andriiw charles salley
TRANSCRIPT
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THE STRAT:r GRAPHY AND SEl) U1ENiOLOGV 'bF THi:: UPPER
.JOHANNf$:SEURS AND TURFf;ON'TSIN SUI3SROUPS IN TH~
90UTHWEs·rERN F'OR'f ION OF THe WELKOM aOLOp:c EL.:O
___ r_. ·.., .......... ,...........,. __ ··110$40_· ..._:F~ ... ~,i-~ ....~~(~~ .._..,,_. , '..:~
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ANDRiiW CHARLES SAlLEY
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i>A) t.hOlSi;s ~I..it:uni t.t.I?»d t~' the r(';).(:ul ty C)f Sc::iel'1e:c:t
Univt:?r~:tty Qf t.ht;,t tlJi·l;.wc:\t~rGt-e:md9 Joh.;4f'H'l(l\:Isbul"'g
for i.::11ePegl"ee of N,;)St.tlH" of Seir:?Me:o ',)Ii ."
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ABSTRACt
This sturJy dc:u:umlti?nt!.7, and interpret~ ths w;tr·a1::ig,"'c;.phye.nclSe(Hmetd:.ary envirol'lmen1::s of the UPPGw" ,,1ohannesbwi"g <il.nd
Tur'ffontain Subgl"'puj:ls 01 the !pJi tNat.er~sr~tld SI...!pergl"'ouP on
St.. Helena Gold r1ine. Tlies$;! data c!lre used to c:onst.ruc:t a
tectono-stratigraphic framework a~~ determine the ganerali'
dist.ribution o'f aeol1Qmic miilellral i!~c!ltion ~,t,I)(j)
Pat.a i't"'om borehole t;:orss <1lnd Jindarg'''ound sxposures areII')
utilizecJ to compile cros$-$act~rons c;tno ;ilSop.tlqihmaps of'I
formations and ,rae'('s. Using \this inforllh:l'!:ic:m f;acies
errangements .";l.nda$$tH:::ie1::ioi"'lS ~\s wall at;; evidence Qf
!:;.yn-sadimen'tary tectl:')nit::$ erik da~~!"'((\.ined.
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The Sasal Rei 0'" C:.1.:!n,,~ti'b;ites tha- ba~VE!l unit 0'1' the Harmony
F'orm~tiono :l'ld both ,th~ fJalsCll- 4pdSteyn fac:~e$ of t.heEl,;asal R,eef are pre$el"~ ott st. He?)}ell& Gold M.l.ne~!l"l tha
overl ying Da9bn~ek FtH"m~ti9n the ~\\mal end Sedel i~ faciesof the Leader Reef oc:c:ur '9r Gt~ \1 Helena 6Qld ,Mine. 'the
Aandt:.>t'll{Chanttel on Sj. Helene G01~, Mine is a mwl ti,-s.tageel"'tHsive scClur-ano ....fill ch"'.lnnel.izea \iweeture~ tht;? oriel'·d~?l'"
tion of which is~n indication001 .\tact~nie centrol. ThaI!
Elaorado Formation coarsene-wpwerd'\1 on St~ Helens Bald\' !
'\\. . '!" I,Mine and alea contains lateral fQci~~ variationa.I;Ii
IIP . .,jl 1 h.!.eposit.l.QI'l 01 cQng omer,~tes and (;lrOn,I.'tes of the HCjrmony~
Dagl:ll"'ee!\ ,: S?e!S Bona and Aanda-nl{ Ft:wmc~tion$ o!:cwrred ontna distal portion of a braid-plain in unconfinadc;:hantlalll'S. SWClIsh-st}"'C,),tii'it:c'ltion during lCII;::elit;eeJ tr'€111$""
(dremsions re$ult~cl in t.he>deposition of ho,d.~QMtCil lem:J.·..
notions in thIS>Top of Re(~f quor'(:zitch P(;?bbly arer'\it~a,
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empl ac:ement by t;)l"avi tv-flow ct(,JPO~1.i.ticn.. O~PQ5.ition oia~gillitma and diamic ces in the Aandmnk Channel
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oc:cul"'re:d $ub~t'lue~fu$lY following. ~ Ml'!ljOI'" tr~t1$gl"'a>$$ibn ~Q ~.
Oepositiot1 Q.f the Eldor~do .t'16rmetiot) ot:~u.rred tinelluvial fan t\ihic:h prQgr-ilded iSS e. f\an del ta intobody of watG~t..._
Al1gulrlr urit:onfc:)l'~mi-t,i~$"a1c.:,f'9 ttrt? ll>J61!Stern margin of the
Walkdm eald~ield and ~Bri.tiona in the thickness Qf~$~diment$ indicGlte that t.5:cton.:tt:uplif~ JPcc:urrtttd during
,'/Ii '. ',' .,
$~;dimentBtion" ihe intensity 0;' tectonic aetiv.i,ty aff!:!c't.-I' '"
i~~g the 'Sedimentation iht:reased wi'th time en'd the 10eu$
,\ oir this tecto"ie ec::tivity" mov(~d prC:)(3I"'e$~;ive:3.:f inwe.n:lg;11tbwards the baain centr.~ 0 8
'i1ir :)
ul'\\t:onfo,"'mit,Y-bPUnd oJ. igofllit:t. conglomeratEls t::Of'it~i:"! tb~
mal$cH"i1~)lof ~~olq minerali4atiQQ; QTl St. He:U:;ma C;:;olp Mine.
lnt~r~e$sd gol.d 9r~des al""l');>l'"'e1.-a~~edto oecurrenCeS" of.,.. ., . . . 1',1
c:w.r~bon .and rQlundr:d pyrite ih d~e eonrJ1omere'te:: matrix ..n . . ~ .•
F\Jr't,her {:lQld.minef"il11z<!>.tion in .. the 'llfiC:inity of St. H~lenBSoll~ ,..fin€itmay Q~C\.lI''' to the,< Wr;1;st./(Cf the ()P'Jres~Pt""day b~:£inmart;lin where th1$'iBasal Reef, Le,IFdet~ Reef and "13" Reef may
f)be preserved.','I
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<)1dec:;lare t.h.lt this dissertdtion i$ my owrf? unaided wCIl'"I<.~
I t is beil"l9 s;.s.bmit-ted for thlll) de~n.~~ of t"liast~r pf Sc:ieneein the tJrd.versl. ty of the Witwatersl"'.:lJ1d~ J'QhannesourQ ~ .1t
has not bee~ submitted before 'for any degree or I.:lxemina.-
tion in ISIny(:)t.her Univers'l.ty ..
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dJNTE:NTS
PREAMBLE • 1.
1
:3
4
1 INTRODUCTION1.1
1.21.31.'4
LOCATIONAIMS ••
DATA ~ ~
,. Ii •
.:I. • 5 PRS::VIOIJS WORI<
1.5.1 TI1~ Welf<omGoldfiel.o. p ~ '," ••• ~. S0,
1.5.2 !:it. Helena and Unisef Gold Mj.nes • •• 9"
; .1 ,.6 FU::GI0NAL GEC.LOGY
• • . . . 9
.1.0
11
.1..6.1
1.6.21n t rotiuc: t.ielf" •
Strue;:tUt'"Eh • •
1.6.3
1.6.4 Wi.twatet'"sr~hd SUpergrout\(1 ,
1.6.4.1 West Ri:lnd GI"'OUP ••••• ~ " •• 14
1.Q. 4·.Z Cen tral R~ncl Gr'oup
1.6.4.4~1 Joh<'lnnesoi.Jrg Sutt;;roup. • •• 14•
1...6.4.2.:2 Turf fon tei Ii Subgl'\"1UP'~~ • • • • .1.1/1.6.4.3 Vt::!ntersdorp Supe~';:gl"'cH.q:). • '.... 113
~ 01.6.4' ..4 I<'aroo Sequence ••
1.7 ~~N~RALISATION.STRATIGRAPHY
. . . 1919
1~6~4.5 In~rusives ••••••••
. .STRATIGRAPHIC CONCEPTSUNCtlNf':ORMtT!gS~ • • •
. (1.. t,t ~ .,. III '. ... •
'C.'
2.3 SiRATIGRAPHY OF THE aruov AREA,IS " _, • .. 0:
o• • 23Johannesourg Su~group
i
4444
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:2 ..:$ .. '3 rJ,'rffon;i;e.in !:hJbgl"oup • .1!.. -, !or
Z.3~3.1 SPl:l!S Eon;:1 FOf'mation •'.r
2.3..3..2
o
ZonS VS:OM " •
Zc:me VS 2-4 ••,~ .. .
:Zone VS 1~ •SUMMARY OF STRATIGRAPHY ••
::; SED IMENTOL-OGY3.1, PETROLOSY
. . .3.2 r;:;ACIES
~j~.l Introduction .. it .is •
3.2.2 Conglomerate faci••'3.2.:2.1 (lntrodut:tion~ ••• p ... M •
3~2.2.:2 Oligomict canglome.n"'ate' fwci:!iH.~
3 ..2.2 ..3 Pt)lymict cla$t-~,Iuppol ...tw..!dconglomerate facias • • ..
'\\glomerQta 'fac::·S,as:;••• C'. ~ •.. ~ 9S
3~~L'3 Quartz:I.tG:? facies"
Ird;.roductiell'1. ",3.2,,-3.2 TrcHJ.gh Cl"'O$!.\?i;)eo' ,id arsn.ite facii.a~ 993 ..2.3.3 P1anar CI"'o$Soad,J,ed arenito facie$ 993.:2.S.4 Plane bedded ~renlte, faeia6 ~',•• 100
.. • b ,.
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'S58
59
63QS,
71 Ii71747781
93as~o
9294
95
9696
97
99
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lO:PPebbl y a,·eni.te faties
Quart;;! watke fa.c:ite$ • . . . • • b 10.13.2.3.9 rllterp.r~tati.onof the
~!Ja.rtzitl.::facies •Argillite fa.cies
,:UPl
"c, ,l.O:G103
Int.roch..tction. ~'
Mud$ton~ fac:il'j\~~.2,A.23.2.4,,3
" .t 103
3.2.4.4 Interpretation of the ~rgillite
4
:3 • ::5 PAL~iEOCURRENTS. • .(". •iI "
PEPOS:r T I o~aAL EN\) I RONME,NTS\,4.1 INTRODUCTION •• ~ .~. ~,;
Q $I D lOS
4.:a SEQ!lMENTARY )S~QWl¥NCE.Si',;;' " n
• 106
4.2.14.2.2
4.2.·1';·4.2d)4.2.64.2.74.2 ..84.Z.9
• ;f • •
" .1.96loa112
P Q • ,
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Sequence 3 • • • •• •• ," • • • II • 1:1.3
Sequence 4 •. ", • • • " " • • • " ". ~ • 11.3
Sequen..,._;) " • • " " p • • • • • _" • • 1141.:1.6
117,'I
• ., '-l'
• • '" 0
• • • • • 116• • • ~ • 120.OE~OSlTIQNAL MODEL
SYNSEDIMENTARY TECTdNICS
;:'.1 INTRODUCT!ON... • 125" .5.2 THICI<NESS 'VARIATIONS • • • • •
FACIES R~LATIONSHIPS • • • • • • #" • ..
• • • 126• • • ;1.265.3
:5 • 4 SVNSEOI Mt:NTt'RV rECTOl\!! C 1NTERPRE1·AT ION
CONC~USIDNS~ ~ • ; • • • • • • • • ~ , ~ • •APPEND1)( .t
APPENPIX,2.APpeND! x
~t3.1
~35•. 4 0'
• • lit .-'-".. •"
140alto, • • •,). .
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LIST OF FIGURES
Figure 1. Lociltioh of the W~l.komGoldfield in.relat.ion
St. Helena Gold Mine .
Sase plan ~nd 9r,'!,dr~ferenc::e 01
Helena Gold Mine. ~ • • • .. " • •
B';"'SE plan and grid refe-renc:!.!61'
5
6
Figu~ 4.';
UnisoH
JI: 0- • -. 'Q
Q7
Figwre S. West / east struc:twral sec.tion A....a ae:ross~t" Helen~ 80,ld Min~.. " • ~ " • .. • • • " " 12Major'. strl.!(;t.w.,resof t.he sout.hwCS)stel:'"f"lpor'-
, 0
tion of the Welkom (301I;'lfield.Also shownis the suboutc:rop pc,nsit.ion of t.he ea$~lReef along the western pa.rt of St. HelenaGold Mine • • • • • * • • • • ~. • • • • • • 13
Figure 7. Generalised stratigraphic column fOr theo
Figure 6~
Well<omBoldf ielct. • .• • • • • " .. ~ • • • • .1;)
Figure S. Det.:ailed st.ratigraphit: r;]olumn for theCentral Rand Group in. ttle sbuthwlfstern
portion of the Welkom • ~ •••••• ~ •• 16
Fil;)ure .9" Ide4l1isl:i;!dstratigr;;aphie cplumn of th~ c»
Har-mony Formation, SL H~lena GoldrJ.l.inl?
Figure 10. !a.'opa!=h map of the Harmony l=ormAt:t"on" •
Figure 11~ Plan _Mowing thE locat~on of sectiortsA-All ~ A' -A", a-a: and C-C; and the bore-holes 'and underground locations Used int.h(~ir c:t;i}1?t.rwc:tion. # • • • • • • .. 11 ~ • • 29
'" .a (.' I) 27
Figure 1Z. Nor'th I sO~,th strike sec:tion A-All of 'the
Harmony to A~ndemk FOI"'trlC).i:.iOl"lp • • • " a... 4;9
Figure 13. West / east d.i:R section 13-a' of t.he Har ....mcmy to Aandenk Formations. • • • • • ~. ~ • 3()
Figut"'1? 14. West. I e,ast dip s~(:!tibn C-C' o·f t.he Har-
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FigurG:? 15 .. Easel Reef $ubdiv;tsicHi$,l St. H!!?len~ Gold iJ
M~ne. • • • •• .. • • • • • • • • • • • 32
Figu~-e 16. Easc~d. Eeef facies cb.stribution. • ." • • • • 33
Figure 17. Oligotnic:t Sase. 1 Reef. '" • • Q • • • • • • • 35
Figure 19. Pplymict southern BQ.sal REef overlain by
'(;"'Ie !(haki shaleh sowth$.rn part Of at.Helena Gold MiMe. • • " • 39
40}'Figure 2.0. Isopach map of the aasal Reef • • . ..Pigure 21.. Isopach map of the Top of Rea"!'! quartzi teo " '42
Pigure 22. Horizontall y lamina ted rop of Reef qwale-1;zt ....\\
it.s overlain by the Midd.ling quartzite of '\.//\ . ,-.:::
quartz wac:l<e c:pntaining SC::cH:tered p~bbleE\ • 43
Figure 23. Isopach map of,,!. the I<haki shale. ·0 i> •••••• 45
Figure 2.4. Isopach map cd'\:thl:.' Middlin9 qU<llrt.zit.:e .. ~ • 46\H
Figure 25. P1$.1'1 of occ:ul"'r~~tes of the iMic!dle Reefs .. • 49
~i;:'igwt"e26 .. Heit;1ht (in metre~\1\) of oecurt'"enc:ss of the
Middle Reefs abov~ the top of the B~salIII', .. tl III' .. iF' iii ~ • 50
Figure ::2.7. slumped' Middl,l!;> Reer* Unisel $old M.ine • ~ • 52F',. 'a
fP'·;~'~li.lrE;28. :rde·.al ised stratigt\.ap~lic; columrl of the nag-_:. : (
I breel<. Formation, st. Halana,:>Gr.:>ld Mitte ••• 53\'/ t! ~I
Figure 29. Isopach map of the Dagbreak Formation •.. 54-f7igure 39'~"_-IPolymj,et t.eader ·Reef. " ...... , ." • 5'.;)/ ..... '
Figure ~rl,,,_,})$OpaChmap o~ Leader Reef thic:knessGI£i. • • 57
I='igure 32" Ids,;:!.! ised st.ll~atigraphic column of the Spes "
Bona Ft.H~mation an('l the Aandenk Channel) "St. Belend. Gold Mine ... , • ~ •••••••• bO. ... . . . \\
Figure 33. Isopach map of the Spes Elona Formation ••• 61
>1:':i,gure,)..i?4. !so,pac:h .map of the "a" Reef • " •• A • • • • 6.2
('
i;;tgure 3'5. IJ:lealised stratigre.iphie column of the A.a.n-,. '.';:;{~
64genIc. Formation, St:. Malerla Gold Mihe~
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Figura 3,{,R South I north strike 5ie?ct.ion PI' -A" of the
Acmclenl< Chaflnea in the e shaft are~ of St.
Figure 39. Isopach map of the A~T'1tH.;mk Channel. on St.Hehm~' G01d NiM'e?and Un1sfi?1 Gold Mine .. ~ • 69
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Figure 39. t.oc~tion of Aandenk Channel-type ele>j:)Qsit$c,
in the southern part of the l!-JellUJfflaold~"
field ~ .. • w .. .. • .. • .. _
Fig~II"'e 40. Palil"'lspathic ,ret:onstrUl::::tit;:m of the A~nder'!C: -,
Channel in the southern P\'jll'"t of the ~'Jell~c;m\
*' iII'·'" • 70
A 72Fi.gul'"e 4l.." Isopath tn~p of the Big Pebbl~ Marl<E:.H"·.• ~\) . "
Figure 42. !so(:).o\l:h map .,;,"(the Aandeni< tt'ormll1t1on. " .. ~ ~lFigure' 43. Height (in ,metres) of pc;::curl"'enc::e$ of the
" "Alt ReC:;Ts above tntl§ top of t.he:.>Big Pebble
• 75Figur-e 44. Plan of oc::c.:urrenees of the' HAu f(~e·t$. • • • ,;7b
""\
F.igure '45. !$opach map of 1:h(?[EldoradQ Form~tion • • • 7~Fig~r-e 46. Southeast l'northwa\ls1! ero$$-see'tiof'l
,_,of ths Eldorado Formation # • ~ 4 •
Figure 47. C.cnglCJm~rate I arenit.e ratio. of the EJ,""
0, dOrado FOI"I"matiol'1. "" • • ... • " " • • 0 • • '0 ala. . 'r!~~~~)..FiSIJre 48. Une;:(.mfr.)I~triable t:ont.ac:t between t.he con""
c.. -c.-.
glOfil\\??r.at;Lc::E'ldot"'(;lOO Formcd:.,~on Clhd ths
e0enitiq' A,'lmdenk Formation. .~ • • • " • • • 84-
Pie c:hbl/it of c:lfl3~t CQffipO$i t.$Ot1$. e:ldol",,~dod_ . ......, .... , .. .. '"
Formrat.;'on. a) vs s :aO~]a b) va 2-4 2c.H;)e •• <i. a5Figure 50. Statistic<;\l parClm~t~rs.. for elastli!l of th~,
('n' -' .. " ......_.,..... . .. ,:·,:;,::_..\'i,:,
".EldQradO Formation.1i ~ ';'" ." w • • • <:11 • u.. fl6Figut"'S> ,e.fl. ihool"'ly sor'tSid \,IS 4 t:c:mglomer.ate of 'l:h~
Eldorado Formation? sOI.l'th!';?r-n' ,;:U",,lu:ao'f
Helena Gold M5.hCh • b • • .. • .~ • • ..
St.
Figura 52. Pie ch~rt of clast c:ompo!'Sitionm in the,VS
;1. ;a,on~ ~ Eldcw"auo Form~tic.m • ~ • a • ~-,')
:'0
,.;:..
F'igwre 54~ Cla'$sificat:.ion diagram ~f ,uart~ite!t>" • Q lr:.i9ur~ ~ SatJim~ntary lSeqU!,H"lCeS t.f\~ upper Johan'"
nesl;)u\"'g end Turff(;n1tt;;in 'Su~F.Jroups •!f_.;i~;I-- __ ('1:~'_ \~
Trough-c:ros$\bed reeclil"lg~,' j;~:r'D.""enj.tes.s .. 'c)il'l and r:lVt1iI"'].ying tho; l3ia$l#i Reef, st..
wi.th-
Helena e~ld "ina ••.•••P<l:l.li!S(.;'<oeurrt:mt.re<l:l.dings in areni tess w.t,t'hin
" /J"..~_ - - __,' _ ;;!\ ,;~
~nd Qver'lY(2)Jthe L.ead~r Re~'(, St. H~lene
Gold Mine ~... ~ • " i~Z~}<! ..h • ~ • • ••• • •
Tt"QU9h-cro$l~bed reatdl.l,ygs from ial"enites of. ... . J
the Sh:!oredo F'\::)I'"'mt:'lltio~~51::.· Helenc.\ moldv Mirl~~~ s) va 2-5 ~Ol'\es. b) va .1. ~onq;::* .. • .121Figure 59. Schemati.c reconstruct.ion of t.h~ e;i(~r.II:';~")' ,-
$ition~l .el'wironment 'of t.he Ba$el.,d~eef. " .122. "~
II
.124
roete uru:on'formi ty angl G!$" ~ • • • " • • • ~127•... ..)
Figurl;ll 62. Plan of the Qo",..thl"4el'.5t:erl'l PcEll"'t.of St..Hsll.:ma. Gold M$,i"lo, l.'il)t'ller9~d from Fig A 11.
13cH"eho~'e I'lUmI:'J(!'H'"s $':\'nd the lQc:ci:·t.iOfl 0'11,.
\l
seG;:i.:.ion$ll 0"'0' ~ S-".;E' a..u:i F-F' .. b)oF'lan p~
thei.1iO subout.c:rbp pq$)i t4.Qtl of the aa~al anti(".. . '"
I...eade·f" Reeh; ,sl;tei'n'fut t'~'~e nail R~~f • ~ ~ .~ 4126
F'l.t;jurf:ll 63 .. fl<~I"'l.:ho I south' $tr:il~e $~c:tiol'l 0,' .•,ip of 'l:h~
Hal"':'VlonyFormation" Oegbreek FC)I"'rrtat.ion qnd
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• \\ .130\tJ
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oFi9t.!F'e 66# ~l;.'!(;~t$.QfI 01 bOI"eh(:JlelS l099mti en EH~iIHClll~nQ
6C'.ildMih~ and tlnisel Gold MinG.'... • ... ~141
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LitST OF TABLES
T~b!a .l~ Compari$.iQIlof coh91om§'rat.e c::hal'"ac::tel"'iat.ies
Of thE' fac::ie~ 01 ..the? gese:!. Reef? St .. H~lt;)naGole1 i1.ine _ •
'table 2~ COmpi£lr.l.SOn O'i~ c:onglomS?I'"Jate' C:;\1al'"ec;tSl"'istit'!'1S
C)'i' M;telC'l1t~- to VS R~$f$41 S:l;,. Helt?n~ Goldf"line • '1, • • "b .:ti -fJ t;I. til. : b . {it CJ U<It .. 111
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Table 4. Compel"'i!PQh of various c:h~rac:t.al'"i$tit::!:.; ofv. '
''0
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• liEl
~Uwvial fen, fluvial. ¢:ind marins depositl!5 ';. .107Q
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C\
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CJ)) 0
110
'CJ
F\Jnding ~ ae:c~$S t.o date" .~~""jd~.upPOl"'t,,'fQr t.his study wa$1\ 0 ' (i"~
pl'"ov,;id~t! b\" G~nmin" In addition ~ '0 ~\finenc::i<Zll el$$is,t<tlt'lc::e,.. ,) -,
'h~om 'th~ C"S.,r',R~) <Antic) the uni~~I~$itY"'91, tfy~ ,Wittt4ate~~I'I'"~ncl
is 9r~tp1ulllt cC3Cfknowteo9I!1d"c: t1es$G?r's E;"E" Tli:j~'.H~dielJ,/, i' V~n
G'~<ue\I''lll S~ 1!11!!r'-ii~"'·1.C.. C'Bl"irif~~T. L'91,j~tll A..L..~ Fori'"~s~~)Ii; !pntl'thGt $t~f'( of i:he ~(~mmin0t1in~w~ \5~oi~~tOmp~rtm~rH: p IrJ!~J.lkQ~.;lI"'G thanlu~'d 'fof' "!!h~iw aS$i$tanc:~, dUl"'i.bg v,1\riou$ St.~II,~J.::..~~•.•of
, • (. " I [" ,
t.his I"\j"'o·,jli':;\>c.t. 1'1,1,~ , I I1\ ,i I , (I
Mr.. A"B. Cfadlao$UP~~Vi~ed b ..e pl"'oj'el:!t amv is ·than~fwi~ :,101'".
..:!:'th:::;nQen:Dth: i:::~Si:~~~est~:::e:::Fid:::, t;.J4i:,;:.,\'t::ol4itl'"'ibutCZlci.generol.\,ply 1to !f:.he c;ont~nts Q'f this $,:I:;.~div .arlcl
Ii ';. i!' ./ . " . '~!:~ihe~!ps.?dwith t.he inti.tial Pr'QPo$q,l for th~ prt\lj~'t mr#~l.~i.1'1. , , l..~w ,1:s thtlf1ked felr the '~~DY". hours" (yf d~~II', ( .iQn
r.::ofr~t:ei"'niM9t.his study and t.~e t\fi'l:;""satgrsre.I'bt:i Sl".q:;l~r;gl~iU~' in,If ,," ".," ...' • ',',' "",'" ,"", ' _<;, :'i," ",_._ _ II ,Ige~~~lral~ ?roflaH$$Or 1' ..9. l'1cCiP.rthyl' Dr .. 2. Ciliri'c:r~~$ aM''Q
''m~i~£9rs S"tf .. Eenel<.e\t M~.J. H?U~nd am:! vai"','ioUs'l, tl1tfl~.r~'~t~f'fWil'1.(6t studrmts crf ths O~pal"'tmellt Qf Gt~'o lOQY~ o Uni.DI~l"'si ty 01
, , .; " (\
t~le Wit..wet.e.l"·sr~nd, Cl:re t:·...tH:;el:} '{'elf" t.heir a$6i~t£:!nC(';hI' ,I
y,h lUe;bl e $!•.!(il9!$'$tiof'S and d.lSCrI..lssi(;)l'\s II
I
G (j
rJ
" (: c
,p
(1 I)
o
1
.1. INTRODUCT!ON ...\)
o
Since the disco,yeri.y in laS6"$wper'9rolJi=) the or:t9.in of this un.:1.tfue t?~d.:1.mel'ltary
$mqUGH'It::ll?'p and th(~ abLtl1dant gold m:lnere'lli,$~tipn 'i';;bntained
therein v hills D'Fen debCltteti. P{1¥po$~\ti6n~1 s-nv·,j.I"'of1ment$-, :'. ,", ' " "-', " " {. " , _/\
inc :!.1Jdet:r"ivers $ lakes oc:ec.1ntt" ;£lnd eve.n.ofJa.nio~ in the ,;1 cUI"'t'"amt, ;blit~l"'aturSi
.fl' ,-
fll.rviali d~PO$'it,£on of tMr:w $l$diMemt.s"tJ . ',:
proPQsedelthought$.\tb~r$
91ec:iers~, '. t/gener.:.tlJ.y'fh$ gold
Ii', •
min@ral i$li!'!;;iQIi hiiX~ tr$cl.i tional! y besn viev'J4'!?a ,;~!i7 havin;:tI " , '. f,:_. "
t~ithel'" ei.\ \~:l~diihentibry Qr 8 hyd,rothermal tJrig.in a'no currentmineral i$~~.ton mipd.ets ·.",V"'-l'"Y from a "rnodif ied plBlcer"
t ." ~-'C, ' J' Ij
theory ttl a'h !kpil;;l'\i:nei;.iC: origin oj '''the gold.0' i'll
The d i $Se.."er-y ,,1 t fillL vi",I It tim 60 Idf t..I" c i~~~th.. l.940' "ampha$ised 't.he g~tS'~t extent elno Ip,tlSi'.J"'~/l eQr'l'tl~~w.itY of the
seQiment.'g and miu)sre'll i$stion o'f fhe Witweatel~$t..and 6Up~f·'"graup~ ReaearchcQl"'"ied out in ~ha W&~ka~(eCldfl.1d toa~te 1'fi),5dealt. p:l"'im~rily wit.h the Ela'S&l and Ls~dei'" R.•ef$
l..~ef$.'F Although $J:.w~e:tfic: '1~;~rfl1at..ton$have beJ::H1 $tudied~ no(i
ns,tutliss nsve encamNl~ SGld a t'llit;Je :tn~rvel of the r;stl ...et;t ....
oQr&.phy~ FCH"o t~h.i$ l"e~$pn t.\ sedimsntolo9it:cU 8m:1 $'i:I"'¢::I'ti'"
'9l"'ilPhiC" invest.igation Wi)S unde,l,,"taken of the se.diment&ryo
~~~quence from the baS($> of the Harmony FormatS-an ~;,o tha« .
';'~
.L 2 L.OCAiIO,j\J
pr~m''ZlrilY t'm 6tc HI~lenil t~old ·Mine ,nne! to Cl lO$\'SQr ewteflt
on Unisel B1=»ld M.i'''l''Ir~ .(Fig. :!.) ft Th~ s'l;:.ratS.graphy studien::i
2\~\s
, c
!, (I
II o
\
II
1
o :~ll{ 10.t~~~.·~
o
Uo,u~~. .il,~ II
~J)
l.Qc("ltic;>rtof the I>,!oll(t:;lffi Gc:'Ildfield .in rel.::ltioSj to tht.lWi tIAhl'tIiH"'Sral"ld Sasin. Nines arm ,1,) St. H6;:!lsnn~ 2)Llni$e~ ~ :n FrQsgpld South) 41 Harmony, 6) F'roegt"Jld{$"H':lipl.tte1!f.i .and Sr'fds~l)~ 6) l:'"l"'msgold Nor{~h,l 7)L.ol"~inoll 8) Jsanotte~ 9) Y3ei$8 (Ol"'y)q;' 10) SO<lt'ri)c,1.1.) wQ!;?l.
o.
o
\
1/ n
encampas$es the upp,~ portion uf the Johanhasburg Sub-group and the ,Yurffontein Subgroup which are tag~t',erCQliipOsed err 0 the Harmoi1Y, Oa~tweak, Spas Son.? ~ Aantlewi~ phd
I), '- {.\ - I' -
Eldar~ldo' F'ormClt:l.cilns. 1"hese formatio·ns ~~~~iM the 8asSll,(J "
Middl.e'!! LeaCler~ ",EP', Sig Pabl::;le MaJ"'ker, nA", ~nd VS eo
Reef!':';. 'On bath '$~." HSilena <t\f\·ct Uni.sel Gold Mines the F1':!tsal'.._j. ..... <
Reef i!J5 t:be principle prtlduc::el' of ore and the remaining.1.5 percent of the ore mined is der~ved from Ule LeadCii!r
(\Reef.
1 ~3 A.tMS I./i !~)
ri
The aim ot, thiJ! $tu~'y i$ to docurtHiimt and intel"pret theh
stritHdgl"aphy a~ld slt'diment>'iI"Y anvirQnm,ents~ tram the ba:e
\)of the Harmotv!; F'ormat.;ion in t.he Johannesburg Subgroup t.o
the top of tt Tl.ll"'ffC:lI~tein Subgroup. Within this n"ame-worl< t.here a I sew~ral '$econda.ry tlbjec::tive$~
I ',II
,f:!!). To raco~/<::.truc::t u tec:tono-$trat;\,~raphic: 'framewr..'ll"k"1'.01'"
~he u'Pp~r Johant'1e~burg Cl.lldTurffontein a.ub9rOup~L ihl...!Bt\eeoi'l$ t.~tction inc lw;:ies detel"Cr1ining "the" ext'tim i; t.own'iChJ'syn-sediment&ry tectoniC" have induen.,,"ssdime ~ta.tion., "
b) To ~rtet"'mine de)?ositiof1a.l enviremments and to re-t!on$t~!\'.l(::t the palaeogeography o'f the uppew" Jc?pannss-
'.iburg ~nd Turffontein Subgroups.
c ) To dstel"'llIine tht:;_1 'general dist.r.tbutio("\ o'f go:U:I,
uranium, pYI"'ite and carticm with r~spect to the %ec!:i-mentary fac::ies in specific reefs.
o
o
.
4
oo
1.4 OAiA
PatCA for thj.~, study were
period ~ j The logs of moreboreholes dJ"'illed on "St •
coi lec:ted over ,')a twelve m®the-
than 10 000 short underground
Hel.ena 8"ttJld Mine WSI'"'S used
together wi.tll 20 $urfaca borehole;;; ;which contain
reprssantczd:.ive inter::sections at, the stratigraphy.
underg.roul"ld observations w~rs made at 60\:
lpC<'11i t,tes on both St. Hel ena and Unisel Sold Mine,~.. ~
Obser·"'\~tions W,$I"et me1ld~in Eas<'11 and Leader Reef stopes
and at Qthsr intersections of the HClrmony, Oagbreel(, SpesB.ana, Aanden!<., and Eldorado Fc.H"mations.. Underground
I' a ~
studie~~ of the Basal: and Leadsr RlWef's ware:;!'iimited to thearea Off 'Under·gl~ound develapmet'lt (Fig. Z).
