o u s m a s s e s . P y r i t e a l t e r s t o j a r o s i t e a n d g o e t h i t e ;
40
the Golden Gate mill site. Alter~tion associated with
with the gold ore sequence seems to be restricted to
the more permeable units and does not vertically
transcend bedding noticeably. This would seem to indicate
that if one were to look for other alteration associated
with gold mineralization, one must find an actual
altered outcrop.
Weathering
WeJ3.thering of the silver ledge or more characteristically
of the Mtypical jasperoid" is typified by alteration
of sulfide minerals to sulfates, carbonates, or oxides.
Stibnite that was once present alters to stibiconite
and sulfur. Copper-bearing sulfides alter to azurite and
malachite. Azurite and malachite can be found on the
old dumps to the west of the old Carrie Steele mine.
Some azurite and malachite was found near the old Silver
Cloud mine. Jarosite, malachite, and a blue-green alunite
are found in the quarry areas of the old Sparrowhawk mine.
Weathering of the gold ledge is typified by the
alteration of sulfide minerals to sulfates or oxides.
Gypsum is found in many of the oxidized areas. In the
protected areas underground halotrichite is locally
abundant and is usually found in the oxidized zones.
It takes the form of stalactites, helictites,needles, or
fibrous masses. Pyrite alters to jarosite and goethite;
j a r o s i t e m a i n l y g i v e s t h e a l t e r e d s e q u e n c e i t s y e l l o w
c o l o r . P i s a n i t e - m e l a n t e r i t e ( s o l i d s o l u t i o n s e r i e s )
i s p r e s e n t i n s e v e r a l l o c a l i t i e s a t M e r c u r a n d i s t h e
m a i n m i n e r a l i n w h i c h c o p p e r i s f o u n d h e r e . P e c u l i a r l y ,
i t i s f o u n d p r e d o m i n a n t l y i n t h e r e l a t i v e l y u n o x i d i z e d
p o r t i o n s o f t h e o r e s e q u e n c e s u g g e s t i n g t h a t t h e d e g r e e
o f o x i d a t i o n o f t h e o r e h a d s o m e i n f l u e n c e a s t o l o c a t i o n o f
f o r m a t i o n . T h e p i s a n i t e - m e l a n t e r i t e u s u a l l y i s f o u n d
t o o c c u r a s f r a c t u r e f i l l i n g s w h i c h m i g h t h a v e r e s u l t e d
e i t h e r f r o m t h e m i n e r a l ' s f o r c e o f c r y s t a l l i z a t i o n o r
t e c t o n i c a c t i v i t y . A y e l l o w v a r i e t y o f s c o r o d i t e w a s
f o u n d i n t h e G e y s e r - M a r i o n m i n e a r e a a n d w a s f o u n d t o
h a v e r e s u l t e d f r o m t h e d i r e c t o x i d a t i o n o f o r p i m e n t w i t h
t h e a d d i t i o n o f i r o n .
T h e w e a t h e r i n g o f t h e L o n g T r a i l S h a l e i n t h e
B r i c k y a r d m i n e i s o f i n t e r e s t b e c a u s e o f t h e l e n s - s h a p e d
n a t u r e o f t h e u n o x i d i z e d p o r t i o n s . C l o s e t o t h e s u r f a c e
t h e o x i d i z e d p o r t i o n s , i n m a n y i n s t a n c e s , s u r r o u n d
t h e u n o x i d i z e d p o r t i o n s . A t d e p t h , t h e u n o x i d i z e d
p o r t i o n s f o r m c o l u m n s s u r r o u n d e d b y o x i d i z e d m a t e r i a l .
F i g u r e 1 6 s h o w s t h e l e n s - s h a p e d n a t u r e o f t h e u n o x i d i z e d
p o r t i o n i n a s t o p e o f t h e B r i c k y a r d m i n e . C a r b o n a s s a y s
s h o w t h a t b o t h t h e o x i d i z e d a n d u n o x i d i z e d p o r t i o n s
h e r e c o n t a i n l e s s t h a n 0.1% c a r b o n s o t h e b l a c k c o l o r
o f t h e u n o x i d i z e d m a t e r i a l i s p r o b a b l y d u e t o t h e p r e s e n c e
o f f i n e l y d i s s e m i n a t e d p y r i t e a n d a r s e n o p y r i t e .
jarosite mainly gives the altered sequence its yellow
color. Pisanite-melanterite (solid solution series)
41
is present in several localities at Mercur and is the
main mineral in which copper is found here. Peculiqrly.
it is found predominantly in the relatively unoxidized
portions of the ore sequence suggesting that the degree
of oxidation of the ore had some influence as to location of
formation. The pisanite-melanterite usually is found
to occur as fracture fillings which might have resulted
either from the mineral's force of crystallization or
tectonic activity. A yellow variety of scorodite was
found in the Geyser-Marion mine area and was found to
have resulted from the direct oxidation of orpiment with
the addition of iron.
The weathering of the Long Trail Shale in the
Brickyard mine is of interest because of the lens-shaped
nature of the unoxidized portions. Close to the surface
the oxidized portions, in many instances, surround
the unoxidized portions. At depth, the unoxidized
portions form columns surrounded by oxidized matprial.
Figure 16 shows the lens-shaped nature of the unoxidized
portion in a stope of the Brickyard mine. Carbon assays
show that both the oxidized and unoxidized portions
here contain less than 0.1% carbon so the black color
of the unoxidized material is probably due to the presence
of finely disseminated pyrite and arsenopyrite.
4 2
S e m i - q u a n t i t a t i v e e m i s s i o n s p e c t r o g r a p h s a n a l y s e s
o f t h e o x i d i z e d a n d u n o x i d i z e d p o r t i o n s s h o w n i n F i g u r e
1 6 a r e p r e s e n t e d i n T a b l e 3.
F i g u r e 1 6 . P h o t o s h o w i n g r e l a t i o n s h i p s o f w e a t h e r e d ( m o t t l e d y e l l o w , w h i t e , a n d b r o w n ) t o u n w e a t h e r e d ( b l a c k ) s t r a t a i n a s t o p e o f t h e B r i c k y a r d m i n e .
42
Semi-quantitative emission spectrographic analyses
of the oXidized and unoxldlzed portions shown 1n Figure
16 are presented 1n Table J.
Figure 16. Photo showing relationships of weathered (mottled yellow. white. and brown) to unweathered (black) strata 1n a stope of the Brickyard mine.
ALTERATION OP THE EAGLE H I L L INTRUSIVE
T h e c h i e f v a r i e t i e s o f a l t e r a t i o n o f t h e i n t r u s i v e
i n c l u d e , k a o l i n i z a t i o n , s e r i c i t i z a t i o n , a n d s i l i c i f i c a t i o n ,
K a o l i n i t e i s p r e s e n t i n s m a l l a m o u n t s t h r o u g h o u t
t h e i n t r u s i v e . T h e a m o u n t o f k a o l i n i t e i n t h e i n t r u s i v e
i n c r e a s e s m a r k e d l y a r o u n d t h e S a c r a m e n t o b r e c c i a p i p e
w h e r e t h e I n t r u s i v e h a s b e e n h i g h l y a l t e r e d . T h e r h y o l i t e
d i k e a t t h e m o u t h o f M e r c u r G a n y o n h a s a l s o b e e n h i g h l y
a l t e r e d a n d k a o l i n i z e d . T h e o c c u r r e n c e o f
k a o l i n i t e p r e s u m a b l y r e s u l t e d f r o m e a r l y h i g h a c i d c o n d i t i o n s
o f t h e h y d r o t h e r m a l s o l u t i o n s , K a o l i n i t e h a s n o t b e e n
r e c o g n i z e d p r e v i o u s l y i n t h e i n t r u s i v e .
S e r i c i t e i s v e r y w i d e s p r e a d i n t h e g r o u n d m a s s o f
t h e i n t r u s i v e a s w e l l a s i n t h e a l t e r e d s e d i m e n t a r y
s e q u e n c e . I t i s d e f i n i t e l y a l a t e m i n e r a l a n d w a s
p r o b a b l y f o r m e d u n d e r l e s s a c i d c o n d i t i o n s t h a n t h e
k a o l i n i t e .
C a l c i t e i s p r e s e n t i n t h e i n t r u s i v e a n d i s p r o b a b l y
t h e r e s u l t o f h y d r o t h e r m a l a c t i v i t y a l t h o u g h s o m e c o u l d
b e t h e r e s u l t o f w e a t h e r i n g . Some o f t h e c a l c i t e r e p l a c e s
p l a g i o c l a s e . b u t m o s t o c c u r s r a n d o m l y d i s t r i b u t e d i n
t h e a l t e r e d g r o u n d m a s s .
S i l i c i f i c a t i o n i s t h e m o s t w i d e s p r e a d o f t h e
a l t e r a t i o n t y p e s a n d h a s c o m p l e t e l y a f f e c t e d t h e i n t r u s i v e .
Q u a r t z h a s b e e n a d d e d t o t h e f i n e - g r a i n e d g r o u n d m a s s
ALTERATION OF THE EAGLE HILL INTRUSIVE
The chief varieties of alteration of the intrusive
include, kaolinization, sericitization, and silicification.
Kaolinite is present in small amounts throughout
the intrusive. The amount of kaolinite in the intrusive
increases markedly around the Sacramento breccia pipe
where the intrusive has been highly altered. The rhyolite
dike at the mouth of Mercur Ganyon has also been highly
altered and kaolinized. The occurrence of
kaolinite presumably resulted from early high acid conditions
of the hydrothermal solutions. Kaolinite has not been
recognized previously in the intrusive.
Sericite is very widespread in the groundmass of
the intrusive as well as in the altered sedimentary
sequence. It is definitely a late mineral and was
probably formed under less acid conditions than the
kaolinite.
Calcite is present in the intrusive and is probably
the result of hydrothermal activity although some could
be the result of weathering. Some of the calcite replaces
plagioclase, but most occurs randomly distributed in
the altered groundmass.
Silicification is the most widespread of the
alteration types and has completely affected the intrusive.
Quartz has been added to the fine-grained groundrnass
4 4
i n a l l t h i n s e c t i o n s s t u d i e d . Some p h e n o c r y s t s h a v e
r i m s o f c o a r s e - g r a i n e d q u a r t z .
T h e a r e a a r o u n d t h e S a c r a m e n t o b r e c c i a p i p e i s
h i g h l y a l t e r e d ( F i g . 4 a n d 1 ? ) . M o s t o f t h e q u a r t z
a n d b i o t i t e p h e n o c r y s t s h a v e b e e n h y d r o t h e r m a l l y r e m o v e d
a n d a l l t h e p l a g i o c l a s e a n d s a n i d i n e p h e n o c r y s t s s e e m
t o h a v e b e e n h y d r o t h e r m a l l y r e m o v e d . T h e a d d i t i o n o f
q u a r t z c o n t a i n i n g n u m e r o u s i n c l u s i o n s i s p r o n o u n c e d i n
t h i s p a r t o f t h e i n t r u s i v e . T h e i n t r u s i v e h a s b e e n v e r y
s i l i c i f i e d h e r e a s h a s t h e s e d i m e n t a r y s e q u e n c e n e x t
t o t h e p i p e . T h e a l t e r e d i n t r u s i v e i n t h i s a r e a , a s
p r e v i o u s l y m e n t i o n e d , c o n t a i n s k a o l i n i t e a n d s e r i c i t e
a n d a l i t t l e c a l c i t e .
T w e n t y - t h r e e s a m p l e s f r o m t h e i n t r u s i v e a n d t h e
a l t e r e d s e d i m e n t a r y s e q u e n c e i n c o n t a c t w i t h i t w e r e
a n a l y z e d f o r Mn , Z n , A g , a n d C u b y a t o m i c a b s o r p t i o n
s p e c t r o p h o t o m e t r y ( F i g . 1 7 a n d T a b l e 1 ) , T h e p u r p o s e
w a s t o s e e i f a n y a n o m a l o u s v a l u e s o c c u r r e d i n t h e
h i g h l y a l t e r e d p o r t i o n s c o m p a r e d t o t h e l e s s a l t e r e d a r e a s .
T h e m e a n p l u s t w o s t a n d a r d d e v i a t i o n v a l u e s w e r e t a k e n t o
b e a n o m a l o u s v a l u e s w h i c h f o r t h e e l e m e n t s t e s t e d w o u l d
b e : Mn ( 1 3 5 * 3 p p m ) , Zn ( 3 ^ . 6 p p m ) , Ag ( 7 . ^ p p m ) , a n d Cu
( 1 3 . 1 p p m ) . S a m p l e s 1 0 2 , 1 0 9 , 1 3 0 , 1 3 2 , a n d 1 3 3 s h o w e d
a n o m a l o u s v a l u e s b u t o n l y 1 0 2 a n d 1 0 9 a r e I n t h e h i g h l y
a l t e r e d a r e a . No t r e n d i s r e a d i l y a p p a r e n t b e t w e e n t h e
h i g h l y a l t e r e d a n d t h e s l i g h t l y a l t e r e d s a m p l e s b u t a t o m i c
in all thin sections studied. Some phenocrysts have
rims of coarse-grained quartz.
The are3 3round the Sacramento breccia pipe is
highly altered (Fig. 4 and 17). Most of the quartz
44
and biotite phenocrysts have been hydrothermally removed
and all the plagioclase and sanidine phenocrysts seem
to have been hydrothermally removed. ~he addition of
quartz containing numerous inclusions is pronounced in
this part of the intrusive. The intrusive has been very
silicified here as has the sedimentary sequence next
to the pipe. The altered intrusive in this area, as
previously mentioned, contains kaolinite and sericite
and a 1ittle calcite.
Twenty-three samples from the intrusive and the
altered sedimentary sequence in contact with it were
analyzed for Mn, Zn, Ag, and Cu by atomic absorption
spectrophotometry (Fig. 17 and Table 1). The purpose
was to see if any anomalous values occurred in the
highly altered portions compared to the less altered areas.
The mean plus two standard deviation values were taken to
be anomalous values which for the elements tested would
be: Mn (1)5.) ppm), Zn ()4.6 ppm), Ag (7.4 ppm), and Cu
(1).1 ppm). Samples 102, 109, 1)0, 1)2, and 1)) showed
~nomalous values but only 102 and 109 are in the highly
altered area. No trend is readily apparent between the
highly altered and the slightly altered samples but atomic
^ 5
y > . t 305
Hob
*«3« _ «4Ci
Mob \ JUBi • 133*
Seal* 0 £ 3
> 131* ,,'
1000 f«*t
Kgb
ieg&nd Mgb Great Flue Llm?ctons ch Eagle Mill rhyolite Altered intrusive *• Silicified country rocK ! * Sample location » fault
N JO5 fcV Hgb
eh th
1
\ Mgb
G e n e r a l g e o l o g y m a p s h o w i n g a t o m i c p t i o n s a m p l e l o c a t i o n s .
T a b l e i .—Atomic A b s o r p t i o n V a l u e s
Sample Mn Zn Ag Cu
H i g h l y A l t e r e d 4 ppm 102 6 ppm 10 ppm 8 ppm 4 ppm
109 45 3 7 . 5 4 14 305 7 7 . 5 1 7 . 5 1 .5 5 404 9 16 k 2 . 5 405 5 9 1 .5 11 406 6 7 2 . 5 5 407 69 9 1 .5 6 702 2 0 4 . 5 2 . 5
S l i g h t l y A l t e r e d 46 130 100 46 6 4
131 101 2 . 5 2 . 5 6 132 1 6 2 . 5 9 4 2 . 5 133 50 10 8 2 . 5 134 35 4 2 . 5 11 301 40 7 . 5 1 .5 6 302 5 2 . 5 7 2 . 5 2 o 303 65 5 . 3 4 4 306 8 6 . 5 14 2 2 . 5 307 90 0 5 2 . 5 309 65 3 2 . 5 11 401 35 5 4 . 5 2 . 5 402 6 2 . 5 8 4 . 5 2 , 5 403 65 2 , 5 5 2 . 5 4 0 § 103 3 2 . 5 1 .5 0
1'------ , 134 •
,
\ \ ,
IlJ - ' ,,....-.~~ "
-"" } .. _---\, ' , ' , , , , .... , , \ , '
45
L~.~&nd ~6b (::rc,t FL.lt' Lim'::'Gton1J ch E.lC~:~ ;!1ll rhyullt.
~::- ~~ t~r("d 1l".t:'US1VC
~. ~11!clC~~d co~ntry rQc~
• ~~:fie lcc~tl~h
... ... "
Mgb , '- ~ " ... - I"
th
, - - .~.I ~ I
" th ,----" " ...
\ \ 11gb '-':
',"\ ,--'
Seale
o 1000 h.t ~=C-::::J , ,
"" '... , "" ..... --,
Figure 17. General geology m~p showing atomic absorption sample locatloDA.
