Volume 22, Number 11, July - September 2006
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(Follow this link for abstracts of past issues)
OLD OPAL FIELDS REVISITED AT COOBER PEDY
I. J. (Jack) Townsend
Consultant Gemmologist-Geologist
Plympton Park, South Australia
ABSTRACT
The miners at Coober Pedy have for many years been asking for assistance in
finding new areas ultimately to find new opalfields. These requests have
been satisfied in the past by subsidised drilling prograins, and in 2001 an
Opal Symposium and the launching of a CD database to assist the individual
miner. In 2004 the South Australian government promised at least $A50,000
for a drilling program and commenced negotiations with the Coober Pedy
Miners Association (CPMA). This figure was later raised to $A100,000 and the
CPMA purchased an investigator Mark 10 Anger drilling rig to use for the
drilling prograin, which the government was to supervise by logging all
holes, surveying and Updating the existing CD database for Coober Pedy with
the new and previous drillhole information. and look at possible other
methods for locating opal. One new method tried by the division of Minerals
and Energy Resources was High Resolution Resistivitv which was carried out
over known areas with a view to later extending to unproven but interesting
areas. Miners were partly subsidised in the use of the CPMA drilling rig and
lower costs per metre/foot in areas at least 500 metres away from proven
fields.
TORRINGTON AND ITS GEMSTONES
Hylda Bracewell
Mitchelton, Queensland
ABSTRACT
This short paper will present the location and general geology of the old
tin mining village of Torrington. Also included will be some of Torrington's
more interesting mining and fossicking history, and some of the minerals and
gemstones it has produced.
The gems that fossickers seek from the now Torrington Conservation Area will be described and illustrated.
THE VARIATION OF GEMMOLOGICAL PROPERTIES
AND CHEMICAL
COMPOSITION OF GEM QUALITY TAAFEITES AND MUSGRAVITES FROM SRI
LANKA
Dr Karl Schmetzer1,
Dr Lore Kiefert2,
Dr Heinz-Jürgen Bernhardt3, Murray Burford4
1
Taubenweg 16, D-85238 Peterhausen Germany
2 AGTA Gemological Testing Center, 18 East 48th Streer, Suite 502
New York, NY, USA
3 Central Microprobe Facility, Ruhr-University, D-44780 Bochum,
Germany
4 136 Beechwood Avenue, Victoria, British Columbia V8S 3W5,
Canada
ABSTRACT
Gemmological, chemical and spectroscopic properties of two transparent
faceted taaffeites, a rough semitransparent taaffeite crystal as well as a
faceted transparent musgravite from Sri Lanka were determined. The three
greyish violet taaffeite and musgravite samples are coloured by various
amounts of iron, and the purplish red colouration of one taaffeite is due to
traces of chromium and moderate iron contents. Gemmological properties such
as specific gravity and refractive indices of the four samples examined are
compared with gemmological features of known gem quality taaffeites and
musgravites from Sri Lanka. The variation of gemmological properties of both
mineral species, taaffeite and musgravite, are correlated with chemical
properties, especially with the sum of transition metal contents. Varying
values of specific gravity and refractive indices are mainly due to a
variation of iron- and/or zinc contents of individual samples. According to
a similar chemical composition and crystal structure, gemmological
properties of taaffeites and musgravites overlap. For an unequivocal
determination of faceted gems of this mineral group special techniques such
as X-ray diffraction and/or quantitative chemical analysis and/or
micro-Raman spectroscopy is needed.
TEST CASE FOR THE REFRACTOMETER - OLIVINE OR SINHALITE?
Alan Hodgkinson
MINING AND EXPLORATION FOR GEMSTONES IN AUSTRALIA
Frederick (Lin) Sutherland
School of Science, University of Western Sydney,
North Parramatta, New South Wales
ABSTRACT
Gem materials currently extracted from Australian sources include
significant amounts of precious opal, diamond, sapphire, jade, chrysoprase,
agate, silicified ornamental materials and pearls. New ruby mining started
in 2005 and amber has recently been described. Limited amounts of emerald
and other gem beryl, topaz, zircon, elbaite, garnet, pyroxene, feldspar,
olivine, gem quartz, opal, titanite, prehnite and other collector stones are
recovered.
| The gem sources vary from west to east across the continent in their geological and geographic context. This leads to inherent differences in the gem materials. Some gem resources, such as precious opal, diamond and sapphire are dwindling and current exploration and research projects are aimed at proving new deposits. Australia retains much potential for new gem finds and increased gem-based tourism. |
 Diamond crystals from Australia. ((LHS) Merlin pipe, Northern Territory (104.3 ct). RHS) Ellendale 9 pipe (11.5 ct). Photo by Paul Ovendon, courtesy of The Australian Museum. |
ELEPHANT PEARLS: TRUE OR FALSE?
Bobby Mann
Temple Hills, Maryland, USA
Grahame Brown
Albany Creek, Queensland
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ABSTRACT Genuine elephant pearls are rounded calcified concretions of dentine that are recovered from the soft tissue pulp that is contained within the continuous growing tusks of modern African and Asiatic elephants as well as the now extinct woolly mammoth. The ten so-called 'elephant pearls' that are described and illustrated in this paper had structural features that revealed that they had been fashioned by man from molar teeth of, most likely, the Asiatic elephant. |
 Specimens of 'elephant pearls' investigated in this study. |
MINERAL AND MELT INCLUSIONS IN SAPPHIRES
AS AN INDICATOR
OF CONDITIONS OF THEIR FORMATION AND ORIGIN
Vera Pakhomova1, Boris Zalishchak1,
Vita Tishkina1, Marija Lapina2,
Nikolai Karmanov3
1 Far East Geological Institute of Far Eastern Branch of Russian
Academy of Sciences,
2 Institute of Ore Deposit Geology, Petrography, Mineralogy and
Geochemistry of Russian Academy of Sciences, Moscow,
3 Geological Institute of Siberian Branch of Russian Academy of
Sciences, Ulan-Ude, Russia
ABSTRACT
Any and all proposed theories regarding the origin of sapphires are still
very much open to debate. Critical inconsistency arises on the magmatic
petrogenesis mechanism of sapphire crystal formation. The Nezametnoye
deposit of Far Eastern Russia is one of the most prospective placer deposits
of jewellery grade corundum (sapphire) and zircon (jacinth) in Russia, and
is known for its native and alluvial gold-wolframite-tin deposits.
| We present new data obtained from mineral and primary melt inclusions that are syngenetic with corundum. Electron microprobe analysis indicates that rutile, zircon, albite, zinc-bearing hercynite, columbite, and fluorite represent syngenetic mineral inclusions. Silicate melt inclusions are almost always associated with carbon dioxide inclusions; this correlation suggests that a heterogeneous fluid-melt system was present during corundum crystallization. |
 Corundum from Nezametnoye deposit. Primorsky Region, Russian Far East. |
Distinctive features of chemical composition of the inclusions, along with their agpaitic coefficients, ' indicate that corundum crystallization occurred from granosyenite (quartz-syenites) melts. Primary carbon dioxide rich inclusions form random groups, or are associated with melt inclusions. Pressure-Temperature conditions for corundum crystallization have been calculated as 780-820 0C and 1.7-3 kbar, based on data from primary carbon dioxide and melt inclusions.