113M-compat.it> 1e Pers,on is 1 COJilputer. Computel'"
isopaehs of tzClrl"'~cted i;Sata were then plottedC)
1), wsing stahdard base.> pl$ns (Figs,! :s and 4).Q
01' the. stratigraphy wa('~ co'hstructed from
gen!?r$ted
(Ap~jeMdixIi
crops-ssction$
bOr,l/ehole ,.10gs,'/
Eoh:iiholr;:.> logs'/
U . . . .. . -c~mput.r logging programma and th~ logs of boreholes with
rf~p,~r::H;~entative intersS'ctions » of the st,J"'ati~taph:y have
~een !=11ot.ted (Appendix 2) "".Oepositic.mal errvir;;~m'ent$!)hd\le ..'Ii;p~en eon$~l.lcted fr,om vartieal aOd latera t faCt6HtIUarrangements arid associations. Cross""sections eonstl"'uctedq. • ~
j' 'from· thickhess ;t.nformatitln have been used to determineil
f the amount a'ncIIIi'I anoffi$l ies
111//?,Ij
fII/!t "/1
undergroundwere comp.iled
and isopach maps.
rBM mainframe
location of syr,-sedirnentary thickne$i$in the .tratigraphv~pl"esEli~t.
\\\Ii.
Pi fty-fowr Il thi~~ sections p reprlr;!l;H,~l"\tirtg ths ~ntire$tratil,;!.r.aphic it\I,l!¢rval studied, h~va el'IDO bt:!:e!11Ii;?Kemj.ra~d
I'
togethe,w' with hdfnd Sp6'?cilmens from both '..lhd~r9rownd
Iio
1'0
<) ,
ou
NAI1
7020GO
t./
~
\
-rca 000
\\
N
,........
104 000
\.\(.1$ \
<: e:t",\$ 106000~~f..titqO --t-~. . '\
/,It.
/
-
a
l.ocal.i.ties .:1.1'\0 bbn';!holes. Ac:fdition~l mitlsralogic:::al dataW!:"""e obtained· frolt\ XRO and XRF ana lyses.
1.5 PREVIOUS WORI<
1.5.1 The Welkom Goldfield
The lirst pUblished studies 01 a specific portion of the
L'JelkomGoldfield were undertaken by Winter (1957, 196.4a),
who studied the geology of the mines in t.he Virginiaarea. lAJintel" (1951, 1964a) idEmtified disconformities a.ndcotrcluded tf1at most reefs were formed in a neriticenvironment associated with ma.rginal uncorlformi ties anddi5c:::onfo,...mities~ Wint:.~r (.t964b) conclUded that $ubsidencedue to folding occurred during Witwatersrand depo.itionaltimes. Minter at al. (1996) summarised the gener.lgeology of th~~~oJell(,pm Goldfield and c:otH::luded that eightmajor fluvial-'fan fo.rmations were deposited in response
;1
to 10cdl foldin~l and that the f"~ns were not affected by
the major 1dul til7lg in th~ Welkom Goldfield.
In t.he first $S'dirl~entologiCdl study of the Welkom Gold-field Antrobus (1956) documented the Ba$al Reef asc;onsic.sting of two prit"tc:i.pal fecies ~ namel V at;).01 igr;)mict.
'\\
13asdl Plac:::er and an' overlyin9 polymic;t S1:syn Pl~c~r. 9imB(1969) studied the detailed sedimentology of the main.:auriferous conglomel"ates of President Brand, .and f'lr-esic'ent9tayn Gold Mines, concluding that. deposition occurredwith a fluvial system entering a land-locked sea.Kingsley (1984) pr-oposed a datai lad .(I1L1del for the dapo·-
sition of the Leader Reef and the overlying Pa'=l"lreekFormation, with "depOsition by a fan-delta. l<ingsley(1987) was the ~irat to publish a detailed model for Lhe
Eldorado FO"'matiClrt, proposing the'l:: the Eldorado FOI"'mation
9
result.ed from c:ye1i.e: ~lluviCll fan sedimentat.id·n andacl1:.howledging that synsediment.;ar-y tectonics h.ad oc::;curr<'!'d 0
dUl"'ing deposition of' t:.heEldorado Formation.
V~'l'"y few structural studies Qf the Welkori'! i3C11dfiel~d have
beem undertakF.ln" Dell (1982) studied the Da9bree~~ f~ul t
on '<\Ie$tJ1rnrloldings Lirni ted Gold Mine. He cone ludl1\ld that,
the tau1 t wtal'S a complex syst.em which formeci as a tea'"
fault.under e compre:!scsive stn?$S ~'e9iml$?~ with later re'"activation a.nd v{';!rtic::.a.lmovement~
1.5.:2 st. Helena and Unisl'?l Gold Mines
The sedtm~ntation and large-s~.l. soft-sediment defC)~m-
ation te,~:tw:~e$ of t.he Middle R<:e'Tsc:Jr' Unisel GOld Mines\ . . ':
were document.ed by Ellis (1968). Ri=-)'~n..c¥lds d:~a6) con-~
eluded that 'b~",ocP,,,u:scing alluvial ffAns oeposi ted the
fQcie$ of the L~ader Reef
depo\S.ttion of
deposi, '\:.ion of
'~he
on St. He?lena Gold Mine?, with
fat?_" from the west ahi]
fan 1,,,,,·omthe stlut.hwes,t. Thc=
chemical composit.ionf'O).neralogy of the southwestern.,
Goldfield was docum~nt.ed by Law\
and Law (1990) • N~,lmerous ~~ncor urtpub 1,'Laned in tern.s 1
bulletins dealing with the loc.:alised geology of St.
Helerlr.\ and Unisel Gold Mines have also been compilElrl(Appendix '"$).
ra-gionally persistentper-titm Of ths ~el kern
at a.l_ (19SSa, bJ 1990)
1.6 REG!ONAL GEOLOGV
()
The Witwatersrand Supergro6p cona~&ts of a 5km thirarenat:eO\J& end argillaceous sedimentary set:/uence tS,l"'mec!
10
the West RaMoGroup .:andan oyed ying ~l~m thick CZlr~t'laceOU$ \\
ar.d conglomertatic $@dimen'l'.';wy sequence tel"tned the CentrC':ll
Rand Group" Peposition o'r this epi""'cr:.mtinental sedimr,.:mt.....
ary saquen~e took place between 3060Ma and 2700Ma (Arm-strong et al. ~ 1990) ~ followil1g deposition of the $~di-
mentary ~nd yo~c<$\nic Dtlmil"lion Ri~ef Sequence on granitesand greenstones o·f the l<~c,\f::)vaar croton. Witt""ater ....randSupergroup sedimentat.ic;.u',vJiilS followed by deJpositioh of
volcanics and sediments of the Ventersdorp Supergroup.
1.6p4 Structure
1;";quthwestern pOI,..u.on o'f the ~li·:.water$rand b.!l$inwhichOCcurs as a north I south tren~~lg synform. Tha rocks of
tJ:1S Well~C,)mGoldfield eontain a complex teetonie hi$tory,with both syn- and post.-deposition<al deformat.ionrec~rd.d" The tecto~ltt style of the Wa~kcm Goldfield and
that the northern portion of the Witwatersrand basin;'A, ,ably !Similar, wi.th mtArginal c)monoelines and
a.ssQciated 1"1::)\Jers&faul tint;) c:hq.f"ac:terising both tl1a$1!?
areaa during Central Rand Group d.pasitional times (MYErsat al.~ 1990). Faulting in the Melkom, Boldfield is pre-
dQJld.nantl y dextral ob1 iqua-slip!/ with down-throw to the
west.
Three major pha$.ms 0'1' structur,:ffl deformation ~ra ,"'eeord(o\ld
in t.he Well~l;:)mGoldfield ~ The 4firJst phase pf deformationoc:c:ul"'red during Witwatersranp and pr(,'It-Ventet"sdorp tim!!;s
t"lhen c:ompress:i.on~l t.ec:t.oniC:~b resul ted in foltJin~ andfaul t..ir'H,;}occurring on tho w~stt?rn, $tJuthsl'"n,~nd easttH'-nmal"'lilins of the Wl¥ll<om Goldfield O::C'.!llowClnd Myars$ 1,966).The S(l)t:Qndpha15e of dC!forml~t.:i.on b~gen w.i'.,th t.he olJtpo~t,ir;g
'Of thE' Klipri'ViersbE'rg. lev~ ch.H~in9GX'l:en6ional V~nt.~~\'s-
dorp-age tectonics. This Vanteredarp Gxteneiansl tectonic
11
regime ial~o resultedthe Welkom Goldfiald
ih horst- ~t')d gr'aben -formation in
(lSuclt \I 1<190) u Ths fOI"ma'tion of the
Oagbreel<, 'Arr1arat~ Stui.rrm.enspant Hpm(iaiStead~ De El"'t)t'l ahd
Virginiu fault systems occurred during ~nd after this
Ven.i::l$il"'sdorpextensional 'tectonic: pel'"iod~ Ths third rtl<!jtW'
pHCise of d~forfllation is post-Ventersoorp in age$ with
r(?-~at;tiv<l3.tion the l.aFge obU,que"'slip f$ult systems with
minor- r-e?ver-setaul ting occ:u,"'r-ing(Minter et al. p .:t.9Sb)" .CJ
~\TI1e stl"'uc:ture of S:c.. Helena Sold Mine is dominated by a
syncline and .::.ntic:line ~$ well.Cis north I south stl"'iking
normal and oblique-.lipmargin s;1:ructure (Fig$~
'fawl ts paral Hi?15 and 6). The
on St. Helena
t.o the westerndip of thl!?
Gold NiNe isgenerally betwean 20° .and 40(1 eS\st. Thli:?large.st. fa.ult. is
t.he obl ique-sl ip OagbrE:?el<Fall! t which ha.!S a d!;:lwnthrow to
the weiSt of <zqJpr-oxim&1'1:ely450m .in thIS! northel'")"f pOl"'t.ion of
St~ Helena Gold Mine and of 200 to 250m in the sdutherr\
por-t.ion 01 the lid.ne, wher-e the f~,ult. ·split.s. t\~~oti';l)(tra'llalong strik.e
movement is 11:50m, c:alculated fl"'om thic::l<.ness data of
fClrmations and .conglomerates .acros)::;;the fQult~
The Walkom Goldfield has under~ona lower gr.en~chist. . //faCies metamorphism with temperaturas of 350oC~ ~O~Ciand
pressures of i~2 kilobarE recorded (Phillips, 1987a).
rna baSement to the e.;:H:;t. and west. Of the Witwatersrand
Supergroup in the Well<.om area consist.. of Archaean
granitOids (Orenn{:l.n at al. D 1998). Tl"le Dominion S;"oup
dieconfor-mably overlLea the ba.amant granitoids below theWi twatel""srand Supergrcup to the nort.h and we~t of IiJe:tlkam
·;?
12
AWEST:a
EAST~j,
~~.--.~~--~·-~~·---.~·~.~-~~~-·~~·--~~~·~K~~~·~8r~~~~~Cl~.~~~.. • Ii> ! ';'.;""";'~!~~;"~"";'I1"'"<o;r~"";',...,ir-'Ii"-"
(i
VantaradQ~p lava
A--·----
J.OOO m
\1
1)Ii
... ltJast(Solddip~'
I eil~t structuralMinaR Not(a'! the w(?stC?l"'nsct>c.tionA-a ~CI"'ClS$ St. Hela!i~
~'1nc::linO' and tha sast.C?l"'ly
o \\
13
11
o SMa'ft.
~ Rovol"'sO fault'::,,'!\lOrma.l falJl t .;,
$TU!RMANSPANFAWI..T
(I
" !Sync: J. il'\o
.,tAntit:.l.tne
.)',\
M.:ljor $trl,ll:tur~£, Qf tho $Qt.\'I:'.I"'l"·w.~$tQrr\ r:>ol',·"t.:i.ont:$f th~t'llo!korn .Goldiliol1:l.. A!r.;d SMO,«'~j is tho subQwtC:f'Qf,':lpo~it.io!1 of t.l1e 9k~Sql Reof uLa,;:;'9 tho toJ(;;?l;,torn Pdr~t ofSt. Holf:;?rm Gc;,l.d M£t,,\o. !\IO'ft:: 1: Tho 6uben,.At.erop Qf '\~heBasa t Ra(":Jfis a re5'3lJ.l t tJ·p upU ft and 't1"uqeati::Jn hy ar\t:~l'·th~$outh tronding strl,u:turtl t(N{;n':J11 as I:h~ "W015trul"l'luh,)I"'~l.'i.s1 ctruc.: tu I'"e " • "
14
o
~the study are~ is shown in Fig. 7.o;t.Q.4 tlJit.watsr'sl"'and Supergroup
bOt"ehOlssl1 ~11
the W.U.:.wa.t.ers-n ,:
r<:lnd Supergroup. The sediments intsrs~c:t.ed '~emp"'i$e,\, .:'
arenaceous and arg iII aCSOIJ5 com.pOf1emts of l\ th~ Ho~tt$1 1Hi11~ Government and Jeppestown Subgroups which OVIi;I'\:J: it!;;thE!basement litholog,isS'\t although the bA$,$!l c.;onfact. ''6,.{
',-::;
t117&tJ.Jeai;i Rand 'Group has mot. been, exposed in the L'IIell<.oln' ",",,:
In t.h~ ':iNSs,t.err1fHj,1",?+iOri of G St" Helena Sold, Mine th~ West} J
Rand GI"'OUP has (, (6GO inters~G ted in 6
located to the we~t of the spboutGrop of
\J
The JohanneSl:lUI"9 Subgr·o\..qJ in the WeH:om Gel1dfield i;:; Sl.lb"'P "-7)
divided ,into 5 ftl,'"metion$ (ri.g. 9). The lowermust sub-
diviSion is the Virginia RormBtion (Lo~er Footwall, LF
1-6) which consists of sUblith1c arenites with rarematrix-supported c:onglom('S)re,~esand the ul'lcordol"'mable Ada r.:'::'
Mi;\Y o;lei$a) Rlt'ef at the bZlse~ The Ada ,Nay Reef is ilH1
small pebble conglomerate
mirH.':H"al i;s,ation and gold<;,
cQnt~\inil1g
and uri.\hill:lmcrystallLne pyrite
If
Overl ying t.Me Vir9in:j'.a J='Qrmati,,ion .ts thC1fut'\ct.'lt1fClY'mi ty-based St" Hel.erHl. Format,ion (~~iddl(9 rQot11<J<",H11I MF 1-4)
which CtH'llprises predominarl1::.1y sul:>lithic- tel t1Wart2
al"'snit:f"'~; tll'ldscattered pebDly sarlastono.s. Noar the t.op.of
()
15 III
I.
~! ·1"I1/Il1/II;
~ d~~~~ ~ ~ ~'
S JBGROI.Jf! GROUP ,l..."..,~--,,----....,_fl-""";'''''''_---ol).. ------,- ....~---r__-""'lI'!,:::::' , AdeH\'id~ B@~u'fort <40(1) . 11:.':.~: Q (J !
.F_':";,;';"_'!,I"""'''''_,-, -----.,,_..;;.,.--;:.,...,,-...,_.-..,jj----,-.---,-{\_-:. Volksrus.t::7:: __ -:::i ----l!• '.' V 10.' d\":.'.r: ry"e,1,.
~.~d~••~~ __ -- __ ~--~----_~ __ ----~ ----------~~H="yk<a (50m)
FORMATION
I(AROOSSQL.n;:i\m:E
-.
Eec,a(450m)
~ I(Hppan P)"1;J;I"rll ~l\P.9. ( 150m ) VENTe:r-1SP~I~P~~~-'--~---....-a---,.-.....--~-------.""""'i!SUPf!RGROllr
VV Orl~r'lev('?) Klipri\li~l"'$bl"H··9 ~.!
Vy, ($50m ) ,',\r-.........,DOD0,0009
/i/J() 1'1r~:: TI.lV''f fon ';;e?in 1;l
:()'.~'. (466m) ,I:n\' Cer)'tr~l Re.nd~()~()~()~~.----------~------~,-----i(le60m),i"tf;, ••00 ()" ..· .DOC••• t·iI' f il " •.. 11 ...., "., "."'."b'o 0'.-" " ... ~• 'I ., ~ .. ;,1fi:~:::;.~~~:+-.,._-~~~..r-_-...,~,,_.........--+-,...:::!---..-L-' -----I•• 'i, ~•. "t 1Ii."-~
b, ' .. '" "..... ,l'.....
()JQhal1nc:.>~~H)l"'g(139:5m) It~!~n~.AT~RSRANOc SUFIERGaaup
I,
SQvel"nm$ht·~:~::~:!+~--------~!~~------~~•. f. ,,'.44,.,,,,... ,t·" ." .,'Ii'. hf •• 't
~j •• ~+' ----- ....... +-:"".~~~--::T:. .:)'__• fI,.....( .... ,
wept R~nd( +\~&~650m)
HospitCillHi!l,~.,
Ii
g a~n(:!'rali~sd t3ti"'ilti9~iiAt)h,i('; e;!olUMI"I1t:}F"tho LlJolkem'G('Jl¢;I~b'iald. il /,'
I
16
[~~-'MEM-E-E-R--',-_.-, ---''''''I'FORMAT,X'-, O-N--r ....S...U-a""'G-R-O-U-P-...-'"1
'"",...----- .. -~Q""".q'""9'"!'1ll',l'4. "." '# • ., •..... ,-.,.00000000,000000(1000.00000
REEF'
Uj.tl~yl(Sot.lldel'"
VS 1
ape? SC)I'}~
(20m)
Har-mony(15m)
,
','
Johanl"lc,sbuI"'9
Vil"'g:.inia(7eOm)
o
//J
i)ot8il~d titr8t:i.gl"'8i!!M.ic: e:olumn 1(;,)1"t.h~t Contr'al RandGroup in tht!: !3tluth·..tpJC:H'ilt~rM PI~l"'Y;,:V,~rrt:i1 ltJoUU::llWGa:lef1!ield~' .f:r"
,1'i./,/,~'
/'Ii,
17
"the st. H~lena FOI"'rnatiol1 is the !nt~rmediate (Fro5t.) rk~E~!"f
in the cC:Jnglom~'rat.,ic MF 1 'Zone:" The lntermedi~te Reef isan oligomic'l: small pebble r;tmglo(i\er.at~ which is gerH~ral1ythin and no of economic:
The Well(oll'l Formation (Upp~(" Footwc::ll ~ UF 1-4) uncon-«fOll"ma!'lly QVl1irl ies the St.. Helena Formation and is
,(,;;p(tlposed of planar":: and tr'bugh cl"'o$sbeddsd, ilirHi:?- to
e;oal'"se-gr-e.if't@d 1i 'Chic- .and sublithie aren;i.tes with acharac:t~ri$t.ic: sp.ec:f<ling of yellow met>'llpelita and blac:l{
Cher, j~raitHs. Disseminated pyrite ..on bech.:ling plane5l)int~eri\~dded quartz aren~~t.e$ ,a7fl scattered polymict p(a\bbly
!:San,';1tones also occur 1.nLithe tfielkol1l Goldfield.
The Harmony F'orm.!ltion uncen fdl"'mab 1y c)'verl iee; th~ Welkom
Farma\~:i.on t'lnd Has.at it=:; base the Ba$~l Reef which has
yielded >60% of the gold mined in t.he t<Jell~om .(uoldfield too
data.. rh~ easel Relil'f i(ll uQconformity-b&sed and la:terallypersiste:nt, end is overlain by cMarac:::terisitic vHu=l<e$5 <irtnd
al"'eni tess .Of the H<1:lr(l)Qny Formatitm ~
'the unconfl?rmi ty-ba5led Oagbr~el~ FcU'·matiot'l ' ;.$ tl1~ upp~r-'I ,_
mos~ fot'mat-ian of tht:;? Johz:lnneH5burg Subgl"'Qupu At its base"
i~ the Leader Reef vJhich h~s y.ield~d appro~d.mat~ly lS% 011., .... 0
F1~6.4'.i~~:2 iUl"'ffontefn SUDgl'"t::H.!P
"'~, ' ~ih~ l(::lw.el"'fIlJ~$t of t.he three formc.d~iQns Ct'lmprtsin9 thel'urffonteinbt(q;:olJ~~$ -l:.he unconform.it.y ...based $pss SQnaFcwmation t'lhieh sont;~ir1$ the ('\~V'-~~I ~~~f r4t its ba~e::.: The
..It" Re"f ceo 1\"in" SP"1'"l1CI~c b\-li"n "I'''11Y low 9"1 d""VliIl"''''' ,
i(
\\
18
The Sp~$ Bona Formation is eroclllit!in thl':?southern pOl"'tiol1of St~' Helena 601d Mine by th@ 'Adnder'lk G;he:\nrH~l~ Where t.h~
A~l"ldenk Chdnoel ,~$ not PI"(;:l\';sent \~he Big Pebbl,1:i1! 1'1el"'l(Il'H'"
forms t.he unt:onT'ormsble b.atse of th~ Aandenk F~rl'htltion'" To
the ;;:;oui;:.hof St." Hell!'na Gold Mir'l~ t.he Aandenl( ChC1nnel
C:Oliteil"l!'5 mineral is,ed CQnglom®retes" The &~ig Pebble i'laV"I~Gt1r
cis poorly minmralised in th(:S>Well~.omi301dfiold.
The ul'lI':on-formity-bes::ed Eldorado Fcrcmi:)).tion is the upper-, .... 0
most IJnit."crT the Central RQlhd GrttlUPin th~ Well~t:lmGold-'
field end is eCjljivalent t~. f'he MOrldeor' p.m;;$E:lsburl;;j1\ i:'j
~Qrl)}ation$.. NuffiSrQIJS uru::.ionformi ty",!::I.:lsed congJ.omerat.os" ... \, :-
Qct:ur' in the;,) Erldol'~Cldo Forma'l;.ion !:IIJ't 'to date 00 tCooglomer"'"
ates of economic importctlnce have been loc;.;atedon st.H~lena So18 Min~~
c:
ThO Vsnte-rsoQrp Supergroup ~n $'t~ H~lena Gold Minei$l"'5'ladlivaly thin cand is ,"'epresent.ed by t.he l<liprivier;;;berg
Group (Orkney Forfl'lation) of dC);lr:k7"'9reen a.lli'ygde.lo.:b:!al leva, . '. • '. il
end tufT'"1i The thit:kl'1es$ of the 1<1ip.riv.i~r~berg lav~ de-'~' 0
t:;ree$GS re.pidl y in c-l weste,"'ly dil"et:tion ae:rO$$, 9t. Helena
Gt:tld Mine .:to a pair!'\:; where th~ I(aroc> Sequ~ne.e rG;lS'!>tl'$\"
uncon'formabl y on t'i'V} Witwatersra.ncl S(Jp$>n;jrl!nJP~ Unisel
Gold Mine hae lava the I<liprivie\"'eber9 Forml3>f;ion lUrId• GeJ..tIstie Clnd e:cnrbQnatb sed.irntEH'ltlS of the over 1y:hl~1t(lippi;lnFOI""matioo· of the Pt.atberg 61"oup pl~est5lrvsct,.
o ()'
On ,\
Unisel (Gbld
SeqUGill"\ttt':: of ~ge ~~OO-1$O Ma (SACSn 1980) i%'i p'r.r;?sGl>rvfficl"
Shale and cli;~'nic:t.i i~e o·~ the nftJyl~w. F'Cll""matioo f~rm th$ baser.}'F the I~aroo Sequeru;;;e ,_endDwyl"8 Formcn:tioi'l:t~ pve~)leii'l lly
19, ii
(_)
\{o
Ecc.:a.::lOciBeaufort Group sedim~:'t$. The Vryheid F'ol"'mation
Clf the Etca c:Jroup comprises sandstones and thin coalseams. wh~re the overlying Beaufort Group compriseS sand-
r.
stones and siltstones pf the Adel.aide Subgroup-
p
Ir:tt\' of eal~ly Ventersclorp age occur throughout the,
Welkt. .....bldf lard ilAndare related to axtl"'t.H$ions of the
Kl ipri\'iersberg lava. Late":::'Venter.soorp age intrusives,l<arl13o 'd'cleritas and fdmb&I'"lit.esals;;o occwr s;pol"""",dic.al.1y
throughO\ft the Well~om Goldfield •
.1. .. 7 M!NERALiSATION
Ths general C:Ohsensus as to the ari.gill of' the gold
minel"'aU:sati.on in the Witwa tersl"'''.md Supergroup in ,th$.literature OV($It'" the las;t twenty years is orre of pre ....dpmihantl y place," or modi fied pl.ec:er o'''igin. Reascms for
thli::! CI::msen$US .srI':?the clt';l~e relationship betwlltsl"l gold"
distritHJt.ioli .and $e;diment.~ry i'setures" th(l;! iMferr:.~c:I lackof afteration in the deposit, the lack of permeability to-1l\11ow pt:'.lst-depoSiti.on&l flt.ti(i movCi?m~mt, the lacl<. tiT
vertical <toning. end the ilii:lbi 1i ty of f lu;i,ds t.o transnort~ .. • '. r"
gold (hGillbauer Clnd VOt"l Gshlmn, 1993).
A PQst-depaSlitional origin Tal'" the mineralistlt,;i.on of t.Me
vJi twa tsr$ran~i Supergroup h~s b,~an 1'~~-emfJMasi~edin re(;;ent:
worj, by l:ahill.tps (19S6a, 1:1, 19a7a, 1:1, 1'198), Phillip!.;" at
al'1- (;t1787h L.av') at el~ Cl9a8a~ bb 1990), l..nw 0.990) i;\nd
Phillips" a.t"lej Myers (1990) ~ ThG? aboVE;> wcu'''kers id~ntified
prol:Hems with t.he pf.:lt::(:;ll'"model much tlS the lar.:;k of if'"'l:Ji'\,;;;- ,
C\xide$ but i'ilbw.rtd~I'le:eof pyrite:; unU$I..Ii'.ll~utphid~$ in. t.he
rsefs.~ detrital tr"811,p.;;porto'f 1..\i"4':Ird.n:V!:.e 9I""ains ~ the<J
20
o
il"li'erenc~ \ ·of hydi"au.lic equivalence of\ ;
basinwith ....it:hemical <lSSOC iations, and thegold itself (Phillip~ et al., 1ge7)~
l"'ee'f minerals:ttt
source O'f the)
Q
Welkcm Goldfield is
I'II.,
#
I,
o V I)· J"'
genel"'ally confined to lmcaniormity-b<ased c:an91of{ler~tes..(I " ~
ccmta.irH;?d 11'1 ths 9..u::a1
o
al:)I,.md~nc(t!cd' por"oua l"'Ol.1ndpYI~ite and the carbQ.n (kerogen)
cot"lt.ent of the, host-conglomertate. Although small-scale
ancmalies in value m<:\y occur across faults~ neither
i"sg:f.onal nor "systematic trends of gold miner~,~.l.i$t.:ttioh
I'
I\'
tI
"I"elatl?d to fault, structures .Cltr~detq:cted on St. Helsri..t!l
(Eioltl f1ine.
C)
21
i)
2 STRATIGRAFlHY
:2.1 STRAT!GRAPHIC CONCt=:P'TS
St.ratigl"'¢'lpl1:ic classification is th~ sy$t~matic:: arra.nge-ml;?ntof rock strata int.o units wi tl1 n~i'erenc::e to any ·ofthe ,:,wopel'"ties that thp. roc:!~s may possess (SAC$; 19,87).Dna of the accepted methods 91' stratigraphie classi-fication is 1i,~hostra.tigr"~Phi(:! classification (SACS~1980).. A litho$'·tratigraphic:: unit is one wbic:h is unifiad
[i. . :}
by consistih9 pl':,~domj.n~ntly of either a cej,.tain rock t.ype
or other sign! f ieant' lithological T_saturas" Sequel'"lCe
strC'.!tigraphy arId t,.,~c.~t.J:fostratigrap"'9 ar~ a1.tere~tiva>$ 1Foli thostratigrO!lphy '1.'·hiCth are ne·c:essary t.o ref lee 1: the
tac'tonic:: develd}Jment o,f a depository iilnQ the genetiC::reletitmship of eliffenmt l.i.thostratigrapl1ic w1i ts.SS!quenc.::e stratigraphy l.S ba\ned on saquenees, whith arebounded by unconformities and correlative caAfdrmitias
.(Von Wagoner et a r , ~ 1988). Tectono$tratigraphy i$defined as the relationship between tectoniCS, sadiment~~tion"and 1:?r(:)$ion (Brink, 11.:]96).
A lithostratigraphic subdivision over an araa the size 01the Wel!<omGoldfield only "provides partial J.iltrs.tii~I"'aPhf~-!)
as a lithostratigraphic subdiviSion does notrefl~ct the tect.:mie: developmenic. of ,the d61pcnsitc:w'Yadequately tWiMt.:e"~ 1985) u This r bl.,-,~u.e of thepreset'lcl;! of lear!.'); later"al J i thofacies va''''iations teo g.
,Jo'"
intar· ..tonguiflg '.!.mii1$) in the daposi tol.""Y "cannot be
adequately presented in a lithostratigraphic column. Thouse of litho$'t:ratigr-aphy' pve,'" a smillier ai"ea, .t:l.nelspecifiCally that of St. Halana Gold Mine, is possiblebecause 1t::\1'"gS 1at~l"al 1i t\l)o~at:i~s yariat.ions do iI(\)t occur
in the Hermcmy p Oagbre;ef<., $pss Bona ¢'andA~'lnde~k,Forma-r).oils. I 'i. the c~sa C)'i~ thti El,o('1racto ~ormat.ior1 lcatet"e:\l//1/
c
()
lithofacies variations da occur~nd saquanCG stratilraphyis QPplicobl.e.
:2~.!UNCONFORil-1! r I ES
An unconformity isn
oldor stratGp along~~ro$iQnal truncat:i'~n
e ;:;5urf~c(3150!:lal"'at.ingypungor fromwhich tha,"'e is 5.1?v:i.d~nczeof Gi:'i tht1r
exposure, with b
,,'SignS'Ficant t'iiatusC:£nd:tcat'!'id (Von Wag<:ll1ar~t i!ll., 19S5).Uru:::onfcH'mi ti(?l::) are Tl.mdalOsmtal for determining gG!nat.ic
p':H':I~.~9~~£ of rocks <t1tnd&ubsequsntJ. y for stro:Ugi"aphic-:
the major
Slul"'.:Vferoue congl(;:)(naratos of 'the Witwetat"'a,"and Super4;jl"'ou.p
and are "ehtwac:teri.sed by their thAi: or slightly Ut1-
c:h.d~tcry tHi4tW'S and vertical fQciets .changes from Bf"enito
below t.1·lSll.mconfol....mity ttl conglomel"'liltl!l' ~bQve the l..mcon .....
formit.y. ThQ conglomerates Qvorlying unc:onTorm.ities
Qenor~.ll y c::ontain Clbove-~vel"'<!hge gold ~ UI"'Cilnl.Um.and pyri to\:::;
minol"'<111isat.ion ~nd the unconTol")~it.ier:;alt;t) form the bnt:lo. . .. ~\ ~err t':tll'lmcml).' lJpward....fining unite t~l"'med pal"'e-$CiJqu(m~eS QI'"
sequcmc:es <Yon vJ~90nel"~ et al ~, 1!:Jaa) "
Tho i:lngla of .;:tf1 . uf1eol1'ft:'JI"mity dopot'II:J£O ort the I"'ato o~
uplift~ Ol"'or:;;ton, bCll!;>in $ubmidltmco and ~~ihmenta1;.ior"p wit.h00 uplift producing muportmposod
1976) ~ On tmcQn'rermity mul"'Yt.:\cos
LQW-imQle ur t;Qnfor'm:i.tiCl~ «21l) o·f tnt!!, Centr'<iill R€m(~ SrCHJp
l;onvG?1'"9$ t"'·Ill)l),J.d!S tho basin edg8!S1'- in~ \"f\~tin9 th61t "pulso~:s
of us;<li1t .pr.:curn?d oithtH'" during 01'" f\, \.t:.)t,"3ing~u·:.!l"i?de 01'I ':
oodimoMtdtiQn~ Uplift was ffiQI"'S int~nsQ ~t tho basinftlOI"'C)in p compol"'tt?t:l to the basin j,n1:.0I'"ior • F(apid (;w'Qsion at
i/
o
,--the upllAted strat.tgl"'C\phy took pl.~J.ce tlnd F€tI1.Jef v..!(tiS
$UbSOHln:l'.,Ientl y \"edu~tl!'d ~ a ftor !tJnil: h the? d¢'wpwt;;,f.t.iQrHI~1. eye: lebegiSll"l ~gain ~
Uneo1formitias <tire ct:Hnmon to -sed.tment.at'y basin£; which
UndGj'>go upU.ft and erosion together- with dj~pasitiafi. t:J1d
I..U1S~'~?Oi"'mit:LGl'$ltJhic:h o:c:ur in the Witwat~I""5Elr.nnclSuper-
group are simi lor to those described by Ribs (197', andi
Ant31don at 8'11" (1ttSQ) fl"'om the Span.i,sh F'y,"eness nncl to.~,(
(Miall. 1919). Detailedformitias on St~ Halen.