Table 1.--Atomlc Absorption Values
Semple Mn Zn Ag Cu
Highly Altered 102 6ppru 10ppm 8ppro 4ppm 109 45 37.5 4 14 305 77.5 17.5 1.5 5 40lJ 9 16 1~ 2.5 405 5 9 1.5 11 406 6 7 2 &; 5 • .1
407 69 9 1.5 6 702 2 0 4.5 2~5
Slightly Altered 1}0 100 46 6 4 131 101 2.5 2.5 6 132 162.5 9 L~ 2.5 133 50 10 8 2.5 1Jl} )5 4 2.5 11 301 40 7.5 1.5 6 302 52.5 7 2.5 2., 30) 65 5.) 4 4 306 86.5 14 2 2.5 307 90 0 5 2.5 309 65 ) 2.5 11 401 35 5 4.5 2.5 402 62.5 8 4.5 2.5 403 65 2.5 5 2.5 IWq 103 32.5 1.5 0
• • lC~
)O} •
J
4 6
a b s o r p t i o n v a l u e s f o r o t h e r s a m p l e s f r o m t h e a l t e r e d
s e d i m e n t a r y s e q u e n c e s h o w h i g h e r v a l u e s f o r Zn t h a n
i n t h e u n a l t e r e d s e q u e n c e .
S i l i c i f i c a t i o n o f t h e c o u n t r y r o c k a r o u n d t h e
i n t r u s i v e ( P i g . 4 ) i s a p p a r e n t l y r e l a t e d t o f l u i d s w h i c h
e m a n a t e d f r o m t h e i n t r u s i v e . T h e d e g r e e o f a l t e r a t i o n
a r o u n d t h e S a c r a m e n t o b r e c c i a p i p e i s q u i t e p r o n o u n c e d ;
t h e a l t e r e d s e d i m e n t a r y s e q u e n c e s h o w s i n t e n s e s i l i c i f i c a t i o n .
T h e a r e a o f s i l i c i f i c a t i o n a r o u n d s a m p l e s i t e # 3 0 5 a n d
t h e a r e a t o t h e s o u t h a r e p r o b a b l y r e l a t e d t o t h e
d e p o s i t i o n o f q u a r t z b y h y d r o t h e r m a l f l u i d s f r o m t h e
i n t r u s i v e . T h e s e t w o s i l i c i f i e d a r e a s w e r e t h e o n l y a r e a s
w h e r e l a r g e p y r i t e c r y s t a l s a n d p y r i t l z e d f o s s i l s w e r e
f o u n d . S a m p l e # 3 0 5 w a s f o u n d t o c o n t a i n 1 6 ppm g o l d
( 0 . 4 6 o z A u / t o n ) w h i c h s u g g e s t s t h a t g o l d d e p o s i t i o n w a s
r e l a t e d t o h y d r o t h e r m a l a c t i v i t y t h a t a r o s e a s a
c o n s e q u e n c e o f i g n e o u s a c t i v i t y . T h e s i l i c i f i e d a r e a n e a r
s a m p l e s i t e # 3 0 9 i s a l s o e v i d e n t l y r e l a t e d t o h y d r o t h e r m a l
a c t i v i t y . T h e s i l i c i f i c a t i o n t o t h e SB o f t h e SB c o r n e r
o f F i g u r e 4 , n e a r t h e i n t r u s i v e , a l s o i s p r o b a b l y r e l a t e d
t o h y d r o t h e r m a l a c t i v i t y . T h e s e o c c u r r e n c e s s e e m t o
i n d i c a t e t h a t t h e c o n t a c t b e t w e e n t h e i n t r u s i v e a n d t h e
c o u n t r y r o c k w a s f a v o r a b l e f o r t h e p a s s a g e o f s o l u t i o n s
w h i c h r e p l a c e d c a l c i t e a n d d e p o s i t e d q u a r t z i n t h e c o u n t r y
r o c k . T h e t h r e e r o o f p e n d a n t s n o t r e m o v e d b y e r o s i o n f r o m
t h e r o o f o f t h e i n t r u s i v e s h o w n o n o t i c e a b l e a l t e r a t i o n .
absorption values for other samples from the altered
sedimentary sequence show higher values for Zn than
in the unaltered sequence.
46
Silicification of the country rock around the
intrusive (Fig. 4) is apparently related to fluids which
emanated from the intrusive. The degree of alteration
around the Sacramento breccia pipe is quite pronounced;
the altered sedimentary sequence shows intense silicification.
The area of silicification around sample site #305 and
the area to the south are probably related to the
deposition of quartz by hydrothermal fluids from the
intrusive. These two silicified areas were the only areas
where large pyrite crystals and pyritized f~ssils were
found. Sample #305 was found to contain 16 ppm gold
(0.46 oz Au/ton) which suggests that gold deposition was
related to hydrothermal activity that arose as a
consequence of igneous activity. The silicified area near
sample site #309 is also evidently related to hydrothermal
activity. The silicification to the SE of the SE corner
of Figure 4. near the intrusive, also is probably related
to hydrothermal activity. These occurrences seem to
indicate that the contact between the intrusive and the
country rock was favorable for the passage of solutions
which replaced calcite and deposited quartz in the country
rock. The three roof pendants not removed by erosion from
the roof of the intrusive show no noticeable alteration.
T h e c h e m i c a l w e a t h e r i n g o f t h e i n t r u s i v e i s very
s u b t l e . I n p a r t s o f t h e i n t r u s i v e , w e a t h e r i n g h a s r e m o v e d
m o r e o f s p e c i f i c l a y e r s r e s u l t i n g i n l a y e r e d r i d g e s t h a t
g i v e t h e r o c k a f a l s e - f l o w a g e c h a r a c t e r , N e a r t h e S a c r a m e n t o
b r e c c i a p i p e , s m a l l h e m a t i t e s p o t s i n t h e i n t r u s i v e m i g h t
r e p r e s e n t t h e f o r m e r p r e s e n c e o f f i n e l y d i s s e m i n a t e d
p y r i t e . Some o f t h e b i o t i t e f l a k e s a t t h e s u r f a c e a r e
w e a t h e r e d .
T h e E a g l e H i l l i n t r u s i v e s h o w s p r o g r e s s i v e
m e t a m o r p h i s m i n t h e M e r c u r a r e a . T h e g r o u n d m a s s w a s
p r o b a b l y t h e f i r s t t o b e a l t e r e d w i t h s a n i d i n e b e i n g
a l t e r e d t o k a o l i n i t e a n d t h e n t o s e r i c i t e w i t h d e c r e a s i n g
a c i d c o n d i t i o n s . P l a g i o c l a s e p h e n o c r y s t s a r e r a r e i n t h e
i n t r u s i v e a t M e r c u r a n d a p p a r e n t l y w e r e h y d r o t h e r m a l l y
r e m o v e d . T h e a m o u n t o f b i o t i t e p r e s e n t a p p e a r s t o b e a
g o o d i n d i c a t o r o f h y d r o t h e r m a l a l t e r a t i o n . W h e r e b i o t i t e
i s a b s e n t o r s c a r c e h y d r o t h e r m a l a l t e r a t i o n h a s b e e n m o s t
i n t e n s e . T h e i r o n f r o m t h e b i o t i t e i s b e l i e v e d t o h a v e
g o n e t o w a r d t h e f o r m a t i o n o f p y r i t e . S a n i d i n e p h e n o c r y s t s
a l s o a r e l e s s c o m m o n w h e r e h y d r o t h e r m a l a l t e r a t i o n w a s
m o r e i n t e n s e . Q u a r t z p h e n o c r y s t s a l s o s e e m t o b e i n d i c a t i v e
o f t h e i n t e n s i t y o f a l t e r a t i o n a l t h o u g h t o a l e s s e r d e g r e e
t h a n t h e l a c k o f b i o t i t e , p l a g i o c l a s e , a n d s a n i d i n e
p h e n o c r y s t s . Q u a r t z p h e n o c r y s t s a r e n o t c o m m o n i n
t h e i n t r u s i v e n e a r t h e S a c r a m e n t o b r e c c i a p i p e .
47
The chemical weathering of the intrusive is v~ry
subtle. In parts of the intrusive, weathering has removed
more of specific layers resulting in layered ridges that
give the rock a false-flowage character. Near the Sacramento
breccia pipe, small hematite spots in the intrusive might
represent the former presence of finely disseminated
pyrite. Some of the biotite flakes at the surface are
weathered.
The Eagle Hill intrusive shows progressive
metamorphism in the Mercur area. The groundmass was
probably the first to be altered with sanidine being
altered to kaolinite and then to sericite with decreasing
acid conditions. Plagioclase phenocrysts are rare in the
intrusive at Mercur and apparently were hydrothermally
removed. The amount of biotite present appears to be a
good indicator of hydrothermal alteration. Where biotite
is absent or scarce hydrothermal alteration has been most
intense. The iron from the biotite is believed to have
gone toward the formation of pyrite. Sanidine phenocrysts
also are less common where hydrothermal alteration was
more intense. Quartz phenocrysts also seem to be indicative
of the intensity of alteration although to a lesser degree
than the lack of biotite, plagioclase, and sanidine
phenocrysts. Quartz phenocrysts are not common in
the intrusive near the Sacramento breccia pipe.
THE GOLD D E P O S I T S
T h e g o l d d e p o s i t s a r e r e p l a c e m e n t d e p o s i t s t h a t
a r e l a r g e l y s t r a t i g r a p h i c a l l y c o n t r o l l e d . T h e y a r e
c h a r a c t e r i z e d m i n e r a l o g i c a l l y b y t h e p r e s e n c e o f o r p l m e n t ,
r e a l g a r ( F i g , 1 8 ) , a r s e n o p y r l t e , f i n e l y d i s s e m i n a t e d
p y r i t e , a n d l o c a l l y c i n n a b a r . G a l e n a , c i n n a b a r , s p h a l e r i t e ,
s u l v a n i t e , a n d c h a l c o p y r i t e h a v e b e e n r e p o r t e d a l t h o u g h
t h e y w e r e n o t o b s e r v e d b y t h e a u t h o r . S p u r r ( 1 8 9 ^ - 9 5 ,
p . 4 3 0 ) r e p o r t e d t h e p r e s e n c e o f r e a l g a r a s b e i n g a
f a v o r a b l e s i g n o f g o l d m i n e r a l i z a t i o n , b u t n o t a l w a y s .
A l l p r e v i o u s i n v e s t i g a t o r s r e p o r t t h e g o l d a s n o t b e i n g
v i s i b l e i n p o l i s h e d s e c t i o n a l t h o u g h i t w a s r e p o r t e d a s
b e i n g v i s i b l e b y u s e o f t h e r e f l e c t i n g m i c r o s c o p e o n c e
t h e o r e h a d b e e n r o a s t e d . T h e a u t h o r , t h r o u g h s t u d y o f
p o l i s h e d s e c t i o n s f r o m t h e o r e s e q u e n c e , w a s u n a b l e
t o d e t e c t a n y v i s i b l e g o l d .
T h e p r e s e n c e o f o r p l m e n t a n d r e a l g a r i s u s u a l l y
a t t r i b u t e d t o l o w t e m p e r a t u r e h y d r o t h e r m a l e n v i r o n m e n t s ,
s u c h a s h o t s p r i n g s . T h e g o l d d e p o s i t s a t M e r c u r p r o b a b l y
a r e o f t h e e p i t h e r m a l t y p e a n d w e r e p r o b a b l y e m p l a c e d
a t s h a l l o w d e p t h s i n a t y p i c a l h o t s p r i n g e n v i r o n m e n t .
N i c h o l s a n d P e t e r s o n ( 1 9 7 0 ) o f t h e U . S . B u r e a u o f
M i n e s m a d e a s t u d y o f t h e m i l l t a i l i n g s a t M e r c u r a i m e d
a t d e v i s i n g a p r o f i t a b l e m e t h o d f o r e x t r a c t i n g t h e
r e m a i n i n g g o l d f r o m t h e t a i l i n g s . T h e y s t a t e t h a t t h e i r
" q u a l i t a t i v e a n a l y t i c a l m e t h o d s s h o w e d t h a t g o l d i s
THE GOLD DEPOSITS
The gold deposits are replacement deposits that
are largely stratigraphically controlled. They are
characterized mineralogically by the presence of orp1ment,
realgar (Fig. 18), arsenopyrite, finely disseminated
pyrite, and locally cinnabar. Galena. cinnabar, sphalerite,
sulvanite. and chalcopyrite have been reported although
they were not observed by the author. Spurr (1894-95,
p. 4)0) reported the presence of realgar as being a
favorable sign of gold mineralization, but not always.
All previous investigators report the gold as not being
visible in polished section although it was reported as
be1ng visible by use of the reflecting microscope once
the ore had been roasted. The author, through study of
polished sections from the ore sequence. was unable
to detect any visible gold.
The presence of orpiment and realgar is usually
attributed to low temperature hydrothermal environments,
such as hot springs. The gold deposits at Mercur probably
are of the epithermal type and were probably emplaced
at shallow depths in a typical hot spring environment.
Nichols and Peterson (1970) of the U.S. Bureau of
Mines made a study of the mill tailings at Mercur aimed
at devising a profitable method for extracting the
remaining gold from the tailings. They state that the1r
-qualitative analytical methods showed that gold is
4 9
F i g u r e 1 8 . P h o t o s h o w i n g o r p l m e n t ( y e l l o w ) a n d r e a l g a r ( r e d ) i n t h e u n o x i d i z e d z o n e o f t h e B r i c k y a r d m i n e . T h e w h i t e p o r t i o n s a r e t h e s u l f a t e m e l a n t e r i t e - p i s a n i t e w h i c h i s p r e s e n t .
a s s o c i a t e d w i t h a l l m i n e r a l s w i t h a h i g h e r c o n c e n t r a t i o n
i n t h e o r g a n i c a n d m a g n e t i c m i n e r a l s * ( N i c h o l s a n d P e t e r s o n ,
1 9 7 0 , p . 6 ) .
G o l d s e e m i n g l y h a s b e e n m i n e d f r o m t h e a l t e r e d
s e d i m e n t a r y b e d s i n c o n t a c t w i t h o r f r o m t h e b r e c c i a
z o n e s a t M e r c u r . T h e t w o s i l i c i f i e d b r e c c i a p i p e s a c t e d
a s c h a n n e l w a y s f o r h y d r o t h e r m a l s o l u t i o n s , b u t d o n o t
a p p e a r t o h a v e b e e n m i n e d f o r g o l d . T h e z o n e s a r o u n d
t h e b r e c c i a p i p e s h a v e b e e n m i n e d f o r g o l d , w h i c h s u g g e s t s
t h a t g o l d d e p o s i t i o n p r e c e d e d p i p e f o r m a t i o n o r t h a t t h e
z o n e s a r o u n d t h e p i p e s w e r e m o r e f a v o r a b l e f o r g o l d
d e p o s i t i o n t h a n t h e b r e c c i a p i p e s t h e m s e l v e s . T h e
f a u l t b r e c c i a z o n e s a p p e a r t o h a v e f o r m e d l a t e r t h a n t h e
Figure 18. Photo shol<ling orpiment (yellow) and rea lgar (red) 1n the unoxidized zone of the Brickyard mine . The white portions are the s ulfate melanterite -pisanlte which is present.
associated with all minera ls with a higher concentrat ion
in the orga nic and magnetic minerals· (Nichols and Peterson.
1970 . p. 6).
Gold seemingly has been mined from the altered
sedimentary beds in contact with or from the breccia
zones at Mercur. ~he two sIlIcified breccia pipes ac ted
as c hannelways fo r hydrothermal solutions, but do not
appear to have been mined for go ld. The zones around
t he breccia pipes have been mined for gold, which suggests
that go ld deposition preceded pipe formation or that the
zones around the pipes were more favorable for go ld
deposition than the breccia pipes themselves. The
f quIt breccia zones appe~r to have formed later than the
50
h y d r o t h e r m a l a l t e r a t i o n , b u t g o l d e n r i c h m e n t c o u l d h a v e
o c c u r r e d f r o m t h e s o l u t i o n a n d r e m o v a l o f c a l c i t e .
C i n n a b a r w a s m i n e d c o m m e r c i a l l y f o r m e r c u r y
o n l y a t t h e S a c r a m e n t o g o l d m i n e i n t h e M e r c u r c a m p .
M e r c u r y w a s r e p o r t e d t o o c c u r i n t r a c e a m o u n t s a s
c i n n a b a r w i t h t h e g o l d d e p o s i t s i n t h e o t h e r m i n e s o f
t h e c a m p . T h e c o m m e r c i a l c o n c e n t r a t i o n s o f m e r c u r y
a t t h e S a c r a m e n t o m i n e c o u l d b e c a u s e d b y t h e s a m e p r o c e s s e s
t h a t f o r m e d t h e S a c r a m e n t o b r e c c i a p i p e . U n s a f e c o n i t i o n s
f o r e n t r y t o t h e o l d m i n e w o r k i n g s d i d n o t a l l o w
e x a m i n a t i o n o f t h e o r e s e q u e n c e u n d e r g r o u n d a t t h e
S a c r a m e n t o m i n e . E x a m i n a t i o n o f t h e q u a r r y a r e a d i d n o t
r e v e a l t h e p r e s e n c e o f a n y c i n n a b a r .
G e n e r a l p a r a g e n e t i c r e l a t i o n s f o r t h e g o l d d e p o s i t s
c a n b e g i v e n f r o m g e n e r a l f i e l d , p o l i s h e d s e c t i o n , o r
t h i n s e c t i o n o b s e r v a t i o n s . T h e r e p l a c e m e n t o f c a l c i t e
i n t h e l i m e s t o n e b e d s b y q u a r t z p r o b a b l y o c c u r r e d f i r s t .
