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.