Cha~tar .;;i.
dElscript;tQns ofGold Mine (!>I"'!&
2.3 STRATIGRAPHY OF THI:t STUDV AREA
The str'::l'tigl"'<'lpl"lY s'tudiad in d~t.i 1. i$.1 ,(I"'om the l.\l:)\:lar
PQr'!.ion 0';: the Johannesburg Subgroup f.:lnd the.;] entire
T\.\.I"ffon'tein Subgroup. This enc:ompes$!:!1£t, the l-'armony,
.Pl:lgbroel~, Spl;:lS aQh(t\~ Aanoenl< c';\ndEldcH'''aoQ FOl"'me.tionsu
G each of which are dms~ribed in detsiJ below.
Tho· atrCltigraph.i.r.: I1Qlnl:i'?nelntwl"'a utili.sed in t.his !5tudy _is"
th';lt whieh is in U$a in thO' currant 1i t.erCltur'w aV"IdonmaflY of tht? miftas in the Wallt.om G(..')ldfield. Minor di'rfe~-om:Qa ba'twel1m th~ nOlllerH;:lat.ura I..H3ed in th~$ $twdy end
thil\t of SACS (19909 Fi9._ ~~2.3.) and Minte.'H''' ~t. aL (1996);-:) . . . .... ~::>\(. ... I:'
~Q t:U::;CUl""~ rha dii"fereneas in nomenclature and tt1e lClC!{.of
e(:)fI'llluni.t::<ltiol"l .betwClen minC-}$hevt: rc")sul tad in cc.,rrelat.1.emon a goldfield-scale rem~inlng uncertain (Winter. I'B5)*
24
II
The strdtigraphy of the etGdy eraB WBS constructed fromthe e)(amin<:ttion of borshol",> cores (Pig. 8) and the thick-
ness of sedimentary intervals caltulated from isopach
maps ~ The isopar' .m.:;.pe constructed for each sc:elifTl(;!ntary'
interval show th~ wastern margin subQutcr~p position, the
position of which is wall constrained only in the centraland no,,.thern porticms ·of St. Helena Gold rUne. The
stFatigraphy preserved towards the cantre of the Walkom
Goldfield (e.g. President stayn Gald Mine) is in places
twice 'as thick as that pr'esent on St. H(:;!leMaGold Mine.
In the ,desC!I'jipt:ion of COf~g lomerlates tne term aU,g6th'ic t
''''efer'S to a conglomer'at.e contain.i.ng >95 percent 01: ei thar
d.urCl.ble or ncm-c:lurCltble clasts. Durable c.),,:p.stsiar-e d~fil'1ed
as consisting of either quar-tz or chert, and non-dJ~able
cla~t.$ consist "of ~ither metapelite, quartzi.te, iiane~U$
or volcanic mat.~ial.\\
2.3.2 Johannasburg Subgroup /)
The Harmony Formation ,.is defined :i.n th.ts st1,.l.dy 4$
including the Easel Reef as th~ lowermost unit. of the
Harmor')y FC>flllation (i-.tg. C?) ~ The Easal Reef i$ ir,c;luda~1 at
the top of the WE:)}korl)F.ormation by SACS (1990) and Mint,!';!r
et a l , (1986), but. this aut.hor at1d ott1ers (Mcf(.i.nnevet.
i'll., 1~:~A1 Wi.nter, 1964a$l b; Sims~ 196C!; Cal'low and
Myers, 1986; C.S. I<ingsley, pers. comm, ,1.989; A"R. IIC:ing,
pars. C;r")mm~.1,989) have fotJ.nd no justification f'1.l" cll:lirlt;J
so, as thD Basal Rl,~efoverl.ies ~\ ·major wrH;:onfOrmj.i~. Thus
,1.n tel"m!ii of the prir :iples of St:!quence str.ntigr-<J;\phy the.~
E~sal ~~ef 10g5,<:a11y 'forms the ba$al unit of the gen.~t..icpaelulge termed., the Harmony FOI"tn.;~ti(jn..i cC~:
},\ 'i I
"25
r---'--THICI<NESS
J. Sm -, , "'" ......., .. '"
'\ ... ,
......'1' '" ..... ",IS) ();'
t1Q," .,' Middle.. ..
, " .. 'Reef
,.tOm,
" "' ,'It '\._).., ,, ' \
'IJ:()j.'~~)Middlc~ Reeff' .. ',~t' " ... ,~.. , ,fo. .. . ...~ .. " -..... ., , ..iii .. to Ii' I'". \. it,_\ v ,\'
5ro [\ \ \i' " ,
:J
s&:r:I:L~.r~• II
Il•~ Fine-grained $ec:limamt.s
[J Quart:: arel"i te
o ' ~ Qw.tlrtz t'll<:'l.cl<.m
()
Idealised ~ratieri~phit:; CClllJffil'l ,~f the Hnl'''fI1i:li'1)'Fcw'm.ntion, "'st .. "HfE.llerH:l. G!']:)lr.:l M:trHl,h o
,.)
TO the ~~out.hWt::lkom ant]
dist.inction
Of Unisal ~old Mine the litftologies of the .
Ha...."" y FtII'Ill"t;'on'" "r'e. si ..il ",.., .."k1"9 }based solely on lithology difficult,!
part.iculal'~l y when thj!?l""S is no Basel Ree'(-davaloplnl::!nt. The
Hal""rntlny f!:'ormetion., present to the SQut.h of t.lniselGold, i
tl1;i.ne ilnd in pl,aC::~$in the southern portitm t:rF St .. H~lenaJ .
Gold Mine is c:list.it}f)uished froM thCl ~Jelkom F'ol"'mat.iQn byif
the pl"'C?$enCs of {~orou$ r'ound pyrite .f1odUJ,es .', in the
Ht'l.rm~ny F'c:wl'rIation ~
TheGold
tisopach map of the H~rmO~y For;1atiQn 011 St. HelenaMine (Fig. ;1.0) inc:J.ucteS the ~ombined "chic:kness of
I.. ..... . DBasal Reo'rJ rop of Reef qlJart1J'i,;tr::, l<htalti s~le and
. ,\
Middling quart.aite. The Harmony Far'matiQn~thickensc
the
(Sold Mina", ih~ HarMony Fo,"m.ld:ion thins5 ~.~ the ~a'i9i'l;.:pf \;';the
OQgtn"e(~R fihU1.t ($ec::~.iorl ~\-A; Fig$. .:1;'1 end ·,12)" The\1 *
thic:krH~$~ of the Hermony Formation .inc:reasa>.""sl;' \1tlo .8 nbrth&rly direction acroa. St~ H.len5~e~ldMiM*.(J ,0
, () ,'.'
in
, ,-:st::ast I ~'le!'\)t oriented .ec:tioha thrt'n.l.gh St. Helel1<t\ (:Sold
Mine aro chel"illcte:H"'ia\$'d Py' the 0\1(;:1"811 1:.1111"11"11"9 .<1Sti'dt.runcatCFQI1 of fc;n-mationa in ill w~:H~1;~I"ly direction(l3ectit:m~? s: ....1'3, ~nd C:' -c'; Figt's.. 13 end 1'4). In the (flt>rs
sQuthsrl y £section (I::':t.9·~ is) the Basal Reef .$t.~b-CIlJtCl'"O,tl'$,'.
<tlgaif'H;5't the I.,..eaderReef but' to tho !,\Ql"t.'n 01 th:i.ltS ($action
C'-C7 Fig_" 14) thO' El~$al and
II
o 21o
o
';
IiII
\)
o
5....1~~m \,
10...15'\)\'
o 1(1'(1 :2~~~~ __~~#~.~J
/swtU::u..Itc;rQ)'J
/''{!stimcatC?dI glJbout'~l"".pp
,.1.//' F'i4ult loS5s
. c17tg;Q'pct\ch m~p ofitn'tt::l"'val ::;l Sm..
28
o
o'-' ........... .,..1,
Q
o
AI
/J'()
(i'
o
Pl~n stu:mt:i.ng_ t.h~ lQt.!elt:i.ofl crt t3oct.t~n1J A-AU i! A' -r~\11~a·..,o· t!.In'd 0:",C-1' ~ntj thci hOI"'{91"lolCHS unt! unellJ.lI"'ql' ....{,1UiMd !d'i:-at..iJ'Ot'\15 IJSOd ";(,1'1 thoir eonlZ"tt"l..!c'i::.iem" " l'MfW nt;;)l"'th~'JO$to~"'I'
. J)Ql"'ticm (,1'1' $t~ Hml~n~ ~h! ,)Nine5' is OIH.ul"~i:'d "in f:!'ig" G20
oc)
ff'i'I>}I ""';'If!!-+ ....;,-.,.}&i?I~~4--
ff1Ii
sec,i:iarl d,:'j·..·~1 Jt"l~ tho ,H8rmC}l1')I tQm~ Tl:'l~ biiUSt; 01 t~he EloQt"udQ rQl"'m-
u.s.a~,..'4S'dat\.\m. \...or.:J~t.iQl"tit::. nMown inver'tJ.'''~l r;nw,g~x:H'''.at$.:.t1j~. 0
\ Ii/Ij!r,
- I~
i.)
North I I;SQUAand·enk Po.:J,tion lias'Fig ~:U ~' fIlC)
C)
/1 30
»1>'lIlt:;
ISIS
,"
~,
~'l~~a I Ot:lt:Jt di.p soet.tOfl ;! W""'S' ~'f t.:.1·lf~""l81"ili~flY to Allrl ....r'fJt'mc'tit:)n6~ The b~,$G Qf thc:~ ~ldoi"'C\dO t::ol"'flI<:ltianb~t?r'l used, as da t.um~ l,.Qca tt.on tiS I::>f~~!f'm ift i.:tg"
Nett? VOt"'\';ical t;;!x<'},ggof"'utir.m ~
ttJest.dGnl{M~E:1.1 •
I}
D
...ill
'.~
31
14'::81, C
TIlt)
RE:F',,~l!Mt:u\It ""DtIWlf,C!'I'I'tlZ
...<W- (t:M(lO aUP~flCSl'Il':)l1fO)
o ~~~Ntrl!
~. CONG~OM~p.Ar6i'4 PQRClHOt.~
i)tAO{\\R 1'lt::6:fl'MI!)Ot..C; r.m:up
[iHARMON~• :" aASAt.. RSSIll
W~st I t::~$t dip $t,Jcticlli c::....C· of the HarmCln~'to A.?n-d.!lJnl~FQI"'rn~t:icm9. Tpe bast? 01 tho S;ldQ.j"~dQ FQrm~tic:'H'I'~m t;l13:on u~ee1 ns datum., t",t:H.':(';ltion is ehe:tltJI'\in Fig n
11. Note vOI"'tic:crll oHngQsr.mtion"
32
gen~l'"ally 01igornict Eas;!).! 'fac:ilZls .and the sOlJthS'rn pol y-mict St~yrl i'acilZlsl1 the bounde'!I'")I b~tw~en '.PJh,i,t::1;\'oc::eul'"$ in
G
t.he northern portion of Stb H~l~na Sold Mine (Minter~l~7R). ihe BaB<'ll facies em 5t,. Helena Gold Mine:?1$
fl.ll'"thel'" divided into the! ol,igomict and cardon seaM 1""i::Hi?T
i)
The polymic:t Stayn facie$ is divided into thCl'"pol ymir.::t southern I'"eef 9 the "Ml-xed ree·f and the:; ai"'enite
reef an St. Halana Gold Mine (Fi9B~ 15 and 16'.
-E......•...••.C~ntr~. mi"~d reefFACIES ••.• •..••• ••••- Pol ymic:t southern reef
Arenite reef
The f·ae;ias distribut.ion of $ub-divl.sion$ of the SasalR~!;1f bGH!.lt"'S no \"'ele'!tion to the subou;te.rop position of the
< '. •• • • '. ': ~':>"__';:'::::::';'.= It)
Easal ~(~'i§f, with -foul"" of the five fac:ie!) abutti~9 against.the west.erly $uboutcl'"QP line of '!:.h®S$$&l'\ 'R~ef on St,.
Helen& Sold Mine.. 17l1e f~cill?$ of !l,t'ht? 13a$a.l.,Reef ~(l$o snQW
no relation to the sync:t-'ine and ~djac::~;.;nt. antiQlil1\iil
prDsentnin the western porti~n of St. Helena Gold Mine.The Sa$al Reef S.ubdivisi,0ns on St~ Helene .f~Cll~Mine are
c:~'mpcUrli:?d(1#.)b1e .1. ~ end al"'S dss,t:ribe:d belQw~
~~~=I
r••1 type and occurs in the northwestarn portion of
St. Holena GolC;! J"lineo Th~ oligomic'!:. clasts and PQr'ous"
t~Qund pyrite? (F'j.~. 17) C:1I:::t;ur..~j?rimal"'lly in !5hallt:n'!l'\ - ~ ->.
belOt'l ,'l;' thin l~yGu· of ~'it.ab-
c I.::
".:1
l
\
\Ii I;:) \'ll:)t~U ftE.~r
S" pOl-Vi'll C1" jU!:EI'
C:J~\~~NO'fFAC'tJe.S,"\
~~ /' ~ubt:)u te i":Q\')
'\ ... '~$t.;tma.t~d'.,l'" su gC)\.l't. erOil
o
~ji}_.l.~\\"
.di~t.Y"it'.\utJ.on ".
I, "~j
REEF iMltK~. ~ORTING(~~SS
~,' ~< ~,-"*-",,,)DAStlLREEF' O"40cm good· cl!rtoLIomUCTjo mall 10
1/
MAfiElaTE :; GUAfm ~RErl!n~ SPC
SL ARENITEe SUBLltlllt~, M~lmE UP!:'
LPC,;ll!tI :: rml~~nLnAnOIl
vt:m n ¢ (lEW QUARTZ
!J
CCH1q'~1riE;1filt':J:eli,'; e
I) \\
o
o
(3
o "
Ci
o
34
LATERAl.COHmmm
~EEF COI1IlENTS"
~~~~~r---'-r-------+-----------r----r-----'--~----~~--------~--------__--~+-------~------~'---------~--------------~BASALREEr' Q~4fj poor llatrb supported spC:~GPC:~etapl.!lite, vein q., liH art!oite, rare founded, dissem" poor 7 conglomerate, rare spc"lpc, dltsto111.[(ARENITEREEF chert, rare volcanic .rara q \'Iackes 'ioatedl stringl'lrs granultistone 'la~ at bllsa
,
'. r.· r;hanI1I!W~d trough lI~bedded" interbedded tooglon·, !11-q arenHr:, al"ate and a1'l:oit&;).~ rapid fac!es changes
Fig.'~--~-------+----------~----r--------------4~-"--~-1~~~--~2."25t:!\\ poot ..goca clast support'2d spc:·lpc. \fein qttartt, cbert sl ..q arenite 'rounded and crystallinll nollerate-good dlsconUn- trl')ll~1IIt'"bedded basal t:ongl!:Hll.!rat~tOiler ueus .sl ...q aranite,
q·f.Stl Iludera te
BASAL REEF(POlyrncrSOUTHERN REEF
BASAL REEF(Ol.IGO~ncT 1
. PYRITS H!tlERALIZlliIUIl ECUt!DHIC '.I1lNERALlZATlON
THICK-NESS
SORTING PEE8LESIZE
CLAST 1JPfS lNTERNA!,PARTINGS
,)
aatrix oupport~d ope v~.\n q., chert, meta."pelite, tare arenite,'101canit Clnd ignaous\\
sl~q ur(1nite tabderate"'good t\(ld!lr;t!! Aurounde~ and ~rystal1ine uno U
channelized trough xMbedded rara disseninated,in place$ arenite, rare carbon near base
granulestOilfis
R£FeRE~S?C ::SMALL ~gaBLE COllalO~F.RATEQ ARElllTE1: QUARrL AREIHTt
HIITRIX
~ry$taUine a!\drarllrounded pyrite
Q.5-7a paorupper '!
cbst supported ~pc~lpt Getapelite, vein q'lcharty rare igneous,volcanic and arenitt:
"arhole
;)})
SL ARENtrE ~ ~iJnL1tHtC AREtltlE
L AREtHTE :; LtTH1C ARENliE0,l.?C ~ LARS~ PEnSLE CON&LOMERATE
VEtil Q ;: Vlml OUARTZ
~~D5DDEn ~ CROSSBEODEO
.;
!.'9.t.11@,.. ,1.. ~ Conlp';H"'isc';)M of cCln~ lQltlel"'at:e ch~r~cteristi.c:s of thefac'as of the Sasal Aeef, St. Helena Gold MiMe.
35
(j
FiRUI"'I?~JZ: 01 igemil::;t aaS1~l Rl#e1'. Nett;;? al:l!.lndant porous rowndedpyrite. Coin diameter • 20mm.
36
have the bcH~e of the Harmony Formation defined byeither a scattered granulscongldmerat~ Or a discon-tinuous layer of porous round pyrite. Increased goldvalues in the oligomict rea' era associated withporou$ round pyrite end also with the presence ofpyrite on foreseta and set surfaces of associatedquartz arenites.
b) CarbOh seam reef. This consists of either single ormultiple carbon (kerogen) seams or flyspeck (dissami-nli'lted)c::arbon~overlain by eitht~r Col.nolig'omic::t reef orby scattered oligomict j:>l'lblesi.11a sublithic ';H~enite,of iMing-up to -'"'l; quart2 C'i.renit.e. Gearboh abundCol.ncede-CI"'t;'tl.SS!!:5 in a $b\.1thwt:.~!St.erly dil" t:irm across St. HeleneGold ",line(Fig. HI). High gol1:.1,~"d uranium values .:trecommonly associated with Qccurrances of both carbonand porous round pyrite gr~i:n$. Th~ transition betweenthe carbon and oligomic:t r'~ef subdivil:;iCln$ of theBasal Reef is gradationa1, with disseminated carbonoccurring in are.~ Q oli90mic~ reaf.
c) East I central mixad reef. The mixed reef is transit*ional in character ~nd thickness between the 01190-mict and carbon reefs in the north and the polymictreef in the Bbuth. Disseminated ~~rbon occura inplaces in the mixed reef.
dl Palymict southern reef. The polymict cPhglamarata'''eefha~ a sharp upper t:ontac:;tand i$ generally over-lain by the \.1n-m~~ 'ralised Top of Reef quartzite and &narrow Scm thick khaki-coloured si~tBtana unit inplacl'!:H$ (Fig. 19) ..To the south of the main develelpmet'lt
. I
of the polymict ,v·'!""u.thernree.·f t.hl.!?basal oligomictconglomera·tt;! is frequently absent ~nd the cong.lomeratethins in a southerly direction.
a) Arenite reef. This fa~jeB compri.es Bubllthic- and1:i thie ermni tms with mihcw intf.?I"bedd~cl polymict I;on-~lC)rnC£!n;d::e!5 .. The arenite reef facies is I"astr~,t:tol::l to
II
37
c00ao o Q i
oo
e
08(.)
oo
o 0°
e
o ooe
o 0 0
°0cai;l 0e
o e
o 0
o
"-,
Carbono
<:) Shaft
~F;~Ult loss
n == 109
\
km :2.---1(-->
IiIi,1/(
D,i~trit)l.J,t.:i.t:ln <:n\ CiSlrb.QI"l '\ i<.ero91."tf't i.. Pata ,;rare 'fromUr\dar;,gr'ouncl borel')ole lQ9~,~and inc ~..udes both c:aroQnseams and r.:li$seminatsd <::il)rbcm.
. '
38
Ej,.gUl"'!?19 : F;)clymic:t Sputhern a~$al Reef overlain by. the Khalr.;f,$hale,. !Southel'"npart of St •. Helena Gold Mine. CO.indtameter • 17mm./1
39
the scu..Ithern and sQuthwS'$tG'rn port..:U::m of St .. HelenaGold Mine a.nd is the least I<nownof the Basal Reefsubdivisions of St.. Helena Gold Mine.
f) Transiti<::lnal areaSQ 'rhe mi~HE!dreef is a. transitionalfor'1\ which oc:c:ur$ between the Basal and Ste>tn faCiesof the Easal Reef ~nd 110 sharp contact batwear-I t.he
Basal end Steyn Reefs hall> been recorded ttl dat.S in
undergrClund eXf..'JoS\:1reon St._ Helena Gold MitH;. A
~ransitional area also occurs between the pmlymictsouthern reef and the aremi te reef in the southern
part of St. Helena Gold Nine. iran$itiPrl areas havecharactelrist..ic::sof the adjoining reef types and aresimileI'" to the transition areas descr.ibed em President
.-;
Stayn Gold Mint;? by" Sims (1~69) ~ Channelling ~ wh.ieh isa feature of tl1e mixad~ southern and arl;;.'niteree-ftypes also results in the juxtaposition of di1feringccmgl01erate f.;.\(::ies maldng the precise \~ransitiph
point between facies wn~lear.
Concentrations of detrital minerals appear to be relatedto gold mineralisa.tion in the Sctsal Reef on St. Halehel
Gold 'Mine. Detrital miner'als include chrornite, 2ircon,
leHJ.coxene, certain forms t:l"f py:~-,te and possibly detritalgold. In geh(::)ral the amount of mineral iSGltio'l.."l. of the,:>
uncC)hformity-b.~;a~d cong lomerates (';\'1 st. Helena Gold Minedec! e8ses with .increClsing height up t.he str.st.igrephy ~from the SeBal Reef u~werds.
The isopach map 1'.)1' the Sa!:'"el Reef (Fig. 2Q) dO~$ hbt
iliclucle thickness da ta for e1thel" the Top 01' Reef quart;: ...·
i te br the I<h.aki She.la 4 The :Basal Reef is th;j.cl<estin thecenlr<al portion of St.. Helena Gold Mine and eubo\.&tt::rops.in thli.'? westarn pOl'"tipn of t,he mjt"l~. The i~opach mep of
th~ easel ·Re~f correl5POndllS to -ChI?1ae:i~s cli,~tributiol" of
the Be.sel Reef (Fig. J':5) v~ith are~s of thin' ree'r
40,1
.0:_. .'0'· -: ... - _.· .· " _,• II· .
Data POints
',. .... \~ ~
v ..... -.,,...;
'1/: ·• 1/. •
• •.jl •• ,.. i.
o1__ :2~ 1
r--.1-L!.....J --
IV
I0......1. In
/ $uboutcl'"°P"".....,..&:$tim~~~ct,/ Subouterop1/ Feul t 10$$e Sha.ft
X$opach m~p.ofI1l\t'ef qu~,..t:::i te
the aasal Raaf. (ExctudinQ tha Top ofand the I<halci. shi!:ll.c;;». Contol..!1''' interval
41
correspoliding to occurrenc~s of the carbon c\1nc:!oligomie:treef type. ~nc:!the .~e. 01 thickEst reef coinciding withthe polymict southern reef type. In the western synclinea.rea oT St. Halenl3. Gold Mine the Basal Rt;>efi$ >lifJthick.up to the point of subou'tcrop, but th$! thickne$s is notaffe)ctad by the wlFistern syncline.
I:JI2.3.2.1.2 Top of Reef Quartzite Member
The lOP of Re$!_fquartzite is l<nown loc=a.lly as the Cle.nSa.r, White Bar 01" Middlint:! Quartzite and QverJ.iel?>theBasal Reef in the c::entr~al Cind $outhern port.ic:In$ of St.
Helena. Gold Mine~grained subl(~thic.....to quartz a.renite of' maKimUCit 1m thick(Fig. 21). Bedding varies from horizontal laminations(Fig. 22) thl~ough a$ymptotieally ba!::1ed trci'ugh crossbeclsto small-scale (5-20cm) trough cro.abeds~ Far.sats aradefina.d by al'"g:illaceous mat.erial and disseminated and~rystalline pyrite. The TOp of Reef quartzite containsroare sC<:I.tt.el"'edpebbles aMP occasional pyri t. ~;tringers on
fareS$!te but haR no gold or uranium min~ralisation ofeconomic importance" :Brec=ciation occur$; in ~>l1':\t::as.~with a
breCCia-fill of chlorite and pyrite.
The contact between the Top Qf ReST quartz:! te §;md thE;'Basal Reef on St. Helena Gold Mine is Sharp. The uppal"cont.act Of the lop of Raaf cfuart2it. with the I<hale£. shalei~ variablep ranging from a gradationAl contact, in thenartharn portions of St.. HelGn~ Gold Mine and onPresident Brand Gald Mine (A.R. King, perm. comm., 1988),through intarlamination$ of arenite Clnd l<halU shalGl:t to a
sharp contac::t in the "'''Iorithea.si:<r!lrn~r~a Qf 91;.. H~lena (iloltlMina (Mint~r e~ al., 1996). Where the~e iG no KhaLi sMal.develQ~lnent the contact betw~en t.he T~" 10f A~eT tjual"'tl'irite
42
<I
/'c/
\:)
.0.':\'1:.8 POif'ltnsn :.= 109
6. til<
• II I'."• • • 1'" •
;.. . """, e .. "It•• t).14 tl • .. /. ..
.. it •
Q = 0 ~Oc:m
[]:= ~O .,.. 90c:m
ii] = ~ 90.:mf •I'
I.'
.•
G) Shq,i.ft ..
I SlJb6utCcI"'t)~
;f/FI':lUl'l! lO$SiSkm
(~I
XSQI:hlCh.intel"'V8.l
m,:ap (;)1' tM)~:;:~ :SOc:m~
(,
TOp
<,
(,I
_:;\
~ HC:lr.i.:z:ott't.ally 1:~Nlil"i~~9 Top t.;)f Ra\l:'f quartzi\.~r~) ,) ,;! \'-::./, >~ . ',\-'
Qv(:?d C!iin by qUQrtz ;:'wack~lS of the Middl10g
quartzite which ccntai~ acattered pebblesoCQin r.:liemiat.er :;:.:17mm.
]'
11
.11I)
()
I)
D
~nd the! Middling quart;,zite is el~osive, e~t~F in the west-"
ern area of 9t. Helen¢'!. Gold JVline (Fig. 21.).
2.3.2.1.3 Khaki Shale Member
ihe I(hald shale is a yellow- to I~haki-coloured claystonewhich is phyll i tie; in places. In the sO~ltherrl and westerrl
~portions o~ St~ Helena Gold Mine the Khaki Shale is Bc.oarse-gr'a).l"lsd grey .cs:LltstotH::l. Bedding is rarely pna-
served if1 the I(haki shale bec;ausa of ov~rpr.inting by a
perv~$iva foliation, although $ymroetri~~l ripples andIl
horizontal laminations occur in pIeces. The thickness ofthe Khaki sl1Ble rBr':'1gas 'fl"'om 0-2m, W;tth the th~!ck~st areas
ol:c;t1..i--ringin the north.srn portion of St..oHaler'Ia Gold Mine
(F 19• 23).. 1'hs uppal'" con tae t Witil the Mit;lq.1.i.rtgqUBr'b: i ta
Tha MiddlinQ QUBrt~ite Member on St" \}Helena.· Gold Mine(I
c;on.sists 01' quartz WBck~:1s (the Micldl intfj quartzi te) wi t.h
interbedded laterally impers,i.stent. r.::cmglc;'narates. (thf.;!Mil:Jd3.e ReGl'I'!5) end rare Cjuc;ll:ta.\;Ireni te iI'H:el"'bads. "~
I:\; 1'.....'·';1.:;
.a\) Middling qUi'H'·t;(?:i,. te. nd.~ c:o~\$ist$ of a c;l'ta\,.,~ctGh;.}~t.iC'
dr'db brONn-grey (,1U"i>t:z N,:1.licke t.::r.mtaining S.1;::~~~;!~redII ~.\I
~n9\.11ar C;hert ant:!.tjuart:r: g~rains and I=l(."~bblc;>stll) St.JI
H~h~ne Gold MirH'!l. The MiLddU,rtt;] ql.l~1rt~ite Elxhibits
simil'7;'r thic;lmes~ tl".aner~ to t.hose of the Harmc::myForr;jP.tiol"l) tht.c:I~(iH·ling
d:i.I)e:ct:ion and th).nnifHJ
Bald Mine (Fig. 24).
£n e northarly $ond easterly.)
to the southwast ·01' Sf::. Helema
45
'\ ...v,.
\"d' •
~ ". .t..IS. .~:
.:~~ ~~4....
!$(,.Ip.'0.C:h ma~ elf:20em ..
tho I'h.;i'!!~i ~t"IehJ. ContCltJl'" intorval-) \)
('
N
I
t EstimatedI $l.!bolJt.erop
VFi.'3Ult l\':)$s
(:) Sha'rt
[JID ~ :> 1~1U
/' S~tl(,~utc!t"'l:)pI' "/' e'stirru.n:ed
./ SlJDQutt:I"'~P
46
((,I
O.$1t;~ POirr'tl'SIi m ~9~
if
IV
II
\)
a - .t~.
'1)
It I.l
c
I~Hilpdr.:f'I IUQr,l c;1'I~il"ltervcl'l ::;l ~ll'l.
\\. . z
th~ l'1;i.dd1t~S' t~~t!H..t*i a:
o • Cdh~c"u r:.o
I)
j/
(I
to 6'
47
\\» ;/;:,1it!hic- to quart;.? arenite interbeds ,;cdccur j·n places.The a.l"'enites display bottl tr'ough- and planar cross'"
bedding and fine upward i.n grain size from coarse- to
f.ine-gr<"iined. Horizontal laminations also occ:u·r in
places. 01"1Uni$el. Gold Mine typical quartz wackes are
less abundant in the upper portion of tha Middlingou.artzi ·te, being I"eplaced by Cl highJ Y vat'"iable
sediment assoc.iat.ion ranging ft"'om taxturel1y mature,light'-grey fine-gl"'Ed.n~1i c:ro$sbedded quartz c:irenites totexturaHy imlYl.:).tur(:?WacKGJs. Evidence of soft sedimentd9lformatioli ·ot:c.::U1'"S throughout the Ml.ddling qU~H-tzite
(Elli$p .1998) ~ Soft sGJdim~nt defol"mation featut"9jF
include load c~sts? dish structures, large- Clr1rbsn'laU-scale flame st'f"uctures and dawaterir'g featul"'es11
b) Middl'~" Reefs "(Saaiplaats placer). The Middle RE:E?fs are~ener~11y thin and poorly developed on St. Helena Gold
j)Mine. The Middle Reefs are $ub-di ..visible intI':! cher"t-
rich, qua~tz-rich an~ narrow carbon seam reef types(Tabl~. ::n ~ The M~ddle Reers oecur spora.cli.cally in ths
Mortht;H':n .:1'1d eas~ern portion eT; St. Helan.:i Gold Mine
(t=:- ig.. :ia(5) and in a broad \'!q.rea" ac roms Uni sa 1 Go1d Mine'lEIlia, 198B). Occurrences of ·the Middle Reefs an St.
,\Helena Gold Mir.le ar;:~generally nsar the bass of tl"l1'3
Middling qWi:lrtzi te (Pig. 26). \\
On Unisel GC)ld Mine ,the t"lidd IeIi
ItReef~ are
~'istinctive hC)ri zc:lntall y laminated and crQssbeddad
ql.l~I,..t.~ oar~~nitett;. "tn geMeraljt econom::',~tniner.:iJ:i.S4tiOh
of ·th~ Middle Reefs '~(SJ;:urwhere the s·eef~ are ;it~atedin ,'j:he lowI;H~.4m of the H~i"mony t=ormatiq.,n; close tJ.'i the,. . G....._;
easel. Re;ef (1~h,lc::k~ 1983) • 11"1the 50utherr~ portion ~i'
Unissel Gold !"line CQngl.ofl)fJ,?rateeQf the Middl~ Re!i\!f iu'id
the underlying ..l3asal R~ef arE;> .$imi 1aI"" in compcmition,
~, (I
,IIr, !,
< <'" ii,', '':,\,c'&Q -._.~c ..."..~,----~ h ,_, " .. -.'_ ", - ,,~ -""'''.; ...,..... -~ ..-,.~ '~
G 11 !