L o c a l l y s e r i c i t e a n d i l l i t e a c c o m p a n y t h e q u a r t z . P y r i t e
a n d a r s e n o p y r i t e d e p o s i t i o n f o l l o w e d w i t h a n h e d r a l p y r i t e
f o r m i n g b e f o r e t h e e u h e d r a l p y r i t e . A n h e d r a l p y r i t e
a n d a r s e n o p y r i t e v i e w e d i n t h i n s e c t i o n o c c u r b e t w e e n
t h e i n d i v i d u a l q u a r t z g r a i n s i n r o c k s f r o m t h e B r i c k y a r d
m i n e . E u h e d r a l p y r i t e , i n p o l i s h e d s e c t i o n , w a s o b s e r v e d
t o h a v e f o r m e d a r o u n d t h e q u a r t z g r a i n s . O r p i m e n t a n d
r e a l g a r a r e a p p a r e n t l y l a t e m i n e r a l s s i n c e t h e y o c c u r
a s f r a c t u r e a n d v u g f i l l i n g s . Some o f t h e b e s t
50
hydrothermal alteration, but gold enrichment could h~ve
occurred from the solution and removal of calcite.
Cinnabar was mined commercially for mercury
only at the Sacramento gold mine in the Mercur camp.
Mercury was reported to occur in trace amounts as
cinnabar with the gold deposits in the other mines of
the camp. The commercial concentrations of mercury
at the Sacramento mine could be caused by the same processes
that formed the Sacramento breccia pipe. Unsafe conitions
for entry to the old mine workings did not allow
examination of the ore sequence underground at the
Sacramento mine. Examination of the quarry area did not
reveal the presence of any cinnabar.
General paragenetic relations for the gold de~osits
can be given from general field, polished section, or
thin section observations. The replacement of calcite
in the limestone beds by quartz probably occurred first.
Locally sericite and illite accompany the quartz. Pyrite
and arsenopyrite deposition followed with anhedral pyrite
forming before the euhedral pyrite. Anhedral pyrite
and arsenopyrite viewed in thin section occur between
the individual quartz grains in rocks from the Brickyard
mine. Euhedral pyrite, in polished section, was observed
to have formed around the quartz grains. Orpiment and
realgar are apparently late minerals since they occur
as fracture and vug fillings. Some of the best
c r y s t a l l i n e r e a l g a r w a s f o u n d i n l i m e s t o n e v u g s
s u r r o u n d e d b y c a l c i t e c r y s t a l s . T h e t i m e a t w h i c h
g o l d d e p o s i t i o n o c c u r r e d i s u n k n o w n b e c a u s e g o l d c o u
n o t b e s e e n . S i n c e g a l e n a , s p h a l e r i t e , a n d c i n n a b a r
w e r e n o t o b s e r v e d t h e i r p a r a g e n e t i c r e l a t i o n s a l s o
a r e u n k n o w n .
crystalline realgar was found in limestone vugs
surrounded by calcite crystals. The time at which
gold deposition occurred is unknown because gold could
not be seen. Since galena, sphalerite, and cinnabar
were not observed their paragenetic relations also
are unknown.
51
ELEMENTAL ANALYSES OP ROCK SAMPLES
Q u a l i t a t i v e e m i s s i o n s p e c t r o g r a p h s a n a l y s e s o f
r o c k s a m p l e s f r o m t h e g o l d l e d g e s e q u e n c e a r e g i v e n i n
T a b l e 2 . T h e s i m i l a r i t y o f e l e m e n t a l c o m p o s i t i o n b e t w e e n
r o c k s f r o m t h e s l i g h t l y a l t e r e d L o n g T r a i l S h a l e ( C - 1 0 3 ) ,
t h e a l t e r e d L o n g T r a i l S h a l e ( 6 0 2 ) , a n d t h e c a r b o n - r i c h
r o c k ( G - 1 0 1 ) i s o f I n t e r e s t b e c a u s e t h e I n t e n s i t y o f
a l t e r a t i o n a p p a r e n t l y d o e s n o t a f f e c t t h e e l e m e n t s p r e s e n t .
T h e u n a l t e r e d L o w e r G r e a t B l u e L i m e s t o n e s a m p l e ( 5 0 1 )
w a s c o l l e c t e d f r o m t h e s o u t h e r n p a r t o f t h e G e y s e r - M a r i o n
m i n e . T h e a l t e r e d L o w e r G r e a t B l u e L i m e s t o n e ( 3 0 5 )
s a m p l e w a s c o l l e c t e d f r o m a s i l i c i f i e d - p y r i t i z e d z o n e
n e x t t o t h e i n t r u s i v e . T h e d i f f e r e n c e s i n e l e m e n t a l
c o m p o s i t i o n a r e o b v i o u s b e t w e e n t h e s e t w o r o c k s a m p l e s
w i t h t h e a l t e r e d r o c k s a m p l e s h o w i n g t h e p r e s e n c e o f
g o l d . T h e p r e s e n c e o f A s , B , A u . P b , H g , K, S i , A g , T l ,
a n d Zn c h a r a c t e r i z e t h e a l t e r e d s a m p l e s a n d a r e b e l i e v e d
t o r e p r e s e n t e l e m e n t s d e p o s i t e d f r o m h y d r o t h e r m a l s o l u t i o n s .
S e m i - q u a n t l t a t l v e e m i s s i o n s p e c t r o g r a p h l c a n a l y s e s
f o r t h r e e r o c k s a m p l e s a r e g i v e n i n T a b l e 3. T h e v a l u e s
g i v e n s h o u l d n o t b e t a k e n t o r e p r e s e n t e x a c t v a l u e s b u t
o n l y t o r e p r e s e n t a n e l e m e n t ' s p r e s e n c e . T h e d e t e c t i o n
l i m i t f o r t e l l u r i u m i s 0 . 0 1 $ w h i c h i n d i c a t e s t e l l u r i u m
i s n o t p r e s e n t i n s u f f i c i e n t c o n c e n t r a t i o n s i n t h e s e
s a m p l e s t o b e d e t e c t e d . O t h e r u n p u b l i s h e d a n a l y s e s
ELEMENTAL ANALYSES OF ROCK SAMPLES
Qualitative emission spectrographic analyses of
rock samples from the gold ledge sequence are given in
Table 2. The similarity of elemental composition between
rocks from the slightly altered Long Trail Shale (C-l03).
the altered Long Trail Shale (602), and the carbon-rich
rock (~~101) is of interest beoause the intensity of
alteration apparently does not affect the elements present.
The unaltered Lower Great ~ue Limestone sample (501)
was collected from the southern part of the Geyser-Marion
mine. The altered Lower Great Blue Limestone (305)
sample was collected from a silicified-pyritized zone
next to the intrusive. The differences in elemental
composition are obvious between these two rock samples
with the altered rock sample showing the presence of
gold. The presence of As, B, Au, Pb, Hg, K. Si. Ag. TI,
and Zn characterize the altered samples and are believed
to represent elements deposited from hydrothermal solutions.
Semi-quantitative emission spectrographic analyses
for three rock samples are given in Table 3. The values
given should not be taken to represent exact values but
only to represent an element's presence. The detection
limit for tellurium is 0.01% which indicates tellurium
is not present in sufficient concentrations in these
samples to be detected. Other unpublished analyses
T a b l e 2 . — Q u a l i t a t i v e E m i s s i o n S p e c t r o g r a p h s A n a l y s e s o f R o c k S a m p l e s P r o m M e r c u r , U t a h
E l e m e n t C - 1 0 3 C - 1 0 1 6 0 2 5 0 1 3 0 5
Ag X X X A l X X X X X As X X T r X Au X B X X X X C a X X X X X C r X X X X X F e X X X T r X Hg X X X X K X X X T r X Mg X X X X X Mn X X T r T r Na X X X X X P b X X X X S i X X X X X T i X X X X X T l X X Zn X X
c - 1 0 3 - - s l i g h t l y a l t e r e d L o n g T r a i l S h a l e C - 1 0 1 - - c a r b o n - r i c h r o c k , S a c r a m e n t o m i n e 6 0 2 — - g o l d o r e , L o n g T r a i l S h a l e , B r i c k y a r d m i n e 5 0 1 — - u n a l t e r e d L o w e r G r e a t B l u e L i m e s t o n e 3 0 5 — - a l t e r e d L o w e r G r e a t B l u e L i m e s t o n e
X e l e m e n t p r e s e n t T r — t r a c e o f e l e m e n t p r e s e n t
Table 2.--Qualitative Emission Spectrographic Analyses of Rock Samples From Mercur. Utah
Element C'-103 C-10l 602 501 305
Ag X X X Al X X X X As X X Tr Au B X X X Ca X X X X Cr X X X X Fe X X X Tr Hg X X X K X X X Tr Mg X X X X Mn X X Tr Na X X X X Pb X X X Si X X X X Ti X X X X TI X Zn X X
C-103--slightly altered Long Trail Shale C-10l--carbon-rich rock, Sacramento mine 602----gold ore, Long Trail Shale, Brickyard mine 501----unaltered nower Great Blue Limestone 305----altered Lower Great Blue Limestone
X---element present Tr--trace of element present
X X X X X X X X X X Tr X X X X X
53
5 *
T a b l e 3 - — S e m i - q u a n t i t a t i v e E m i s s i o n S p e c t r o g r a p h i c A n a l y s i s o f R o c k S a m p l e s F r o m M e r c u r , U t a h
Unweathered gold ore Weathered gold ore Carbon-rich rock Element Brickyard mine Brickyard mine Sacramento mine
Ag .0001* .0005* .0006* Al ca 4.0 ca 5.0 ca 3.0 As .12 .13 .02 Au N.O. N.D.. N.D.. B .008 .008 .01 Ba .02 .03 .01 Be .0003 .0003 .0002 Bi N.D. N.D.. N.D. Ca .003 .05 .20 Cb N.D. N.D. N.D. Cd N.D. N.D. N.D. Ce N.D. N.D. N.D. Co <.001 <.001 <.001 Cr .005 .004 .006 Cu .80 .20 .15 Pe ca 4.0 ca 4.0 ca 3.0 Ga < .001 <.001 < .001 Ge N.D.. N.D. N.D. Hf N.D. N.D. N.D. Hg N.D.. N.D. N.D. In < .001 <.001 1 .001 La .01 .01 <.01 Mg .15 .15 .15 Mn .001 .003 .0005 Mo <.001 <.001 <.001 Na .03 .07 .30 Ni .000? .0004 .0005 P .04 .06 .03 Pb .0004 .0004 .0005 Pd N.D. N.D. N.D. Pt N.D. N.D.. N.D. Sb .001 .001 .001 Si ca 20.0 ca 20.0 ca 20.0 Sn N.D. .0003 .0003 Ta N.D. N.D.. N.D. Te N.D. N.D. N.D. Th N.D. N.D. N.D. Ti .15 .15 .10 V .003 .004 .006 w N.D.. N.D* N.D. Y .002 .002 .003 Zn ca .1 ca .1 <.01 Zr .008 .013 .005 N.D. not detected ca approximately < less than Analyzed by R. Woods, Kennecott Research Center
Table J.--Semi-quantitative Emission Spectrographic Analysis of Rock Samples From Mercur. Utah
Unweathered gold ore Weathered gold ore Carbon-r1ch rock Element Br1ckyard m1ne Br1ckyard m1ne Sacramento m1ne
Ag .000U .0005% .0006% AI ca 4.0 ca 5.0 ca 3.0 A8 .12 .1) .02 Au N.D. N.D •. N.D •. B .008 .008 .01 BIt .02 .03 .01 Be .0003 .0003 .0002 B1 N.D. N.D •. N.D. Ca .003 .05 .20 Cb N.D. N.D. N.D. Cd N.D. N.D. N.D. Ce N.D. N.D. N.D. Co < .001 <..001 <..001 Cr .005 .004 .006 Cu .BO .20 .15 Fe ca 4.0 ca 4.0 ~a 3.0 Ga < .001 <. .001 .001 Ge N.D •. N.D. N.D. at N.D. N.D. N.D. Bg N.D •. N.D. N.D. In < .001 <.001 .( .001 La .01 .01 <. .01 fig .15 .15 .15
"" .001 .003 .0005
"0 (.001 <.001 (.001 !fa .03 .07 .30 .1 .0007 .0004 .0005 p .04 .06 .03 Pb .0004 .0004 .0005 I'd N.D. N.D. N.D. Pt N.D. N.D •. N.D. 8b .001 .001 .001 81 ca 20.0 ca 20.0 ca 20.0 8n N.D. .0003 .0003 Ta N.D. N.D •. N.D. Te N.D. N.D. N.D. Th N.D. N.D. N.D. '1',. .15 .15 .10 V .003 .004 .006 V N.D •. N.D. N.D. I· .002 .002 .003 ZD ca .1 ca .1 <.01 Zr .008 .01) .005
N.D. not detected ca approx1mately
< less thlln
Analyzed by R. Woods, Kennecott Research Center
5 5
s h o w t e l l u r i u m i s p r e s e n t a s p r e v i o u s l y p u b l i s h e d a n a l y s e
h a v e s h o w n . T h e b o r o n p r e s e n t i s b e l i e v e d t o b e h e l d i n
t h e c r y s t a l s t r u c t u r e o f t h e c l a y m i n e r a l s . T h e s o u r c e
f o r t h e b o r o n w a s p r o b a b l y t h e h y d r o t h e r m a l s o l u t i o n s
t h a t a t o n e t i m e p e r v a d e d t h e s e q u e n c e . T h e h i g h
p e r c e n t a g e o f c o p p e r i s o f i n t e r e s t s i n c e n o p r e v i o u s l y
p u b l i s h e d a n a l y s e s i n d i c a t e a n y m o r e t h a n a t r a c e o f
c o p p e r . T h e h i g h c o p p e r a n a l y s e s c o m e s f r o m a p o r t i o n
o f t h e s e q u e n c e t h a t d o e s c o n t a i n m e l a n t e r i t e - p i s a n i t e
b u t t h e s a m p l e s e l e c t e d d i d n o t h a v e a n y o f t h e s u l f a t e
m i n e r a l v i s i b l e .
A t o m i c a b s o r p t i o n a n a l y s i s v a l u e s f o r Mn, Z n , A g ,
a n d C u f o r o t h e r s e l e c t e d s a m p l e s s h o w e d a h i g h a m o u n t
o f z i n c t o b e p r e s e n t i n t h e a l t e r e d s e q u e n c e c o m p a r e d
t o t h e u n a l t e r e d s e q u e n c e . T h e u n a l t e r e d l i m e s t o n e
( 5 0 1 ) s h o w e d a h i g h a m o u n t o f s i l v e r ( 1 0 p p m ) w h i c h t h e
q u a l i t a t i v e e m i s s i o n s p e c t r o g r a p h i c a n a l y s i s f a i l e d
t o s h o w .
55
show tellurium is present as previously published analyses
have shown. The boron present is believed to be held in
the crystal structure of the clay minerals. The source
for the boron was probably the hydrothermal solutions
that at one time pervaded the sequence. The high
percentage of copper is of intereRt since no previously
published analyses indicate any more than a trace of
copper. The high copper analyses comes from a portion
of the sequence that does contain melanterite-pisanite
but the sample selected did not have any of the sulfate
mineral visible.
Atomic absorption analysis values for Mn, Zn, Ag,
and eu for other selected samples showed a high amount
of zinc to be present in the altered sequence compared
to the unaltered sequence. The unaltered limestone
(501) showed a high amount of silver (10 ppm) which the
qu~litative emission spectrographic analysis failed
to show.
IMPLICATIONS OF CARBON AND ORGANIC COMPOUNDS
T h e a s s o c i a t i o n o f c a r b o n w i t h t h e g o l d d e p o s i t s
o f M e r c u r h a s b e e n k n o w n f o r m a n y y e a r s . Many i n v e s t i g a t o r s
h a v e s t u d i e d t h e a b i l i t y o f c a r b o n a n d o r g a n i c a c i d s
t o p r e c i p i t a t e g o l d f r o m s o l u t i o n . Ong a n d S w a n s o n
( I 9 6 9 ) h a v e f o u n d t h a t c o l l o i d a l g o l d c a n b e p r e c i p i t a t e d
f r o m g o l d c h l o r i d e s o l u t i o n s b y c e r t a i n o r g a n i c a c i d s .
