cl in support of interpreting gem deposits g. e. harlow 1 e. sahm 1,2 j. hunt 1,3 1 american museum...
TRANSCRIPT
CL in Support of Interpreting Gem Deposits
G. E. Harlow1
E. Sahm1,2
J. Hunt1,3
1 American Museum of Natural History, New York, NY
2 University of Utah, Salt Lake City, UT
3 California Institute of Technology, Pasadena, CA MVE02-3-1 (SSS)
Instrumentation
• Hitachi S-4700 Field-Emission SEM with BSE, EDS and a Gatan MonoCL3 detector & monochromator system (Peltier-cooled high-sensitivity PMT). The grating is a low-dispersion (21.6nm / mm slit width), with peak response (blaze wavelength) at 500nm and useful range of ~200 - 1200 nm.
CL Applications
Cathodoluminescence is an extremely powerful technique for examining zoning in minerals and can lead to fundamental interpretations about how they formed.
Targets in this presentation:– Jadeitites: jadeite, zircon, grossular?– Corundum deposits: ruby, sapphire, painite
Guatemalan Jadeitites
Jadeitites have been interpreted as crystallizations from aqueous fluids derived from subductions channels based, in large part, on CL observations.
In Guatemala there are two distinct serpentinite mélanges containing jadeitite, North and South of the Motagua fault.
How do the CL signatures of the minerals compare between the two distinct sources.
Jd-1
Jd-2
Zrn
Phengite
Qtz
MVE02-8-6 Phengite Jadeitite, San Jose
Ttn
Omph
SOUTHSOUTH
Panchromatic
480 nm Blue
270 nm UV
Jadeite-phengite rock (MVE02-8-6 – SOUTH)
Jadeite
SOUTHSOUTH
Jd-1Jd-2
Zircon Panchromatic Jadeite-phengite rock(MVE02-8-6 –SOUTH)
Panchromatic
Zircon, Secondary Electrons
BSE
Jd-1
Zrn
Jd-2
Zircon
500
410
315
240
505 nm Green 685 nm Red
410 nm Blue315 nm UV
Zircon in lawsonite-eclogite
(MVE02-6-1 – SOUTH) Zircon, Panchromatic
230 nm UV 490 nm Blue-green
490
230
Panchromatic CL
BSE
Pmp-Grs-Jadeitite(MVE04-20-1 – SOUTH)
Grs
Jd
Pmp
JadeiteJadeite
330
600
940
Panchromatic CL
BSE
MVE04-20-1 Pmp-Grs-Jadeitite Jadeite
Panchromatic CL
SOUTHSOUTH
Panchromatic 300 nm UV
600 nm Green 940 nm IR
MVE04-20-1 Pmp-Grs-Jadeitite Jadeite
Panchromatic
Panchromatic
BSE
Grs
Jd
Pmp
GrossularGrossular590
335
475
~850
Pmp-Grs-Jadeitite(MVE04-20-1 – SOUTH)
Jadeitite, Río La Palmilla, North of MFZ(MVJ84-9D) 2 cm across (courtesy of S. Sorensen)
NORTH
NORTH
Panchromatic CL image of same area. Note healed fracture in jadeite grain.
NORTH
Close-up from previous image
NORTH
Altered Jadeite (MVJ84-9B) at boundary between Jd and Ab+Ne
NORTH
Scale bar is 1 about micrometer.
Room Temperature Spectrum Imaging
Spectrum Image (40 X 40 pixels) of adjacent area
NORTH
Point 0 Point 1
Point 2 Point 3
Room temperature CCD CL spectracourtesy of Paul Mainwaring
Nepheline?Nepheline? Albite?Albite?
Darker JadeiteDarker Jadeite Lighter JadeiteLighter Jadeite
~700~560~480
~700~560
279 nm UV
350 nm UV 547 nm Green
Zircon, Meta(?)-Jadeitite(MVJ84-9C – NORTH)
547
279
350
Jadeite-Phengite rock (MVE02-8-6 -- SOUTH)
Pmp-Grs-Jadeitite(MVE04-20-1 -- SOUTH)
JadeiteJadeite
270
480
330
600
940
~700
~560
Altered Jadeite(MVJ84-9B -- NORTH)
~480
Comparison of CL Spectra from Jadeite
UV to IR peaks, but too soon to make generalizations other than color zoning observed by Sorensen and co-workers.
Zircon, Meta(?)-Jadeitite(MVJ84-9C -- North)
547
279
350
Zircon in lawsonite-eclogite (MVE02-6-1 -- South)
490
230
Jadeite-phengite rock(MVE02-8-6 -- South)
Zircon
500
410
315
240
Comparison of CL spectra from zircon
Main peak near 500nm and lowest near 250nm, but …
All are features show only primary growth.
Ruby (107643), Mogok, Burma in Marble w/ Spinel, Blue Cancrinite, Sodalite, Scapolite, Phlogopite, etc.
694nm - C
r
320
840
Panchromatic
BSE
320 nm UV 695 nm Cr-ruby
840 nm IR 840 nm IR
Artifact of mirror
Ruby-1, Namya, BSE Ruby-1, Namya, CL
Ruby-3, Namya, BSE Ruby-3, Namya, CL
Painite (CaZrBAl9O18) from Namya, Myanmar – rare gem mineral probably grew during skarn formation CL shows fine growth layering, implying growth pulses.
Panchromatic Inclusions: Cc, Baddeleyite (ZrO2) & Srilankaite (TiZr2O6)
Some ConclusionsCL in zircon, jadeite and garnet of jadeitites
is likely due to REE based on enrichment in these rocks.
Zoning structures suggest growth from fluids – for Zircon in jadeitite this implies growth at T = ~ 300°C at P > 1 GPa.
Considerable spectral structure from UV to IR is seen via SEM/CL.
Lots more to do.
Many Thanks to:
Jade & Ruby HelpersJade & Ruby Helpers: Jinny Sisson, Sorena Sorensen, Carlos Gonzales, Mauricio Chiquin, Will Maze, Bill Larson, George Rossman, Jamie Newman, U Han Htun, Dr. Saw Naung U, Mint Soe
The Founders of the FeastThe Founders of the Feast: AMNH, NMNH, Frohlich Charitable Trust, Astor Expedition Fund, Sprague Fund, Michael Scott, & the National Science Foundation.