I,Ii. I: fc
4~ '/ j..If !0 o Q
""
;k-I!
d " Q
l" j,'1,
o. ii, Ij I"
- r:~ c'.:) it"
':' -WJ,r. ;' 1
.. ~~';.#.', .. \,,~
RES;~ lH1Cr.- SORTlliG PACW'iB PEBBLE CLAST TYPES MATRlXc \'YRITE lUiIER' ~totmH~C lImlHI, !lESS ~nE 1 mNERAL!ZATlON CotlmlU
II Ir, ~rll C;
"
VS :) 0-2.Bm mtJderatl'l clast su~ported spC:~IllPCvein q tlnd chei'tt Tarf.! dark ChlaritlfC Tafl~ rounded ~(Ii, r very 1011 letl'ticuliliBEATRIX?l 0~tapelita and arenit~ $1 ill'tmite I' cryst.alIine I, I, II P
, " I;I ' ;'r--1""....,
"AU REEFS 0-1.2a , moderate clast supported spt:-mpc 'J'~in q and I:nllt't 51 arenite : rare roui~: .r very lIlil lenticula
/i
I, ' "
, /1,
raprr-:- iH~;_ 1""O"Qfl Cioderate elast supported lpt 'vein q, rar~ chnrt, !il-ta~~~iilr' m!ld~r\\\tq ri3i,1~tit:£~ 1m' 1
'~, ,Mttipelite-, ignlloulil
Ii
and arenite !: " ",I;
/'I' ,;.tJ'~~ - ~h
<una RE~"';""l~
(j-3ti poor , clast supported mp::··lpc oetapelite, Villa ll'l l~st arenU;o fbundlllit n?!I!'iden . erratic! 101' ? :i0 voltanicQ igneous, ii
.' \,i~ ~. !ithert and arenite "<'.> () .Jh." ~'~ ~ ..~ 7'"'it"""""'- --LEhDER REEF O~1611 poar-oaderate t last supponQd spc ..mpt: ~~tapelitel vein q~ lwsl aq:n1te . '.Iilotleratertlunde~ ;'lIon moderate 1e'i\til: ul,a
ZONE thert, rare igne{ltls and trY!ltaIHne .I I
volcanic Ii .,,)1
"=.:::;::;:
1<o-..4·-·~ I:'-- - -- '~I
LEimER REEF <H.7~ J.),oderate-yood clast supporter1 spt:-opt: vein q and chert, rare sl-q ar~nite .rounded and tryl$tallin~ moderah>-high rotisnne 1;:ii'larel'lite
I ' II i.
"'J" (-~- .
lUDDLE REEFS 'O~S!'J poor-floderate clast supported ~Pt vein q Jlnd I:hertN rare q arenite rOllndea and c(ystalUnl: erratic, Hgh l'Jnti;:ulil(UrUSEI. 6.H.) arenite cmnpl!i)l(
.1
", I '.' "----~ ,;-- -MIDDLE REEfS O~60C:e\ CiMerate~gC!!)d e last supriorted spc"l~c v[lin q an~ th~rtJ ral'e _q Ill"enite rare rClul1.d~~ Ilhci erratic, 11m lentieul<)(S.Ii.S.ll.) arenite 'Iitd m!lhpel itE~ t:rystal1i!)~1 " ~!l(fipley.t)
,C ,', -----,,~,-- __..,~ ,_.,~- - .......,._~~
....... ..,"* ¥" "('
rara base inversely gr~#edrilre carbon speck';
"
-i------.oJ,-----.;;.-'-,r-----;'r tOmUfJil, $1 arenitetlateraUy variabl/e "
rar!? q arenite '
--~----------'---~~--~--~i~'eo rare, q arenite not altta,s pre5~fverl,.generilll y. fineS up--+-~----------~--------~',~~soft Sediment d(lforiA-ation CGmooo,Fig. 1.7;
r,
o
II
1)-'
{I
D
,./i
SP(t",1l: Si16LL PESBLE COllSI.Ot:ERATE-; '(l
5L ARE~iHt ,\: ~tliHlC AREIlHEo D ,,-.,-' (,
u 0
'~
\
\~\I,III~
'I\"!
I1\
\\'\
~i r1\I'i'Itit.:1
o
I!)
/10
,IIIi
'0, r II ' 'f>
.'
i1
o.,il '
IIpe :: M~D!uH PEBBLE CONGLOnEMT~I,
LPC ;: i/ARIlE PEUllLE COllGLOtlERATE'/ .. ,X~D£D~fn ~ cRossB€nnED
:(il1/
Compal"is .~il .~-.(l,f.Midg It!?"" 0 'tIS
,'<1(",( i
I,
1,\
(1 Iml::; HlNEfl~LH~nor{
IJ~Ht Q 1:q,nl(~UMnD" '1- ,',
\)'0
p
• I)
L~~
\'
-: () '(, (_\
~C!n91qpe;·~tt/' t~hn\\,t;\t;~e~~s;,~SoRa.fm. St. Halena Go'd ~. " ..?- II
a I ~() P
..'
r , lit:]
I, <::I /:1
II (I0 [I C1
0 (J
49
~ ®. @~.~
Data PQintsn ::; 361
,-',-.---_".'
S St:\iaft.
I/,Faul t It)$s
\\
o km 2ll ........ _-...r
o
Plan at\Qdcurrencea Qf eM. Middle Aeaf.o ,;,
(j
\~ .,. A
50
itI;
UlIIIuCOJ 20!....!...:1uua
ci 10c:
5-111'1 7-'1111 e'C19-";j,lmIi {j ~~().m
\\"~~,"
H'e.i.ght {.in {'f,~~tl'-ee) of occ:urremces 0;;. th~ MiddleRsaTS .abeI've ths t.oll of the l3a$C'l.l Re>@f.
51
particul d.rly wh!:>!"eth!:>interva1. betWE;'En tht=!two ree'F5is les$ t.han 3m.
The Middle Reefs are characterised by soft sedimentdeforma tion strwt:'turt?s (Fig. '27) • The deformations.tructures range from small-scale undulations tolarge-scale diapiric structures which have led toduplication of the conglomerate in1'96). The Middle Reefs are generally
'\\l~teraJ.ly impet-sistent to be of economiC: significanceon St. Helena Gold Mine. On Unisel Gold Mine the
places, (ElliS,too narrow and
laterally extensive Middle Reefs are widely exploited.
The PagbreE?k Formationir' on st. Helena Gold Mine COl1Sistsof the Leader Reef and ~eade~ Reef Zone at the baseover 1ain by the Dagbri&ek Quart;!ite (Fig. 28). The UpperShale Marker~ Which farms theo uppermost zone o~ theOagb,'"eekrelrmatiol1 to the 'east of St.. Helena Gold MiMe,is not developed on St. Helena Gold Mine. The DagbrepkFo,'"mation thickeMS in an E?C\\sterly dirar-tion from thewesterly suboutcrop to over oQm ...thick in t.he no,-theasternportion of St. Helena Gold Mina (Fi~.29). Are3S of thickPagbr-eS?¥ Formation dctur in the northeast and south-cE?n'tralpelrtion of St. Helsna Gold Mine. Sections thrClughthe Odgbrael< rormat.iCll1 :i.nc.1icatetha·t the Leader R£;1,!J;!f i.slaterally impersistent and of varying thickness makingCClrrelation betwaMn boreholes tentative (Figs. 12 and14). ConglomE!rates higher up.in the Oagbreek Formationare al~Cl l-aterally t!i.sc;:ontirtuous.The angle of uncon-formity between the top of the Dagbreek FClrmatiClI1thebase of t.he Clvel'"lying"BH Raef along the western marginof St. Helena Gold ~ine increaSes in a northerlydirar::ti(;'Jrl•
52 C'
()
j'
Slumpf.i?dMiddle Rasf of vein qUCilt'tz c::la$t$~ chertc ]cp.sts und rC:»..tndl':?d pyrite grain$> in the Midd 1ingquartz it(,::·;~!(qu.art:i! wacke) 01 \J1,;isel (301d Mine. Tht:!core is ';d"~:,\U.edvertic:ally~ perpendicular to bed-dihg.
om~~~ Leader R_e_~_f_· ~
53
r~e:~r:I MEMBER
00000
\
REF'ER~NCEo SublithiC:: and lithic: art;!ll.1.t~
o Gll.1.art%arel'litEl1m Conglomercate
Figu~~q ~ Idealised sstl"'at.igra.phiC: c::olumn of the Da.gbl"'eel,Formation~ St. Helena Gold Mine.
iH!CI(NESS- "40;-
20m000000000000009
1°di;Po%'eqp~~9 Leader Reef Zone~d£J;o~~d'Qooo~o
O~t...,. Po;!,}")''-J
IV
I•..c~
.~
C]:::: .10-3'0 m
IT(
;.:.:.:.:. :::: >- 40 m-_ £;'st:.tmetedSUbOUi:.c.:rQP
..:tSOP.:a<:::h rna.p.:irtterv<!Il ~
.....7 F,a!.o.t 10$$
(i) Sh.aft
Th~ basal conglomS?rates and arenites of thl,e OagbreekFormation on St. Hel~ma Gold Mine unconformab1.y Qverl iethe Harmony Format10n and are subdividad into the 01190-
mict AIm""facies (rr;aferred to as the Leader Reef) and the.overlying polymict Sedelia facies (referred to as theLeader Reef Zc:lnt:!) (F'ig. 30). ihe bas.:a.l Almt1 facies is apyri tic 01igomic:t cong lom~rute whiCh is ovarlai!'! by aquartz aren'ite. The Alm.:a. 'I' H-:ies is aroded in places bythe younger aede~ia facies, with channelised occurrences
Of. the SedeU. f~tie •. of .ZOOffi wide B.nd 3m .deep (Kingsley,1984) • ThE:!-Lead~Jr Reef on st. Helen~ Gold Mine oc.curs astwo separate north-northeast I south-southwest trendingIlIreas; ~nd thickens to the ee$t of the Dagbreek fault(Fig. 31).
Where the Leader. Reef is not developed either polymictconglomer'!.ld!es 0''" areniteS; of the L~Bder Reef Zone(B~delia 'facies) rest <tnconformably on th~ HarmonyFormation. Ths Le,a~er Raaf Zone! consists o'f a maximum of16m of altarnating trough- and planar croBsbedded$ublithic arenites and sm211- to mediwm ....pebble massiv~;;polymict conglomerates whichThin «:SOc::m) I..lpward-1J:ning
~re fre~uently c:hannelissd.oligomict. conglomerates and
'\
quartz arenit.e partings ah;o occur. ·'there.is <3\, clecreas.11' the text.ural maturity of the ar~nites vertictill.y fromC!uartz- to l$,thic arani te. Thi$ textural variation is
accompa.lied by subtle colour" changes, from a light- todark-grey colour Elt the base to yellow-brt:lwl1 and brown-,)gray towards the top of the arenite.
The Le~der Ras'r and overlying Lel,ader Reef Zone on St.Helena Gold Mine accounts for approxImately 15 percent ofgold produc an. Gold m~ner.lis.tion of tha Leader Reef
56
F'olymic:t Lr..>adS?1'" Reef. Coin c!.\J',~etet"' == 20mtli.!<,-:!'
"
57
\\
Data po::intsn ::;:laS
\'"'.
:.:::~e - 100m
> lQ5m,1
/' SUbQutc:I'"OP
/ ~$timo01t.ed/ Sw.bj.':)Ut.cI'"OP
o lUll 2~,--~~~~~~ Shaft~ Fault 10$$
IsC)pc.h:.h map tJf L..sader Reef thicknesses ~ Contourint~rva 1 ;;:;35c:m ":.'
(I
58
is erratic w~th scattered values 1requent~y occurringvertically over mQre than 3m Of conglomerate. Increasedgold grades are associat.ed J!with 01igr.,mictconqlomerates,
(,
al though gold mineralisat:::tin cUld increased quantities o'fporpus pyrite occur in place1s in the polymict t..e.:;aderReefZane conglomerates and on 10l'"eS&ts in interbedded aren-i·tes.
Tne"Oagl:1reek quartzite is defined asRe~1 Zone conglomeratas (Kingsleyquatt~it. is a yalldw-grey lithic-
overlying the Leader!I
1984). The Dagbr~ekto sublithic arenite
cont~lining scat.tere,t:.!,impersistent, pol ymict granule- tomediun •.,lIi:~bbl~cc:mglomel'"'atE!'s.Clast compositHlh.S are
\_" .. t\
similar to those of the Leader Reef. Coarse~grained;1
arenites ,~'Wetexturally more matui'"eaDd lighter colouredthan the yellow-coloufed fine-grained ~renites. Con-gli!l'meratsclasts deCr€:!e,l.sSin sizt:! and frequency tOI/Jardstnt:!tpp of the Pagbl"'aek FC'lrmatiol1with the upper 5m Of
the Oagbreek Formation deV'o:i.dof pebbl~"'i. Trough c:ross-'beds with set thickn~$s~$ of S-26~m are common and rareplanar crossbed sets ~f 30cm thick also occur.
Ths TUl"'ff,prlteinSub9rouP~_p;.
Welkom Goldfield 1sin the western portion 0·1 the
a ctlarsening-upw;;).ro arenite andThe basal J,reclomin 1tty arenitic
Spes l3onCl.snd Aandemk FormaticHi$ are collectively knowfilas the Kimberley c:ong~;pmerate$ (Jordaan, l.c~86). Uncon ...formably overlying the Klmberl~y conglomarates is the
o"c:onglomer.$\tit::Eldor-OleloFbrmatiori.If
I!
50/
//
2.3.3.1 Spes Sona Formation
The Spes Elona Farmation aCc.:un" at the base of theTUl'"'t_,tont!;';iinSubgrowp and ha$ at its base the "S" Reef
(Fig. 32). The Half Reef is c.:harac:terissd by large porous
pyrit(i)l n9dul~s and a polymict c.:last composition contain .....rat~e il1 the
'i
TtlE: lI'an Reef..~;
underlying Johannesburg $Ubgl"oup (Table 2).I,
contains increased gold gracias in the vicinity of theVi
Ba'S;alReef suboutc:rop in the northwestern portion of St.H"51enaGold ~p.ne:: (J.R.F. Handley" pers.~ comm.).
IiIf
The remaincJSI" of the Spes Bona rCH'''tllatir;:II'lc:ompl""J.ses
yellow- and brCllin-grey massive and tr;!ough cro$sb.edded
sublithic- to lithic arenites. The arenites are inter-
bedded with laterally impel'"'E:Lstentmedium-pebble polymict
conglomerates. The Spes Bona ,Formation Coarsen!:; upwards
above the liB" Reef~ with the ratio 9f conglomerate tor;)
quartzite also j.nc:reas1ng upwal"c:!$ (JcH"c!§lan,1996)" Pebblytl <.
arenitel':5 of scattered polymict pebble'!:! with a sublit.hic
arenite matrix are well developed in placas in tha Spes
Sona Formation.
The thickness of the Spes Bona Formation on St. Helena
~Qld Mina increas$s erratically in an easterly direction
to a maximum of 26m (Fig- 33). The thickness iscalculated from the base of the "a" Raei' to th(; base of.tha ~$,Q Flebble Markerp irrespective of thl::1develc)pment of
the Aandenl~Channel. The thiol<.ness of the "1:"1'1 Ree·f i.$,o
erratic with the th1c.:.I<a$tctlnglomeratt';! d)~:velopmel'lt''occur-
1"'11'19in the c.entral and northern pl:)rtion 01 °St ~ HEillen.a
Gold MiNe (1=19- 34). The u13" Reef is la'terCillly persistentand relatively easy to c.orrelate 611.1;;I1I:)I.U;:)h the t;)verl}':ing
Within the
I)
o
60
~--------~--------~------~--------~20m -::::,_'::;"_'::'::'~-~
r:ORMATrON ..
o
TH:tCl(N8SS
r:,
As,nth:ffl"tk Ch~nnelo
Spes BOh<S quartzites°o~ 0° and c;ang lomel'''ates00 0Q
SPES SdNA
~EFERE~g_E.
~ Argi ll.ite
o Ara:mite
I~l CQngl om!:?rra. te
E23 Oi~mic:ti te
,')_ iJ
o
E.iS,!,l.c.~"';?J~= Ide<!llised stl"'iiltig 1"'8P hit.:. e:olu.mn 01 ttm; Spea ElcneF<;'H"'m~t:iQn ,llnd ~~8t"'H'jenl( Chal1l'''101>>St~ HmlerHl ·(3~ld Mine~
6t, \is
<,
I) v
() \ \)
\~,\
f)
II
~~
;:::; () ,'" 1.,£J1i\
o~t.Gl POint.Sr'I z 'i5q
// E9',t.i,ii\at.ecl/ SIAPbU:tef'OQ
(/ "$\i!bQ\.I. t.er'oP/
I;) S\''I'E\ft
// F'a.).ll t. lQS$
t':Sopaeh (tItJ.\') OfI,Vi;r~\"eS ~
\\
\\
/,'(./
.-I ~,. " .~, . . \
it.'
of(/
the "au\)
II /,l((
i)
lab~I"ally irnper'Sistent, ma.k1.ng C:Ol"'relation of these Spes
saba c:cmglomel"'~tes teJ!)t.~tive (F'i£ls • .1.2~no 1;;».
The AanCle)ikFcinnati6h c:onstitut$?$ an, overAll fit'1ihg'-Up
setiimeht<!lry succession which c:oMpl"'i$es the lenticular
Aanosmk Channel at, t.11;eba$e overlaih by t.he laterally'persis'tent. Big Pebble' Marl<.er (Figs~ 32 and 35) •• Overlying
the Big Pebbl~ Ma,I"'ker are the Aandenk a ,'·eI1}.tes wJlich c::on....\)
(, t.ain sporadically devaltlped "A" Ree:rfs (Figs. 12 ahd 13).
The Acmden.~ Channel (1<4 Reef)' Kimberley chanl1o,l) ,is an
erosive sc:our-ano""fill c:hannelised feat.ure c::onsisting ofIllonglomer~:l:.e, F,J.renite, al'"'gil1 i t,e p pebbl y mudst.ones and
,- '>-• .--.<
pebblW a,"'en.it.e.The channel-fillat. overlain
generally c:omprisl;ls oil
by pebbly sublithic
ar<;lnites~ scat.tered diam~:ct.ites and argillites. The oase
of. the argi11 i te in tl1~ Aendenk Chaf'lIls!is charact~risedby a diamictite which varies between 10em to 1m in
o 0
Tbe diamictit.esmall'" to larga- pol ymistiC pebbles il1 an argillacso~lsmatrix. The upper pOl"'tion pf tha cha~Mel- fill comprisesinter-lamil'"latacl argi 11i tes .:l.ncl ,'";aremediurn.... grained $ub-lithic: ar-enites. Tha argiIljtas cO"$ist.o~ inter-laminatedc~t,aystone antl s11tstons which ar-e tec;::ttmic:~lly disturbed,
Q
ccihtaining ~~oTt-sediment deform.;).t:ion features such as.c
dl2wat~ring 41'\d ball ....end-pillow st,ruc:tur::es (F,';f.\g. ~6).
{_)
The geometry of the Aahdeml<.C~1annel illl bast illustratedwhan tt'"la Eli~'Pabble Ma~l~er is used as da-tum (sectionA· ....AIl; Fig. 37). The Aa.ndenk Chantlelcons;i.sts oT a seriaslit sctlur-~nd-fill features wit.h sc:attared cOMglomeretl$:!}.:;,
o
64
Om
om1/
o
o Al"'ef\it~
.~ Cong H::HneY"<tltf;?('
nj~eli$!;'ld stl"'<"lt:igf"apt1iC:: cQlumn of tl"l~ At';lntionkF'cl"'fI\et;.ion, st~ Hel:ena Gold Minc::. o
(>(',
65
n
i)
66
cfp()'6 ~
" ic:"rS
~~~ •.~' .. "".".'.,".:;(f/
Lt.I...
(f~.) _ ••')-7,-,~i
••
. f"() ,
I»t.+---"~$
" ...-~.,
Sout.h I nCll"'th $t.ri!(~ $<£?ct1em A' -All, '¢T the AC).(ler~nlt.Ch<5llnnel in. the a shaft ~re~ ~:f S1;." Helena Gold Mine.TI"\IS' top .,of thQ ~i9 f!'ebble Marl~etr h~$ bef7n useU· asd~t.\JI)h Not.e t.he VGl"'ttc:al eHC\9gerai:.icm. .co
67
diamLctites and at least three periods of 0~udstDne
c:ha.nnel.-f!ll~
ErOSion associated with the Aandenk Channel on St. Helena
Sold Mine has removed a maximum elf 25m of the Spes Bona
Formation"
maximum of
On Unis('l ($old Mins ths Aand~nk Channel is a,\
23m dee~'~ iilnct 'the "a" fie' f;to;:; remoV'{;!d in
places bec.ause of Aa;ndenk C!1i!\nnel erosion. The Aandenl~Channel occurs in th~ sO,"J.therrportion 0': St. Helena GoldMine, where it im about 4km wide. and ovar most af Unisel
Gold IVLine (Fig. ::sa). To the ·north of Unis!.'H Gold tUne ths
Aandetik Chann~J. has also bes!~ c;jocUITII,mted(Sims, 1969).
Minor o;:;Male-fi 11ed chanl1ell in~l in the Aandenk F'ol"mation
(the Carbonaceous Shale) ~al documented on PresidentE1rand and We':t>'t:.ernH"'~dings Gpld Mines (Borr,ego, 19136). On
Harmony Gold Mine {former'"1 y Merr_!\espru;( t), Wintel~ (1967,
1964.) described the Aandank Channal as a 2km wide and
7~m deefJ 1.inear scour feat.ure which has I"'emoved the 13,1.9
Pebble Mark€ll"'. Uncert.ain corrl!?latic:rn ac:.:rO$S the W~lkom
l;3oldi\ield may roe.;!.nthat the r:l41 Pebble Marker on Hal"'«lony
Gold Mine is incol"hE)ctly correlated to Spes 130naForm-
ation c::onglomar.;?tes em $L Hall'?na Gold Mine.
A pa:tinspathic rt'.!e:onstl ...~d~:iol'l of c:.:hannel in the St ..
Helena, Wni.sal and Harmony Gold Mit'\¢:) c:''H'''eas~ r'estoring the
righ~-lat.el-al displ{!:\cement. of tflo no.rth I 5;~uth 'br'endin~1'·fL,
Oag'I"a~.kI' St.ui,"manspan ,~ndDe Sron Tau! t.!:>, show$ tnt?lQcation of ,the channel as f\;;w'mil1l~ a 1..inear 'fe<;\tuY'e
across the southern portion ~f the Welkom Goldfield(Figs. 39 and 40).
On St. Helene ~old Mine no gold or uranium grades of
ec:t'.'ll"1omiC imp(lrtance QCl;!ur in 1:hC)l'.:\anctenl< Channol al thoughIf
\
I ••J' •
[] < 601
6 ...12m> 12m
68
e
3 km_ ....... ..__...l
'n ";<';111
........'~$tim<;ltadI Subc:w,terop.
r Subcutt::rOI'l
41 r='ault
~ Sh.t\ft
1$opeetl map of thE¥' AiarH::l,Qnl\ Channel en ~t ~ .Helrrm.t\Gi'!lld Mine" and Unisel t:!cltl 1'-11:"'10. Co"tOt.ll'" int~l"'val
69
-----------,
N
11/,-.:ClUl.,t . toss. (thl"'oW Qnd1/ movement ~1$C) shown)
o km 3....__.._._,
~Qcation of the Aand&nk Channel in the southarn partaf the Walkom GOldfield. lJ at Helena Gold Mina,2) Unisel Gold Mine, 3) Harmony Gold Mine. DatafrOM Harmony Gold Mine are from Winter (1957,.t964l:l) •
r;;
70
I' -) PeJstul¢.\ted ewt;el1i;,(_..I of Aal1denl~ Ch"uitlel
'\\ .
\ /\7'.
\
..... .....
?...
PCll irH;;p,I\rthic: rec:ol1stl"'uctiol1 of A.hr'Ic:l~nl~and Sp~s Sona ~ge. channels in the south-ern pa~t Q1 the Welkam Goldfield (Dataa~e from Fi9. 39).
71
both round pyrite and qligomict conglomeratas do occur inthe channel.
2.3.3.2.2 Big Pebble Marker
The oligomict 8ig Pebble Marker (Big Pebble Conglomerateor apC) overlies an '-Inconformity at the base of theAandenk For.lJlatipn. Underlying the unconformity are ei tMerarenites t/ ';)the Spas BOrh::l Formation or interbedded sub-lithic are~/~tes arid ar.gillites c,f the Aandenk Channel.The lUg Pebble Marker is < 2. 5m thick oVSlr most of St.Helena Gold Mino.:l with the thic:l~est occurrencea in thenorttmrn po.rtion of the mine (Fig. 141). To the eAst ofthe Pagbreak fault on S·i:.. Helena Gold Mine the Big PebbleMarker thickens, with oc:cur~rent:e$ further e~.st onPresident Brat1d Mil.,e being polymict and up to 17m inthickness (King, 1986).
/iThe remaind~~ of the Aandenk Formation comprises massiveand trough crossbadded sublithic:- to lithic arenite!";; andrat".) Ie terally imp~r$istent, small- ,to met.ium-pebblepolymict cong'omerates. The conglorM?rates fine upwards inclast size and occur predominantly near the base of theAandank Farmation, resulting in a generally fining-upsequence. Rare occurrences of inten-laminated siltstoneand Claystone in the Aandenk .renites occurs in thenorthwestern portion of St. Helena Bold Mine, together
\I,!
,,,,ith a locally-d~veloped 30cm thj.cl< diamictite. A pebblyarenite also occurs in the vicinity of the "A4 Reef.
The i50PClCh m~lp of the Aanc;let1k Formatian comprises the
stratigraphic interval from the base of the Big PebbleMarker ~o the base of the Eldorado Formation (Fig. 42).
72
Date Point.s('\;:;::74
:("...,. .-----
C];:;:: 0 2 ..5m
I~];:;::2.5 4m
ITI~=: > 4m
ItI
i:::etitil<'!htl:!dSuboutc:rpp..
o Shaft
!/Fault. 10$$
113PpaC:h mClp Qf the !:;lS.g Pebbl.ec<,krl~I.'.\'I'" cap!,,!).Contours:; in metr'e!',).
Data Points /I
n ~ 67III\.\
73
IV
I\\\
BEFERENG.S.
0= 7·"14 m
I~= Ill.
\\
'I •~...
,,/Estimated,.,. Supow, tca·c)p
cI,.
km 2ri......J
J:$t:,,:>~c::hmap of the A.andenl< Formation .. Contourinterval\ = 7m.
74
The Aand~nl~ F'tW'(I'\ationthic:ltc:ms in a northerly cmd east-
erly direction to a m~\>d..mumof 22m.
2.3.3.2.4 "An Reefs
Th~ Acl:1ndenl~Formation contiainl't.\ thrae impl:H·"$.ist.entoligo'"''"mict conglomerates in placas in the Walkam Goldfield.
classified by Jord.~,n' (.1996) as thll? L.ower$ l"liddl.e end
Upper itA" Reef placers. Tl1ss($li!.\\l"'elat.erally equiv<:alent t.o
the Witpao and Uitsig pI £.\1::8)""'$ J:.dentified by 1<.arpG:"I::a
(1984). On st. Helena Gold Mina the otigomict "A" Raafconqlomera'ces arE;' laterally impersist.ent. and vary in
stratigraphic pOSition from abave the aig Pebble Markerto 30cm b\l')low the contact. with th€.?Eldor.ado Formation. Nocorr(:';!lation of the nAil ReeTS on S'!:.o Helena aold Mine wit.h
those occurring in other parts of the Walkom Goldfield
ha.$ b$~M pO$sibl.e. Th)\ majori.ty of bt;lr~hole J.ntersactians
of tha UA" Reefs occ~~ within 3m of the top of the Eig
Pebble Ma.t'kar wi th oCt::Ul"'r~nce$ o'f conglomer·.ate h1gh(;1rthan om ~bove ·1;.h(~Big Pebble Marker being ran~ (Fig_ 43).,"ht.~ occurrence of conglcHnerat(:?~ at varying .tr~:l'tigl"'aphi(:hei9ht$ $uggeets that the HAJI R.~fs comprise severallent.i.culCil'''' un; ts $ the clistributi(,;)M of which have beenplottsd (Fig. 44).
The IIAI,' Reefs arC? 6\')(p103.ted in various areas
WalkoM aaldfield~ howevar on St. Halena Gold Mine
Reefs are not exploited as they ct:1l1tc!lirl lowuranium vc!lluas. Higher gold 9r~de$ ara contained
"A" Reefs on at. Halana Gold Mine eml y wha,"'g
Reefs c.losely overlie the SiS P,ebble Marker.
of thl);>
the "A"gold and
in the
·the ItAu
II
75 ~
n ;:::;3216
14til 1:2IIIuc 10OJ~I...
8:luu0 b•0 4c
2
0<2m
Figure 43 Haight (in metre.) of becurrencas 01 tha "An Ra.faabove the top of th~BPM.
')
76
Data Pp$.nt$n ~ 64
J.
Ci.'> $h~ft
//F&Ult
~.
77
Th~ EldCll"'ado FOl"'nh~tion (histQrlc:a~ 1y rt;~d:st9r~d to as t.heV~ntel"'!;;1dOrp Sedimc:;nts) unc:onforrn<,\\bly overlie 'the Aw.nd~n!{
Formation. The eldorado Formation in the W~l!<.omGdt~i=ieldc;),
;""
c;c:msists 07' two distiru;t 'facies n<ingsley, 1997) =.
a) The Loraine {northern) faC:i~)$ of predOminiJIntly quert~
erenite a'iindoligomic::t conglOmerates,.b) The We~l~om (sowthel"n) f;ac:ies of predominantly pol ymic:t
conglomerates and Lithic:- end sub,lithiC: 'a.r.en1.1::et5.TheWell~.tz~fac:ies oc:c:urs on Western Holdings Gold Mine,
.::;:_:
st.. Helena Gold Mine ~nd the CJ.re~to th~F sowth ;am:!
ea$t of st. Helena Gold Mine.
, . S;:l"l:.h the I...o'raine ahd Welkom Taei.ss of the ~ldor$.doFormation al"'(:t! charaet.erised by rapid lateral. f~cies
variations 1rom c:obbl. si.ed conglomerates ta arenites
over ol,ly 5r.(.mdOItJn the deposii:';ion6!l1. $lope. The nC:lI'nen-
clatura used for the W.lkom ~acia. 01 the EldoradoForll1C?ltionon St. Hel.mna Gold Mine is restrict..d to theunc::onfol"'mitY....baSied va 1~. vs 2-4 anc.:lV$.,S 20nes (Tabl. ~).
The _lelorado Formation thins in a wastarly diractian
ac;r05;S !;It. Helana t:iI;)ld Mine from (;W(;;1.'r 'SOOro thic:l~ in theeast. to • pO$i1~ic:m where post-Ventersdorp f.iH"'Qs!onhan;removEid t.he entire Eldorado Formation (Fit_3.4S). A ~out.n-east. J north,!,",II~$tc:ross-sac::U,on of the €ldprado For-mation
(sec tion a-a'; Fig. 46) ill us ·b"'sl'4:.S's the ganera 1 thinn in9of the Eldor~do Form~tion in the northern portion 01 St.1':'/
Helena Gold Mine. Oaspit. the rapid la1:erm.,l faciesvariations ,which oc:ct.lr~ partic::ul.:1ll"'lyin the va J. to va 4zone\";); litho$tr~tig1"'aphic:.: P.iubcl:i.vis;;l,onililnc:j the c:ol"'rGlqtionof c::ongiQm(;O/..r~tes on t)\ bron.d scale .tll"'S j':JQssi"ble.
17
o
ThIS'Eldorado For',naa'tion (his'to,"ic:all. y ref~rred to C1lSthe c
Verri'tersdorl) Sediments} uncQnformably ove''-l:i.e t.he Aancleqk
For-Illation. The Sldor-ado FormatioM :in the Welk.o!i'lGoldfiE'ld()
e:Cl'1sists tili' blo d:istinc:t facies·· (Kings.ley, 1967) II
a) The Loraine (nor-thsrn) fae .1.(;;)$ of predomin.antl y qual"'~:Z
ar~nitE¥ and olit;lom:iet (!onglomel""oi:e.sob) 'l'hti;>Weikom (sou.thern) faeia$ 01 predom:i.nantly polymi::t
r:ong16~,,'rQ\te$ and lith:i.c- ,Cl11d sublit.hi.r: ·arer.ite$~ ThG'..Well<orli;f~ei,~s OC:C:UI"$ ~~-~West.ern" Holt:l:i.ngs Sold Mine"
St.. Henr;;.>na .~C'ild Mine am:!, thr:!' areCl t.o th~ sou,th (~nd
9$.$1;. of st.· ~~lel'ta Gold Mir'H:~*
Eloth the !-or'aine and t'Jat'lkom facies of the Eldorado
Formation ate c::haraet.eri$ed by rapid lateral faC:.iss
vi:1lriations from cobble sized c:C'mg1Otrlc:!>I"cd:as to ar$ln.ites
over only Skm dC)wr'l th~ dSj.losit.1.0nC1l1 slope. The nomen ....
c::lat.u.re used for the Welkom T.•;;:H;;.ies 01 th(? E:tdorA..!o
Fonlle.tion en, Sf:.. Helena Gold Mine is rsstr:.ic::teti to the(\)
unconi'ormity-based VS .:I.~ vS 2"'4 and VS ;:; ;zone\iS (1'.able :S).
east to a poeition whel"'l:? j.lost ....Ven·c.C'!:Il"'sdorp el"'osion has
removr:utl th,,~ entire E::ldoratlo F)Ol"'filCjtiQ\j (Fig. 46). A south-
east:. / northwes~c cross-section r t;I"L} r.;:ldt:'H"~do i-"clI"'mCi:ltion(se.n:tion a-B'; Fli.g" 4~l illustt'ates the~ ge.mel",ul thinning
of th();\!E::lor;t,'"atlo FOI""llh:.\tion in the northern\\ pc:wtion of St.