T h e y s t a t e t h a t , * i n a c i d i c s o l u t i o n s , f o r e x a m p l e n e a r
o r e d e p o s i t s w h e r e t h e pH i s o f t e n l e s s t h a n 3 , g o l d c a n
b e t r a n s p o r t e d a s g o l d c h l o r i d e i o n s . H o w e v e r , o r g a n i c
a c i d s a r e n o t s o l u b l e i n t h i s a c i d e n v i r o n m e n t a n d a r e
t h u s i n c a p a b l e o f t r a n s p o r t i n g g o l d . I f o r g a n i c a c i d s
h a v e b e e n p r e c i p i t a t e d n e a r a n o r e d e p o s i t t h e g o l d i t s e l f
w i l l b e p r e c i p i t a t e d f r o m s o l u t i o n a s c o l l o i d s o f m e t a l l i c
g o l d a n d i n c o r p o r a t e d w i t h t h e o r g a n i c m a t t e r * ( O n g
a n d S w a n s o n , I 9 6 9 . P - 4 2 1 ) , T h e y g i v e n o c r i t e r i a f o r
s t a t i n g t h a t o r g a n i c a c i d s a r e n o t s o l u b l e i n a n a c i d
e n v i r o n m e n t o f l e s s t h a n a pH o f 3» R a d t k e a n d S c h e i n e r
( 1 9 7 0 , p , 9 7 ) , who h a v e d o n e w o r k o n t h e C a r l i n g o l d
d e p o s i t , h a v e c o n d u c t e d o r g a n i c e x t r a c t i o n s o n c a r b o n - r i c h
g o l d o r e s a m p l e s f r o m C a r l i n , N e v a d a , a n d h a v e f o u n d
t h e m t o c o n t a i n h u m i c a c i d s , ( I f t h e y m e a n c a r b o x y l i c
a c i d s t h e i n f r a r e d s p e c t r a t h e y p r e s e n t d o n o t c o r r e s p o n d
t o a c a r b o x y l i c a c i d s p e c t r a . ) F r o m t h e f l o w d i a g r a m
f o r a NaOH e x t r a c t i o n g i v e n b y D e g e n s a n d R e u t e r ( 1 9 6 4 ,
IMPLICATIONS OF CARBON AND ORGANIC COMPOUNDS
The association of carbon with the gold deposits
of Mercur has been known for many years. Many investigators
have studied the ability of carbon. and organic acids
to precipitate gold from solution. Ong and Swanson
(1969) have found that colloidal gold can be precipitated
from gold chloride solutions by certain organic acids.
They state that. -in acidic solutions, for example near
ore deposits where the pH is often less than 3, gold can
be transported as gold chloride ions. However, organic
acids are not soluble in this acid environment and are
thus incapable of transporting gold. If organic acids
have been precipitated near an ore deposit the gold itself
will be precipitated from solution as colloids of metallic
gold and incorporated with the organic matter- (Ong
and Swanson. 1969. p. 421). They give no criteria for
stating that organic acids are not soluble in an acid
environment of less than a pH of 3. Radtke and Scheiner
(1970, p. 97), who have done work on the Carlin gold
deposit, have conducted organic extractions on carbon-rich
gold ore samples from Carlin. Nevada. and have found
them to contain humic acids. (If they mean carboxylic
acids the infrared spectra they present do not correspond
to a carboxylic acid spectra.) From the flow diagram
for a NaOH extraction given by Degens and Reuter (1964.
5 ?
p - 3 8 5 ) o n e w o u l d e x p e c t t o e x t r a c t h u m i c a c i d s . T h e y
b e l i e v e m o s t o f t h e g o l d o c c u r s a s a n o r g a n o m e t a l l i c
c o m p l e x i n t h e Au ( I ) v a l e n c e s t a t e a n d t h u s m o s t o f
t h e g o l d I s n o t p r e s e n t i n a f r e e s t a t e i n t h e r o c k s .
V a r i a t i o n s o f t h e o r g a n i c e x t r a c t i o n t e c h n i q u e s
g i v e n b y D e g e n s a n d R e u t e r ( 1 9 6 4 ) w e r e u s e d b y t h e a u t h o r
o n s a m p l e s f r o m M e r c u r , U t a h ; G e t c h e l l M i n e , N e v a d a
( s a m p l e t a k e n f r o m d u m p ) ; a n d t h e N e w m o n t m i n e , C a r l i n ,
N e v a d a ( s a m p l e f r o m t h e e a s t p i t ) , t o d e t e r m i n e i f
h y d r o c a r b o n s w e r e p r e s e n t .
T h r e e m e t h o d s o f e x t r a c t i o n , w h i c h w i l l b e d e s c r i b e d
b r i e f l y b e l o w , w e r e u s e d o n c r u s h e d c a r b o n - r i c h r o c k
s a m p l e s w i t h t h e o r g a n i c e x t r a c t b e i n g d i s s o l v e d i n C C l ^
b e f o r e b e i n g i n j e c t e d i n t o W i l k s c e l l s f o r u s e i n a
B e c k m a n I R * 2 0 s p e c t r o p h o t o m e t e r . T h e i n f r a r e d s p e c t r a
o b t a i n e d w e r e c o m p a r e d a g a i n s t t h e s p e c t r a f o r p u r e
C C l ^ t o d e t e r m i n e w h i c h o r g a n i c s w e r e p r e s e n t . E x t r a c t i o n
t e c h n i q u e s i n v o l v e d u s i n g a m i x t u r e o f b e n e z e n e , m e t h a n o l ,
a n d a c e t o n e ; 0 , 3 N NaOH; o r 0 . 5 N NH/jAc s o l u t i o n s .
I n t h e b e n e z e n e - m e t h a n o l - a c e t o n e m e t h o d ( 7 0 : 1 5 : 1 5
b y v o l u m e ) , t h e B-M-A m i x t u r e w a s f o u n d t o l e a v e a n
i n f r a r e d d e t e c t a b l e r e s i d u e w h i c h w a s d e l e t e r i o u s t o
i n t e r p r e t a t i o n o f t h e M e r c u r , C a r l i n , a n d G e t c h e l l s a m p l e s .
T h e o r g a n i c e x t r a c t i o n t e c h n i q u e u s i n g a 0 . 3 N NaOH
s o l u t i o n w a s f o u n d t o b e m o r e e f f e c t i v e t h a n t h e B-M-A
p. 385) one would expect to extr~ct humic acids. They
believe most of the gold occurs as an organometallic
complex in the Au (I) valence state and thus most of
the gold is not present in a free state in the rocks.
5'1
Variations of the organic extraction techniques
given by Degens and Reuter (1964) were used by the author
on samples from Mercur, Utah; Getchell Mine, Nevada
(sample taken from dump); and the Newmont mine, Carlin,
Nevada (sample from the east pit), to determine if
hydrocarbons were present.
Three methods of extraction, which will be described
briefly below, were used on crushed carbon-rich rock
samples with the organic extract being dissolved in CCl4
before being injected into Wilks cells for use in a
Beckman IR"20 spectrophotometer. The infrared spectra
obtained were compared against the spectra for pure
CCl4 to determine which organics were present. Extraction
techniques involved using a mixture of benezene, methanol.
and acetone: 0.3 N NaOH; or 0.5 N NH4Ac solutions.
In the benezene-methanol-acetone method (70:15:15
by volume), the B-M-A mixture was found to leave an
infrared detectable residue which was deleterious to
interpretation of the Mercur, Carlin, and Getchell samples.
The organic extraction technique using a 0.3 N NaOH
solution was found to be more effective than the B-M-A
5 8
m e t h o d . I n t h i s m e t h o d NaOH w a s a l l o w e d t o p r e c o l a t e
t h r o u g h t h e s a m p l e w h i c h w a s o n a f i b e r g l a s s f i l t e r p a p e r
i n a B u c h n e r f u n n e l w i t h t h e s o l u t i o n b e i n g a l l o w e d t o
c o l l e c t i n a b e a k e r . T h e l e a c h a n t w a s t h e n p l a c e d i n
a p l a s t i c b o t t l e w i t h C C l ^ a n d s h a k e n o n a p a i n t s h a k e r
f o r 3 0 m i n u t e s . T h e C C 1 ^ # w h i c h i s h e a v i e r t h a n t h e
NaOH, w a s d r a w n o f f a n d p a r t i a l l y e v a p o r a t e d t o c o n c e n t r a t e
a n y o r g a n i c s p r e s e n t — t h e s o l u t i o n w a s t h e n i n j e c t e d i n t o
a W i l k s c e l l f o r u s e o n t h e i n f r a r e d s p e c t r o p h o t o m e t e r .
E x t r a c t i o n u s i n g a 0 . 5 N NH^Ac s o l u t i o n o n t h e
M e r c u r , C a r l i n , a n d G e t c h e l l s a m p l e s a l s o w a s f o u n d t o
b e e f f e c t i v e . T h e NH^Ac s o l u t i o n w a s a l l o w e d t o p e r c o l a t e
t h r o u g h t h e s a m p l e o n a f i b e r g l a s s f i l t e r p a p e r i n a
B u c h n e r f u n n e l . T h e s o l u t i o n w a s e v a p o r a t e d i n a b e a k e r
b e l o w 8 0 ° C o n a h o t p l a t e . C C I 4 w a s t h e n a d d e d a n d
s t i r r e d t o d i s s o l v e a n y o r g a n i c s . T h e C C l ^ w a s a l l o w e d
t o p a r t i a l l y e v a p o r a t e t o c o n c e n t r a t e a n y o r g a n i c s a n d
t h e s o l u t i o n w a s t h e n i n j e c t e d i n t o a W i l k s c e l l f o r u s e
o n t h e i n f r a r e d s p e c t r o p h o t o m e t e r . An i o n e x c h a n g e
c o l u m n o f a m b e r l i t e MB-3 w a s t r i e d b e f o r e t h e a b o v e
d e s c r i b e d m e t h o d t o r e m o v e t h e a c e t a t e i o n a n d g a v e t h e
s a m e r e s u l t s .
T h e e x t r a c t i o n s a n d f i l l i n g o f t h e W i l k s c e l l
s h o u l d b e p e r f o r m e d u n d e r a f u m e h o o d w i t h t h e W i l k s
c e l l b e i n g f l u s h e d w i t h CCl/^ s e v e r a l t i m e s b e t w e e n s a m p l e s .
T h e i n f r a r e d s p e c t r a f o r t h e s a m p l e s a r e p r e s e n t e d
58
method. In this method NaOH was allowed to precolate
through the sample which was on a fiberglass filter paper
in a Buchner funnel with the solution being allowed to
collect in a beaker. The leachant was then placed in
a plastic bottle with CC14 and shaken on a paint sh~ker
for )0 minutes. The CCI4. which is heavier than the
NaOH, was drawn off and partially evaporated to concentrate
any organics present--the solution WqS then injected into
a Wilks cell for use on the infrared spectrophotometer.
Extraction using a 0.5 N NH4Ac solution on the
Mercur, Carlin, and Getchell samples also was found to
be effective. The NH4Ac solution was allowed to percolate
through the sample on a fiberglass filter paper in a
BUchner funnel. The solution was evaporated in a beaker
below BOoc on a hotplate. CC14 was then added and
stirred to dissolve any organics. The CCl4 was allowed
to partially evaporate to concentrate any organics and
the solution was then injected into a Wilks cell for use
on the infrared spectrophotometer. An ion exchange
column of amberlite MB-3 was tried before the above
described method to remove the acetate ion and gave the
same results.
The extractions and filling of the Wilks cell
should be performed under a fume hood with the Wilks
cell being flushed with CC14 several times between samples.
The infrared spectra for the samples are presented
59
i n F i g u r e 1 9 a n d 2 0 . T h e 0 , 3 N NaOH e x t r a c t i o n
( F i g . 1 9 ) w a s f o u n d t o c o n t a i n o r g a n i c s o f t h e a l k a n e
g r o u p w h i c h h a v e a c h a r a c t e r i s t i c i n f r a r e d a b s o r p t i o n
b a n d a r o u n d 2 9 0 0 c m " 1 . T h e 0 . 5 N NH^Ac e x t r a c t i o n
( F i g . 2 0 ) w a s f o u n d t o d i s s o l v e c a r b o x y l i c a c i d s ( c a r b o n y l
g r o u p — n o t b e l i e v e d t o b e a c e t i c a c i d ) w h i c h h a v e a
c h a r a c t e r i s t i c i n f r a r e d a b s o r p t i o n b a n d a r o u n d 1 7 0 0 c m ~ *
a n d s o m e o r g a n i c s o f t h e a l k a n e g r o u p . ( A l k a n e s a r e o n e
o f t h e m a i n h y d r o c a r b o n c o n s t i t u e n t s o f p e t r o l e u m . )
O r g a n i c a c i d s a n d m e t h a n e a r e k n o w n p r o d u c t s o f b a c t e r i a l
a c t i o n b u t t h e a u t h o r i s u n c e r t a i n w h e t h e r t h e c a r b o x y l i c
a c i d s a r e b a c t e r i a l p r o d u c t s . T h e c a r b o x y l i c a c i d s
c o u l d a l s o b e o r g a n i c d e c a y p r o d u c t s i n t r o d u c e d b y
g r o u n d w a t e r .
Some m o b i l i z a t i o n o f c a r b o n i n a h y d r o t h e r m a l
e n v i r o n m e n t h a s b e e n s u g g e s t e d b y J o r a l e m o n ( 1 9 5 1 . P - 2 7 3 )
f o r t h e g o l d d e p o s i t a t G e t c h e l l M i n e , N e v a d a , a n d b y
H a u s e n a n d K e r r ( 1 9 6 8 , p , 9 3 0 ) f o r t h e g o l d d e p o s i t
a t C a r l i n , N e v a d a , T h e a u t h o r f o u n d n e a r t h e S a c r a m e n t o
b r e c c i a p i p e a s m a l l v e i n l e t o f i n t e r s t i t i a l c a r b o n
a l o n g w h i c h a s m a l l o f f s e t h a d o c c u r r e d . T h e s m a l l
f r a c t u r e p r o b a b l y s e r v e d a s a c o n d u i t f o r a n o r g a n i c
r i c h s o l u t i o n w i t h t h e c a r b o n d i s p e r s i n g i n t o t h e
s u r r o u n d i n g r o c k . N e a r t h e s a m e l o c a t i o n c a r b o n - r i c h
m a t e r i a l a b u t s a g a i n s t a h i g h l y a l t e r e d o u t c r o p o f r o c k
w h i c h m i g h t b e a l t e r e d i n t r u s i v e a n d w h o s e p h y s i c a l
--,
59
in Figure 19 9nd 20. The 0.3 N NaOH extraction
(Fig. 19) was found to contain organics of the alkane
group which have a characteristic infrared absorption
band around 2900 -1 cm • The 0.5 N NH4Ac extraction
(Fig. 20) was found to dissolve carboxylic acids (carbonyl
group--not believed to be acetic acid) which have a
characteristic infrared absorption band around 1700 cm- 1
and some organics of the alkane group. (Alkanes are one
of the main hydrocarbon constituents of petroleum.)
Organic acids and methane are known products of bacterial
action but the author is uncertain whether the carboxylic
gcids are bacterial products. The carboxylic acids
could also be organic decay products introduced by
ground water.
Some mobilization of carbon in a hydrothermal
environment has been suggested by Joralemon (1951. p. 273)
for the gold deposit at Getchell Mine, Nevada, and by
Hausen and Kerr (1968, p. 930) for the gold deposit
at Carlin, Nevada. The author found near the Sacramento
breccia pipe a small veinlet of interstitial carbon
along which a small offset had occurred. The small
fracture probably served as a conduit for an organic
rich solution with the carbon dispersing into the
surrounding rock. Near the same location carbon-rich
material abuts against a highly altered outcrop of rock
which might be altered intrusive and whose physical
6 0
Wavelength in Micron* 4.1 •
—i r • S T T.I t t to II II 14 1, 10 10 40
—i 1 • i i • i 1 1—H r—i-*"-!—i 1—r CCI4
Sacramento Mi no, Mercur, Utah
Brickyard Mine, Mercur, Utah
long Trail Shale, Ophir, Utah
Carlin. Nevada
Getchell Mine, Nevada
1000 1000 1*00 1400 1100 1000 100 *00 400 Wavenumber Cm"'
F i g u r e 1 9 . I n f r a r e d s p e c t r a o f 0 * 3 N NaOH o r g a n i c e x t r a c t i o n s f r o m r o c k s a m p l e s a s s o c i a t e d w i t h g o l d d e p o s i t s .
Wavelength In Micron.
"I I ••• ••• • ... , U • '0 It II ..,. 20
Sacramento Mine, Mereu" Utah
Brickyard Mine, Mere ur, Utah
long Trail Shale, Ophir, Utah
Carlin, Nevada r-----..,------.......
Getchell Mine, Nevada
.000 JOOO 1000 •••• •• 00 1400 noo .000 .00
Wavenumber Cm-l
Figure 19. Infrared spectra of 0.3 N NaOH organic extractions from rock samples associated with gold deposits.
.00
60
.00
F i g u r e 2 0 . I n f r a r e d s p e c t r a o f 0 . 5 N NHjhAc o r g a n i c e x t r a c t i o n s f r o m r o c k s a m p l e s a s s o c i a t e d w i t h g o l d d e p o s i t s .
l' u '.1 1.1 • ... , , .• e " '0 "11 ,.. '. 20
Sacramenta Mine, Mercur, Utah
Brickyard Mine, Mereur, Utah
long Troll Shale, Ophir, Utah
Carlin, Nevada
Getchell Mine, Nevada
4000 3000 2000 1eoo 1600 1400 1200 tooo eoo
Wavenumber em-'
Figure 20 0 Infrared spectra of 0.5 N NHaAc organic extractions from rock samples assoc1ated with gold deposits.
600
61
10 ...
