13th Society of Geology Applied to Mineral Deposits Meeting.
Dr Yannick Branquet (University of Orleans, France) discussed the tectono-stratigraphic significance of a regional emerald-bearing evaporitic breccia horizon in the Gachala-Chivor-Macanal area of Colombia. This horizon contains evidence of sabkha-like evaporitic sediment reworking and destabilization on active sedimentary slopes. Detailed field, petrographic and structural evidence highlighting the role of evaporites in the formation of Colombia's eastern emerald belt were presented. The emerald deposits formed 65 million years ago in local extensional structures related to the initiation of a foreland bulge and associated flexure, via the migration of hot, saline and overpressurized fluids at depths of 5-6 km.
This author investigated the oxygen and hydrogen isotopic compositions of emeralds from the Ianapera deposit at Madagascar. The isotopic data indicate a magmatic-hydrothermal origin for these emeralds. The oxygen isotopic composition of water in equilibrium with emerald coupled with the hydrogen isotopic composition of water in the emerald channels fit with the isotopic water values defined for S-type granitic magmatism.
This author also delivered a presentation for Dr Jean-Emmanuel Martelat (University of Lyon 1, France) on the U-Pb ages of zircon and monazite from tsavorite-bearing Neoproterozoic rocks of south-eastern Kenya and the significance of static crystallization of the tsavorite. Detailed field investigations, geochemical studies and U-Pb radiometric dating of various geological formations in the Kasigau and Kurase areas showed that the formation of tsavorite in the Voi region was the result of a metasedimentary sequence preserved from strain but heated by surrounding granulitic rocks between approximately 600 and 595 million years ago.
Albert Gilg (Technische Universitat Munchen, Germany) used a variety of non-destructive methods (Raman and UV-Vis spectroscopy, and portable EDXRF analysis) to characterize more than 90 rough and 25 faceted gem-quality pyropes from various localities in Bohemia, and compared their properties to pyrope samples from other significant locations worldwide as well as red Cr-poor magmatic pyropes. This resulted in criteria used for determining the provenance of Cr pyropes in archaeological and historical jewellery (i.e. Merovingian cloisonne jewellery from Bavaria, religious objects of the St Vitus treasure in Prague and Bohemian costume jewellery from the 19th century in Sudetendeutsche Museum in Munich).
Dr Daniel Ohnenstetter delivered a poster on the boron isotopic composition of tourmaline from tsavorite deposits in the Neoproterozoic Mozambique Metamorphic Belt, with a special focus on the mining districts in Kenya. Dravitic tourmalines associated with different types of rock from tsavorite-bearing metasedimentary sequences in Kenya, Tanzania and Madagascar show two ranges of isotopic compositions. The first range is for dravites associated with tsavorite in nodules, which clearly involve continental evaporitic boron material. The second concerns dravites from clastic metasediments, metapegmatite and marbles intercalated in the metasedimentary sequence containing tsavorite nodules, which reflect a magmatic source for clastic dravite and probably an evaporitic one for dravite in marble.
Dr Juan Manuel Garcia presented a poster on the first known occurrence of green quartz related to a polymetallic Cu-Au-Mo porphyry-type deposit in Argentina. The quartz is hosted by a vein-related shear zone and is associated with sulphide, sulphosalt, carbonate and manganese oxide minerals. Preliminary data suggest that the shear-zone-related deformation in the deposit, along with the circulation of hydrothermal fluids and reprecipitation of silica due to pressure dissolution mechanisms, led to the generation of green quartz from the deformation and dissolution of previous smoky quartz. A genesis from a radioactive source is discounted since rocks with high potassium content were not found in the study area.
Andre-Mayer A.S., Cathelineau M., Muchez P., Pirard E. and Sindern E., Eds., 2015. Mineral Resources in a Sustainable World--Proceedings of the 13th Biennial SGA Meeting, Nancy, France, 24-27 August, six volumes, 2,134 pages (see Vol. 4 for gem-related abstracts).
Dr Gaston Giuliani (email@example.com) Institute of Research for Development at CRPG and University of Lorraine, France
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|Publication:||The Journal of Gemmology|
|Article Type:||Conference notes|
|Date:||Sep 1, 2015|
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