Helen.:a Gold Mine. Oespite t.he f·,tipid la.tt::l"'.t:tl faci~$ \\ Q~ - o·variations which oer:ur$ particultlll"'ly iM the \.~\? '1 to VS 4
zones, litho13tratil,;waphiC:: subdivision and the ~\\'l1ri""elat.ion
of C:Qn9lt:lm~I"'a.t.o$.on broad sc~le ~re pOSH$;id:.);t~. ",
{J
{{
o
/L,/
78
c
o
SACS(3,960)
Borchers~ndl;Jhita(1t}l4:5)I====:=ll=====:t=====f~~=-==!=====F",~-:::~.~::;:._..=:::;_,.....::;.rl>=" ..*n~..__ ....."..,..:;;;;=~~[
tJlin,;(:Ciir~t e1 ~(l<7a~)
~ingnlay Thi9 wor~;( .:l.997 1 S t~ J:!£'l'!_tpO.il
O~:;1 .....Lt~ "
Van Don Haever5-HGHiNC:W'S'"I rl,lstl"'I.!St. I"IElImcl;'.l1'"Msr..:tJer~.~'~------'-+--~~~--+---~~~~~'----~~'~--~~------
VS 4
WiFltert l<i'67 >
Wintel'"( 1964.1:1)
EC
• Uitkyk U1tkyk601..\1der Mamber va :I.
(240m)
\"'US"tMember 'IS .2....4-
(145m).,
ROl':iedel e 'Roo(rn;\·tllle ROsedaleMemb~r 1'-1o:mbiE!r Member ~---v~ S '
(15m)
lata..l,e.~....3: S'tI""a'tigrCiphit: ct:ll"'relat.ichh Clnti l"Iol'i)(:;)nc:lata..lro used few" the::Eldorado .,FQrmat:i.ol'\ in various parts of the Wolltom Sold-f iel d. The t.abli') ah,o' shows the o.vor<!Aga thic:tmO$$ of$otlimont5 ill the study area (no\:' to $c.ille)..
IJ
()
ot,"
"
POST-
Ef~OS:rON
1/
CJ < 400m
~J:> 400m
<i'
19
\ c'
G
n ~ 41
km
(")
!$ope.c:h map of thQir\t~l"'vill :;::100m..
(I'
o
eo
oi~~ ~~!~~,~.~~~~~~~~~~.~~~~.'
.i-.I/)
r'.,
(>
\ g!\\))
$CIl..ld;;h-east" I rtOl"'th-tl\lest 5~~ tit.lnTho ~op ~lf t.he
as 0<;\'1:1.\11\ .. Noto!! VOl"'tiC':.al
13-13* 01~ld(.'JrodQ r::(::II"m~til'Jn
OXQ9q'~at.iC)n •
the tn dql"'ad(.':)has
(1
FOi"'met..i.on.~~it?n ~!5l:;?d
~I'UI
ffilli0:
/i,!,~
j]c-
81
The Elf;lol"'aClo F'cH"mation changes frdm c:ampr;i.sing Of >95perc::ent cOMgl.o(ll(;;H"'ate i.n the Mt::H"'thwl11sstsl"'nU PQl"'ti.on of atd
Helt,?na Gald Mine to <·40 pfi?l"'t:ent c:cmglqmerate in tnt::sOU·th@illst@,"'n pOI"'tioM Qf Uni.s(i?l Gold Mine (Fig. 4'7). On
St. Helena Gold Mine the Eldorado Formfll't.i.on al $0 hels.'t\
arenit:.~s ;nne! conglomerates in the va $ t:'.nd VS 2-4 zonesto the laY··9~':pebble c::ol''fllllomer-et@s of the VS 3. 4!ona. On a
smaller scalm~ however, both hOl"'ffi&11y- and invel"'sely-~l"'&doct i!:ong lOIllGl"'at!;?sOt:.:Ul'" thl"'CI\J9hcH..A't ·thE! r:::ldcU'"Sdo
POl"'mation on St~ Hl!?lena 0011;1..Mine. Tht? Eidor(':\do F'or'matiorl
is e:ha~eterr$ed by a d:i.$tinct dal"'I~"'9reen to blac::k meltrix"and colpYrfwl pol)lmiCt;. blas·t as<;.1embla(,,1e, primar-ily of
yel1Qw·an~ black metapelite cleRts ~nd white vein qw.rtz':·1
C tests... On Unisel Gold Mine thm E:ldQI"ado Forrnation ia
lighter 9re~h in ~bloul'" th~n on St. Helena Gold Mina.
Tn$)' eldol"'<;).r..IoFormation iri' th~ Wellu.)tTl (goldfield gen1!?rally
eontiZlina ldW goLd vellysa but on L.di"'aine mold }"line aa m.!H'IV
a~ 16 of tht!: 01igomict R<.'linbow ReeT\;; are 1Qc.;?l1y
ex,p1 Qitc:::lc:I.. (MiI'H:.er 9t a1.,·" '-0 •.. I'
nClt\.lr~ of ,_:'the El'doraoQ ,F'.s>l"'mat~t:lnand ·thiil'
~rO.ional uncenTOl"'l'llities, il1 'the vi<::ini~yf(
Gold MirH~ Oh"!\~G.f tho. pl"'(l)~\\ect of et:onpm~l.c minsraU.sation~,Jl "
poor. On both $,t. Hel~ni!l end Unb:;E~l GQ1C$Min~. low gold
gl"'c";;desocr.ur througtv;::)\ ..rt ~he Eldorudo I~ol"'m~'ltion t c l.g/t)
ItJith anomel.o\.t!3 values. Qcc:u,".ring only in 'Cth~ V$ S ~aQf I..lt
l<1Sb). The tl;9)(tt..:lrcaUyimm~l::urGtIt'·. .Ij,,pCK of M.::lJOr
.)
of at .. 'Hel~nC'l.
The VS 5 2Clna is th~ 14::HtJt;?St stratiQI"'~phi<: u.n'-t 01 t.hG
Eldorado FCl"'mation and has at it. belS., in plac.s, tho va;; Raef (~Qs~d.:llo plwc:el'", :e:ac$n BOtJtl"'i)-t Reof). iho
oli9t:fffiil.'llt V9 $ Rt~ef is O..·3m 'l!hic:l(. uno is eepal'"ut.ed ft"'Qm
82
o
PO$t-von ter$(:lc)l'''p
erosion Datan
as~aNCJi~\
f~J70''''.1.00%
5a-7~%conglomerate< 50% t.::OI"l!;:)lomerateektimatcd$uboutcl'"C:>P
COl"lglomc;<rate IF'ormai:.ir,:,n. Contoul~
(J
of
83
the "overlying Eldcn'"'ado Formation by an unconformity
(Kingsley, 1997, J.H. Geni$~ pe~•• comm., 1999). Thecontact of the va :5 :zcIMe wi th the;. unde.rlying Aandenl~
Formc?),tion is uMt::onf~:)I"'mal:llsem a basin-II. ',de scale.
The \)S :5 zone on at. Helena Gold t"line is dark'-grey in
colour9 t::ompared to the yello~')-grey arenites, of the
I.tndsrlyit'll;'J formation$ (Fig. 49) A Clast types are colour-
ful <1\lnd~he clast aS$embloge is pol.y,mic:t (Fig. 4lta). The
va;3 is texturelly more immature~ has larger pebbles ahd
a greater propt::lrtion of quartz ,-="0 c;hert c:l11lsts '(':.Manthe
o\l£~H"lying VS 2-4 :zon.1a><Fig. 50). The VS ;;; 20ne is
overli$11n by the first maJor" arenite of the va ~!""4~one.
I'n the no1~thern portion of St. Helena Gold Mi,"e the
c:onglomeratic n'i,l'I::.wre of the entire fUdor:tidO i=!'ormation
mal<es the SUbdivision 01 the V5 5 a.ri'd va 2...4 zonesdiffi'cult;.
r,1 ~( i))
The vs->ofSt_
lternClt.ing ~renit~s andu
Helan~ Gold Mine. In theconQlomaratas over much ofnorthern portion ~Qf 51::* Helena Gold Mine the
di:H"'I<-grey poorly-sC)rtad metf,l.um- tt) large"'pebbh polyroict
conglomerate (F.i;. 51). In the Uni$.l a~ea the va 2-47.0ne is predominantly a 1ight'''''grey, C'r'otlJ)becld~d eoal"'S;;t;1)-
grained arenite with r.;\\~""~con91om~rc:\te$. Trough crO$$'"bedded S!:llts of 5-30c:m thick with C:O$ets 01' 60-S0e;:;m t.hickand plahar sets 5-S0cm thick occur" Fining-upward, a'''erlita
to 'siltstone units of .t""'4c:mthick, 'diamic:ti't.e$ of 3-10cmthic:l~ tind slumped sil'tcstones at·. also pr.$ent~"
Textl,H*ally, the V$ ~-4 ztma'is the:?most mature of the
three I:Hdorado F'crm,'lticm swbdiv.i.sic)l'1S in tht;> stUdy arelll~i!chert and quartz
84
Unconformable contact between the conQlomarattc VS 54'o·n£.?of the Eldorado Formation (dark .....grey) and thethe ar~n£tic Aand~nk Formation (ye~16w-grey).Notathe abrupt colour chang. from dark-gray to yal1aw-gray across th~ unconformity (arr.owad).
c
il :::92
n ::: loa
quartzit.e 16%
.~cid vole. 4%igneous 2%
F'.i91!!'jt ...1~~ = Pi~ c:Mart of c la$t COffiPO$;i. t.101'\5~ G:ldcwac:ldF'ormatic)n.' a) VS 5 '4Ql"Hh b) \IS 2,,,,4zone.
()
o
NOl'1INALD:tAME:TC:R
(mm) SOR1"!NG
OLIGOMICT IPOLYI'1ICTCLAST RATlO
CONGLONIARENZ "fIERATtO (%)
VS J.
VS 2-4
va 5
E.i.9.I..!!:.i't....5.0 = St~tS.stic:CI"l pcu'sll)eter$ for c::l~Hs'ts o'f thl'.'le:ldoredo,Format;iCln. Npminal d:i-ametel"" ;::;'(long ~xi.s x inter-mediate aH.i$)~. sorting (c:;:) ~ standard d£i1viationlmean af clast size. Data from borehol@$ Sh24 ~nd1476.
.: )
Ifu
87
Ii.1
Poorly $orted VS 4 conglomerate of the EldoradoFormat.ion, sout.hern are':LOT $t. He lenCi. Go,td M:i.h~.Clast type- are quartz arenite (G), vain quartz' tV),black and whits chert (C) and yellow and black meta-pelite (M).
\ 88c.
with similar clr.ast compositions to t.hs under- and)overlying aree$ (t='ig~ 49b). Sm~Uer pSbbles? incrsa.ssdsorting and a greater proportion of arenites than aitherthe VS 1 or VB :5 zonee occur (Fig. 50).
A persistent polymic.::t conglomsrate and overlying SL.\b~lithic arenite form a marker of l.ocel 5iCjnii'ic::ance at thetop of ths va 2-4 ~ona. The overlying VS 1 zone comprisesa ~hick suc.::c.::a~.ionof distinctive robust polymict con-glomerates at the base.
2.3.3.3.3 Zona va 1
The V$ 1 is texturally arlO. mineral.;:lgic::ally less maturethan ~ha underlying arenite-rich va 2-4 ZOrle (Fig. 50)but also ..consi$ts 01 a polymic.::t f,)c:;)bbleassemblage (Fig.52). The VS.1. is a massive, large-pebble to (:obble t:;on-91omer&!te t'llith occa5ionci'1 $ul:)lithic- to lithic.: arenita
Poorly sorted matrix-supported diamictite •.occur in the VB 1 zona in the northwestern portion of St.He"IG.'rlaSold Mine.
Twa sublithic- to quartz arenite markers occur at 40m and100111below the tc!p of the Eldor.:ado F'orm~t::.ion)'rl!i?spect-ively. The 40m arenite marker (;ts genaf"'ally betterdevli:?lopad than t.hetrough crosSbaddirlg~
100m er~nite ma 1"'1<.er and di$pleysThe 100m arenite marker frequently
coeraens up from a 1ine- to coarsa~grainad arenite and issap~rated 'from the 40m m$1rt~erby a la'tarally persistantmadium- to large-pebble polymicl: conglom(:)ra;.t:aconsistingof vain quartz, matapalite~"d iQneoua c1. ,ta of 2-6cm in
I~'si~a • -'''=:::';:/ 0
iI
89
n = 183quartzite 5%
.acid voICe 4%igneous 8'~
Figure 52, Pie chart of clast compositions in the VS 1 zone,Eldorado Formation.
L 2rm
Figure 59 Polymict VS 1 clasts Q~ the Eldorado Formation, 9t.Helana Gold Mine. Note the extreme induration andlack of matrix material. Clast types are vein quartz(V), metapelite (M) and igneous (I).
1_"
90
cycles also occur. In.Mtram~ly well packed.
p1<.:1I:::e5 0' thscontaining <20
conglomerate ispercent mat.rix
\ miater::aI. Compacticm lUndappC)rel1t Ip$$ cd matrix materj,al\has re'~u!t.d in numerous indurilltad c:J~asts (Fig .. 53).\ncturation occurs between val"yirl~1 types of C1al'i.ts~ ~\lith
\\b~th durable and nan-durable clast types affe~ted. The
in\'l;.ensitv of the indur~tipn and lacl~ o'r 1'118tri)( mcaterialin p!2.1ces incUC:.<ltes that the clMOUl"lt of, compc1;let;i..onwhichhas Qccur~acl is substantial. Whan sean in bDrahdle inter-
sections the campacttan and flattening 01 pebbles gives
the incorrect impression that the clasts are imbricated.POQI""ly defined imbl"ication does t::Ict::1J1'"and .i:$ b$lst s~an it')
UfH:.lSl"'ground .~xPQ$ur'e. A't, the top of the a,1dOI'''<ldciForm-
at.ion in't.~rbetlded cClng-)lomarates and l.nva of ~fle,ov!:\'ll"'lyin~Ventarmdarp Sup~rgroup occu~ in placas.
/,
2.4 $UMI'-1AR'(OF STRATrGRAf'HV
• 'the E'fasal Re<:!a'Tis il"l(::llJdad in this'study Q,S ct::lMst!tutift'::"l
the baaal unit of the Harmony Formation because the BaaalReef ovel"'i.:;\es a regional uNconformity and const.:Ltut(.;!'$ ('.\
~\_, - - \.maje,l'" li'thl.)l,Qgieal C!Mange~ The !aasal i=<e'af in tl'il.E1 WolRolll(3t::11dfield c.onsists (:Jf the ~.~S'!:ll and Stl'$!yn
bownd<ll"'Y \,botwee~1 whit::h ot::eurs in t.h~ nOl"'t.'ll!!rn
St. HelS?ni.'l Gold 1'1it'lo.
faei·o$, the::port.ion t::IT
The Baaal faciaD of the Basal R_sf in a~b-divided int~t.he o3lit;)omict- <:md ct!ll"'bon S0i:lt'il r'1:'''Hnf t.ypes en St .. Halm1,:h
Gold Mine. 1"he Si::oyn fi'4Cl.IlH3 ~f the a~$al Roef i~ sub-
divided il1to the pt.11ymic:'i::. St:ll.l.th"ol"'nI"'e~"r, the l'l\ixad t"'eaf
amd" ::hCl> sl"'cmH:~ l"'ee'f..rh~ d1std.bution t:\f tho abovCl
1eac:iss beat""'$ no r101ation i~o 'the $~boutc;:l"'op posi t.it-1M 01(,
'tha i3<!)l$alReef, with fClUI'" of the f;i,\/~ faeiol» abut\ting
91
against t.he westerl y $ubcut<::l"'op 1ina df t.hm S;as,'ill RI$l~f on
St. Hel~na Gold ~ine.
The Laada~ Reef on St~ Halana Sold MLne consist. af the
oligomic:t Alma facies, I"'s'ret"l"'ed to &s the Lead\l1t" Reef,6lnd the p",lym.tet l3edeliC!\ facies, I"'sfel"'red to inS th@
Leadsr RS£lf Zone.. 'jhlE? laterall.y persistent "au R!i!fef atU . .•the b.:u'5t',¥Q'r the Spes Sona F:~t"mation hl'::lsa polyml.ct cla$t
<::0111'''10$1.tion c:hC!!,"ac:terisetl by large _f~orous pyrite nodulesI'" • Ii'"
and igneous clasts.
The Aantlenk Channel on at. Ha\ena Geld Min. is B multi-
stage erosive seowr-ando·fill c:henneld,sed feeture. Th~
channel-fill C(,;lfopriees diamietites, polymic::f::. c:onglom~r"'"
etes, pebbly sanda and argillites. The Sig Pebble Marker
QCCl,.U"S Cl\t the btase of th~ Aandenl<. FOl"'tOat:i'.c)M tand oval'"l ies
the Atandenl~ Ch!!lnnel, Whal{~ t.hm A.;;:,.ndenl< Cheu/ine1 is\~
d(:,l~eloped ..
L•.:-d:.erally discontinuous; oligom:i.c:t congloms'''"C'.i:es are
present at varyir'~l strq~ ~gl"'.nphic heights in .both th<l?
Ha.I"'mony Formtat:.icm antI ths Aandenl~ FOr"tOat:.ion. The i"1iddla
Aeef., which occur in the Harmony Formation, c:6ntAin
s'j.H;.)rad:i.cgold ('(miner;;:"l i!'SClIt.ic;m whi 1$.'it the HAn Reefs, whie:h'\::::-',
ot;,~:4.1'":i.n the Aantietlk FQI"'mation) "'-I"'epoorl y mineral ised.(',\
On/St. Helene G()ld Mine onl'y the tAJell(om (!'Southern) f<:1cies
of the' E:1doredt') FQrm<£ltiory,.te *J1"'S'i5<1.)ntand thi.$ is sub-
divided into the uv'tO;::t:lnfQrf1'lity-tH;l~edVS 1, va 2-4 <'3ndva e4tlnEH'~. On at:.. Helene Gold l'1ine the Eldol'"<:;ldo Fot"'tOat.ion
c:oer$sns-upwal"'d end I"'apid fec;i'.s$ che:mges, from >9$.,%
t:t)n91.bl1\(1l"'clt~ to <40% c:cmglomer-nte,. oc::c:ur laterally ac:rO$$o
92
3 SE:lJIME:NTClI..OGY,
3 •.1. PETROLOGY \\
The qU.::1r-t:zitec:la$sific:atioJ1 l:ieh~mS,u$pd :!h this study isthat of t..at~ et a1.,. (ltr90) who I1l"Qditisd the sc:hem~$ L?l:f
Dot.t (1964) and Pettijolil" et al. p (1972) ; (Fig. 64
Law's clas$if:lc:·ation sc:h($)me iSS) <'i'lppl.it!"sble to the
<aecClndary minerDI assemblages of the quart;;;::itGttof theWitwatersrand Supergroup. This secondary sssemblage whichresul ted fr'om pervasive fl~id eU;(;?rat.icm~ arrd inpertic:ular destnJt::'t;L·ol1of the labilep pha5e~ is reia-ted to
diagenesis c;lhd metamorphi!;;.m of the original detrit<:11assemblage (I..'~,w. et ~~., 19a5.a, 1941'0). The c:lassi'fic:atiC::)M
system suhdivides tht:1\\quart~ites (:l'r the Wi,twatersr.anod" ~. c ,:.1
based onorig\ pI mat:.I"'iX content, stl"',~titic:·at:i.on arid sorting_ TheqUal...t'2~ tes Iilre separated into i'our gn:iI,.lp~ OMt.h.e 1::1";'$1$of
"th~ir- app@'arance:
r.
'l 0a) Quartz al"ani t!:\HS" Of >cl5 {.:lerc:ftlnt qU0tz. Tt-.a it:lp of
Reef quart~i te is the iIlO$. 1:. common ;-~xem~le'~ 81 though
quartz arenites are not abundant.b) 5ublab:i'.:le <1lrl:'.mite$~cQmpf'i~in~ i';;}-~5 percent. qUClrt~.
; .
Thm remaining percentage"of unstable lla~ilm) fr4g-mer'\ts er'~ ('10 longer distihguishablG> as e..1, that'
feldsp~thic: or uS 1i thic fragments. f<ecogl,'~sable
lithic fragments aracpredominantly m&tapelif~- andr"W't1 :l.ghSOU$ gr'aim~" As these /filet.apelitlj;;l and igneQus
grains are more "abwm:J('1lntthan feldspathi.c gl".ins inth{;;' study ~rea th~' tat'm II1i thic It r,,-,ther than
,(, II
"labile" is I.l$Qd. Subl.:tthic arerl~·tv~c-{f'jOm(:'Il"'i5& t\\e(,....... /
START
t7111-"I£!.""'F"flI;:)
;Wi~ ~::,1
~"(HART fvR THE VISUAtESTIMAilON OF SORT!NG
.......0r?-'& !ltc,~. '(;1
L1[;} '_',N ..f,~..£lint-<l!Jlr ~,~
~ t...t#o
~:J<c_!l-e e,01->·~w" tlJ~
!l13'
D""{,
..;JClJJ,ti'Nt-1~
"'rois} tI!:!llffiATa'( $Illm~
iMiER fill.K.I11U
t'GPr.1.¥ $naii:1l
Ui-u SIllH'fO
0:<J~i~~OO~~?o~Y{jjj~~e ":Q~~.~.::::j~~Q~~~~..~:...s-'~·O·······~·
~~:~;:~~:::.:d"" {:.;::" ~~~--:-n.'''_ ... " • -:;.:;,~.o'~q;l·-"~l<, lC::_-:=_"::' U~~~®~
-I
[,
()
c lABiLE t.ff,(I{!
'''''''_;',lF!iAlll".flliS •• ,
fEW5PATHIC\4A(I{E
!ill}
1 i15PA~>l.llli1CfRAG'rluUS
SUB!.Ai.!n.e -_Io!1Q111E{PililJllQ.UAflTZilEf
11,.I1lti:>fIS,~jl.R
. EAAG~US
sua"!lim:.......Ailfl!ITE
L.
u.allE
I {mm'/ALEm' TERriS avEU rn flRAl:,l{£TS}
c)
cou:
~
c
,.....:::::;
i;
94
,0 1 ~Adomihant ,llrtm~.t~ group, ~onstitutil,g 9J.pproximate y r w
'/ percent of the ~uartzi te~ st.t.u:iied~
c ) '...abite cu"ani!E?s?of <75 parO$1nt quartz ;,~,ith the n? ....maining percentage of gt'ein$ comprising labi 1m
fragment$. As in the c:a~~ of aubla6ile arenites the
labile fr~gmeh~s~re recognisable as metapalite- andrare igneous g.raii'ls and ther-efore tMt:;; tefm It 1i 'Chit:"
rathEa' thClI'l "lab.i.l&" is used. Lithic: arenites may be
well bedded ahd well sorted.cl) Qual....I;~ w,:U:lts5, c:ont~an"ng qUl"lrtz grains in a fine-
IIgrctl.1.tled mCltl'"ix. Mal(" ...x matet~ial~ c:ompriees >1.5
p~l'tr;ent of thEi!~)"oC:J~, althou~ isubll.t.hic:- arid lithiC:i.,
aY'{i?nits~ c:ommonty ccmt.ain ;10 perc:ent matrixmateric$:L The qUilr"tz wt'lc:kes g~fH'-.?r<"llly oVfii.H'·lie an
ero~ive basa and are poorly sorted.
", '\
The mifU'i,lralcuJYtif the '~";~I"'t'.l!it.es is simple and !r-egionally._-;;-<::::.:~;f~
pers1ste({:t'with quartz mU$ic(;.Ivite pyrCJphyll.its -\,
'c:hlorite - c:hlori toid tiMO p}'ri te ubigu;i. tous ~ irresR,ec:tiv~~po( rocK texture r!!lnd$eCl.imen't~I"'Y c:hi'iJ.rc..u;t(~ristic:s. L.es$t:'ommon t:t~mponent$ are r.:utiie. tourmalim~, cMromite,2:£.1"c:onanci leuc:.;o}(~na. Feldspar hall">not been det.ected in
thin section or by XRD analysis of 60 samples (L.awata1., 19<iY0). Colol,..u'" Vt;),1 .;,a1:.iol"l$ whic;.h occur "are attl'"ibutad
to variations in the 'pa, abundance and grainBize 01matrix minerals.
tli>IO dietS.netgroups J b~5ed 17m both 1::0101.lr and c:ompositiornal MU5CQvita- anB pyrophyl1i~a-r~ch light coloured mats-
j \~:>$t:H:i:'iments~ whS.ch cccur throughout :ths ui!H::Iar Johannes-tiw·g $ubgr'Oup and t.hiS' Spa~ t$ona and A",lflch:'mlt I:'orm.zj.tions
~!
r:l,
rr
wM;i:1~e?through various shades of grey. The miner~109Y
01~ this group remains> e:onstiilnt thfflt:lUghtH.l,t o!lll th~
fOrllli1l'tiorlS,pYrophyllite.
b) Chlorite-rich dark-gr$;Y meta-$ediment$~ which comprisetl'H;1' ~~do,"'adC) ,FclI"·mc:L'l:.itJn ,em St. Helena Bold M;f;Mlt'. The
,./;;:~__::.-_.::-,:~:::=::-.:';:::::-:.-- .z:mif'llE;'},"(:).logy is dom~::y{~t.ec!,!::ly ,At quartz mUsl!'ovite -
c:;h '",I"·:tt!t:... C:hlorif~id 1'l5st:unblage ,and colours range
from <,;wey ,to cark-g,"ey dr' b1.:,1(:k,.
dominated by
FaC:is$ ~r~ used to dsst:ri,lpe the sum total of i'e,,a'turest\
whit:h e:h,arar.:teri!.lH~ a sediment as having been daposi ted ina 9iven erwirontilent. ,Funda.mental to the use of faci5'5 for
th~ i.ntEilrpreta<,;.<ion of e!i\ sequel1t:e of' $ediroe;~)'ta,"y rocl~$ is
Walther"s L~w of F'at::I.es whit:h st.ates: JlA t:,pnformable
ver~ical Baq~anc~ of faCies waB ganerated by • lataral
soquenc'i? o'f enVirOI"lmSI1.t.!!)II (Mi.ddlatclns lc;l75) ~ ClH:hpugh
Walther's law appliali;\ only ,to succ,t;?!5sions withQ~t major
bl'"aek$~ Perahl(;;!'ter~ fQr fec:;i.~s de1ini ticn .I~e1ithology p::;,
'ZSt:ilc:limantarystrwr.:tu~~a,!, palOle.ontolbgy, gaomatry .ngpal~~oc:urrer'lt pattarn~;" These fec:.i:turss are Olpplicabla toI .
arG,?~S Q'f extr.iH'\siva c.'lutc:;I"'Op 1:)1.''1:.da.te from borehole corai'll:'ld limited ol..ltr.:rop 1savss li tholog:i.cal dat.a to P!i!lY th~kay role ·lor f~l:ia$ dafini'l:.ion (Selley, 197Q).
I.n this stUdy the desr.:ript.:t.bn oof ,facies tyt;ltn$ :i.;a. l:.i:'mitad
to \\r,"a~Jfion.l ha.;pos ~J~.~.ma.l!lsiVl'l1) 0 roatrix ....stupported\3r~~~~if) '1'01'" ease t)1' reu.tf:i."g ~ l"'trtth\'l.!l"':: than utiSin9 ap~sndadfaCi~!tl. tfd'do~ foUut/lI:i.hg th~ terminolQgv 'ot l'li'::'\ll (1.177"7);
, ~e.g. (;1~1$.Thl"~~ tlilsic critcH"'i<ll exist i'c:w' (.the l"'eIZQl'Ist'''"l.lct-
96
ion of dkposlt1onal mnvfronments; fa~la$ d~finitton,facies contacts and facias f:?50ciat.ioilS(Cairnc,""oss, 1996). A facies model canst.rut:ted which l.s a gert£i?riH summary ofs;ed.inumtary environment.
01'" sequenc:E:'sthus b~ con-
a, specific
3.2.2.1 Introduction
The term oligomict refers to a congloinel"'ate c:ontC,'lining
>95 percent of eit.her durable or- non ....dl.lf"'able c:lasts.~! .
Durable c lasts are .l1efined as c:onsisting of quartz and11 (,
chert. while ndt'l"'ourable c:la:lt.iS consist eN
peXitfi.'?
stL,Jdy
ait.h~r meta-quartz itej! igne(;:>u$or volcanic: tnat.~l"'ial. qn th~
area both oU.gomiet. .'1.nl=fpolymic:t clast.-supported=onglomarates and polymict matrix-supported conglomerateaoccur.
the. stud',' al"'oa are clast ...
$uPpc)t"'t.eo, mass,tve and contain ><15percent. qwart~ aJid/ol"'",chF.i!rt.. clast.s. 'the oligC)(Oiet·congl(;}m5'rQt.es dtrS?gt:net'~llyw~u p<::\c:kedwith 2-4cm'diameter c.:las"ts, al"l' (;'H'·Olrdve b~s~~u sharp upper e:cJI'lt.act and they commClnt'l .overlis eith£':!1"un'confot"'mitiC:s or erosion sut1ac:es. 01igc:':jtl1ic:teong lom!!?r-
<ates ill"e geru'\!I"',OlUy between $cm and 1m t.hiiS'k, alt:hougo t.he
Bi; Pebble Marker is >2m thick in places and consists
solaly of vein qi:ltn··tz cla$ts cd 4-$cm eL1:ametel"'. Thin01 igomiC:t. ccm91omerate~ are referred to a~ . ~ithe\ shs4'\ttc;onglOI1)~;t"ates or lag deposits., 01 igornict c la$t'''\!lIu~~,orted
<:cbl'1g1omel,.~tes Ma'j,:l1:;':l~ t?Jo11 $d~ted (bl.r'fIlodal)samJ~~l;:me
\r.latr'il( and 1:1ragenerally lcrtar<illly e~(tl;msivo. 01:tgom\ct
:3'J
97
t:ongj,omgrat~\$ are oft~n i.nt.erbetfc:l~d with~ and Clv<':!rlain
by, trough- and plana~ cras.beddad &ublithic- and quartzarsnit.e$~ "the ~,a\$a:t feci(:.j!$ of the aCt.scal RIi?~f is oUgami;ctalthough bath the Steyn facies of the Basal Reei and theLead~~ ~eef are comprised Qf an oligomit:t con91omerat~
at the base averlain by palymiet conglomerates.