400
r e l a t i o n m i g h t b e d u e t o f a u l t i n g . Some c a r b o n
s t r e a m i n g i n t o h e a l e d f r a c t u r e s i n t h e a l t e r e d m a s s i s
a p p a r e n t . T h e a l t e r e d m a s s c o n s i s t s o f c a l c i t e ,
k a o l i n i t e , q u a r t z , a n d i l l i t e . T h e c a r b o n i s n o t
r e s t r i c t e d t o o n e r o c k t y p e a t t h e S a c r a m e n t o b r e c c i a
p i p e , w h i c h s u g g e s t s e i t h e r m o v e m e n t o f c a r b o n a n d / o r
h y d r o c a r b o n s o r v a r y i n g d e g r e e s o f a l t e r a t i o n . No
e v i d e n c e f o r s o l u t i o n t h i n n i n g , w h i c h m i g h t h a v e c a u s e d
c a r b o n e n r i c h m e n t , w a s s e e n i n t h e S a c r a m e n t o m i n e a r e a ,
b u t t h i s d o e s n o t m e a n i t d i d n o t h a p p e n .
T h e p r e s e n c e o f c a r b o n i s b e l i e v e d t o b e d u e t o
t h e r e d u c i n g a c t i o n o f p a s t h y d r o t h e r m a l s o l u t i o n s
o n a n y h y d r o c a r b o n s t h a t m i g h t h a v e b e e n p r e s e n t i n
t h e s h a l e s a n d s i l t s t o n e s . T h e q u e s t i o n o f w h e t h e r
h y d r o c a r b o n s a n d / o r c a r b o n a r e m o b i l e i s a n u n a n s w e r e d
q u e s t i o n , b u t f i e l d e v i d e n c e a n d t h i n s e c t i o n s t u d y
s u g g e s t t h a t t h e r e h a s b e e n a n a p p a r e n t m o b i l i t y o f
c a r b o n a n d h y d r o c a r b o n s •
62
relation might be due to faulting. Some carbon
streaming into healed fractures in the altered mass is
apparent. The altered mass consists of calcite,
kaolinite, quartz, and illite. The carbon is not
restricted to one rock type at the Sacramento breccia
pipe, which suggests either movement of carbon and/or
hydrocarbons or varying degrees of alteration. No
evidence for solution thinning, which might have caused
carbon enrichment, was seen in the Sacramento mine area.
but this does not mean it did not happen.
The presence of carbon is believed to be due to
the reducing action of past hydrothermal solutions
on any hydrocarbons that might have been present in
the shales and siltstones. The question of whether
hydrocarbons and/or carbon are mobile is an unanswered
question, but field evidence and thin section study
suggest that there has been an apparent mobility of
carbon and hydrocarbons.
SULFUR I S O T O P I C DATA
T w e n t y s a m p l e s o f s u l f u r b e a r i n g m i n e r a l s w e r e
c o l l e c t e d f r o m v a r i o u s m i n e s a r o u n d t h e g h o s t t o w n o f
M e r c u r , U t a h , f o r a s u l f u r i s o t o p i c s t u d y ( F i g . 2 1 ) .
P r i m a r y b a r i t e o c c u r s i n t h e s i l v e r l e d g e f r o m w h i c h
s i l v e r w a s p r o d u c e d i n t h e e a r l y d a y s o f t h e d i s t r i c t .
S e c o n d a r y s u l f a t e s o c c u r a s j a r o s i t e , a l u n l t e , m e l a n t e r i t e -
p i s a n i t e , h a l o t r l c h i t e , s c o r o d l t e , a n d g y p s u m .
N a t r o a l u n i t e w a s f o u n d i n s e v e r a l p l a c e s o u t s i d e t h e
M e r c u r c a m p ( C l a y C a n y o n a n d W e s t M e r c u r ) . P r i m a r y
s u l f i d e s o c c u r a s p y r i t e , o r p l m e n t , r e a l g a r , c i n n a b a r ,
a r s e n o p y r i t e , s t i b n i t e , c h a l c o p y r i t e , s u l v a n i t e ,
s p h a l e r i t e , a n d g a l e n a . S e c o n d a r y s u l f i d e o c c u r s
s p a r i n g l y a s e l e m e n t a l s u l f u r . P r i m a r y s u l f i d e s a r e n o t
c o m m o n i n t h e d i s t r i c t . P y r i t e i s t h e m o s t c o m m o n s u l f i d e
f o u n d i n t h e o l d q u a r r y a r e a s .
S u l f u r d i o x i d e w a s p r e p a r e d f r o m s u l f i d e s a n d
s u l f a t e s b y m e t h o d s o u t l i n e d , b y M » L . J e n s e n a t t h e
L a b o r a t o r y o f I s o t o p e G e o l o g y , U n i v e r s i t y o f U t a h . T h e
s u l f i d e s w e r e b u r n e d i n a v a c u u m a t 8 5 0 ° G f o r 1 5 m i n u t e s
w i t h c o p p e r o x i d e t o p r o d u c e S 0 2 • T h e SO2 a n d C 0 2
f o r m e d w e r e s e p a r a t e d i n a s e r i e s o f c o l d t r a p s . T h e
S 0 2 a n d G 0 2 w e r e f i r s t c o l l e c t e d i n a l i q u i d n i t r o g e n
t r a p . T h e f r o z e n S 0 2 a n d C 0 2 w e r e a l l o w e d t o s u b l i m a t e
o n c e t h e l i q u i d n i t r o g e n t r a p w a s r e m o v e d a n d c o l l e c t e d
SULFUR ISOTOPIC DATA
Twenty samples of sulfur bearing minerals were
collected from various mines around the ghost town of
Mercur. Utah. for a sulfur isotopic study (Fig. 21).
Primary barite occurs in the silver ledge from which
silver was produced in the early days of the district.
Secondary sulfates occur as jarosite. alunite, melanterite-
pisanite, halotrichite, scorodite. and gypsum.
Natroalunite was found in several places outside the
Mercur camp (Clay Canyon and West Mercur). Primary
sulfides occur as pyrite. orpiment, realgar. cinnabar.
arsenopyrite. stibnite, chalcopyrite. sulvanite,
sphalerite. and galena. Secondary sulfide occurs
sparingly as elemental sulfur. Primary sulfides are not
common in the district. Pyrite is the most common sulfide
found in the old quarry areas.
Sulfur dioxide was prepared from sulfides and
sulfates by methods outlined; by M~L. Jensen at the
Laboratory of Isotope Geology, University of Utah. The
sulfides were burned in a vacuum at 8500 C for 15 minutes
with copper oxide to produce S02. The 502 and CO2
formed were separated in a series of cold traps. The
S02 and CO2 were first collected in a liquid nitrogen
trap. The frozen 502 and CO2 were allowed to sublimate
once the liquid nitrogen trap was removed and collected
6 4
i n a t r a p o f N - p e n t a n e f r o z e n b y l i q u i d n i t r o g e n .
An i n t e r v e n i n g c o l d t r a p o f a c e t o n e a n d d r y i c e r e m o v e d
a n y w a t e r p r e s e n t . A l l o w i n g t h e N - p e n t a n e t o m e l t ,
g a s e o u s C 0 2 i s f i r s t r e l e a s e d l e a v i n g t h e S 0 2 . T h e S 0 2
i s c o l l e c t e d i n a g a s f l a s k f o r m a s s s p e c t r o m e t r i c
a n a l y s i s •
T h e s u l f a t e s a r e p r e p a r e d b y r e a c t i n g t h e m w i t h a
m i x t u r e o f H I , HNO^, a n d HC1 p r o d u c i n g H 2 S w h i c h i s
b u b b l e d t h r o u g h a c a d m i u m a c e t a t e s o l u t i o n t o p r o d u c e
C d S . T h e C d S i s c o n v e r t e d t o A g 2 S b y a d d i n g AgNO^
s o l u t i o n . T h e d r i e d A g 2 S i s b u r n e d b y t h e s a m e p r o c e d u r e
a s t h e s u l f i d e s t o p r o d u c e S 0 2 •
T h e S 0 2 s a m p l e s w e r e a n a l y z e d o n a m a s s s p e c t r o m e t e r
b y J o s e p h J e n s e n w i t h t h e c a l c u l a t i o n s b e i n g m a d e b y t h e
a u t h o r . T a b l e 4 s h o w s t h e r e s u l t s o f t h e a n a l y s e s .
S u l f u r i s o t o p i c c o m p o s i t i o n o f a s u l f u r - b e a r i n g
m i n e r a l i s c o n t r o l l e d b y a n u m b e r o f f a c t o r s i n c l u d i n g ,
a c c o r d i n g t o O h m o t o ( 1 9 7 2 , p . 5 5 3 ) " ( 1 ) t h e r e l a t i v e
i s o t o p i c e n r i c h m e n t f a c t o r s o f a q u e o u s s u l f u r s p e c i e s ,
( 2 ) t h e m o l e f r a c t i o n s o f a q u e o u s s u l f u r s p e c i e s , a n d
( 3 ) t h e m e a n i s o t o p i c c o m p o s i t i o n o f s u l f u r i n t h e
s o l u t i o n s . " O h m o t o ( 1 9 7 2 , p . 5 5 6 ) f u r t h e r s t a t e s t h a t ,
" t h e m o l e f r a c t i o n s o f a q u e o u s s u l f u r s p e c i e s r e l a t i v e
t o t o t a l s u l f u r c o n t e n t a r e d e p e n d e n t o n t h e e q u i l i b r i u m
c o n s t a n t s f o r t h e r e a c t i o n s , t h e a c t i v i t y c o e f f i c i e n t s
o f a q u e o u s s p e c i e s , t h e f u g a c i t y o f o x y g e n , t h e p H ,
64
in a trap of N-pentane frozen by liquid nitrogen.
An intervening cold trap of acetone and dry ice removed
any water present. Allowing the N-pentane to melt,
gaseous CO2 is first released leaving the S02' The S02
is collected in a gas flask for mass spectrometric
analysis.
The sulfates are prepared by reacting them with a
mixture of HI, HNO J , and HCI producing H2S which is
bubbled through a cadmium acetate solution to produce
CdS. The CdS is converted to Ag2S by adding AgNOJ
solution. The dried Ag2S is burned by the same procedure
as the sulfides to produce S02.
The S02 samples were analyzed on a mass spectrometer
by Joseph Jensen with the calculations being made by the
author. Table 4 shows the results of the analyses.
Sulfur isotopic composition of a sulfur-bearing
mineral is controlled by a number of factors including,
according to Ohmoto (1972, p. 55J) -(1) the relative
isotopic enrichment factors of aqueous sulfur species,
(2) the mole fractions of aqueous sulfur species, and
()) the mean isotopic composition of sulfur in the
solutions.- Ohmoto (1972, p. 556) further states that,
-the mole fractions of aqueous sulfur species relative
to total sulfur content are dependent on the equilibrium
constants for the reactions, the activity coefficients
of aqueous species, the fugacity of oxygen, the pH,
CONTOUR INTERVAL 40 FEET DATUM IS MEAN SEA LEVEL
g u r e 2 1 . Map o f p a r t o f t h e M e r c u r . U t a h t o p o g r a p h i c q u a d r a n g l e s h o w i n g c o l l e c t i o n s i t e s a n d s a m p l e n u m b e r s f o r t h e s u l f u r i s o t o p e s a m p l e s .
CONTOUR INTERVAL 40 FEET DATU M IS MEAN SEA Ll VEL
.65
Figure 21~ Map of part of the Mercur~ Utah topographic quadrangle showing collection sites and sample numbers for the sulfur isotope samples.
T a b l e 4 . S u l f u r i s o t o p e d a t a .
S a m p l e 6 ^ s A r e a o f C o l l e c t i o n
1 - - o r p i m e n t + 4 . 8 3 G e y s e r - M a r i o n m i n e
2 - - r e a l g a r 7 . 1 3 M e r c u r H i l l m i n e
3 - - r e a l g a r 6 . 2 8 G e y s e r - M a r i o n m i n e
4 - - o r p l m e n t 4 . 6 3 B r i c k y a r d m i n e
5 - - o r p l m e n t 1 5 * 8 0 B r i c k y a r d m i n e
6 - - r e a l g a r 8 . 9 0 B r i c k y a r d m i n e
7 - - r e a l g a r 6 . 5 7 B r i c k y a r d m i n e
8 - - b a r l t e 1 5 - 2 6 G e y s e r - M a r i o n m i n e
9 - - o r p l m e n t 9 . 5 1 G e y s e r - M a r i o n m i n e
1 0 - - p y r i t e 1 1 . 5 5 S a c r a m e n t o m i n e
1 1 - - p y r i t e 4 . 7 8 M e r c u r H i l l m i n e
1 2 - - b a r i t e 3 . 7 3 G e y s e r - M a r i o n m i n e
1 3 - - p y r i t e 9 . 8 7 S a c r a m e n t o m i n e
1 4 - - s t l b n i t e 1 0 . 1 2 G e y s e r - M a r i o n m i n e
1 5 - - p y r i t e 1 7 . 1 2 S a c r a m e n t o m i n e
1 6 - - b a r i t e 2 . 8 8 M e r c u r H i l l m i n e
1 7 - - a l u n i t e 2 . 6 0 G e y s e r - M a r i o n m i n e
1 8 - - j a r o s i t e 3 . 1 3 G e y s e r - M a r i o n m i n e
1 9 - - a l u n i t e 2 . 6 4 G e y s e r - M a r i o n m i n e
2 0 - - r e a l g a r 1 0 . 2 9 M e r c u r H i l l m i n e
Table 4. Sulfur isotope data.
Sample
1--orpiment
2--realgar
3--realgar
4--orpiment
5--orplment
6--realgar
7--realgar
8--barite
9--orpirnent
10--pyrite
11--pyrite
12--barite
13--pyrlte
14--stibnlte
15--pyrlte
16--barite
17--alunite
18--jarosite
19--alunite
20--realgar
6 34S
+4.83
7.13
6.28
4.63
15.80
8.90
6.57
15.26
9.51
11.55
4.78
3.73
9.87
10.12
17.12
2.88
2.60
3.13
2.64
10.29
Area of Collection
Geyser-Marion mine
Mercur Hill mine
Geyser-Marion mine
Brickyard mine
Brickyard mine
Brickyard mine
Brickyard mine
Geyser-Marion mine
Geyser-Marion mine
Sacramento mine
Mercur Hill mine
Geyser-Marion mine
Sacramento mine
Geyser-Marion mine
Sacramento mine
Mercur Hill mine
Geyser-Marion mine
Geyser-Marion mine
Geyser-Mar1.on mine
Mercur Hill mine
66
6 ?
a n d t h e m o l a l i t i e s o f p o t a s s i u m a n d s o d i u m i o n s i n t h e
s o l u t i o n s . T h e e q u i l i b r i u m c o n s t a n t s a r e m a i n l y a
f u n c t i o n o f t e m p e r a t u r e , a n d t h e a c t i v i t y c o e f f i c i e n t s
o f t e m p e r a t u r e a n d t h e i o n i c s t r e n g t h o f f l u i d s . " M o r e
s p e c i f i c a l l y O h m o t o ( 1 9 7 2 , p . 5 5 1 ) b e l i e v e s t h a t t h e
pH a n d o x y g e n f u g a c i t y o f a h y d r o t h e r m a l s y s t e m c a n
c o n t r o l t h e < S s 3 ^ c o m p o s i t i o n o f t h e m i n e r a l .
J e n s e n e t . a l . ( 1 9 7 1 a , p . 6 2 4 ) p o i n t o u t t h a t
a n d S 0 2 t e n d t o e q u i l i b r a t e b y t h e i s o t o p i c
e x c h a n g e r e a c t i o n :
^ S 3 ^ + s 3 2 o 2 J * H 2 S 3 2 + S 3 ^ 0 2
S i n c e t h e p r e d o m i n a n t g a s p r e s e n t a t h i g h t e m p e r a t u r e s
i s S 0 2 a n d H 2 S a t l o w t e m p e r a t u r e s , H 2 S i s e n r i c h e d
32 3 4 i n S ^ a n d S 0 2 i n S ^ a s t h e t e m p e r a t u r e i s l o w e r e d
( J e n s e n e t . a l . , 1 9 7 1 b , p , 7 6 ) , M g u r e 2 2 i s J e n s e n ' s
d i a g r a m a t i c r e p r e s e n t a t i o n o f t h e c h e m i c a l r e a c t i o n s
t a k i n g p l a c e i n a f l u i d a f t e r i t h a s l e f t i t s s o u r c e .
Some c o n s i d e r a t i o n s t h a t m u s t b e t a k e n i n t o a c c o u n t
i n a n a l y z i n g t h e M e r c u r s u l f u r i s o t o p i c d a t a a r e t h e
a d d i t i o n o f s u l f u r f r o m a u t h i g e n i c p y r i t e , a s u l f u r
b e a r i n g m i n e r a l ' s f o r m a t i o n r a n g e , t h e pH a n d o x y g e n
f u g a c i t y o f t h e h y d r o t h e r m a l s o l u t i o n , t h e t e m p e r a t u r e
o f t h e s o l u t i o n , a n d t h e m i x i n g o f g r o u n d w a t e r s w i t h
j u v e n i l e w a t e r s .