The palyrnict lJl:onglomel~ate 'f.acies cont.airu.'i roassl,ve clC\\$t.-
supported r.;onglolTi(:;)r"atas with >5 pen:ent metapeU.tetC:Il..lartz atreni te; iI;Jhaous o.nd acid voleanic c la$ts. Pcily-mict clI::mg lOmanl.~a$\~re generally not a$ wall pac!t.ed at1
ol'igomict c:ong lomara.f.\c;;~ and are u$ual1y >30cl» thick ~ ·,'i'he
scirt.;i.ng Q'f &&'l;;H;;lstone(m~trix matel ...:tal tends to be pOQr\::' \'
(polY'~modal) ant..\ the c:las.$ ~i2a is v<:'1l"'iabl(;;\.,...'from <.lc:m to":\':.: ',\
>6t:111di.:lmat~r~ peq,ymict c~n91omerat(l1$ commonly display ..~\
fin.ing-upW81'"d Cl.;5ist-sizf:i.' mo,e.~f although t:i:)~.I"'${;?ninQ""upI!\)Ql"'d
.in t.:Tast siZe does Occ: . 'in th~ ma~sive polymietc:onglomel..~te$ of the ~ldorado Form~tion. Partings of$ubHt.hic::- ""nd qua.rtz OlII"en:tt.e I.:ommonty occiur within the.s I) .:;
c:tlnglom~r.:lte$. Thin, latel"',:1l1.y impel"'sistent polymic:t
c:ongl~me~ate l~g$ ~ommonly have ar-,
~~ntact with tnm underlying arenites.o'f tli~ cO''1g1omered:.p'' is va·'''ipbt.r~p
c;)radational ba$al
Tht:; upper d;:'n tactbUt f reqWE'mt~y
horiz..1ntally
of th~ Oilgbrtnsk" Spa? Bona."Polym~t:t. t':ot1l;jlomerates are
1.::amirHll 'aed
and Aand~l~l<:gfEl.neral1 y
.of 1=>01'"0(..15 roumd f:tyl"'.i te,~
gl""adet'S ,;.al tl'it.lu9h arsa~mocier".Fb';!?Qold c;:p....:',\des
~, .,.. • 'I
disp';(1Y ~ithuw' en Il:rol(;ivG or a. f!C:\t b'lSH':!.""~'\
-,,~~.
end l~ck imtu":l.cation. The pr~$ehc:e
~s an indicator of increasad goldctlntain:i.ng little p,}<rite bl.~t
do ot:;:c:\.U"'" PQly:nic::t t:ong lomerate::i
G
Massive, crudely bedded and hori20ntally-b~dded poly-£01I::1:i<: c l.ast-suppol'0t~d cong lom~rat.a$ formed fro£O th~m.:f.gr~tion of 10ng.1tudinal bars, t.:Iiagcmal bars and sieve
dep~~it$ une.:!er I::onditiom:; of 't:.raction cur.rent.s and low$edimen't $l.IpPl y. Pepoel ticn of pol yI\U.ct. I::on9 lomera't(?soc.::cul"'reo in c:o~3,r$e"'gr~ined proximal brlStided river";" and
v
br·c:d.d-pled.F1 set.tings. In t.his f ).uvial environment nrO$s-
$trat.ified gravel\::!. are rare ':ompared ttJ massive grdvels(Rust, .1.975)# The.>stratif.icatit:m of the t:cmglomE)r'~tes,
-:
dafi9ad by c;ompo!:litiQnal, $or'1:ing 21lid fabriC: c:hangesf isa rSSiult of T(.lreset accretion in a down-c:urrent dill"act.ion
(Hal"tlls' E:.lt al'1 .1.9a:2) " 'The chanl1elised base of the poly-mic:t cemglomerates i~ a c::c.:unmonfeat.ure in alluv.i~l. fan
C-'-)settings (Miall ~ .'1.977). Wel1....PClc:t~(:!d c:::onglom~ratem'--also
resuJ t.ed from t.he dsflation, Wi~(lowing and reworld,ng ofearlier pebbly sandstone depcHs:i.ts as a re!5ult, (;:)f lewsediment supply. (r
WeU ....pac::"ed cligcmict c:::onglomaratelt:\ resul t from the ra-world.ng o·f pebbly s~nclstones and )lolymic::,t eonglomeratesand therefore have !icomplex histeri!i;~s. The re""worldng of
di.st.al PC:H··t.iona of a b,"'aid-plain in a beac::h or T?re-shorS'
environment following progradation of alluvial fan andb~aid-plain sediments into a standing body of water aleo
oeC::t.,I,'"red" Oligomic:::t conglomerates do not possess a w~H-
developed gl'-adi\l;tg and do not N-ave s(:Qured bases because
high .....enel ..gy sheet floods spread gl"'iwel over t,ne iar'1\ ,
I5Llri'.sc:::a <£:s a she\ 't: conglelmerate (AUen~ l.99S; Friend,(_IlCl1a; Rust, 197a). Oligoroic:t lag .tIGiposits result from'
deposit.ion from the short-livod transport 'of pebble$ OM
c::hml1ne~.bed<;:; to prot:h.tI::~ eli rJ~u$e· gr'qvel sheets (Hain,
()
99
In the elaS5ific:~tiol"l of qO"'l"'tzit.$$quart.z
the termsandIIsilic:eoos",
"argillaceous", dEscribing a lithic aren~t., are avoided.Thii;!tmrm quartzi te inelwdes both aremi tl':?!5 and wilckes.>. :'I"l;,:i
term granuleconglomerate ha$ bel:n wsed few grains of2~4mm in size and i. a size clasaiflcation aquivalantto "grit". In the st.Udy area trC::It.f~h- and pl':ll"l.$;'lrt:rtlssoed'"
ded, planar bedded, 1l'tC1$Sl,Va- .:andpebbly arenites occur aawall as quart.2~ack.s.
I)
Troughlithic-plac~$.
cl"'o$sbedded fine.... to very cOc'arse""grained $t),o-
to quartz aranite~ contain scattered pebbles inCross bed sets vary from 10cm to 50cm iM thick-
ness, commonly fine-upwards in grain size, and &re
char'c'acteri$ed by round and euh.dral pyrite and c.hl.ol""iteconcE'ntra.t.iOll'$ en fo,'"esets, together' wi. th $ll1all pebbl!i'.(lS
of m~ximl.\ln zcm di.ameter'. Sets are laterally extensive(>4111)and Err·osivaly based. irough 1:;r'C)ssbeddil"lgis ttli)
most c~mmtlnsecliment&I""V structUI"e in the areni ta faci'~s,occ~rrin~ Ae aaymptotically-basad sats of variable thick-ness in all the fC)rm.ntions tlf the Cen~t~lal ~and Group_Trough croB.~.ddBd arenites oC.cur interbedded with bothpoly~ict- and oligbmict conglomerate ••
rile plii:har' crosabeddect a-r-an:.i.te Tq.cies:i comprises m~lldium""to vary coarsa-grained sublithic arenites whic.h contain
lOO
although $m~ller sCdle (+\-20cm) crO$sbed$ are cammoh.Planar cras.bed sets ~re )3m in length ~arallel to flcw.
Planar cr'ossbeddecl arenites .::.arerrot ,:J.ound.antbut do occur
in Clll the fprrnations studi.ed. Chlcw'ite and pyri te
concantratipn~ on planar faresets are rare.
"'~.2.3.4 Pl.nne bedded at--enite i-aci(';!s;f-
PlatH;?beds arOc-4:~t1~pr:li$ec!01 1ina- t('l very coarse-grained_ ,"r~
lith:ic- t('l $ublith:i.c: arenites separated by thin &r9i11a-Cepus laminations up to 2cm thick. Horizontal laminationsand low al191e stratitic:ation 81"'. common in thE! Top ofBeaf qual"'tzit.e. Scattered small pebbles occur on beddingsurfaces.
Tha massivs arenite facies comprise finl?- to very coarse-grainad lithic- ta sublithic arenites which contain nadiscel"'nible bedding and up to so percent scatteredpebbles. Massive arenites conta:i.nin!J sca,ttered pe;>bbles
are a c:he;rac::tel"';i.s'tic:af th~ Spes aona Formation and occur/~
in bot)y;f'tht? Aandenk Chamiel and th(;? e:ldorado Formation ..
~.2.3.6 Pebbly arenite facies
Cll1:l.:;ts al"'. I'HJt in c:pntac:t with one another and, thisfaCies contains HiO p.ercent. sands.;'Cone. The $Cl.nostone l.llS
fine- to medium....grained and is mOdel"'at~ly- to poorly-$ot'''i..ed. 13edcUng 1$ c:ommcm1y ab$H$!nt and the fabric;: israndom. Thickness of this; facies varies 1''''01'1'1:::$c.:mto oval'"
om and the clasts are 0'; mader<1t'te- to pocwly-sortad"chert.~ vein qIJtlrt:z, quartzite$ metape'lita and igneolJs/
/,material.. ":he pabble$ ~re ltlOderately- to Well-roundedand range in si:ae:i', irbm ,,<:.t.cmtCl 15cm di.nmetar" Pabblv
.101
'c:::,
arenites ara characteristic of the spa~ Bona Formationand also occur in the Aander'll<. Channel,
f'~e au..:;ir't~ w<.:1cke1",31:" ias compri;"t,.s wack~$m.f~ix material. nQ ~iscernibl. bedding
tot'ltaining >15%and ur tc 50
Helsl'a Gold Mine is; a 12m thick c!:,)art.;ochert and vein quartz pebbles.
!:'~,wacke containj.ng
3.2.3.9 Interpretation of the quartzite~acles
"Planar- and tl"ol.lgheros$bedded al'-smite facies arE:!';~r'med
by the migrat:i.ollof sal1dwaves and dun'~=!!s (meoga-ripples) 1
re~pS'c:tively. Sand ""aves io,,"e 2-dimensional stra.ight-crested. bedforms which have a long It/avehmgth cbmpaiJd to
thai...height, ~heraaB dunes are 3-dimansional sinuows-crested beclfor.ms. Theose bedform!Q .ar'e well documel"'tad fromshallow-water flume studies (e.g. Harms et al., 19132).
were
arerr:ii:elEl whichi;'
The croasbaddad quartz-OC::CUI" ih the study ai'e<a on a braidedalluvial plain (braid- plain) of a bajad& 8S shaet-l1~edapo$ita~ Ra-workihg af distal portiQns of the braid-
~~lain in a beach or fore-shora "enVironment followingprogradation into a standing body'af watar resulted int.he form.w.t.ion of hori~ontally laminated quartz aremiteswith s~Ii"" parallel lJSmin'he. l-Iori2011ta1 lamination.& ·f ' min a wiJ~ 1'",;,\,11ge of sediment $i'ze~, and with 'I''I:"yingcurraht veloc::ities.
Fluv1,,1 deposiitio~' elf fl'iodarataly- to w!l'l11'''''$orteCipebblyarenit~s also occ'urred it' this brai,d"'plain set:ting)
(:1
102
anc:.i with no
preferred clast oriemtatiC:JI1 resulted Trom the dr~pt:ls.ition
of clests b:Jgeth€?r w.i.th the arenaeatlU$ matri~ rn.:i.terial in
a dl::?l:!l'"i$-flr::w,l enviro'''lrnent (e.g~ Herh\s et al., 1~:a2).
IVIi$\ssive wac:l~eH:; of the Middling q4~rtzite and massive
~'lreni,te$ It:).c::I( tr",'!c:tion currant features such as c:ro'$$-leminations. The lael< i.rf text.ural vari.;~tiOM in wac::.kesis
("
concent.ratedenvironrnent~
sediment dispersions. il"l a d[~bri~.-flowl'1aS$ emplacement deposi tJ.Ci'" by ~r;f;~vi ty flow
variable slope., depEnding oM ~~a'intensity9t"a.in pressures (Miqdleltt1n arHt:i Hi;unp'toM,
.'mc!'iY occur emof d;\'spersiva1976) •
Argillite is the general, term for ..a mUds'tcne (mudrcn:::I<)
h,u"derHed by incipient metamorphism ""nd show:lng a slaty
c::lecwc;.9e:! (Blatt at .;xl. ~ l~aO). Th~ t,sl"m mLldstci,:f~l;irn::lw;:les
c:.layst;one and ail tst!.ll'1l?#~ w:\, th a maximum ~.~a,il'1$izt;;?of
1/16mm. UE. of the term shale ie .ntrandhad in the
literatureirrl';:spec:tiv.lamination
and
ofshale@ithal"
g.raoin9
t,o
grains:i.:aoof r!m
oV?,rprinted by q foli~tiQn (e ..s~ in t.he I<h<?\!d.sheale) ~ due~ainly to the ductile nature of the argillite.
103
~.2.4.2 Mudstone fac~s$
Laminated and mas.iva mudstelE drapesEldoraop Formation and fining-up unit.sItll..ldstone arS' common in both the A.noen;.
occur in t.hefrom arenitG? tClChannel and the
Eldorado Format;i.!:ln0 Eoth lamin.:.\'t,(;?dand massive mUd$toneunits occur sporadically throughout the Middling quertz-:i.ts and ih distal depos.:i.t.ionalsettings the eldoradoFormatioh. The I(haki shi311agrades frorfl C!i.. ail tstone in t11e1
sout.hsr" port~on of St. Helena Gold Mine to a Claystonein the northeastern portion of thli?Welkom Goldfield.Siltstone and claystone occur as narrQW interbeds in both
pol ymic:t c::tmg lomerates and sublithic- and 1i thicarenites.
lntarld(l\ina.ted $i 1t$tone and c 1ays.tona (l aminated mud....rock) is abundant in the upper portiC!h of the Aandenk
Channel and contains $oft ....stadimemt defr,H"'mation ·feat\..1re;,~
such as dish- and ball-ancl- pillow structures. Th.contact between laminations is sharp. Int~rlamin~tedsiltstone and claystc:le is aSSOCiated with tsUblithic- and
l~thic arenites am wall ~s pebbly arenites.
Diamictites era massive matrix-supported conglomerateswhich contain a matrix of mUdstone comprising )50 percent
of ·the rock. The fe.briC:::of a diamicti t.E:1 is random end
thickness 1"1:\1"'19.5from :Scm to oVer 3m in pJ.ac:es. The cla'!.H:as'ZE'i/mblC!.ge consists (;)f poorly-sorted and poorly .....peck.so~hart~ vein quartz.material with clasts
quartzite)of <1cm
metap.lite and igneousto 10cm diameter. Rare
porou$ p~'rite clasts of lcm diamet.er C)ccur in diamicti teacontained within the Aandank Channal. Diamict.ite.chClI'"'actsl"'isethe Aand~nrt Channal and diemictites of' <;seem
104
thick occur in the Eldbrado Formatian. ~he diamictitesare a9sociated with bot.h the (;tmglomera'te ~nd arenite-facies.
3.2.4.4 Interpret.atfcm of the ari;lill.ite facies
ArgiUite deposition ot:curred by mec'ans o1:suspensiondejJ.osition in low energy environments~ Narrow fl)udstonedrapes contained 5.n co.nglomel"ate$ and arenites weredeposited during pertods of .tillstand followingenerg,etiC: flow condi ti9ns. '-he Aandenk Chemnel contain$interlaminol.t!~d ,'siltstone and claY'i!>tone whi!;';h resultsft-om a.ltl$'rna1:ing E-?IJl.sociei!!of bedload deposition andsuspension setUing O.31at.t et al., 19130). Laminatedmudstone is indicative of cyc:lie sedimentat,ion and ead1lamination may ba the pr~dutt of fine-grained densityunderflows, classified by Stow and Shcmmugam' (1980) as;fine-grained ~urbidity current lamihae (T3-Tb), simil~r
"
to the '0' i3.nd 'g' sequence turbidite clasflific:ation forc::o.n·sfer-grainE':!'dturbidites (Souma, 1964).
Oiamictites ilr'(;& emph:;ilc~d as masS....flow deposits eith<i;!rsubaerially 01'" subaqueously with 'deposition by downslope,1IC)vementand sUb$equent "free%in~" of m~'\terial (Middletonand Hampton~ 1976). The movement is episodic and occursin I"'g$pOmle to 9ravi ty on slopes with varying gradients.The &iam1ctites of the A~ndBnk Channal, which are asso~~iated to mUd$tones of up to 2m thick, were depo$jtedsubaqueousl y. Thet d1<:1m1ctitee cf the gloor'ado Formationwel"'edeposit~-ad subaerially by debris floWB. Swc::hdebrisflows are promoted by steep slope"0 short periods ofabundant watel'" supply and Cl. sell"lres/providing debri$ witha muddy matrix (Bull, 1971).
105
3.3 PALAE:OCURRENiS'/
Trouc,;jhcrossbedding axes are the most. rf.:";abl.e pcOllaeo-measured wherever
pO$sible~ Paleeocurl"'snt measurements for cont,;llomer.:\tes
are confined to crossbedding contained in in";~rbedded and
overlyin~ ererd.tes of the same depositional cycle as the
conglomerate.. All palaeocurrent measurements are
presentl$ld in $l::1ct....on 4.2 (Sedimenta.ry seq"...1enC::G!s).
i'j)
Pal aeocurrent trend$ ::bf the HermQny Il Oagbr'eek ~ Spes; Elona
and Aanclenk Ftu"matior.s are:! tolf.'.:ard$ t.he northea.st in :thevicinity oT St.. Helena Gold Mine and the trends show no
relationship to the western margin structure O!t St.H~,lE1naGold N£rHi?" Palaeocl..l,"'rEH')ts of thE=!E:ldorado ~6rma-
lj
tion in t.he St" Helena Go.ld Mine .iraQI illl..lst~iate a.,tow~r'd$ the southeast.
\\
\1
(J
106
4 DEPOSITIONAL ENVIRONMENTS
4.1 INTRODUCTION
Int.$!r"preta.t5.on of dE:l'positional envirohments for Protero-zoic:: seoiml;':?ntsusing equivalent mod~rn envirCH"lment.sis
~r'C)b~emati.t:,due mc';)inlyto the lac:k of pre-Oevonianvegetation~ No anvironmant can be identified usingindividual p.:aramet~rs but rat!":er combination!l of-parameters are necessary. Depositional environment.postulated for the Central Rand IBI"'OUP inc::lude marina9
lacustrirH::l, a mal"'zne-fluvial interface and fluvial ilndalluvial ff.ln settings. A c::ompar:i.sonoT various paramaters
Cl,ssoC:iated with .these ehvironments is made (Tabl.e 4).Eased on the paramaters used and on previr.::Il.•'i:i ~t.!ork,depos.l. t.ion of the Wi t.\~atersranc:i' Supergroup is interpl"'etedin this $tUdy to be predom.inant.ly .fluvial in ~ brai.oed
alluvial. plain (braid-plain) setting on a bajada. MintJrmarina influeneea did p~cur and alluvial-fan depositionis evidenc1:l!din the upper port.i.on ot the stlt:a:tigraphy.
The strat.igraphy of the study area i~ subdivided into
Ti:vfF<~:sedttl)lS:'htJ:\rv ssquences~ termed sequences 1. to 5.
Between pari~ds of deppaition~ uplift and erosion tookpla,t;:e w:,;';i..ch r~.sul ted in the widespv·ead dsvaltJpment. Of
unt:;onformiti'~ls which are flJndament.~l t.o t.he identi-"ficaticn and definition of aachQEmdimentary sequence.
4.2 SEDIMENTARV SEGlUENCES
4.2.1 IntrtJduc:tion
The detailed daptJsit.ignal environments of each tJ1 theQ.. I
f(.)rmatiorts in the study arll"a hOVe b~en desc;ribed with the
or-,
\\
lot.
PAfW1EiER .. :'ALLUViAL FAM GRAVELS FLUVIAL GRAVELSDFFSHORE GRAVE!. BARS AND
BRAnED 5TO&1I ~AYERS "
CLAST sm {SOOCtl ( 20em flveralle Z"5c!!l, 1l1i11(imuf1 ottlCLAST Poor rounding I}ariable J'Ourldil1g ~ell,·tCiUl1ilt!dtlas!S""""",:-=·"""""'---IROUNDNESSUATI'UXfiATERIAl,__ ..........-+ - ~--------""'"""":"---,_+___:_~_:___,STATlsnCAL. Haturity and rounding inc:rear,es, fiaturity ami rllIJnding int:r!?asl!s, I}i\riablaPARAHETERS j-,::.!cl~a:::..:5t:..:s::.;i:;:;'Ztl:....Il::.';·e~cr:...::Il.!:.:(J5::.':r:.:t..S.:::.do:::.:;ti~n5::.:.1::.';1l!);.::.!!!_ ....... ~da£t. !Oize dec!'lmes d0I111S1ope ,LATERALEntrn' United 110'5 Ilf.!tres) Limited (1QO'5 !letre;)NATURE OF CuntinUDUs in radial dp14~1"q, ,ditect'" COi)plex tOi\9Ior.lera.~e bars, throughBEDFORMS ion, tRaple» in trosS~f<l1l 1~\',±itJll, nUllerous ero!;iooi\( :)lId depositional
uith cut"alldM1Ul structure!), ~vlints after initial l\lrf;\aiio(l.l.enticular bedforms predoailHlte Indistinct and lenticular gravel
_____ ..---..; ......_..Yf.dforo!i resultVilriable
----+----------------··'------1lieU sortedPoorly sorbd
Lihrallv 'Ilxtensi:ve "Elollgate, 11:ll1, nlief ~,on9tllileriliebarsDiscrete cooglotler.ates present
VERTiCAL PACKINe Variable G~nera,11y increa5e5,up~ards, «ith__~ ~4F_~ -- ---__~·--__r~nnO~i~l)~r~ta~n~t----------~
Clast. to aatw: supported, variilb12 Clast 5upporterlJ sandy tlatri~ Clast to aatri~' !;upported, Sil'ilny .sortiM emil f1t-.tril: " . tlatrh _..._..,...__ .....,Variable arenit(l~s liflited fi~rArenites. Baited fines Arenites ullif extensive tinesGenerally sharp Sharp or gr~datilllJill Sharp
TEXTURE
FACIES ASSDCIATIOlITOP CONTACT
"
."
TEXTURAl.. AND!tIN. l!ATURITV
I HAR1N£:AllbS
Itatllt!! tu very maturetnGature to ~ature
.~EDFOR"SLatera,] Iv el(terlSiv(l , "NUD nilAPES Laterally ir,exhnsivel.atmHv in(!lltensive
Laterally inex(~nsive, of trsns-verst: sandllaves
/1
Veriilblel iru!! ~assive shaei-:.1Wtdepo~its to dunes and r!pple~
laterally exhnsin and verticallystacked sanal'lavp.s (al!lplHude HlJlj
• antf dunes 110"200co sets IEROSIOlIAL SCOURS
OVERALL MORPHOLOGY Wedge shaped! thinning ltilrK!1dly away ihitkells 1rol.l $ol!r~!! Uttle thickness ","riation_. ~_t_""fr"""OI:!:;..""l\io::.:::u.,.,rr..:::.e---"·--..".,"'.;_.." -......_->t-,__,.,...._- ......-'~-,--...' ...., -!_.__:_ ......,.. ~PALAEOCURREtiTS Unimodal ~ sollU ,spread !ii;~OQ It but Uninodalj tooilonly UniMdlll or bipol ar
dOl t" il 8~ ~~r~a~l~a.oa'tern.~ ~I~. __ ~ ~l~O~Q.~s~pr~p~ad~~ ,.~__ ---; __ ~ __ ~ ~ _____OVERALLSIZE 6eot:taily <lOkmt 10"100'$ kill 10~LOO'5 kat
Vatiabl~;~O-1Q' s rnetrll?'jdee,p} frotil.hnheati i!ltision
\l
FLUVIAL nEPosns IJARIIlE DE~OSITS
:. ,'I (.'
c
('.
".
1"/
C;ol'llpa~ist'ln of various ehal';lec.teristic:s of alluvH~l fan,fluvi~l and m.arine depesits. Petta at"e from B.ailey et.al ~ 0.990), MeCcl.V~r19'i$), John:;:,on and t3al.dwin (:l.996hLec:lde and Walk!':?!'" 3( 1962) y' Salaz<;f and Klein (.197:~n)Banks (1973) end Boer"GSm.a~nd Terwind't (1991).
'\\
;:)
108
Ji.1
aid qf characteristic depositional.aqu.ncas and the stratigraphy described
in\\\Fig. 55.
eaquei"lCes. The
are illustrate'd
a) Oescription. Sequence 1 consists of the ol.:i.gomict andc:st'"bon seam reef-t.ypes of the Sasal Reef and
oVl?rlying <i\ran.it.- and ilJ~~9il1;i.ts! Uhits. The 13asalR.ef in the nt:lrthern portion of at. l4E}lenaGold MinI':
is an unconfc:wmity--bC1sad lat.erally continuous 2-50ctnthick t well- $01"'1:..(;1 med.il..lm-PRbble clast- $uppor~;ad
oligomict conglomerat:S'~;;) 1-h(;l! matrix {~atel"ialcomprises~·Cln91otll(?rate contains 5-50cm
,:\f,$ult'll'lithj.t.: arenit.e interbeds .•
C.::1rbon<$lc.eou$'material (kerogen) o6t:urs predot'l'lif'\antliy
q~\al ..t~ arenite 9rd ~thick quartz- and'
1':::1\
at the bt'3se~(.?i"con.glcmeriO\te. Unconfortnably bV~H'"lyingthe eonglOniel"'at~ 1S "ehe Top of Reef qua>.rtzit,e,.~
plat"le ....beddt:.'d quartz arenite of 5-15()c:m thic:f<.ru!!s$
whjx;~ c:ont.ains rar~. t,"ough tnrrl:ls'lSbe,dt!ing and sc:attered
small-pebble olig6m'ict ela~:ts. Tt1~ Top of Reef
quart2ite is i turn ov@!r1e.in ~y the Khaki shale, amUdstone which has at sl1arp,upper contact and which isup to' 1. Sm t,hic:k in t.he nor'thern port.ion of at.He !em a Go 1d ~1.j.t}ee
b) Interpl"'etation~ Therroligomic'l:: Sasal Reef c0l1g1omsr-'"
ate. ware deposited by a braided stream on a braid-plain of a bajao<1l subsequah't to t.hw development. bof ane;xtensivE., flat., unconformity sur-f·ace. Vl;5!ry lqwgradients> oh the dapolSitiohal surfer a lad t,c;) frequeht
'~-'-
channel switching and dapo::d.til:)M Cjf t.axtUi"'all y- ,3,nd
mineralogically matul"'. conglomerates ov~r a. larg.araa. Aaworking and law rata. o~ deposition resulted
r?
(ae~lt ...;i.x) ~0o.cp~.VS5--Ij VS :5 9.fuio'o·, . " ..........__ ....+-~--:.;........ ........_""""'" ,_..".;...--I
HA" • • •• . Aandsnk -;:-~~~~g.• r. ,\, FOr'mai.:.;i.Q[1 SeCju~m;;:~ 7a~JVI OOQOOoO .~:\=:; A.aht~enl(\. Sequence (;)
::~ CMann~l 'c""'0·(;/0' :"1--.........-----I--------+-- .......-~-,.....--l'"'' J f'••• II ~
t .., •• ~
Ha" OO~~~I /:~>~.~.~-------~--~------.----~~--------~.--~.•• l Q'I ..... 4.... ,~ .., ..... It.. ~~....
Spes !3on..aFormation
Oagbl"t;,;lakFOl"'trI'at;i.on
()
F:i.gur'~: Sedimentary sequerHzes in the I..Hoper \It;)h~nnesburg .andTUl"'ffontain Sub9f'OUps ~
=
nH
'-' (l q'I
/)
110
o
in the deposition of dureble clast typ~$ ~nd qu~rt~
arenit.es.
Te~tural arrd miMer'~logic:;al m;stur:i.ty of th~. $ys'eell'l \I~a$
fU1'"ther enhanced by madific:s.i:.ion of distal POI.-tiClns
of the braid- plain in e beach or fOI"f:l'£',horeenviron-
ment with th~ for:metion of a braid dalta from
proJ;}l"'Qd¥ltion into a stendil1g body of ~"ater (c.f.i)
McPhl:H'·sone'l;, al.~ 19a1~p.SZ>; Clifton et al~9 1~7.1.).
This merin4':t' modification result.ed in depo$.it;4)M of
thtt:l pl~ne-bedded quart.z arenite crf the lOP of Raef
qU~H"tzite~ Simi-leI'" modern-day mQdif~e~'i;,jon of t:oa$,t~la'lluv!aal Teln!S (fan del tas) by w~v~ ectit)l1 and long-
shore drift OC:CUII:'S in the Gulf of Aqueilba (Htlyward,
ltt9S) .~ Continued ~.ansgre$$ion re5lul ted in the
depo$:itil.'1n of argillites Of the !<haki <,;\hale$ wM5.ch
are th~ distal equivalent.!;';>, of the underlying Top ofH
Reef quart:.; C\l'''enite.•
F'al<!aeocurl..t:1ntme<ll$lJretnent$ I")f trough crl:)$sbES.'dding 1'01'"
the Sasal Reef on St... Hehma atitt! Mine indic.cate ia" "r.·.~
l"'oft,th- Morth~a.sterly transport direction (Fig" 56)." I• o(~abblas of the Ba.sal Reaf also d.cr.a.~ in size in_nOl"theasterly t::1il"'action ~el"'9$$ St~ Her.na Gold Mine.
Limited measurem(*nts (tiff t~;~.H,;Ihcros%badding in the!. .:) ..
.iop of J.~(}itrf qCJartzite", and ripple strikes of eym....'" .. '
metrical ripples from the Khald shale indicate that
post ...Sasal Reef transport was in a no.rtl'lea.1:it,er1y "
diract.it.')tl. The I(haki shale alsa fines 1rclln·a silt;··Ystemii' to
'Cl'"OS$. $t eI~ l',l'
..1301d1.i.a t·di..,
:.'"~,
a t:laystC:)jIl~ in a
Halana GtUd' Mine
,.northaas'tel" 1y di rec tionand across the WelkQm
'I
111
N
E.iSlJ.re 5.fr:. Tr-ough-c;r'p$$bed ret!\dit1J;;j$ in ~ren1te$ within andt:werly:i.(lg the Ea.$C'\l Reef, St. Helena Gol.d Mir'\e.
/)
o
\\ = ()
c
o
112
I':' "
'j}"
$) .Descript.ion. Se-qu~nce 2 c:onsJ~i~t$ of UnCof'l'fQl"'m~\ 'liY-·bc:lsed B~$al R!?'J~f cOl"lglamGH"'atas fF~i!~ t.h~ $C)t.1th~r'n- ~l'!ti
(' ..~. 0centrcttl purtiOil$ C}j' St. "'hi;>lenl~ GOld Mine. The. a~$elReef in this area i~ ta potymi~~ moder.:a-t~ly-sortedsma::! to lerge ....pebbl~ Qgngloot(;:?r.n.t:t;?of b$tw~en ~Oc:rn
"
ii4nd 2m 1.:hiC:I{.Preserved remn""n'ts oi; €I basal oliQomic:t:~"i /\,.->'<, ,(\' \ ..
cbi'1~;'Qmt\'tI"''''l.te of up to 20em ~.fWc:l(. t:!,1"'~ j:W"S!sent in'il ,
,:~te<;ss.. Tt:a overl yi.ne;! PQI ymic''C cong lomer'ates are
in't:g,\~b~dd~d wi th tl"'ough- ;and plan~l'" e:rO$sbedded ,~'.lbl,H·;hic... =t~~ qu-;tt.tz ar;!!mit.~~'5 01 5""'·,0,1;',/1\. ,{th:.tc:K.::~"Ovsrl yin~ the t:.~nf< ie-rate is t.he lllan~-~~~d$;l~ 'r'Qj:l of-S"-~ '.Reef quartz .al"'~nit.e of S-l~(km thi~kn~ss which
.Y·""'ccontains rel'"s t~i'lU(;;Hi' ,;rQ$$badding -anti $>eattt't'raQ
g$mall- pG:bbl.~ Oli9b(!ll.ct. \,;c::last~" A pool'"ty-dev(;;lopad
Il\udston~ .;l::Itf U!=I to \ lSc::m,thick (the, Khaki sHale)
6v~rlie$ by the: Middlit~9 C!uar:"t:~it.e in 'plat:iE.?s.f)
II
.',b} Int~~J',)retat.~qn. Sequence I"'s$~,.lt.ed, Tl"'Om d~pt)$i tit.'ln
of ,pol ym:tct e:onglomerates "on \~ bra-id-plain of a I:
baJ,ada 'following SOUI'"ca ar'~i!-a re;"·juvination ~nd and; j("-:'.. f
incraa1i!;~ in energy ~t"ra C\t!?PO$iM.on a.,t syst.em. ,'fha'ol:i.gomit't c:las't.s which\ undel"li~ $equ'~f'le:e 1tdbn~lom-eratas are preserved remnc:\n'l:.s 01 sequelhc:e 1 oligomictc»
r.of'lgJ;omerates whi.ch wer'e depo$itet:.l ov~r large area.[31"'i!.\velafld $~nd were deposited by l~ng~t.uct;tnal arid.tl"'ansversql bC).r$ on thm braid-pl.aih i',),$ kheet. .... fi!~e
deposi '\:.$" Periods of I"'apid depo'S.i-Cion r~$ul t~d in th"';
1atG.'l"'d 1 !l;.\ltlit.,l=hil'1l,;J <;11 chanl1~f$ .;J.nd t..~l* fCH-m~ti-ort of,)
ch.aonslis$o latet'",~11¥ discontinuC)u'P pc;tymietil \'
t;on91.t:)1iI~I"ats·s~ The, ird~ensi ty' ~nd th.H''''a t.tQ~1 t:lf sfwsi.l;Jl'1
assot:iated trJi\;h"$equi;:H'C~ :2 de('term;i.ned th~~ e~tel"l\~., '1:0,0.>: ...", .
whiC!h l.u1derlyiti9 '·sti?quen.aa 3; ol.igomiat eon~~lONlerntt'f'$
CI. ~\
from th~ localised reworl~ing of
channel~sed f·lwvial Btr •• mB and
the WiilC:~. as by
the swb$equt~H1t.
113
4.2.4 Sequence:5
a' Descr~pt.iQn. Saquance 3 consists of m~ssive wackaB,scatt.ered granules Bnd t;;mallpl:?bbles of the .Midd~ingqUClI'·tzite. Interbedded with thE!! wacl<es at'"s chann~l"'"
1$eo swbl i t.h:i.c- (l am:! quc,;u"tz art;;)ni tes and lenaoid,
smal1- to med1um- pebhla' oligomiet clast-BUpPQrte~,)
conglomerateH~ of the Middle Reefs. The Midl:Ha Reefs
Contain soft.-Bediment cieforJ'IlBtion featur~a.
b) Inter"pret.atic:m. Sequence 3 resul ted from regress;i.onal'i\
deposition by sitJ?r B mud flow deposit or fine-grained diamictit~\ in an alluvial 'f<1tlnsetting (c. f.
SUlI, 1972)~ Th.Ulnterbe~dect minaralogically matu~eMiddll'i~ Re~'fs and as-:1C'\ciated quartz arenites fOI"med
a) Description. Sequanceunconformity-based
sporadically develt:lped
4 comprises sediments Of the
",
The>:::;:.-:.~;::. "":...--- ;::--~,
Leader Re~f ~t the base at the \De.gbreek F'arMetic.:tn i"S up to 1.om thicl~and is a \,
sm(;);11- t.d rnE>(::\ium p(;?bble plic.Jomict. conglomer'ate "lith
overlying- and interbedded quartz arenites. Eitherbverlying ~Ma Leader Reef O~ occurring on the Harmony
FC:H~'m&tianwhlE;\rs the L.~ader RE?ef is nc.:l't developed arethe pol ymict conglomerates oSIl"ldinte,""bedded sabli thic-
Dagbreek For-meation.
Ii' 'and 1~thic arel1i tas cd' the Leader '~('",ef Ztme wh'ich are• (_:>
a rnaxiffil ..ul'\ of 15m thicf~. The preqominantl.y lithicarenrtEi's of the Dagbreel, Formation OV~71l"l.ie the Lehder
Reef Zpne conglomeratas and contain laterally1/I:;
if );
114
D
b) tl1tE:;rpret.atiot'. Sequence 4 deposition resul ted fromunconformity devalopma~t followed by the depositiono'f 1ater.:'l 11y ewt;en$ive 01 :tgomiet c:;on9tom(~rt:rtE'H:;. in an
envircmment $imilar' to t.hat. reaponsible for $equencN~1 depositioh$ Deposition of the overlying polymictconglomerates then followed in a braid-plain .nviron~ment simila.I'" that responsible for sequence 2depo'i:iitiClrh Sporac:l1c er(tJsion of the basal oligol'llict
I
eor.g lomel""at.es Ol:c'o.l.rred. Fol1owin~l 'depQsi tion of the! . i
pOlymic;:t " '-eadG?l'"l Reef Zone coru;~:lomerate$ c:ol"ltirluad!." "
regrel,Hi;it:m rs<;swit.Ii'J,1 in the fl·uvial "depoai{:ion Of
sublithic- an#~,ithiC ,~r~nite$ and l"'are inter'::ieeldeclIi
conglomerates J6rf .:th& ~I'·aic:l-plain.
Pal.aeQc:ur~fl?ht mect$ul"'eml;'mts of trough- and plaj,iar
crossbedding 'f,rom 'the L.eader Reet Zone j',nclicatlW
tranllSport. in ClI'l aa$tarly directions with r,a 1130«sprmacl 01 ,"'eadings (Fi9. 67). Pebble
deC:I"'~a$e11"1 Fi'l ea~terly direc:ti(;'\n aC:I'"oss
Gold Mine (R~ynolds t 19E1-6)
sizes alsoSt.. Helena
a) i:>esr.:rijJ'\.;.iol"l. Sequeru:\:) :3 c::orl$ist5:'> of the unconf'~rmi;l;.y'"
biSised PQlymit::t IIB" Rsef at the base overlCl.in ..~by.1i)terally discontinuous pol ymict c:onglomerates endpebblyar,nitas.
b) Interpratation~ Depo~itian pf the DBII Reef Qtcurred''following unc:on-rol"'mity clevelopm~nt on a bl"'~id-ptainwith· d.po.iti~,al conditions Similar those ofsequem::e 2. Following deposi ticn pf the ":au Reef $ ~n
overClll ct:)ctrsening-up unit of $eq\..u~nc:e'2 ""rani ttl:fl and
o
115
(I
c
{)
Pal aeC)r:ul"'t'~;mt r'eadit'lgf~ i.n ~ren.i. t.es wi thi.n elld Qver-lying the L.Cladel'"Rs~i', St. Helena Sold Mine~' 'Datafr.om thi~. work. and RSYI'1Qlds (ltJS6) and ;J;nc::luGa both
,)
trt:n.lgh .....ar'ls:i planal"'-CroSsbed rrHi~ra$urernent$.
o
o
(I
o
116
interb~dded laterally imper%istent polymic:t con-glbmerates was deposited on a braid- plain.
}}PalaecH::urrerit directions fbI'" the ".1:)1' He!ef? derivedfrom"the or~,.ientation.,of channel% and limited palaeo ....!:urrent data~ indicate transport in a northeasterlydil'"ect"ion (Minterjl 19a2). ihe clast sizes of the liE"
Reef also decrease in a northea.sta"'ly direction"
\)
e) Dsscripticm. Sequence;> 6 is the Aandenk CrClnnel, anero.si\it~) sC:our......and-fil! channeU.sed 'Featu.re containint;_'polymi1"',t c:1as1:.- supported c:c:mglomer'etes at the baseoverlain /by pebbl.y Qremites(~ scattE:!r"ed 0di~mictit~s.tl.ndSl.tblithic arerd.te$. The diamictite, of .10c:mto 7mthicl~, comprises poorly-sorted small- to large-pebbles in aM argillacaou&matrix. The Uppal'" portionof -€ha c:hannel-fill c:ennprise<s inter-lamlnated fine-Qr.:aina.rJ al"'eni 'te" s.:i.ltatone and c:h-aystone and raremedium,.. gl"'a.ined sublithic a.renites.
b) Interpretation. Erosibn ofFt'H"'n'r~tionocc;:urr~d prior +"0resulted from uplift and
the underlying Spes Bonaseq~enc.e 6 deposit~on andtanheed incision in a
tsctonica 11y un~tt::lble enVirOnment. (c:. T. Hooke, 1967).
SmC\ll"'scal.e alluvial 'fan sedimentation of con-glome("'atesv~ . diamictites and pebbly arenites of thE;)A.:andenkChannel 'l:.hl!:)nfilled th(';? ;,;wtlo.edarea and lOCal.
re"'Jork il'1g of· depOsi tsf had to the deve 1 ?ment ofc:ut-and-'fill structures laterally
Continuedimpersistent oligomict conglomerates.resulted in the sUbaquao~s deposition
"bi' l.amiO$ted siltstone and claystone.
117
The A.:andE?hkCh~nnel trends nCH'''thwest to Bclf,Jthea$t
;scros$ the sCiuthern..portion of t.hF WEo11kornGoldfield~Erosional features similar' in s;ize and sediment-fill
characteristic. and with similar orientations to theAandenk"Channel in the southeril portion of the WelkomGoldfield also occ:ur in other parts of the Witwaters-r-and Supl:?rgroup. The$$ chc'lnnel-U.ke erosion featuresoverly argillaf.;;eousunits and oeCUI'" at variousstratigraphic: heights (e.g. Stanistreet at a1., 1986;Camden- Smith, at ei ,~1986; Elrouwel"",1986; Martin andStanistl""eet, 19a~; Riley and Vil""ing, 1986).
(~'It
4.2.8 Sequence 7
a) Description. The Sig Pebble Marker at. the bas. of theAan~.nk Formation unconformably overlies either theAandenk C~annel. where the A.noank Channel occurs, oralter-n<l'ltively the SSpesElC;)naF'ormation. Polymict andoligorniet occurrences 0$ the ai~ Pebble Marker occurwith thicKnesses rang!"; from Om to 2.5m. Qverlying
the lUg Pebb 1e Ma.rker are 11.thic aremi tea of theAand.hl~ F'orm~tiorl which cpntain t.he ~poradical1 y- . '0.
developed "A" Reefs. The hAt! Reefs are comprised oflateral ty-impersistan t oligomict arnall-pebble con-
g!~mar.tas which occur at varying heights above theBig Pebble Mark.r~
on a oi""aid-plain with depositionalconditions similar to ~hat for ~aquence 2 depos$tion.FollowinQ depo$,it.iOh of the Elig Pebble Mar!~ar d~po-s;i<tion 9" the ilt,"'enitesand ~atel""ally impersist.antpolym.ict "PIli Raei' conglomerc:..t.es occur,"'sd. The "A"Raaf. rasultad from period. of stability when therewQrl<ing of p.reviou~l y deposited braid-plain
JI/j
1.18
conglomerates occurred. The "A" Reefs .::lre similar inI!
appecu-anca and cC1mposititln to the 'Midd lSI Reefs ~~hichformed durin~0sequence 3 deposition.
PctliBeocurrent .me9lsuramen1:.s fo·1'"the l:1igPebble MCli"'ker
""re to the northea!;vt "and E?exst ( l(if'l9 , 1996) and fot'the !lA" R'eef t,'"'ansport is in a st)uth-stH..ltheasterly
d:I.r'l::!ction (Karpeta, 1994).
a,) Description. SeqLlI~nc:e 9 is the unconformity-basedEldol'"ado Formi?tion. The;. ~ldorado Formation is anoverall upward-coarsening dapOsit1ohal packageconsisting predominantly of sMall- to medium-pebblepolymict c:la;bt.-supported conglomerate wit.h c:obble-sh:ed cl.ast.s in proximal arsas. Narrow, taxtLli"'4111yimmature $ublithic- and lithic arenites occLlrinterbedd~~d with the .conglomarates, together w.ith2-1.0cm $11 tstone un! '1:$ and rare 5·...<~Oem thickdiamictites" In mo!""s distal dsposi ti~n.!:).l area.strou",)h- and planar crossbedcled sublithic arenite tarsabundant.
b) Interpretation~ Following d~po$ition of the AandenkFormation $ourc:e area re ...juvination and upU ft alclngthe western margin of the ~1.Jelkern GOldfield ("'esul ~E?din depos.it10n of a c:lassic:: upWard-coarseningalluvial fan $aquenca, the Eldorado FQrmation~Oeposition of coarse conglomerates by braidedhi9h-anergy flow occurred rapidly in the proximalareas of the? Eldorado Formatiel1 cat the northernmargin of St. Helena Goid Mine and the southernportion of WestGilrn Holdi,rH,;jt5 Gold Mine. The la<:l{ of an\,.q::lWell"dfining sequence:! at the to{J of the E.ldorado
119
FormCltiol) indit:ates that equilibrium in the depo ....sitional sequence was not reat:hed.
Characteristic of slluvial"fan deposition is thelarge surface area, laci( Of)! .::l.bunclant' mud flow 01'"
and modera t~j~:v sorted- and rounded;' (
1967). The C:hatll"I<s'll.ing, normal and
sieve deposits
Cla$ts (Denny,inverse grading of conglcHnerates .and baSinward chang'sfrom predominantly canglomerate facies to ~re-dominan:;:t;Jv arenite facias algo support an e.lluvial-
~--::::::.:;:::
Tan interpretatiem (c.f. Hoor'C.e~1967; Beaty, .:1.970;
SchumlY\:)1977; I<ochel. and Johnson,· ,1984).
Lower gradiemts arId le$s energetic:: flow resul ted inbraideCl. s'tream deposition on a braid ....pl.ain with anincreasing percentage of are"i tes Qccurring in distalal"'eas Of the E:ldorado Formation to t.he south ofUnisel !301d Mine. ThesedegradationC,\l and accumUlations of dw·.able clasts andhE:;>avymineral;:; occurred, wi t.h the pre$.ervation Qf"symmetrical ripples indic:ating rare sul::t$c:P, ..u=ous depo-sitiun. The d;i.st.;!l alluvial fan tleposits progradeddirectly into a standing body of water to form a 'randelta in places (c.f. McGowan. 1970~ HC::Pher.on atal~, 1987). The t~b latarally perSistent and mineral-ogicaU y mat.ure areni!\ceous. markers I'H::?<S\r ·t.he tor4 (jf
the VS .1 zone resulted frClm short... lived mar'ine
tY'ansgressiot'l$? al tt10ugh similar shel::'t sChl1dstQnescanbe produced by sheet-f lood daposi ts on the d ifS ta 1po,'"tion 01' an C!.lhJvial flSn (Collinson, 1978).
pabble concylomarates tofn doradt'.) F"c;II"mation
al t,hQugh !t:Ihort-l.1.ved
The coarsaning-upwal"'d nature from arenite and sfllfEll1-cobble-conglomerate. in thee '''''e$ul t. of progradai.:ion,
120
occ:ul'"r"edwhich re~ul ted in i.~tertongu.ingCOf1g lCllnerateand aranita facies occurring. Short- lived periods oferosion in the I::ldorado Formation resulted in theformation of unconformities which saparata the VB 1,VS 2-4 and VS 5 zones of the EldOradci)iFOrmation.
Tr.:lnsportdirections TtlI'"the VS 2"'4 i;J.ndVS 5 zones ofthe Eldorado Formation indicate tran~port in asoutheasterly directitln (Fig. oS8a). Trat\$port in t.heVS 1 zone is in an eeasterly direction (fig. 56b). Thesoutheasterly andcoincide with the
easterly tran~pc)),..t directionslateral 'f.a~ie~f changes in a
southeastel.-Iy direction Berb.s 9t. Hehmd and UniseX
Gold Minas, with decreasing pebble sizes and anincrea~e in the textural and mineralogical maturityof clastsdirection.
also a southeasterly
Sediments sim:U~I'" to t.he gldclI"'a.c!o· Formation arepreserved in the Abitibi greenstone belt9 Quebac.0and~I'·e :i.ntarr,lretad ~s high gradi~nt allu.v.l:al fandeposit'.::; (MUeller and Pimroth? .1.9(7). These fandeltas are u.sually confined tQ tectonically activeareas such as the margins of fau.lt-bounded intra-cratonic seBS and lakes (Ethridge. 19~~) and alongthe margins of many Bctive tectonic basins, •• ;~ the »Hornelen 13asin, westf.!wn NorwiaY «(31oppan and Steel ~19(1).
4.3 DEPOSITIONAL MODEL
rh. overall sequence of evants that lad to the depositionof the Harmony J 'Oagbrael(, $j:.W~s Bona and Aandenk
(Fig. oC:;) II The
n :;.:20
VS 1n ;:; 4
121
N
N
Trough-croBabed readings from arenites of the Eldor-ado Formation, St. Hslena Gold Mine. a) VS 2-5 2ones.b) VS :I; :;ec:\r'\ew
122
NOT iO SCALE
delta
Approximate lo~ationof St. Helena Gold Mine
::'if;lur~ 59: Sc:h!;lmatic reconstrLlctibn 01' the deposit.:i.o.-,ca1enVi~(:H'1mGlhtOT the 13as'.al Reef.
",\
flte deposit.ional environment protlosed in t.his st.udy iasimilar to t.hemodels of Minter \ 1<1759 1<17e3') and Ven"szGen
(1997) and to aspects of tha models postulated by andSmith and Minter (1980), Tucker (196.0) and l<ingsley(1984) for the Wit~'\IatersrandSupergroup.
depositi.onal e;>fivironme'"'ltWClS on the distCll portion of abraid-plain of a bejada with sediments derived fromdistant alluvial fan sedimentation. Thi. braid-plainsetting remained simi 1•.1'" from the;>HQlrmon~~.f;_"to the AQlndenk
\.)POl-mations but the eneH'"QY of the system int:reased with
time~ Deposition Of tljiaoverlying Eldorado Formation wasfrOJIt an alllwial TCiilMwhich pro(;:lI"'adedas' "" ~,",n del t.<a ird:o
a marine .nviron~e"t (Fig. 60).
124
NOT oro SCALE
F;al..llt scarp\
f'.ifln Delta
~~T~an$itipn Zone~. ~ Lal'"go1 body
~ of water
(,
Approximate loeat.ion 'of St. Helen;';l Gold Mine
\ \\
E.;"q4re q.o; Sc:hematic rec::on$truc:tion of t.he deposi t..ic1I'1C:11envit'"onment or tl1e Eldol""arlQ ( ,Formation.
it <,)
\\
125
5 SVNSED!MENiARY TECTONICS!)5.1. INTROOUCTION
Some of the: con~f::7qt.H~nc:es of $yr'l!~edimant.e1'"'Ytectonic$,
i. e. tec:t(;)nic: .:lct.:i.vity c:&~t~mpC:)I"aneouswith $edimerd:--c I',
ation, ara tha" formation of unconformities, the variation5,1"'1the thickness /::)f sad im!::'!tIta and in same caSQS the!
development 01' MJn-unifol"'m lC1ltar$,l a.nd vertical fa·c.ieseswoclatioiis. To ~5Se$$ the) e'ffect of syr'l'sedimentaryt.ectc:mics the C!l-S~,$lJ(llptionis mad~ that the c.ls>):)osit:tonal
"
SUI"'fiSC:e'~ is flatt.at 811 tim~s anti w.l.riat'tons in strati-graphic thickn~$sreflect .Rither subsidenCe o~ upliftwi thin the b':h'ain. AJ""sas IIlhich are rppicll y $ubs.l,.d1ngac::e;umuate thil::;l(.tlH''' $edim~r,~el""'>f sequences whi 1e al"aas
which are rising relative to this, accumulate thinner
It:':i.thel'" se)qul::lncl!:!l'l i.ll'" expariem:a e:lrosion (M~Ca''''thy et {i,)l. ~
J1'">6i) • Repaatel~ ",p11ft or $ub$idance in a. specific::: areaq c:~use rapail!.ted anoma.liG.r$ .in thicknEl1$!:3 in that arG?il•. b/n~mic natul"'a of tectcmi,::!:'S and c;fiffaring cause$ of
upl ift may res\,l.lt in an arl"\~\of rap~at.ad wpU. ,Tt tomigrate l.te~ally with time.
Sym~edimantary uplift along t:he waste,'"n margin of the
Well~omGoldfield occurred MpoJ""iadical1y durin <;a ciapositiofl
of the upp~r-:\,JohC1nne$burg alnd 1'urffontein SubgrouJ.:is andcorltinued ;hroughel\.rt the c.laposi tion of the ijldoradoFormation (WinteJ"", 19640; McKinney at al~? 1964, Oliviar.19651 Kingsley. 1984). Tha thickness variations and
facias relationships Ofillustrate the natura
aedimantS3;.i-
hdveof
Leen l.!$od to
lSyn$stlimemtary
Halena Gold Mine. ~
126
'J
5,,2 iHICI<NtZSS VARIATIC1NS
Syl"\[email protected]"'Yupliftifre'.l?ulte'd in the formation of UI"\I:OI1-
fornl.:i.tit:?s ana t.he thinning of fOl"'matid;~~ in ~ we$te~ly\....... __
dil"'ectidi~.~.r:?sS St. Helena Gold~'-/
sub-outcrop l::n,;.;twea;?1'ltl1~ Sas.;!!l ReefMina. The an91e 6fand tMa top of thai
,;
A.sndel1t< Formstion is 2.111 in the southernH~len.;!! Gold Mi.na C,\nd 1.20 in the! northernHelena Gold Min~ (Fig. 61).
,portion O'le St R
j:)elrt:l:on of cat.
;\''''' ". " \ ~S¥n-$~dimental"Y tCi?c:tQnics peau! ted in comple);{ Slub-outc:rQPpositions in the northwest.ern portion 01 St. Helena BoldMine (F igs. 62 s? band E:\' ;tg • <:;,3). The l_ersd!:'11'" Reef i.,struncated by th<:> "Bu Reef in the cent'''''sl pCirtion" of
aeet.iQn 0-0' (Fig. 63.) whel'"'s uplifted L.e"-'laer and SascOll "
Reef$ OCCl.lI"'. Soth th~ SalSa1 and t..~',,:u:.ierRe~,;f$ (;ll"'(t! poor 1y
developed in this araa but the IIEII Reef 0 is t1ncH'Oalousl)l
thiCK., Sec'Uont; e:....e' a.nd F....F' (Fig. ~f' a ~ m) er~ con-',,,strt,u~tsd roughly perpendic::~lar to $tr-;:'I(.~. In bot.hsections the "1311 Re~f trwnc::ates folded 13<asal and '_made!'"
RSler sediments. In the western portion o'fl sections e:-e'and F-F' the lIa" Reef r~sts unconfo!"'Mably on thE:; WelkoltlFormation CUF 1).
5.3 FACIES RE~ATIONSHIPS
The l:3asal R'<:?ef has both \,cro);{imtlal facies (oligomic:t andif
disseminated carbon reef) ~nd dist!!ll faeies (polymic::t
$Quthern reef) Qccurring aleng the present Sasal Reefsubou'tc:rop ,:loss.tiot).. ine I..eader Reef, 8ig Pebble Mal"'ker
and flAil Rel;'?fs,also hava oligc:lInict reeof facies cn:cul"'l"'ing
il1 the v.i'.einity of the PI"'!9\:sGnt ct;!!.)' be\':iin mel"'gil'l a.nd
showinQ ne spntial relatiQne~ip to the basin margin.
127
Sc:.hematic:: e~st/w~$t. ,\!Sec tiCH'i$ of St.. He'llr;!n~ Gold i"tin~show;ing the onleJ:lping natlJl""O of the 'formations endapprcmimnte l,Jt'1cQnformity anglos.
/iLf
(;
12a
o10 400
------- ..----,.., 97 00010 SOO 10 BOO
1,1
97 000 97 BOO
..541 2647264~
24""~:n\ u
\10 aoo
_..-E'E
o
-r- ,Pip.
11) 400!O 1100
o
~ I'a" RO\!1'f $\.,lbouterClp'f.,
~ L..eilder R.ee·f $Ubc;n,ltcl"'QP
~ Ba$al MS?af $ubQ~.rtc'l""QP
/:'j\-!'lJ')'f. ,:i
: ?lilrl of 'the I"1Qrt.h""'west{;?rn pCli"'t' 0'(3 St. Helef'lCl Gol~Mino~' en1~1"9e]dfrom Fig. 21" e) Borehole f'lU[I1i:lOI'''S''; ilfldthe 1oe~t.i.i:lfl of smt::tiCH');$ £)-0' g ~''''~: al'ld F'-F'. ,I;S 1
o f1lat't {:ai 1~ht) !3yi.:)OU1:C::'''QI',) pwo:i,Tion Q'!( t.h,e aMI$" .:-.I..r.:Hldol'" Reefs D{'j<Hi"l$1.i;.tho "all ~q(,r,
129
o
SOlJTHo NORTH0'
HAFiMtlNV F'M HARMQNY ?N
M'i':: '(:;4~~ =~'H . j'~. .' 0,. 1(193 teat ~9::l9 ~499 II ..==..:r:;·[C7~~$x~~~ 1\ (~.,!;", .... ;t.;.S4a~~~~~~~~:u:::t:=lt.l""'~""""'ll:.l~ ..~~.;n. "'tl1! "gS;.
2r PAGaR!:r;;I~FM t..~llolffi f\tZtu:
(,)
J'.\oj ~!
Rtll!MiNCS '--~"~.
.I.9:t9 aQR!;HQ~.Flc::J AA~Nlil! (r::j
~Wi~·c:t.'!NGr;.Otll;:R~"lt
U9ur~ .6.$: :NQrth I sC)uth s'tt'"il<e s~ctiQn p' -0 01 the Hb.ll"monyFormetiQfl9 t}s.~bre~l< ..~ FCU..../'(h!.\tiQn iill'l..d tho "IS" R¢PI'i'l'flI.:l'Thetop 01: t.he "a" lieef ('nes ~!een usecJ I~$ O.;atUID? t.ell:~t;J,onis $1'1I:;H'II1'1 ;iq" Fig. 62. (Not,e ver'tit.!atl exagg~""a'i:;iQn) ..
1)
130
_II
SOFlSKOl,.tt.
MENU'SCClNf3I..ClI1SFlA'f'S
PAGl;iR~S:', P'~jI.SAt).~R flSEF, ~IIlOC)
HI4RH.?NV FMI()AS~~Rl!EFWf!l..t<::lM FMcur 11
1
1)
HARNONY· Ff1
SOUTH-IUISTF"
sactions 01 the ~ov~rl'lingResf hasis shown in
5.H~cti.c:;)I'l t:;; ... E· b).(Not.e yt';lrticC!.l
F'Ql"'m.ations!Jt'lcc:m TC)l"'m.i t~. "h~ top of
b~ 1 usod as ~at 1m. L.ocation ofF'i'J. 62. e) $t.:)\.1th-west I north'"Nortf"'>-t.-)<r;:!!;lt I sQI"d:.h-~aat sectionexag9~('at;i.tin)"
Pip<'And thethe Ua't$QcticmseastF-F' •
I"'lllonyR~e"
131
'.)
Ul1conformi ty-bassd conglomer<=lt.es.on St.. H~lena Gold Mineshow' a b.road cH;1creaSe?in textural i1lndmineralogical
maturity up the $trenti<;;)raf!lhy~ fl:"'(;lIn the tI'ligomJ.c:'t $tflcall-
pebble Eas.::.l Reef ttl the large-pebble pOlymict ~ldC:H"'QdQ
FormatitlM conglomerat.s$.. The r<1ltio of c:c.mglomerate to
&renits also iner~ases upwards in the stratigraphyp
clJ.lmineting in the conglomeratic Eldorado Forma.tion. The£UdtJrado Forma1,:ion i$ a br'o$ctl Y upw'::'lI"d-coarsllIlning
\$ecjI..1ence Y'Jhich occurs st.rat;igraphically at the tOl"? err the
Wit.w.;aterS;I"'¢lI'lcl.. $up~rgr-oup... which is also bl"'oadly upward-
c:oar<$sning.
ihe Middle Reefs occ::ur wit-hiM the wac:kes of t,h€:llMiddlingquartzite .;and contain lal"ge ......$cale soft.-$ediment deform-
a.tion il'ea.ture$" P:i.~mic:tites ocl::'1..trin t.he #!icllndenk Cha.nnelt-
;; • 4 SYNSE:O!ME:Nl'ARV rE:CTONtC I NTE:RPRE:iAT ION
The pl1'giseru:::e of a.ngula.r utlconi'ormi ties .al!;:lng the western\.1
margin of the Well(om Goldfield, which become di$¢on-
form.ab.le irl'to the ba.sin l! i.ndica..te that upl ift decurrad
eh.iring sedimentt':ltion. This ma.rginal uplift occurredby rotation and upfoldin~ which left the basin interior
relatively undist.lJl"'bed (e.9. Ftibap 1976; MiC!l111 197e).AreaS;; of r~)peated subsidence or uplift. rt.;:sulted in
c:\nomalies in thickness. The ol""ientation and location ofthe Aendenk Channa1) in a broad bancl ac:rO$S thE') sou.thern
portion of the.;>~-Jell~om Goldfield is. an ind~t:a.tio.n of at.~c:tonic c:o.ntl"'ol.
The upX';Lfted mClt.eri&l W~$ a SOUr-cdl of sediment.s, par-
ticularl.y' during depos.l.tion of the EldClradc.'l F·ormatit:lh.
Tec:tonic in$t.~bi'l i ty at the tims of tiaposi t.;i,QI1 tl":L9gar~d
d$bris-f! O~'>J$ ~ re:$u:l t.ing in thl& TtH"m$t.:i.ont:'d~w~c;k(1;1s01 the.
:1.32
'~ ,\Middling quartzite .:\0d diiJItnictites 11'"1the Aandsn~ Chann~l~nd Eldorado Formation. Saft-sedimant deformationT~atul"'es al~C) I"'esulted from teetonic: instSlbf'1ity. On abasin-wide scale diarnit=ti tt;l>$ .nv-e report(;!.d fot"m various
laCal,:i.tie&.1.\ndst.t"'atigraphic heights <7.Indart:) interpreted
by StClnill?treet at. a1 • ~ (1988) as bein9.n .re:sponse to
tectonism. Deposition of spec:ific facies was not related
to ths pre$~nt western l'Ilarg'in structure as there is no
rel<illtionship between speci fie: f·".\!:::ie?sof the :SasaJ.Reef 1
the LeadsI'" Reef ~ tUg Pebble Marl<.ar and 'hA" Reefs and thiTI
,present daw subQutr:I"'0P positiC)rI,oT these conglomerates.
Diff~r1ng .'angles Of unconformities between fc.,.,·mationsir'l.dicatS? \i1ary,ing rat.es and duration 01 upl ift oc;cul'"l"'ed
aIt.')ng thG! W\9$ tern a.nd sOU thern mel'"gins of the We1kern
Soldf iel:d. OCnthe nOY"t.hWe$t~p' pOl"'ticm 0'1' 6t" HeHma Gold
MinS?syn-$~d:i\merrta.ry upli 'i\'~ 01 the basin margin was mor($!
r'&pid them irf the South a.nUwas concsnt''"ated in a narrow
area lSOOmwi.de. rhi~ area 1~ charec:t.eri.sed by int.ense
uf;lUft arid. Told.ing of th~ entire Jonannesbul"'g and nJr''f-fontein· $ubgl'"c:lupSpWhere truncati).;.\n of more than 1300m ofstratigraphy occurred during the deposition of ~he
I,:
Witwaters ..r~nd Supel"'gl'"Qup. Folding and truncat.ion of the
"13" ~eef i.ndic:ates that synset:limll\'ntary tectonics ~lsooccurred or'l a local.ised scale (100' $ ffil$!tl'"e$).
Watel"'srand Supergroup occ:urred wi th time
in a vertical decrease il1 textl..ll'",a.l
A gl'"adual in,c::rease in t.hti' tectonic activity 01 the Wit-which resulted
sedimsnts. F'o11owir1g deposition:)
ofmaturity of the
the Wi twa t~r$I'" andSupergroup, c::ontinued tC':?c:tonicac:tivity led to fracturing
of· the crust and the ol..rl:pouring of the Kl.ipr~vicl\?rG'berg
lavas af the Ventel"'sdorp '~upal"'group. lnitiel lavadepcSi,ttion wassedimentetiQn.
concomitant
1\
The cause of the uplift alan; ~ha we$~.rn margin of theWel.!~Qm Goldi'isl.d May naveL beer' differentiilll movement of
, \~ ..";}
It:!lrge basement bloCK;$ which shifted under a r~gic:.maOcompressive rl.E1c;3imeo Slcc!(, m8vemsnt resultsd in $m~11
displacoIDc;,mts over largl.!' .sreels but with the weSt.En"'"
mCllrgin q.llpresenting e nal'"'row areC'1of c:om'plex and intl.!'n$e
dSTOl'i"matj,on., The tectt7tties et'e not. simp1y vl:tt ...tical but.
consist of bath episoc!ic upl,i ft Clod liilteral movement wi 1:.11bloe;:i(s pivot~,(,l," in varit:ll.\$ directions about .a fixed point 0
\"-1
(Myers et al~~ 1990).I)
(/
3Goldfield w1i;lre$;.yn·"sedimt:1nta.l"'Y and cc::u:npre$s.ional ~ actingil"l an eas:rt-W6)tSl;dil'"ection in tn,1]? vicinity of ~t. Helena
Gold Min~ (Fig. i!l5). Not'th- t'lQ&~nJ::l"'ending fQld~hg t!llOI'l9
the western margin o'f Sc~" Helena SQid"'M~ne did not affecte ... \::Z~
sedimep'bation during upper JohcmMesbut'g- and lower Turf-font.ein Sub~roup de.pos;;it'ional., times. Data from tJ.t!1;i.$study
indic~te$ that the ovsratl int~nsity of tectonic Cit;tivityincrea$sd and the locus cd' the tectonic: ~I;:tivity llIovedprogressively inIMa.I..t:!s toward'$ the basin eentre w;i,th time~,to ~ive the effect Of a shrinking ba.1n.
134
6 ..iL_Q ·1.000
,.,."""Er~;tim~tsd 5ubout.c::rop,/ position
Figure 65 Schamatic fence diagraM, St.. Halana Gold Mine. Thecompressive t.ectonics, .westarn ma~gin structure andunc:clIITormity .angles which dac:raa!;1.s southwo:)'l""dS,aratshClwn. orne El.r.:lclI"ac!o F'c)i"'mat.ion has bee." used as datl..lmand tha H.::trmonys Oa9brQak, Spas Bona and Aandanl~Formations ~ra shadad.
· ---\\ .
135
6 CONCL.Uti!ONS
The WitwCitersrand Supergroup, comprising both Wt:?st Rtal"ldal"ld Can.tral Rand Group rocf<.s? is undl':!rlainby basemantgrani.toi.dsal"ldoverlai.n by the Vel"ltersdorpSupergroup andthe I<.arooSequence, r-e5pectively, on St... Helena GoldMin.e. This stratigraphic and sedimen,toloqic.'.l1study isconfine·d to the Harmony and Dagbree.k Formations of theJohal1naa\ou,rgSubgroup and the Spes Elona, Aandienl~andEldol"'adoFormations of the Turffont.~in Sur.)grouplpwhichtOlJether compr.ise the Centr.al Rand Group.