T h e t w o m a i n s o u r c e s o f s u l f u r r e p r e s e n t i n t h e
s u l f u r b e a r i n g m i n e r a l s a r e b e l i e v e d t o h a v e c o m e f r o m
67
and the molalities of potassium and sodium ions in the
solutions. The equilibrium constants are mainly a
function of temperature, and the activity coefficients
of temper~ture and the ionic strength of fluids." More
specifically Ohmoto (1972, p. 551) believes that the
pH and oxygen fugacity of a hydrothermal system can
control the oS34 composition of the mineral.
Jensen et. ale (1971a, p. 624) point out that
H2S and S02 tend to equilibrate by the isotopic
exchange reaction:
H S34 + s32 0 -. H S32 + S34 0 2 2 ~ 2 2
Since the predominant gas present at high temperatures
is S02 and H2 S at low temperatures, H2 S is enriched
in S32 and S02 in S34 as the temperature is lowered
(Jensen et. al., 1971b, p. 76). Figure 22 is Jensen's
diagramatic representation of the chemical reactions
taking place in a fluid after it has left its source.
Some considerations that must be taken into account
in analyzing the Mercur sulfur isotopic data are the
addition of sulfur from authigenic pyrite, a sulfur
bearing mineral's formation range, the pH and oxygen
fugacity of the hydrothermal solution, the temperature
of the solution, and the mixing of ground waters with
juvenile waters.
The two main sources of sulfur represent in the
sulfur bearing minerals are believed to have come from
6 8
34
(Medium T and Low P) Orifice of fumarole
H2 CO
S02—>S04 (with same bS composition as HjS)
rigin of hypogene sulfates, ich are enriched in s34
(derived from h^S-OSO.,-*^), while associated sulfides are comparatively enriched in S 3 2 (derived from H2S)
H,S to S02, H2S03, and H^O^ at 250*C gives s'A enrichments of +16,+25, and +357.o respectively H.T.
(Hi T and Hi P) ^0
Origin of early pyrite which in many cases is later replaced by Cu, Zn, and Pb. Sulfide minerals with little if any change in cS^ composition
Isotopic equilibrium occurring between H2S and SC>2 (aided by catalytic H2 and H?0 agents) results in gradual increase
3 2 in H2S and of S 3 4 in SO2 (H , s 3 4 + s 3 V :> H o s 3 2 + s 3 V)
f Parent magma or Rocks undergoing metamorphism H O-CO -H S in order of abundance
H2S if pH < 7 HS" if pH > 7
F i g u r e 2 2 . C h e m i c a l r e a c t i o n s a n d v a l u e s i n a f u m a r o l i c c o n d u i t . ( f r o m J e n s e n e t . a l . , 1 9 7 1 . P . 7 7 )
3H2S03-->::!2S04 +S+1l20
Origin of SOZ enriched in 534
(InClllence on tS)4 vallle of marine S04 oC +20.21..]
Indigenous ferric iron disseminated through
rock
68
slllfates, which are enriched in SJ4 (derived from H2S-->S02-~OJ)' while associated slllCides are co=paratively enrlched in SJ2 (derived fro~ H25)
t 14 . ~S variation increasing
between 502 and H2S with increasing ti~e of equll ibration
Origin of early pyrite which in many cases 1. later replaced by ell, Zn, and Pb. Sulfide mineral. with little if any change 1n tSJ4 composition
HZS to SOZ' H2S03, and H2S04 at 2~OiC gives SJ4 enrichments of +16,+25, and +357.. respectively H.t. M2S S02
M S+ZH O~->SO +)H 3H2 ~sotoP1C equi l1briulII occllrring bet .. ·een
H2S and 50
2 (aided by catalytic H2 and
H20 agents) reslllt. in gradual increase of SJ2 in H2S and of 534 in S02 2 2 2 2
(Hi T and Hi P) H20
HZS
CO2
(M 534+5320 ~:>H S32+S340 ) 2 2 2 2
~ ":.~- f::::;:o::::;",g ~u="" •• ~02-H25 in order of abundance
"ZS if pH < 7
HS- if pH> 7
Figure 22. Chemical reactions and S14 values in a fuma.rolic conduit. (from Jensen et. al •• 1971, p. 77)
6 9
J u v e n i l e a n d g r o u n d w a t e r s . T h e a d d i t i o n o f s u l f u r
f r o m h y d r o c a r b o n s a n d a u t h i g e n i c p y r i t e w a s p r o b a b l y
m i n o r a n d t h u s h a d v e r y l i t t l e e f f e c t o n t h e i s o t o p i c
c o m p o s i t i o n o f t h e s u l f u r b e a r i n g m i n e r a l s .
T h e a u t h o r b e l i e v e s t h a t t h e s u l f u r i s o t o p i c
c o m p o s i t i o n o f t h e s a m p l e s w a s n o t c o n t r o l l e d b y pH
a n d o x y g e n f u g a c i t y b e c a u s e t h e i s o t o p i c v a l u e s g i v e n
b y O h m o t o ( 1 9 7 2 , p . 5 5 9 , 5 6 0 , 5 7 3 ) d o n o t f i t t h e pH
c o n d i t i o n s b e l i e v e d t o h a v e b e e n p r e s e n t d u r i n g
h y d r o t h e r m a l a l t e r a t i o n . One c a n n o t e x p e c t t h e i s o t o p i c
v a l u e s o f T a b l e 4 t o r e f l e c t d i r e c t c h a n g i n g e q u i l i b r a t i o n
c o n d i t i o n s b e t w e e n H 2 S a n d S 0 2 a s i n F i g u r e 2 2 . S i n c e
i n F i g u r e 2 2 o n e c o n s i d e r s H 2 S e n r i c h e d i n S 3 ^ a n d
32
S 0 2 e n r i c h e d i n S a t h i g h t e m p e r a t u r e s a n d d o e s n o t
c o n s i d e r t h e m i x i n g o f j u v e n i l e a n d g r o u n d w a t e r s a t
m o d e r a t e t o l o w t e m p e r a t u r e s .
M e r c u r , U t a h , r e p r e s e n t s a l o w t e m p e r a t u r e
e p i t h e r m a l d e p o s i t , a l t h o u g h h i g h t e m p e r a t u r e c o n d i t i o n s
a r e b e l i e v e d t o h a v e e x i s t e d i n t h e i n t r u s i v e m a g m a .
A c o n v e c t i v e h y d r o t h e r m a l s y s t e m m a y h a v e e x i s t e d i n a n d
a r o u n d t h e magma w i t h t h e g r o u n d w a t e r b e i n g w a r m e d a n d
m i x e d w i t h j u v e n i l e w a t e r s . I n m o d e r n h o t s p r i n g a r e a s ,
o x y g e n i s o t o p e s i n d i c a t e t h a t m o s t o f t h e w a t e r i s
m e t e o r i c . S i n c e r h y o l i t e s a r e b e l i e v e d t o r e p r e s e n t
r o c k s o f l o w w a t e r c o n t e n t , a n y w a t e r d r a w n t o w a r d s a n d
69
juvenile and ground waters. The addition of sulfur
from hydrocarbons and authigenic pyrite was probably
minor and thus had very little effect on the isotopic
composition of the sulfur bearing minerals.
The author believes that the sulfur isotopic
composition of the samples was not controlled by pH
and oxygen fugacity because the isotopic values given
by Ohmoto (1972, p. 559. 560, 573) do not fit the pH
conditions believed to have been present during
hydrothermal alteration. One cannot expect the isotopic
values of Table 4 to reflect direct changing equilibration
conditions between H2S and S02 as in Figure 22. Since
in Figure 22 one considers H2S enriched in s34 and
S02 enriched in S32 at high temperatures and does not
consider the mixing of juvenile and ground waters at
moderate to low temperatures.
Mercur. Utah, represents a low temperature
epithermal deposit. although high temperature conditions
are believed to have existed in the intrusive magma.
A convective hydrothermal system may have existed in and
around the magma with the ground water being warmed and
mixed with juvenile waters. In modern hot spring areas,
oxygen isotopes indicate that most of the water is
meteoric. Since rhyolites are believed to represent
rocks of low water content, any water drawn towards and
7 0
i n t o t h e i n t r u s i v e w o u l d h e l p l e a c h t h e r o c k a s i t
w a s b e i n g a l t e r e d . T h i s l e a c h i n g a n d m i x i n g o f w a t e r s
w o u l d a d d s u l f u r t o t h e w a t e r s .
S i n c e m o s t o f t h e s u l f u r p r e s e n t i n t h e s u l f i d e s
i s b e l i e v e d t o r e p r e s e n t s u l f u r f r o m m e t e o r i c a n d
j u v e n i l e w a t e r s , a n y h e a t i n g a n d m i x i n g o f m e t e o r i c
w a t e r s w i t h j u v e n i l e w a t e r s w o u l d b e a c c o m p a n i e d
b y t h e e q u i l i b r a t i o n o f H2S a n d S 0 2 r a t i o s a c c o r d i n g
t o e x i s t i n g T a n d P c o n d i t i o n s . A t l o w t e m p e r a t u r e s ,
t h e c o n v e r s i o n o f S 0 2 a n d H 2 S i n e q u i l i b r i u m c o n d i t i o n s
w o u l d , a c c o r d i n g t o J e n s e n e t , a l . ( 1 9 7 1 b t p , 7 7 ) .
3 4 g i v e r i s e t o s u l f i d e s d i f f e r i n g i n S c o m p o s i t i o n :
S 3 4 0 2 + 3 % — * ftgS34 + 2 H 2 0
3 4 T h e H 2 S V f o r m e d b y t h e a b o v e r e a c t i o n s w o u l d a d d t o t h e
32
H 2 S e n r i c h e d i n S p r e s e n t i n s o l u t i o n i n n e a r - s u r f a c e ,
l o w t e m p e r a t u r e c o n d i t i o n s .
T h e d i f f e r i n g d e g r e e s o f a l t e r a t i o n a t M e r c u r
s u g g e s t t h a t d i f f e r e n t p h y s i c a l a n d c h e m i c a l e n v i r o n m e n t s
e x i s t e d t h e r e a t o n e t i m e . T h u s t h e p h y s i c a l a n d c h e m i c a l
c o n d i t i o n s t h a t w e r e p r e s e n t i n o n e l o c a l i t y d i d n o t
n e c e s s a r i l y e x i s t i n a n e a r b y a r e a . T h i s s i t u a t i o n
p r o b a b l y a r o s e o u t o f v a r y i n g p e r m e a b i l i t y c o n d i t i o n s ,
f r a c t u r e p l u m b i n g c o n t r o l , n e a r n e s s t o t h e i n t r u s i v e ,
a n d t h e a v a i l a b i l i t y a n d a b i l i t y o f g r o u n d w a t e r t o
e n t e r t h e s y s t e m . T h e s e v a r y i n g p h y s i c a l a n d c h e m i c a l
c o n d i t i o n s w o u l d c o n t r o l t h e a m o u n t s o f a q u e o u s s u l f u r
into the intrusive would help leach the rock as it
was being altered. This leaching and mixing of waters
would add sulfur to the waters.
Since most of the sulfur present in the sulfides
is believed to represent sulfur from meteoric and
juvenile watprs, any heating and mixing of meteoric
w~ters with juvenile waters would be accompanied
by the equilibration of H2S and S02 ratios according
to existing T and P conditions. At low temperatures,
70
the conversion of S02 and H2S in equilibrium conditions
would, according to Jensen et. ale (1971b, p. 77).
give rise to sulfides differing in S34 composition:
S3402 + 3~ --. ~s34 + 2H20
The H2S34 formed by the above reactions would add to the
H2S enriched in S32 present in solution in near-surface,
low temperature conditions.
The differing degrees of alteration at Mercur
suggest that different physical and chemical environments
existed there at one time. Thus the physical and chemical
conditions that were present in one locality did not
necessarily exist in a nearby area. This situation
probably arose out of varying permeability conditions,
fr~cture plumbing control, nearness to the intrusive.
and the availability and ability of ground water to
enter the system. These varying physical and chemical
conditions would control the amounts of aqueous sulfur
7 1
s p e c i e s t h a t w e r e p r e s e n t a n d t h u s t h e i s o t o p i c
c o m p o s i t i o n o f t h e s u l f u r - b e a r i n g m i n e r a l s .
T h e a l u n i t e a n d j a r o s i t e f o r w h i c h s u l f u r i s o t o p i c
v a l u e s w e r e o b t a i n e d b o t h s h o w 6 S 3 ^ v a l u e s n e a r t h e
34
p r i m a r y <5S^ v a l u e . T h e y a r e b e l i e v e d t o b e s e c o n d a r y
a n d t h e r e s u l t o f t h e w e a t h e r i n g o f p r i m a r y s u l f i d e s ,
s u c h a s p y r i t e a n d s t i b n i t e .
T h e o r p l m e n t a n d r e a l g a r f r o m t h e B r i c k y a r d m i n e 3 4
s h o w a v a r i a t i o n i n 6 S ^ w h i c h c o u l d i n d i c a t e m i n e r a l
f o r m a t i o n o v e r a p e r i o d o f t i m e w i t h c h a n g i n g c h e m i c a l
c o n d i t i o n s o r a c c e p t a n c e b y t h e m i n e r a l o f s u l f u r w h o s e
i s o t o p i c c o m p o s i t i o n w a s d e t e r m i n e d b y pH a n d o x y g e n
f u g a c i t y w h i c h a c c o r d i n g t o O h m o t o 1 s d i a g r a m s ( 1 9 7 2 ,
p . 5 6 0 , 5 5 8 ) i s u n l i k e l y .
B a r i t e s a m p l e s n u m b e r 12 a n d 1 6 h a v e a l o w
p o s i t i v e s S 3 w h i c h c o u l d i n d i c a t e a r e l a t i v e l y h i g h 32
t e m p e r a t u r e o f f o r m a t i o n s i n c e S 0 2 i s e n r i c h e d i n S v
a t h i g h t e m p e r a t u r e s . A l t e r n a t i v e l y , e q u i l i b r i u m
b e t w e e n H 2 S a n d S 0 2 m a y n o t h a v e b e e n r e a c h e d d u r i n g
f o r m a t i o n o f t h e b a r i t e . B a r i t e s a m p l e n u m b e r 8 3 4
h a s a l a r g e p o s i t i v e 6 S ^ w h i c h c o u l d i n d i c a t e a
p r i m a r y o r i g i n i n n e a r - s u r f a c e c o n d i t i o n s .
T h e s t i b n i t e ( s a m p l e # 1 4 ) s a m p l e h a s a + 1 0 . 1 2 #
v a l u e w h i c h c o u l d i n d i c a t e a h o t s p r i n g e n v i r o n m e n t
o r t h a t e q u i l i b r i u m c o n d i t i o n s w e r e n o t a t t a i n e d .
P r a g e n e t i c r e l a t i o n s f o r t h e t w o m i n e r a l s i n h a n d s p e c i m e n
71
species that were present and thus the isotopic
composition of the sulfur-bearing minerals.
The alunite and jarosite for which sulfur isotopic
values were obtained both show 0834 values near the
primary os34 value. They are believed to be secondary
and the result of the weathering of primary sulfides,
such as pyrite and st1bnite.
The orpiment and realgar from the Brickyard mine
show a variation in oS34 which could 1ndicate mineral
formation over a period of time with changing chemical
conditions or acceptance by the mineral of sulfur whose
isotopic composition was determined by pH and oxygen
fugacity which according to Ohmoto's diagrams (1972,
p. 560, 558) is unlikely.
Barite samples number 12 and 16 have a low
positive oS34 which could indicate a relatively high
temperature of formation since 802 is enriched in S32
at high temperatures. Alternatively, equilibrium
between H2 S and S02 may not have been reached during
formation of the barite. Bar1te sample number 8
has a large positive os34 which could indicate a
primary origin in near-surface conditions.
The stibnite (sample #14) sample has a +10.12%
value which could indicate a hot spring environment
or that equilibrium conditions were not attained.
Pragenetic relations for th,! two minerals in hand specimen
i n d i c a t e t h e s t i b n i t e w a s d e p o s i t e d i n t h e l a t e r s t a g e s
o f b a r i t e d e p o s i t i o n o r w a s d e p o s i t e d a f t e r t h e b a r i t e .
P y r i t e s a m p l e s n u m b e r 1 1 , 1 3 $ a n d 1 5 w h i c h c o m e
f r o m o r n e a r t h e S a c r a m e n t o m i n e s h o w a c h a n g e o f
p o s i t i v e v a l u e s w h i c h c o u l d r e f l e c t c h a n g i n g c h e m i c a l
c o n d l t i o n s •
34
T h e d e v i a t i o n s o f <5S^ v a l u e s o b t a i n e d c o u l d b e
e x p l a i n e d b y t h e n o n - e q u i l i b r a t i o n o f S 0 2 a n d H 2 S w h i c h
w a s c a u s e d b y t h e c o n t i n u o u s a d d i t i o n o f s u l f u r f r o m
g r o u n d w a t e r s . A l s o u p w e l l i n g h o t w a t e r s u n d e r g o
c h a n g e s i n s u l f u r g a s s p e c i e s c o n t e n t a s t h e w a t e r s
a r e c o o l e d a n d t h e s u l f u r g a s s p e c i e s a r e o x i d i z e d .
T h u s , t h e s u l f u r i s o t o p i c c o m p o s i t i o n s o f t h e d i s s o l v e d
g a s e s a r e a f f e c t e d . T h e i s o t o p i c c o m p o s i t i o n s f o u n d
a r e b e l i e v e d t o r e p r e s e n t t h e c h e m i c a l c o n d i t i o n s
c o m m o n l y f o u n d i n h o t s p r i n g e n v i r o n m e n t s .
72
indicate the stibnite was deposited in the later stages
of barite deposition or was deposited after the barite.
Pyrite samples number 11. 13. and 15 which come
from or near the Sacramento mine show a change of
positive values which could reflect ohanging chemical
conditions.
The deviations of 6S34 values obtained could be
explained by the non-equilibration of S02 and H2S which
was caused by the continuous addition of sulfur from
ground waters. Also upwelling hot waters undergo
changes in sulfur gas species content as the waters
are cooled and the sulfur gas species are oxidized.
Thus, the sulfur isotopic compositions of the dissolved
gases are affected. The isotopic compositions found
are believed to represent the chemical conditions
commonly found in hot spring environments.
SUMMARY AND RECOMMENDATIONS
T h e t r u e s t r u c t u r a l c h a r a c t e r o f M e r c u r h a s b e e n
o v e r l o o k e d f o r m a n y y e a r s . T h e r h y o l i t e i n t r u s i v e
o n t h e n o r t h s i d e o f E a g l e H i l l a p p e a r s t o h a v e b e e n
f o r c e f u l l y i n t r u d e d a n d t o b e y o u n g e r t h a n f o l d i n g
b e c a u s e o f t h e d r a g f o l d s t h a t o c c u r , n o t i c e a b l y
o n i t s n o r t h s i d e . T h e t w o e x p l o s i v e b r e c c i a p i p e s '
f o r m a t i o n i s b e l i e v e d t o b e r e l a t e d t o t h e h y d r o t h e r m a l
a c t i v i t y w h i c h w a s a p a r t o f e n d - s t a g e m a g m a t l c a c t i v i t y .
T h e c o l l a p s e b r e c c i a n e a r t h e c e n t e r o f t h e g h o s t
t o w n o f M e r c u r f o r m e d a t t h e I n t e r s e c t i o n o f t w o
f a u l t s a n d p r o b a b l y r e s u l t e d f r o m t h e c o l l a p s e o f
t h e r o o f o f a s o l u t i o n c a v e .
A l t e r a t i o n o f t h e G r e a t B l u e L i m e s t o n e a n d t h e
E a g l e H i l l r h y o l i t e i s l o w - g r a d e i n t h e a r e a ,
S l l i c i f i c a t i o n w i t h s o m e s e r i c i t e a n d i l l i t e i s
c h a r a c t e r i s t i c o f t h e g o l d o r e s e q u e n c e . A l t e r a t i o n
o f t h e E a g l e H i l l r h y o l i t e i s v a r i e d a n d i n c l u d e s
k a o l i n i z a t i o n , s e r i c i t i z a t i o n , a n d s l l i c i f i c a t i o n .
K a o l i n i z a t i o n a n d s l l i c i f i c a t i o n a r e m o s t p r o m i n e n t i n
t h e i n t r u s i v e a r o u n d t h e S a c r a m e n t o b r e c c i a p i p e .
S e r i c i t i z a t i o n o f t h e g r o u n d m a s s o f t h e i n t r u s i v e i s
p r o b a b l y l a t e - s t a g e , d e u t e r i c a l t e r a t i o n .
T h e g o l d o r e s e q u e n c e c o n t a i n s m i n e r a l s t h a t a r e
c h a r a c t e r i s t i c o f a n e p i t h e r m a l d e p o s i t . T h e g o l d
SUMMARY AND RECOMMENDATIONS
The true structural character of Mercur has been
overlooked for many ye~rs. The rhyolite intrusive
on the north side of Eagle Hill appears to have been
forcefully intruded and to be younger than folding
because of the drag folds that occur, noticeably
on its north side. The two explosive breccia pipes'
formation is believed to be related to the hydrothermal
activity which was a part of end-stage magmatic activity.
The collapse breccia near the center of the ghost
town of Mercur formed at the intersection of two
faults and probably resulted from the collapse of
the roof of a solution cave.
Alteration of the Great &lue Limestone and the
Eagle Hill rhyolite is low-grade in the area.
Silicification with some sericite and illite is
charqcteristic of the gold ore sequence. Alteration
of the Eagle Hill rhyolite is varied and includes
kaolinization, sericitization, and silicification.
Kaolinization and silicification are most prominent in
the intrusive around the Sacramento breccia pipe.
Sericitization of the groundmass of the intrusive is
probably late-stage, deuteric alteration.
The gold ore sequence contains minerals that are
characteristic of an epithermal deposit. The gold
7 4
m i n e r a l i z a t i o n i s a s s o c i a t e d w i t h o r p l m e n t , r e a l g a r ,
g a l e n a , a r s e n o p y r i t e , s p h a l e r i t e , c h a l c o p y r i t e , a n d
c i n n a b a r . T h e g o l d i s i n v i s i b l e e v e n w i t h t h e a i d
o f a r e f l e c t i n g m i c r o s c o p e , ,
T h e c a r b o n - g o l d - a r s e n i c r e l a t i o n s h i p o b s e r v e d a t
M e r c u r , U t a h ; C a r l i n , N e v a d a ; a n d G e t c h e l l M i n e , N e v a d a ,
i s a n i n t e r e s t i n g l o w t e m p e r a t u r e r e l a t i o n s h i p . T h i s
r e l a t i o n s h i p i s p r o b a b l y d u e t o h y d r o t h e r m a l s o l u t i o n s
e n t e r i n g p e r m e a b l e r e a c t i v e b e d s t h a t c o n t a i n e d
h y d r o c a r b o n s . O r g a n i c e x t r a c t i o n p r o c e d u r e s a p p l i e d
t o c a r b o n - r i c h m a t e r i a l s f r o m t h e t h r e e g o l d c a m p s
s h o w e d b y t h e u s e o f I n f r a r e d s p e c t r o s c o p y t h e p r e s e n c e
o f t h e a l k a n e a n d c a r b o n y l g r o u p s . A l k a n e s a r e o n e
o f t h e m a i n c o n s t i t u e n t s o f p e t r o l e u m . T h e r e f o r e ,
s o m e f o r m o f h y d r o c a r b o n p r o b a b l y s e r v e d a s t h e s o u r c e
f o r t h e c a r b o n .
S u l f u r i s o t o p e d a t a f o r t h e s u l f i d e s a t M e r c u r
3 4
h a v e a m e a n o f + 7 . 8 8 6 S ^ a n d a s p r e a d o f v a l u e s
w h i c h i s c h a r a c t e r i s t i c o f s u l f u r i s o t o p e d a t a f r o m
o t h e r h o t s p r i n g d e p o s i t s . T h e s u l f u r i s o t o p e d a t a
a r e b e l i e v e d t o r e f l e c t n e a r - s u r f a c e c o n d i t i o n s , l o w
t e m p e r a t u r e , a n d t h e c o n t i n u a l m i x i n g o f g r o u n d w a t e r s
w i t h h e a t e d w a t e r s w h i c h r e s u l t e d i n H 2 S - S 0 2 d i s e q u i l i b r i u m .
R e c o m m e n d a t i o n s f o r f u r t h e r s t u d y i n c l u d e K - A r d a t i n g
o f t h e E a g l e H i l l r h y o l i t e i n t r u s i v e s a t O p h i r , M e r c u r ,
W e s t M e r c u r c o m b i n e d w i t h c h e m i c a l d a t a o n t h e i n t r u s i v e s
mineralization is associated with orpiment, realgar,
galena, arsenopyrite, sphalerite, chalcopyrite, and
cinnabar. The gold is invisible even with the aid
of a reflecting microscope.
The carbon-gold-arsenic relationship observed at
74
Mercur, Utah; Carlin, Nevada; and Getchell Mine, Nevada,
is an interesting low temperature relationship. This
relationship is probably due to hydrothermal solutions
entering permeable reactive beds that contained
hydrocarbons. Organic extraction procedures applied
to carbon-rich materials from the three gold camps
showed by the use of infrared spectroscopy the presence
of the alkane and carbonyl groups. Alkanes are one
of the main constituents of petroleum. Therefore,
some form of hydrocarbon probably served as the source
for the carbon.
Sulfur isotope data for the sulfides at Mercur
have a mean of +7.88 8S34 and a spread of values
which is characteristic of sulfur isotope data from
other hot spring deposits. The sulfur isotope data
are believed to reflect near-surface conditions, low
temperature, and the continual mixing of ground waters
•
with heated waters which resulted in H2S-S02 disequilibrium.
Recommend~tions for further study include K-Ar dating
of the Eagle Hill rhyolite intrusives at Ophir, Mercur.
West Mercur combined with chemical data on the intrusives
7 5
a t e a c h l o c a l i t y t o d e t e r m i n e i f t h e y c a m e f r o m t h e
s a m e p l u t o n . C a r b o n i s o t o p e d a t a o f t h e c a r b o n - r i c h
z o n e a t t h e S a c r a m e n t o m i n e m i g h t b e o f i n t e r e s t .
M o r e p r e c i s e i d e n t i f i c a t i o n o f t h e o r g a n i c c o m p o u n d s
m i g h t g i v e s o m e c l u e a s t o t h e c h e m i c a l a n d t e m p e r a t u r e
c o n d i t i o n s t h a t e x i s t e d d u r i n g t h e h y d r o t h e r m a l
a c t i v i t y . M o r e s t u d y o f t h e s t r u c t u r e o u t s i d e t h e
M e r c u r a r e a m i g h t b e o f i n t e r e s t . M o r e p o l i s h e d
s e c t i o n w o r k w i t h t h e u s e o f p r o p e r i n s t r u m e n t a t i o n
m i g h t b e u s e f u l t o t h e i d e n t i f i c a t i o n o f g o l d o c c u r r e n c e s
a n d r e l a t i o n s h i p s w i t h o t h e r m i n e r a l s .
at each locality to determine if they came from the
same pluton. Carbon isotope data of the carbon-rich
zone at the Sacramento mine might be of interest.
75
More precise identification of the organic compounds
might give some clue as to the chemical and temperature
conditions that existed during the hydrothermal
activity. More study of thf! structure outside the
Mercur area might be of interest. More polished
section work with the use of proper instrumentation
might be useful to the identification of gold occurrences
and relationships with other minerals.
SELECTED REFERENCES
A l l e n , R . H . , 1 9 1 0 , M i n e s a n d M i l l o f C o n s o l i d a t e d M e r c u r C o . : E n g . a n d M i n . J o u r . , v . 8 9 , n . 2 5 , p . 1 2 7 3 - 1 2 7 7 .
A n d r e w s , W . B . , 1 9 3 7 . M e r c u r a n d M a n n i n g M i n i n g D i s t r i c t s : C o m p a s s , v . 1 7 . n . 3 , p . 1 4 8 - 1 5 2 .
B i s s e l l , H . J . , 1 9 5 9 . G e o l o g y o f t h e S o u t h e r n O q u i r r h M o u n t a i n s a n d F i v e m i l e P a s s — N o r t h e r n B o u l t e r M o u n t a i n A r e a , T o o e l e a n d U t a h C o u n t i e s , U t a h : U t a h G e o l o g i c a l a n d M i n e r a l o g i c a l S u r v e y G u i d e b o o k N u m b e r 1 4 , 2 6 9 p .
B u t l e r , B . S . , 1 9 2 0 , T h e O r e D e p o s i t s o f U t a h : U . S . G e o . S u r v e y P r o f . P a p e r 1 1 1 , p . 3 8 7 - 3 9 5 .
D e g e n s , E . T . a n d H . R e u t e r , 1 9 6 4 , A n a l y t i c a l T e c h n i q u e s i n t h e F i e l d o f O r g a n i c G e o c h e m i s t r y , i n I n g e r s o n , E . , A d v a n c e s i n O r g a n i c G e o c h e m i s t r y : New Y o r k , P e r g a m o n P r e s s , p . 3 7 7 - 4 1 5 -
E h l m a n n , A . J . , 1 9 5 8 , P y r o p h y l l l t e i n S h a l e s o f N o r t h C e n t r a l U t a h : U n p u b l i s h e d t h e s i s , U n i v , o f U t a h , p . 6 4 - 7 9 .
E m m o n s , S . F . a n d G . F . B e c k e r , 1 8 8 5 . C a m p F l o y d D i s t r i c t , i n S t a t i s t i c s a n d T e c h n o l o g y o f t h e P r e c i o u s M e t a l s : T e n t h C e n s u s o f t h e U n i t e d S t a t e s , v , 1 3 , p . 4 5 4 - 4 5 5 .
E r i c k s o n , R . L . , A . L . . M a r r a z i n o , U . O d a , a n d W.W.. J a n e s . 1 9 6 4 , G e o c h e m i c a l E x p l o r a t i o n N e a r t h e G e t c h e l l M i n e , H u m b o l d t C o u n t y , N e v a d a : U . S . G e o . - S u r v e y B u l l . 1 1 9 8 - A , 2 6 p .
F r a n k l i n , W . J . a n d V . M i l l e r , 1 9 3 8 , M e t a l l u r g i c a l D e v e l o p m e n t s a t M e r c u r , U t a h : U . S . B u r e a u o f M i n e s T e c h . P a p e r 5 8 8 , 4 2 p .
G e m m e l l , B . C . , 1 8 9 7 . T h e C a m p F l o y d M i n i n g D i s t r i c t a n d t h e M e r c u r M i n e s , U t a h : E n g . a n d M i n . J o u r . , v . 6 3 , n . 1 7 . p . 4 0 3 - 4 0 4 ; 4 2 7 - 4 2 8 .
G i l l u l y , J . , 1 9 3 2 , G e o l o g y a n d O r e D e p o s i t s o f t h e S t o c k t o n a n d F a i r f i e l d Q u a d r a n g l e s , U t a h : U . S . G e o . S u r v e y P r o f . P a p e r 1 7 3 , 1 7 1 p -
SELECTED REFERENCES
Allen, R.H., 1910, Mines and Mill of Consolidated Mercur Co.: Eng. and Min. Jour •• v. 89. n. 25, p. 1273-1277.
Andrews. W.B., 1937, Mercur and Manning Mining Districts: Compass. v. 17. n. 3. p. 148-152.
Bissell. H.J •• 1959. Geology of the Southern Oquirrh Mountains and Fivemile Pass--Northern Boulter Mountain Area. Tooele and Utah Counties. Utah: Utah Geological and Mineralogical Survey Guidebook Number 14. 269p.
Butler. B.S., 1920. The Ore Deposits of Utah: U.S. Geo. Survey Prof. Paper 111, p. 387-395.
Degens. E.T. and H. Reuter, 1964. Analytical Techniques in the Field of OrganiC Geochemistry, in Ingerson, E.. Adva.nces in Organic Geochemistry: New York, Pergamon Press. p. 377-415.
Ehlmann, A.J •• 1958, Pyrophyllite in Shales of. North Central Utah: Unpublished thesiS, Univ. of Utah. p. 64-79.
Emmons, S.F. and G.F. Becker. 1885, Camp Floyd District, in Statistics and Technology of the Precious Metals: Tenth Census of the United States. v. 1), p. 454-455.
Erickson, R.L., A.L •. Marrazino, U. Oda, and W.W. Janes, 1964, Geochemical Exploration Near the Getchell Mine, Humboldt County, Nevada: U.S. Geo •. Survey Bull. 1198-A, 26p.
Franklin, W.J. and V. Miller, 1938. Metallurgical Developments at Mercur, Utah: U.S. Bureau of Mines Tech. Paper 588, 42p.
Gemmell, R.C •• 1897. The Camp Floyd Mining District and the Mercur Mines, Utah: Eng. and Min. Jour •• v. 63, n. 17, p. 403-404; 427-428.
Gilluly, J., 1932, Geology and Ore Deposits of the Stockton and Fairfield Quadrangles. Utah: U.S. Geo. Survey Prof. Paper 17). 171p.
7 7
H a u s e n , D . M . a n d P . K . K e r r , 1 9 6 8 , F i n e G o l d O c c u r r e n c e a t C a r l i n , N e v a d a : i n R i d g e , J . D , , O r e D e p o s i t s o f t h e U n i t e d S t a t e s , 1 9 3 3 - 1 9 6 7 : New Y o r k , A I M E , p . 9 0 8 - 9 4 0 .
He i k e s , V . C . , 1 9 2 0 , C a m p F l o y d o r M e r c u r D i s t r i c t , i n B . S , B u t l e r , T h e O r e D e p o s i t s o f U t a h : U . S . G e o . S u r v e y P r o f . P a p e r 1 1 1 , p , 3 8 2 - 3 8 7 .
H e l g e s o n , H . C . a n d R . M . G a r r e l s , I 9 6 8 , H y d r o t h e r m a l T r a n s p o r t a n d D e p o s i t i o n o f G o l d : E c o n . G e o . , v . 6 3 , p . 6 2 2 - 6 3 5 .
H i l l , V . C . , 1 8 9 4 , O r e D e p o s i t s o f C a m p F l o y d D i s t r i c t , T o o e l e C o u n t y , U t a h : P r o c . C o l o . S c i . S o c . , v . 5 , p . 5 ^ - 6 5 .