An undel"'s'tandingof the overi;!ll sedimentary and tectonicj:)l"'oceSSescrf; the Joh.:;.tnnesburgand TurffOi"l'teinSubgl"'oupshas been gain.d by studying the total sedimentarysuccession rather than the few gold-bearing Unconform-i' I~b~sed cong lomerate$. Tha Wi twcatersraNd st.l"'atigraphy
11at.St. Helena Gold MiNe.:1.$incomplete ~nd represents a
prE.'servedsequence of Unconformity-bound units.
ihe Basal Reef has yielded more than 80% of thl:S?goldmined to datE.'in t.he Welkom Goldfield and is interpretedas constituting the basal unit of tha Harmony ForMationand Not the uPi':l€~rmost.unit of the Wel!~om Formation. The
Basal Reef in the Walkom Goldfield is divided into theSasal and Stavl1 faCies ..On st. Hel1:na Gold Mine tha SasalfaCies i.s in tur" subdivided into the oligomict andcarbon seam reef +.ypes whilst the $teyn facies issub-divided into 'ehe polymict. southern reef $ the mixedreef and the arenite l"'eef The Harmony r-:ormatiohalsocontains the Middle Reefs which occur at varyingstratigraphi~ interVals above the Basal Reef. 80th theMiddle Reefs; of the Harmcmy Formation and the "A'l Reefsof the Aandal'll<Format.ion consist o·f dist:,"ai:ii1!c:har"nelisad
136
oligomict conglomerates locateo at varying stratigrap~icelevatl.cms;•
The ~e.de~R ••f at the base of the Dagbraek Formation isdivided into the oligomict Alma facies. referrad to asthe Letader Reen', arrd the polymict BeoSllia facies,. reter-
reo to as the Leader Reet Zone. The AC'lndenkChannel whichstl"'atigl"'aphoicallyoverlies the L..eade~r and "S" Reefs on
St. Helena Gald Mine is e multi"'sta~~e erasive StZoul"'-a.ncl-
fill chanhelised ,'*',eeture.•ihe orient~e..titm and location ofthe A.andemk Chanl'lel, in a broad ban(~ across t.he southernpo I'"t$.on of the tt!ell~om Goldfield, is an indicatic:m oftec:tord,oc;\~'control•
On St. HalenaGold M~ne on~y the W.lkoffi (southern) faciesOT the Eldorado Formation is present and this is sub-divided into t.he unconformity-b<:ised IJS 1, va 2-4 and IJS :;}zones. The r:,udOl'"ado Formation coarsens-upward on at.Heie:!na Gold MinE;> .;and rapid facies changes occur ':}'crossth. min., with conglomerate being replaced by arenite asthe dominant fac:i,es of the Eld(Jrado Formatiqn in distal
Deposition of Harmony~ Dagbreek, Spes 80na an~ AandenkFormation conglomerates and arenites occurred fluviallyon the distal portion Of a braid-plain in unconfinedchannels. The I'"e-worldng of pr.ll ymic::t cong lomerate:;resulted in the formation of oligomict Fonglomerates~ andthe deposition of sand by traction c:u~rentB resulted in
"trough- and planar crossbadded arenites. SW8sh-strati-1ic<1\t1onduring local is-eeltransgt"essions resul ted in thefOI'"O)ationof horiZontal laminations in the Top of Raefquartzi to.. Pebbl. y arenites and massive wG\ckss res'.Jltedfl'"om tl'Hass-emplac:sment by gravi ty ....f lowargillite-deposition occurred during
deposi tic;'lrl andperiods of still-
cQ
137
stand. Extensive tran.gres.ions are recorded by thedeposition of argit11t(;!.H:' above unconformity-based con....glomerates. The deposition of diamictites was a result Qfepisodic:; melss-flow movements. A. transgt"ssS:!,oh resuU:ad in
th.;?subaqueous deposition (''l ai~g.illite$ and dicnmictitesof t.he A.:mdenl~ Channel. OeplPsition of the Eldorado
IIFormation oc.:cur,"'ed subaerially:' on an alluviC!.l fam which
prograded as a fan deltc!1 in/Ito a marlne eJnvircmment.Marine incurs!"'hs re'I)(::'Irl<eddist:ial pOI..tions of the fCln anddapositad Oligomict. conglome1~t.s and laterally con-tinuous quartz arenites. I
I
IiAngular unconformities alQnQ~the wastern ma'~in of theWalkom Goldfield indicate th~t uplift occurred duringsedimentation. The uplift waJ episodic and occurred in
jidiscrete pulses between periods of sedimentation in anarrow 1500m0wide area with th. intensity of uplift bainggreater in the north than the south 01 St. Halena GoldMina. The intenSity Qf tectonic activity increased withtime which reBulted in a vertical dacreaa. in the tex-tUral and mineralogic<\'!ll mCllturity of sediments and t.hedepo~:>it;i.orlof a generally upwt:.l,..O....c'ocH-seningsedimantar'ysequence. Tha uplift on St. Helena Gold ~ine resultedfrom an east-west orientated compressional tectonicregime and the locus of tactonic: activity moved progress-
ively inwards 'towardS the basil' elE.!ntreto give the e'rfectof a shrinking basin.
Synsedimentary tectanics resulted ~n anomalous thick-nesses of sediments and the uplifted sediments were
re-wQ~ked a source of further ~e~iments~ Synsedimentarytec~dnl.CS al$Q resulted in tht;:i'a:position 01' w~c:ke$ofthe Midd 1in,gsauimsnt$ o·r
quart~ite,the Middle
the .actonically diaturbedReefa and ~n the .edimentary
sedimantary da1a~matidn in the Aandanl(
138
Channel. The formation OT unconformity-based oligomict.
!';Qnglome,'"ate;:;which conteih gold mineralisaticu"I r(;i1$ulted
from syn-sedimentary tectonics. Increased gold ;r~de. are-, s.
related t.o occurrences of carbon and round pyrite in the~QnglomeratQ matrix.
The fB:~ias distl""ibuticm Q·f the Basal Reef occurri ..ng aJ.ong
the wester'l") margin on St.. Htl:!lena Gold I"I.lps has no
rlS'letic:msh:i.pmargin feu.d, t.13as-a1 Reeil
to thE;' l~n"esent~ loce.~tion of the wester-n
The 1~.eC:Qgnit,:on that depQsitic:m C)"f the,!n !i
a;,nd pverl ying un~<onfQrmity-tlc."llsed economic!;
occurred to the west of the pr"esent.-d~y!;
basin margin !'Oi! the Central R;andGroup is important. The.,
PQssibility exists that nat all of tha Wi~w~ter$rlndSupergroup s.edimants cdepa$i ted to tha wes.;p of theprS$snt.-'et,s}\> m~rgin have been Llplift.ed ani::! eroded.
Pote:>J''lti;al for preserved Sasal Reef, LsadS'r Reef endpossibly "13" Reef ssdiment$ theu'efore exists in areas t~1the south ;and we$t of St. Helena Gold Mine. The PS·G/....•
servatit!M of sediments could occur either in a syncline,Similar to the western m~rgin syncline of St. Helena SoldMina or as a down-faultad block~ The orientation of such
a preserved .feat.uY"e wC:HJ.ldbe north ....south, parallel ttl the:prE:i)sEmt-day $trl..lctwrss of the Welkom Golc1f:i.eld.
(J
139<)
7 AP~S:NOI){ 1.
o
u$ing ~ p~r$oMal Cit ut~r ;;\t'ld a spr(;!lC\Qsheet filpj:llic~tiQfh1 . ... Ii
The i$opachiMg peu::'li.:ags uti lized > .c:r$s:tli$)'i::>high r'E1so1uti(!lM
'two- and three- dimen;;ional graphics by computing t\'1
regularly 5~~ced g~id of data points 11"';1'11irregularlyspaced data. Cornputeri.ssd isop<!lch cohstruction hCl.$the
advantage tl"f' detrx;;ting and smoothing l.rg~ irl"eQularitiesr.
in thicl<I"Iess af 'formatit;:)hs due to Taul ting,> <$hd also ofbeit1~ urtbiasl.$;'d. An inver;;;e distance method of int*~·-pOlaticm,!and.?4fi inverse w<;;!ighting
distance $qu~I"'ed) W~$ l.I~GH':!. thepow¢;!r of
Cj1.Jadrant.):)up'licete data'..j
Bize of 20 x 25~$points were averagad out and a grid
creatl:ld (data ~erm.itting) to form
C:dntour map of i!Vl1lri~ble sca.le and cC:II"figurcttiC)n$~ The.',\.-:':'->:
eon tour 1ines were', smoothed using '$~l ine .in~~""pCllation
wi thin t.he grid cells"
o
140 .,
8 APPEND1)( :2
The summeriss 'Of $urfac:~ borehol~s wet'!:? plot.ted using aFortran IV computer program (McCarthy, 1981) run on the
"
tSM mainframe of the University of t,Me !tlitw<;ttersra,ncl,JoManrlesburg. This program ha\':)subssquently been modi1ied
c>
by Mr. A * a. Ci~d1e <.:11',1Dr'. B. C. Cai rnl;; ross A The prog r'am
provides a gr.phic plot of strat.igr~phic thickneBB~• elev<!Ition, secH.ment.arystrul:ture c:'lnd grainsi,ze data and
a110"1$· ,comment$ tQ bt':) aQded. tn,1ut Of delta are by alpha-Co
lOcation of aU borehole!S logged have been plottecl (F'i(J.
66) and the 5uJ,l'I1marised logs are pre¥l.H':?l'Itsd below.
u
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51' 11 1'01.1 nsp. All. HI CII nEE~(}
~ r--su 1111 L·SL An~". L OfF$ l;j; ~$11 '7 Sl!ttAnllll 101'
D"
o (I ,CONTINUED If'
\\
IIII
167
BH V 11 CONilNUEr:.
loiS (.SI·or.,s l\t.l~
·GQ'.7a ec.reM (1.17 -ao.47 GO.irsv o.n~ '~lJ'") rn.taS(! Ih4f ~ 0,$1 '';0.57$1)' \.to
06 0,';0'11.7$ 71.15
~l G.OI)"7;;.05 fa.os
sa -rs.es 111.~5<1.-_05
"r~"Q 1~.tO
q~ 4"'11Q
·O~;.:1Q 03,SO~~IoS4
·o~.al O~,O.G~ I.~l
"&,.4$ aG."-~no 1<41
61"at .U6 aT·oe
i).~t -an •• ~ ll1.J3
(j
FAULtE.~ repPI)\.T ~i'c.1';.\!Lt£O 1(1('
111' mS? 11s.u til'!CS Wtell ~,5P tli'fl)~ 1).'1~u 1mGil Jj!tSP U-SU I{fl
ell IISf' !!II
G
Y QY 1. Allel~z. O"~AIILii' SP(l'Sf~Y .L·~ ""IEII Vi:t 1'1t!Ullfvps. Ufl'Ett ~ • PULY. ).'Loutttt •• OLIOOrO~f. ~n/s '\111l1::PC'll '/
t~l S~eC~L.O L.I.\Y $~ AnEtl
Sf' rill rOLYnAS", SL Alleu~ !l ;.n;u IITlllllSU l-S\, M'1ln!}' 1I1tnVS1V~
SQ ausu nu taR Que '..') tlR~
~~11\'1 'iiI. Antll, I'CLV srliC«~Ulo. ~ IlP !
1:S< Hit PO~f. P~. I) Ar.!m NIHiX aASAl. "~~
o
~\ 168
9 APPENDIX:S
Numerous Ge~\ifjjif1 t.mpublishG:d intE'r~al bUlletins eoncerningI'
Stu Helena Gold Mine h~ve been cO,i'lpilsd t.o d""te butCi
littlta' information f.l"'om such bulle-Uns .heils been
pub1 ished. The bulletins documemt the;: sedil\lSI1t.ol.o~V ""gd
structure of- St .• Hs-lena Gold Mine and the most not<$lworthy
bull~tins a~e Clut! ined belC:Hr.1~
c
i:l) . $edim~ntt:ll09Y. PrClperties of the Ada l'1a.y R~ef IrJet""e?r v ,
Ot,cumen ted ',I'.)y 1\,1iiaYI1hoan':is (19El4e\'l1) am::! the I n t~rmed ia te
Rc;;>e'f by TU:n')~~if"lgton Cl9Sq). .')5he (/Bi'iI~\;aJ.,i'; Reef fac:ies\\
types em St~ Helena Sole;! f't1.iiJl~"wer~ d6t:w.1ente~Jd.. . " .
deseritted obY 110ubray '(~f90~~ v~ppe \, (1953),. Eird
(1954) 5 Potgi.eter 0.964J 9 T~e~djje {~978)~. Han~d.n• ." \1
(197(7) , Rossiter: (196,1.)~' and Mount (1ge.:r). ''1ount',> Ii
(19a4) completed a'de.taij,~d study of the S<S\$ilcitllR~S!f •..0-,;.::0 .\t-' .,~') ,!-,
1h$ Mi~:(!fis< Rela-1fs "'were,; 1, d9fument~d by l<leynh~ns
(1984b), Reynolds. 0.985)_ ~I'd "1;:11$.5 (j.9~12). ~lJ.t.$ and
e?iclley (19aa) s.tu'tU.ed tht1' Oagbre$:~~1 xttJrmtSltion on
Unis$'i Gold Mine. The !lA," ,~,Re~f$ otV,St~ H~larl~ GOld
l'-1ine were documented t Ch~pm~n ,,(19133) • \1
b} Structure. The eomplel'( ,structure and secl,j,mentology Pi'
the western syncline t;;If St. Helen~ Gold Mine w~s\". j-~'
itlVe$t.i.9~ted by Pot.g~,etQ!r (1963), Al9ie (1974) and;-:;
Tunr •.i.ngton (1996). Ii
169
Algie? F. (1~74).. A re-apprai$al of the WE!Sltern sync l.inson St. Helena Gold M.i.rH.2~ GencoI'"Unpubl. into Bull"
26J., l,IJelkom, :SPRI.
Allen, J .R.L~ (19$5). LOOSl~-boundary hydraulicSl ar,~ fluid
mechanic$ ssl!lilcted ac:lvC:incessince 1961. m 13rench-i'
ley, P.J •. 8< WilliamSl? B.P.J. (eds.~. Sedimentology:
Recent develQt'Jl'nent$ and appl ied \aspects. Ellacl~wel1(;\
Scientific Publ.ications, Oxford, 7-30.
Allen., P. (;1.991) • $I:)diments and processes on a small
stream-flow do~inatE!d Devonian alluvial
land Island$. Sedim. GE:!ol.,2'1','31-66.
Anadon, P., C<=lorera, L., C~lombo" F., Mt:lrzo, M~ & Riba,;,
O. (1ge6) • Synteci:ohic intraformational unconfo!'"'l'0....,-,
itie~ in,,:~_lluv~a.~, fal"l deposi tS$ ea~\tE!r~g Ebro a~$inmargJ.ns ~c'\ ¢ Spain). ill AllE:!n, P.A.~· Homewood, P.
- ,j
(r,:'ds.). FI;:)J""elandb,/.asif1$. Spec. Publ. into Ass:
Sediment., f. alad~well7 Lender», 259-27~'1..
Antl""obws, E,,$~A.. (195b). The 01""ig11'\ of the Aur-ifal"'ous
Reefs of the Witwatersrand System. Trans. g~61. Soc.S. Afr ..? 59~ 1-22.
Arm~t,on9, R.A., ~el.iefjlE.A.~ Compston>!!W. 8< Williams,r~s. (1990). Geochronological constraints on theevolution of th(~ Witwatersl"'e.nd 08$in 1 d$ d~dut'"'ed
from $ingle zircc:m U/Pl:3 iO[l microprobe st~)dias. Ext.
Abstr .. Gecn':;ongl"'. '90, GaoL Soc. S. Afr, Cape Town~
24-27.
17'0
:Sail~y, A.C .., Law, J.D.M .., Cadlell A.E • .& Phillips, G.N.
(1990) e The Zandfcnte,in Quartzite; Formation, -athe CerH'.ral R.and Group,
Witwaten~rand Sup~rgroup. S.. Afr. J. Geo!., 90/1,1~5~146.
Salazs, R.J •• De Vries Klein. G. (1972). Raundness-mineralogical relation!:; of sor(lIa .intertidal sands. J.Sed. Pet., 42/3, 425 .....4;~::s~
"l..ower Cambria." nbrth Norway. Sedimentology,
Beatel"', C.D~ 0 ..962). The sigr';;.'f&e.anc:e o.f unconformitiesin the development t::)f Witwat~rsrand gold and uranium
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Beaty, C.13.. (1970). Age and e~timated rate of aet:u-
Inu,lation of an alluvial ian 1 White MountairHaI,Cal.iforn;hil,. U.S.A. Am~ JOUl""'. ~Sc:'i'f~ 269, 5Q-7'7.,.
Elird, HJ-I" (1954). NClt.eson the :BesetlReef at st. ~lelen~
(Sold Mih~$ Limi.ted.. Gemc:ol"'" Unpl ..lbl. into Sullo lOS,
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Blatt, H.~ MiddletoM, GL 'Mur~.y,A. (19BO). O~i;in of
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1Boersma,!'il~"'1 ,''l ~"".-C\ of intert:tdal shoal depo!;f1t.s in a Meso-
~ 11 \',
tidal ,.~!:1'I,~:l;..!ary. Sedimentology, :2S, 151-17-0.
171
Borchers, R. & White G.V. (;1..943). Preliminary contribu-tions to the geology of the Odendaalsrust Goldfield.Tram;;. geo.L Soc:. S. Afr., 46, 1:27-153.
Eurrego, P.M.O.A. (1986). Met.amorph,.;.smof the Witwater'S-rand Superqroup in the Welkom Gold-Held. Unpubl.Hans. prtdect.~ Univ~ Witwatersrand, Joh.M1nesburg,79pp.
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Brouwer,' J. (1986). POst-Carbon Leadar erosion channelcompleK~s 08 the Far West Rand Goldfield. Ext.Abatr. Geocongr. 'S6, Geol. Soc. S. Afr, ~ohannes-burg, 955~95e.
13uck, S.G. (.1980). Stromatolite and bOlt:! deposits withinthe fluvial and lacustrine $ed~ment. of the Pre-cambrian VentersdCH""p Supergroup of South A·fr!ca.Precambr. Res., 121 3!1-~30.
(1963). The Saaiplaatc Quartzite Member; a braidedsY'i:itemof gold- and'wran.ium ....bear'1ng channel pl.acerswithin the ProterozoiC: WitWatersrand Supergroup ofSouth Africa. IN ColHnson~ J.P. 8< Lewin, J~ (eds.).Modern and ancient fluvial systems. Int. Ass. Sedi-men t. Spec:. PUb1., 6, 549-562.
172
Bull,' W.B.
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(1972). Recognition of &11uvi.l~~an depo$~t$It"\
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Hamblin, Wil'<~ (eels.). Rec09nit·~ton affJan'i.!iS'nt sed:i.-mentan' environment.s. Soc:;. Eccm. P....lepntol. andMiner.1., Spla?l,:i. Publ. 16p b~-(3::S.
(1977) • The ~Iluvi,al-·fan envj.ronrnel~t.~ F,"'r8:yp··eS$ in
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Cairncro$$, .13. (19E36). Oepo$it5.onal environments in the
Parmien Vl"'yhaid FOl"'l1tation. j/'~; thS' East Witbank C,oal-f' ,/ "/
+.ielc:! ~ South Afl'"iea ~ \,-",,/Tramewc:.H"'!-:' 'for coal seam
$'tl"'atigr;aphy, occ:;urrence a.nd distribution. Unpubl.
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235pp.
C.:allow, M,../l.W. & Myers, R~~~. (1986). Tectono"'strati-graphic: model for the development of the Well<omplater depo$?tt$: Oi"'ange Free State Goidfield. Ext.Ab$tr. Getlc:;ongl"'.. '96,. Seol. StH:. 9. ATl"'? Johannes-burg9 .:I.9-2.1~
Camdsn-Smith, Fl., St~wart, 13., Tainton, S., Theron~ F.,Wood, A. & I<arpet.a, P~ (1986) .. TI,e stratit;p"'aphy ofthe Witw.:;.t.E?r~l"'ahd Sequerll::e. Excursion guidebook ::SA,
/1)
OeOc,i;n1g r. •96~ Geo1• Sot: • S. Afr, Johanne$ burg,104pp ..
Chapman, G.S.S~ (1983). An investigation into th~eco-
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DepO!:3.i tional the l"!on-
173
bii1rred high-sner9Y n~arshorl? J. $ed. Pet.~ 41,651-6700
Coll inson, .1.D. (·1979). Verti\'.:slsequence and sand ooely
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Pall, R.!tJ. (19132.). M~jor 1<l1ultsYS!ltemsin t.hl$lminin.g Cif"eaof Western Holdings Limited Gold Mine (Hc)ldings
Divisitm) in the Ol"'i:!nge Free $tat-m XSol.dfields.Unpubl. M.Sc. thesis; Univ. Natal" Ou\Po.:an,75pp.
Denny, C.S. (1967). Fans265, ai.-aos ,
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Oott, R.H. (lCf64)• An s-pisodie:view of sh~ 11ow marine
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(1968). A crustal profile in the archa.an baaamantwest of the Wellt;omGoldfield g C!ompql"i$Qn$ wi~h theVradafol'"'tcrustal profile. eCoh. Gaol. Ras~ Unit1
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Ellis, S. (1992). An investigation of the Middle R.~f onUnissl Go-ld l"Iinl:ts Limitad. Gencor Unpubl. int4 Sullo324 ¢1Iddendum.1., W.lkom~ 8pp ..
~ (1999). Larga~$e:ala $oft-a·adiment deformation of th~Middle Reef place!'"',Unisal Gold Minea ~imited,Walkom aol~fi.ld. Ext. Abatr. G.o~ongr. 'S8, Gaol.Soc;". $. Afr~ Durban, .1.79'-182.
174
Ellis, S & Ridlay, M.K. (19S8). A sadLmantolagicalinves:tigation Clf the h;angirtt1wall 5UeC;E1$$ion 01'\
Unisel Sold Mines Limited 1••Be aree, Tarka 696,JI..H~,g~n$HOT 4<tQ and Varmeu1ems !H"aa 1 "'oord 4130-including a detailed stt.,tqy ot tha Leed~1""Raef zpne.SemC:QI'" Unpubl. int~ 'Sull. 406~ Well(.oltl}<42pp.
")1
I:tthr idg(~~ F •G. ( 1995) .. M;!)del'"l'l
deltas. IN Flol"'es.1 R.M.~
alluvial fans and fanethridge, F.G\, Mia11.
A.O~, Galloway'·, W.E, .& F'ouc:h~ T~.o" reds.).,'J ..
Recognition of fluvial rj.~o$ition~l system",i and
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FI"iend~ f).F. (1976). O;lstinctiva faatures of SQme aneiantU( Ni,.;tU A.D. (ed..). Fhwial llSecii-r:l;.vel'" $Y$~ms ..
I' . «;,mel"d.:olagy. Canadiano$pci$t.y of Petl"'o.leum Geolc1gist$?
Mem<;>ir 5, 531-042.
intel""m~l $tl"'ue:tUi~aQ',"'Id gec.:lltletl"'Y in six <1l11uvialfan-fan del ta bdc:!ia!S(Dev(;mi~n-Nol"wSlY) - A s;;tudy inth<:! Gi.grd.i'iccme:e tlf bSdding $et1uenc::~ in cOMglomG1r-
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Ha11bauer, o. K. & von GeM1I)?I"I 9 1(. (19a:s). Th((ll Wi twa tars-t'<and pyri tes t':Indmett':lmorph;tsl\'. MinerQlogic:a.l mag. 11
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Hankin, J.P~ (1979).A sedimentologieal and value studyo'f the Steyn Re~f channel in :;Zi$ dl""ive~ ·Geru:or
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175
HarMs1 ,:I"e, Sout.hard, J.a~~ $pGl!~rin9$ O~R. at \fJ~lker9 R.G.<:
(1975). DepQsl~iOnAl anvirQn~C)ts as interpreted
f~om I!'ri.rn.ary sE1dill'u,mt~I"'Y s'i!ruc:tUl"'9S .and ,,~trC\ti fi-c:etit:ln
8r Wall~er& R..G~ (..tlYS.2)." Structuras and
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n
Hein, F.J. (1974). SravaJ transport
origi~s, Kicking. Horse Aiveri
"i'lhd st'ratiQraphic
(,
Srit;t$h Columbi£1.Unpubl. M.Se. thesis, M~,;l"lastel"Uni ver~i ty, Hemi 1t.on s
r.C1nada? J.35pp.
" c1.......__ & (A.lell(el"'$ R.IEi. (19'7)" Eal'" avC)lution ~Md dev~lcfpm.nt
t:)f $t~i:Atifie:<Jt.iem in the griti,veUy, bri:'LldGo~ I(icklng (;
HorSe Rivar~ Briti!3h Colombia. Can. J .. l2.1ifrth .. SCi"914, $62-570.
Hqol~e, R.L. (1t;'Q7). PI"OCGl$$~S on ari.t:l ....l"'e~ilpr'l al1uvi~l
f am~" J. Oeell,. ~ 75 ~ 4:S6-4QO.
J<=ppe~ J.a~ (1963)~ Type!:; of a~$i511 flee1' end immedi.at<:.'ftlotwalJ on St. kelenrA Gold M:~ne ~nd adjoining
are.a. Genco\'"Ut1publ. int_rnal Bulletin 102, W.lkom."
10pp.
Johnson~ H..D~ & Bal.t:!\flir\, C.T. (19S~). Shallot'll silic:lestic$leaS'.. 1M Reading, H013. (eel.) ~ {aedimentary environ-
176
menta and fB~jeB4 2nd ed. Blackwell Scientific
pub! i<::81t$.on$? Chd'ol"'d~'"229-282 ~\)
Jordaarl, f"1~J. (1986).
f(iml::H::rl.ay pl$,cars
Daposi tional Tra..i)e"'IOrlt.. of thein the Wsl!~Qm '~oldf'l~ld~. I:;xt.
Abs't;t' ~ GeocQngl'" ~ •at;"
Johcarmesburg, 455-459.
Karpeta 1\ W~P. (1984) ~ The sedimentology and ~tf·$t\;i.Qraphicit..
setting o f the HA'I Re~f plaeers,. Aandelhk Fg,:"'tnati.on'~'1-1
or; Fr.as;i.dent Stay" Gold I"Li.na!t ~\lt:'i?ll(omSl Orange Free
fl:H:'iilta. Sxt. Atfstr"J6ao(:';ot'n;rr,. '94, Eeol. Soc~ S •. Afr",/!
';PotehefstrolZlm,,6']'.-62.~)
I<ing ~ A. R. (19S6). ~(S>c:liment.ologte€J.l modal fol'" the Spas
:Scma and Aendank formdt~ons of the Wa'lkorn, 601dfiaJ~ ..
"'Unpl.1bl.. Hons. pr;,o3act, Univ.I;'Johannesburg, ~7pp.
;:({i
l(ingslay, C,,$. a (1994). Oagbraak fillin.....del ta 1: An alluvial
placer.c~~,;;,to prO'del ta $t:lqul:nc;:e in the f'J1'·ot~I"'ozoic:
We1.1<om 1.3010f isld 1I WitW.::tt(;?rsrand s Stluth Africa. IN
KO$tel"", ~. H.. lIt st~s1p R.J. (~\\I$.'h.). Sed imt;?n to logy of\\
'canadian Society ofPetroleum $.eologists, Me(l\\d.r 10, 32.1.-3S0.,
Conglomerates.o
(.1.967). f:ac.ies Ch8rlge:S from fluvia\l t:ol1g1t:},merates to
braided Sandstones of the early Prcl'tero:Zo.ia r;l(:lol",~l(:io
Format.ion, WeB~omi?·Goldf;i.($.>1d, Sout.h Africa~ INEthridge. F~a •• Floras. R.M •• Harvey, M.D. CadS.).Rttlc:ent a.dvanr:es in fluvial l'SediMC:ltltolc:igy .. Soc. Econ.. \
Pa.leontol. anti Mineral ..~ Spse:. Publ. 3tr, 35.9-370.
177,
St.
(19S4e). Ali CiNaluetio!"\. of the Ad~\' ~lC\y
Hel~nc;'\ Golei Mined GencoI"' Unp4bl. intoIo.eynhans,
Sull. 354, Walkom~ 3pp.
_ (.1.9941.'.1).An in\)estigation of the Middle Raaf on St.4Helena t:iolcl Minr.'l>" Sancor UMpubl. int.# aul!. 339,Walkc:llm, opp.
Kochel, Ft~Cd ~ Johnson, R.AD (.1~S4). Geomorphology,. ar'to•• dim.nt;ology of humid-tamperata alluvial 11ans,central \liginia~ IN.. Koster, E:"H. & Steel, R"u.(eds.). Ssdimentology l'}r G,"'a.vels ;::),r,d C~nglomer$l;t.s~I '. -:Cansd.ian Societ.y of Pet:.b-.31eUmGaologists., Memoir lOu
109-122..
Law, J.O.M~ 0.990). 'Mihetalot;)Y$ gecH'.:l"iami$try Cilndaltsl"'s'"
titm 01 t\li twatel~sl"'al'ldmata-sediments i.n the Well(otl.&I"'e&;implicationa for minal"'alization. Unpubl~ M ••2.th.~'iS, Un.i.vw Witwater$r~ntt'jl Joh.;anne$burg~ 199pp ..
Q
street, ! .G. 0.990). Recolis+'I"'l"Ict.iV$ cnpproac:h tCJ th(m
c:1S$si1it:at.itlf'l of WitwC!.tersH"e;nd nqUCi)I ...t~ite$".Afr.. J. Seol., 90/1, a:S-92.
Cadle,
The mineralogy and eampb.~tiQn af ~ata-quartzite. in'the Cent!"'al Rend Group., Witwat.ersl"'an(:J SupeI"'Ql"'OL\th
~xt_ Ab'Str .. l.3eocongr" 'sa, Sect. Soc. s. Afl"'1Durb.;an, 35~-::S5ao
vl~t(ilr$rantl metS'-"'4l'''ehit6'$ ':~ some uni tying pal"'ametars
from thl:? We~kom Goldfield. Combined rUNSA I Assoc;.
o
o
(i
IS"pl. S""," h'\>lII. symRos icum , 1 • 13""1. s,,~. IS. Af r •• IJt:lhcmna:sburg, 19-·tj1.
'" II 0. 0
Leclci..s, II.A. & "W&:i'ker,,;' R.G. (198:2) ~ Storm- ahel t.:.iQ,e-
dominat~d $hol"'elin~w: in Cretaceous Maosebar·"I..c:wJar
(3$te$ tnt~rval outc::rpp t;1quivalent.~ of de&1p basin
9t;'l.1:s tr~ps in() l1J\=!$ternC.;an.atla. Am. AS$~ Petrol.. (3IE!Qlo-,e
o
" I~;uM!:').rt.in!l n. NcB. & Stanistrt.?e¢:, I.G. (19Sa)."An arenaceous
reud flow irrtl!':rpret.ation of the 'Slac:l< Eal'" ~ a c:ase'\l'!
study cih East Rand ProprietCl.~y Mines L;i.mited. Ext.
AbEtr. I$s(:Il::ongr. •88 ~ 6apl. Soc;:. S.. Afr. l) Durban)
Q03-bOe.
McCarthy. T.e. (1ge~).A Fortran IV computa~ program for
rt:l!pid g,raphic display of $~dimel"d::.ar)l borehole logdata. 11"'.."n$.geol~ Sol:., S. Afr., 84, 27.1.-27'7.
DMcCerthy. T.S., Myers. R.E. & Stanistr'et, I.G. (1987).
SeditMlntCl.ry respc)l1se to Witw~ter$rat,oj .:ag~ b~sinmOV~tL"1~t$ c:lfl the Centl"'Cll Rand. (-WIM. Gem. M~eting)
r~t:tol,:ics Piv. aet'.ll.. Soc. $., Af''''q Johann~Sbl..it-g,lFebnH'l.ry 19'97, 6pp.
!"lc'Gowan$ .1.1-1. (1970). Sum HOllow fan dmlt.a, Nueces I3.sy,
Taxas. Bureau af Economic Geology~ The University of
TtlH(aeat Austin, Repcw't cif .i.ny&,stigatit:m 1:19, 91pp.D
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r',-"-_ ,'~;
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I'vi
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Author: Bailey Andrew Charles.Name of thesis: The stratigraphy and sedimentology of the Upper Johannesburg and Turffontein subgroups in theSouthwestern portion of the Welkom Coldfield.
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