H o w a r d , L . O . , 1 9 1 3 a , T r e a t m e n t o f M e r c u r D u m p s : S a l t L a k e M i n , R e v . , v . 1 5 , n . 8 , p . 1 7 - 1 9 .
1 9 1 3 b , H i s t o r y o f M i l l i n g a t t h e G e y s e r -M a r i o n a n d t h e S a c r a m e n t o : S a l t L a k e M i n . R e v . , v . 1 5 . n . 9, p , 9 - 1 3 .
1 9 1 3 c , H i s t o r y o f C y a n i d i n g a t S u n s h i n e : S a l t L a k e M i n . R e v . , v . 1 5 , n . 1 0 , p . 1 1 - 1 6 .
1 9 1 3 d , M o d e r n F l o t a t i o n s D e b t t o S u n s h i n e : S a l t L a k e M i n . R e v . , v . 1 5 , n . 1 1 , p . 1 3 - 1 6 .
1 9 1 3 e , C y a n i d i n g o n t h e W e s t D i p , M e r c u r : S a l t L a k e M i n . R e v . , v . 1 5 , n . 1 2 , p . 1 3 - 1 6 .
J e n s e n , M . L . , I 9 6 7 . S u l f u r I s o t o p e s a n d M i n e r a l G e n e s i s , i n B a r n e s , G e o c h e m i s t r y o f H y d r o t h e r m a l O r e D e p o s i t s : New Y o r k , H o l t R i n e h a r t a n d W i n s t o n , I n c . , p . 1 4 3 - 1 6 5 .
R . P . A s h l e y , a n d J . P . A l b e r s , 1 9 7 1 a , P r i m a r y a n d S e c o n d a r y S u l f a t e s a t G o l d f i e l d , N e v a d a : E c o n . G e o . , v . 6 6 , p . 6 1 8 - 6 2 6 .
S . O a n a , N . N a k a i , a n d G . D e s s a u , 1 9 7 1 b , S u l f u r I s o t o p i c G e o c h e m i s t r y o f V o l c a n i c a n d F u m a r o l i c F l u i d s : S o c M i n . G e o . J a p a n , S p e c . I s s u e 2 , p . 7 6 - 7 9 .
J o r a l e m o n , P . , 1 9 5 1 . T h e O c c u r r e n c e o f G o l d a t t h e G e t c h e l l M i n e , N e v a d a : E c o n . G e o . , v . 4 6 , p . 2 6 7 - 3 1 0 .
Hausen, D.M •. and P.K. Kerr, 1968, Fine Gold Occurrence at Carlin, Nevada: in Ridge, J.D., Ore Deposits of the United StateS71933-1967: New York, AlME, p. 908-940.
Heikes, V.C., 1920, Camp Floyd or Mercur District. in B.S. Butler. The Ore Deposits of Utah: U.S. Geo. Survey Prof. Paper 111, p. 382-387.
Helgeson, H.C. and R.M. Garrels, 1968, Hydrothermal Transport and Deposition of Gold: Econ. Geo., v. 63. p. 622-635.
Hill, V.C., 1894, Ore Deposits of Camp Floyd District, Tooele County, Utah: Proc. Colo. Sci. Soc •• v. 5, p. 54-65.
??
Howard, L.O., 1913a, Treatment of Mercur Dumps: Salt Lake Min. Re v ., v. 15 , n. 8, p • 17 -19 •
1913b, History of Milling at the GeyserMarion and the Sacramento: Salt Lake Min. Hev., v. 15, n. 9, p. 9-13.
1913c, History of Cyaniding at Sunshine: Salt Lake Min. Hev., v. 15, n. 10, p. 11-16.
1913d, Modern Flotations Debt to Sunshine: Sa I t Lake Min. He v " v. 15, n. 11. p. 13 -16 •
1913e, Cyaniding on the West Dip, Mercur: Salt Lake Min. Hev., v. 15. n. 12, p. 13-16.
Jensen, M.L •• 1967, Sulfur Isotopes and Mineral Genesis, in Barnes • Geochemistry of Hydrothermal Ore DeposIts: New York, Holt Rinehart and Winston, Inc •• p. 143-165.
____ ~--_____ R.P. Ashley, and J.P. Albers, 1971a. Primary and Secondary Sulfates at Goldfield, Nevada: Econ. Geo •• v. 66, p. 618-626.
----~~~---e S. Oana. N. Nakai. and G. Dessau. 1971b. Sulfur Isotopic Geochemistry of Volcanic and Fumarolic Fluids: Soc. Min. Geo. Japan, Spec. Issue 2, p. 76-79.
Joralemon. P., 1951, The Occurrence of Gold at the Getchell Mine, Nevada: Hcon. Geo., v. 46, p. 267-310.
7 8
K i n g , W . H . a n d S . R . W i l s o n , 1 9 ^ 9 . D i a m o n d - D r i l l a n A u g e r S a m p l i n g o f V a n a d l f e r o u s S h a l e , M e r c u r Dome M i n e , T o o e l e C o u n t y , U t a h : U . S . B u r e a u o f M i n e s R e p t . o f I n v . 4 5 7 2 , 8 p ,
L e n z i , G . W . , 1 9 7 1 # G e o c h e m i c a l R e c o n n a i s a n c e a t M e r c u r , U t a h : U n p u b l i s h e d M a s t e r ' s t h e s i s , U n i v , o f U t a h , 5 1 p .
M a b e y , D . R . , M . D . C r i t t e n d e n . J r . , H . T . . M o r r i s , R . J . R o b e r t s , a n d E . W . T o o k e r , 1 9 6 4 , A e r o m a g n e t i c a n d G e n e r a l i z e d G e o l o g i c Map o f P a r t o f N o r t h -C e n t r a l U t a h : U . S . G e o . S u r v e y G e o p h y s . I n v . Map G P - 4 2 2 .
M a g u i r e , D , , L . O . H o w a r d , 1 9 1 3 a , T h e R o m a n c e o f a F a m o u s G o l d M i n e : S a l t L a k e M i n , R e v , , v . 1 5 , n . 6 , p . 1 3 - 1 7 .
a n d L . O . H o w a r d , 1 9 1 3 b , T h e R o m a n c e o f a F a m o u s G o l d M i n e , S a l t L a k e M i n . R e v . , v . 1 5 . n . 7 . p . 9 - 1 5 .
M a r t i n , G . , 1 9 3 ^ . M e r c u r H a s New H o p e s : E n g . a n d M i n . J o u r . , v . 1 3 5 . n . 1 0 , p . 4 4 6 - 4 4 7 .
M e r w i n , R . W . , 1 9 6 8 , G o l d R e s o u r c e s i n t h e O x i d i z e d O r e s a n d C a r b o n a c e o u s M a t e r i a l I n t h e S e d i m e n t a r y B e d s o f N o r t h e a s t e r n N e v a d a : U . S . B u r e a u o f M i n e s T e c h . P r o g . R e p t . 1 , 1 6 p .
M o o r e , W . J . , 1 9 7 3 . A S u m m a r y o f R a d i o m e t r i c A g e s o f I g n e o u s R o c k s i n t h e O q u i r r h M o u n t a i n s , N o r t h C e n t r a l U t a h : E c o n . G e o . , v . 6 8 , p . 9 7 - 1 0 1 .
N i c h o l s , I . L . a n d L . P e t e r s o n , 1 9 7 0 , L e a c h i n g G o l d -B e a r i n g M i l l T a i l i n g s F r o m M e r c u r , U t a h : U . S . B u r e a u o f M i n e s R e p t . o f I n v . 7 3 9 5 , l O p .
O h m o t o , H . , 1 9 7 2 , S y s t e m a t i c s o f S u l f u r a n d C a r b o n I s o t o p e s i n H y d r o t h e r m a l O r e D e p o s i t s : E c o n . G e o . , v . 6 7 . n . 5 . P . 5 5 1 - 5 7 8 .
O n g , H . L . . a n d V . W . S w a n s o n , 1 9 ^ 9 , N a t u r a l O r g a n i c A c i d s i n t h e T r a n s p o r t a t i o n , D e p o s i t i o n , a n d C o n c e n t r a t i o n o f G o l d : C o l o . S c h o o l M i n e s Q u a r t , , v . 6 4 , n . 1 , p . 3 9 5 - ^ 2 5 .
King, W.H. and S.R. Wilson, 1949, Diamond-Drill an Auger Sampl1ng of Vanadiferous Shale, Mercur Dome Mine, Tooele County, Utah: U.S. Bureau of Mines Rept. of Inv. 4572, 8p.
78
Lenzi, G.W., 1971, Geochemical Reconnaisance at Mercur, Utah: Unpublished Master's thesis, Univ. of Utah, 51p.
Mabey. D.R ... M.D. Crittenden. Jr., H.T .•. Morris. R.J. Roberts, and E.W. Tooker, 1964, Aeromagnetic and Generalized Geologic Map of Part of NorthCentral Utah: U.S. Geo. Survey Geophys. Inv. Map GP-422.
Maguire, D., L.O. Howard, 1913a, The Romance of a Famous Gold Mine: Salt Lake Min. Rev., v. 15. n. 6, p. 13-17.
and L.O. Howard. 1913b, The Romance of a ----=Pa-m-o-u-s-Gold lIUne: Salt Lake Min. Rev., v. 15.
n. 7, p. 9-15.
Mart1n. G •• 1934, Mercur Has New HOpes: Eng. and Min. Jour., v. 135. n. 10. p. 446-447.
Merwin. R.W., 1968, Gold Resources in the Oxidized Ores and Carbonaceous Material in the Sedimentary Beds of Northeastern Nevada: U.S. Bureau of Mines Tech. Prog. Rept. 1, 16p.
Moore, W.J., 1973. A Summary of Radiometric Ages of Igneous Rocks in the Oquirrh Mountains, North Central Utah: Rcon. Geo •• v. 68. p. 97-101.
Nichols, I.L. and L. Peterson. 1970. Leach1ng GoldBear1ng Mill Tailings From Mercur, Utah: U.S. BUreau of M1nes Rept. 'Df Inv. 7395. lOp.
Ohmoto. H., 1972, Systemat1.cs of Sulfur and Carbon Isotopes in Hydrothermal are Deposits: Econ. Geo., v. 67. n. 5. p. 551-578.
Ong, H.L •. and V.W. Swanson, 1969, Natural Organic Ac1ds 1n the Transportation. Deposition, and Concentrat1on of Gold: Colo. School M1nes Quart., v. 64, n. 1, p. 395-4250
7 9
P a l m e r , L . A . , 1 9 0 9 , M i l l i n g P r a c t i c e a t t h e C o n s o l i d a t e d M e r c u r : S a l t L a k e M i n , R e v , , v . 1 0 , n . 2 3 , p , 1 5 - 1 7 .
R a d t k e , A . S . a n d B . J . S c h e l n e r , 1 9 7 0 , S t u d i e s o f H y d r o t h e r m a l G o l d D e p o s i t i o n ( I ) . C a r l i n G o l d D e p o s i t , N e v a d a : T h e R o l e o f C a r b o n a c e o u s M a t e r i a l s i n G o l d D e p o s i t i o n : E c o n , G e o . , v . 6 5 , p . 8 7 - 1 0 2 .
R o b e r t s , R . J . , A . S . R a d t k e , a n d R . R . C o a t s , 1 9 7 1 , G o l d - B e a r i n g D e p o s i t s i n N o r t h C e n t r a l N e v a d a a n d S o u t h w e s t e r n I d a h o : E c o n . G e o , , v , 6 6 , p . 1 4 - 3 3 *
S c h e i n e r , B . J . , R . E . L i n d s t r o m , a n d T . A . H e n r i e , 1 9 6 8 , I n v e s t i g a t i o n o f O x i d a t i o n S y s t e m s F o r I m p r o v i n g G o l d R e c o v e r y F r o m C a r b o n a c e o u s M a t e r i a l s : U . S . B u r e a u o f M i n e s T e c h . P r o g . R e p t . 2 , 8 p .
R . E . L i n d s t r o m , a n d T . A . H e n r i e , 1 9 6 9 . E l e c t r o l y t i c O x i d a t i o n o f C a r b o n a c e o u s O r e f o r I m p r o v i n g G o l d R e c o v e r y : U . S . B u r e a u o f M i n e s T e c h . P r o g . R e p t . 8 , 1 2 p ,
R . E . . L i n d s t r o m , W . J . . G r a y , a n d D . G . P e t e r s o n , 1 9 7 2 , E x t r a c t i o n o f G o l d F r o m C a r b o n a c e o u s O r e : P i l o t P l a n t S t u d i e s : U . S . B u r e a u o f M i n e s R e p t . o f I n v , 7 5 9 7 . 2 0 p .
S p u r r , J . E . , 1 8 9 4 - 9 5 . E c o n o m i c G e o l o g y o f t h e M e r c u r M i n i n g D i s t r i c t , U t a h : S i x t e e n t h A n n u a l R e p o r t o f t h e U n i t e d S t a t e s G e o l o g i c a l S u r v e y , P a r t I I — P a p e r s o f a n E c o n o m i c C h a r a c t e r , p . 3 ^ 3 - ^ 5 5 •
Z e l l e r , R . P . , 1 9 5 8 , P a l e o c o l o g y o f t h e L o n g T r a i l S h a l e M e m b e r o f t h e G r e a t B l u e L i m e s t o n e , O q u i r r h R a n g e , U t a h : B r i g h a m Y o u n g U n i v . R e s . S t u d . - -G e o . S e r . , v . 5 . n . 8 , 3 6 p .
79
Palmer, L.A., 1909, Milling Practice at the Consolidated Mercur: Salt Lake Min. Rev., v~ 10, n. 23, p. 15-17.
Radtke. A.S. and B.J. Scheiner, 1970, Studies of Hydrothermal Gold Deposition (I). Carlin Gold Deposit. Nevada: The Role of Carbonaceous Materials in Gold Deposition: Bcon. Geo., v. 65. p. 87-102.
Roberts, R.J •• A.S. Radtke, and R.R. Coats. 1971, Gold-Bearing Deposits in North Central Nevada and Southwestern Idaho: Econ. Geo., v. 66, p. 14-33.
Scheiner, B.J., R.E. Lindstrom, and T.A. Henrie, 1968, Investigation of Oxidation Systems For Improving Gold Recovery From Carbonaceous Materials: U.S. Bureau of Mines Tech. Prog. Rept. 2, 8p.
R.E. Lindstrom, and T.A. Henrie, 1969, Electrolytic Oxidation of Carbonaceous Ore for Improving Gold Recovery: U.S. Bureau of Mines Tech. Prog. Rept. 8, 12p.
R.E •. Lindstrom, W.J •. Gray, and D.G. Peterson, 1972, Extraction of Gold From Carbonaceous Ore: Pilot Plant Studies: U.S. Bureau of Mines Rept. of Inv. 7597, 20p.
Spurr, J.E., 1894-95, EconomiC Geology of the Mercur Mining District, Utah: Sixteenth Annual Report of the United States Geological Survey, Part II-Papers of an Economic Character, p. 343-455.
Zeller, R.P., 1958, Paleocology of the Long Trail Shale Member of the Great Blue Limestone, Oquirrh Range. Utah: Brigham Young Univ. Res. Stud.-Geo. Ser., v. 5, n. 8, 36p.
VITA
Name
B i r t h p l a c e
B i r t h d a t e
H i g h S c h o o l
C o l l e g e
U n i v e r s i t y
D e g r e e
P r o f e s s i o n a l O r g a n i z a t i o n s
P r o f e s s i o n a l P o s i t i o n s
E d w i n M i c h a e l G u e n t h e r
C h i c a g o . I l l i n o i s
M a r c h 1 9 . 1 9 ^ 8
A u r o r a H i g h S c h o o l A u r o r a , O h i o J u n e 1 9 6 6
B a l d w i n - W a l l a c e C o l l e g e B e r e a , O h i o 1 0 - 6 6 — 3 - 6 8
U n i v e r s i t y o f U t a h S a l t L a k e C i t y , U t a h 3 - 6 8 — 5 - 7 3
B . S . . , U n i v e r s i t y o f U t a h S a l t L a k e C i t y , U t a h 1 9 7 1
AIMS G e o l o g i c a l S o c i e t y o f A m e r i c a
S t u d e n t g e o l o g i s t , U . S . S t e e l C o r p . , Y e r i n g t o n , N e v a d a , s u m m e r I 9 6 8 ; R e s e a r c h a s s i s t a n t , K e n n e c o t t R e s e a r c h C e n t e r , S a l t L a k e C i t y , U t a h 5 - 7 1 — 5 - 7 2
Name
Birthplace
B1rthdate
H1gh School
College
University
Degree
Professional Organizations
Professional Positions
VITA
Edwin Michael Guenther
Chicago, Illin01s
March 19, 1948
Aurora High SChool Aurora, Ohio June 1966
Baldwin-Wallace College Berea, Ohio 10-66--3-68
University of Utah Salt Lake City, Utah 3-68--5-73
B.S •. , University of Utah Salt Lake City, Utah 1971
A 1MB Geological Society of America
Student geologist, U.S.,Steel Corp., Yerington, Nevada, summer 1968; Research assistant, Kennecott Research Center, Salt Lake City, Utah 5-71--5-72