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A two-stage evolution model for the Amantaytau orogenic-type gold deposit in Uzbekistan
Authors:Jan Pasava  Hartwig Frimmel  Anna Vymazalová  Petr Dobes  Alexandr V Jukov  Rustam I Koneev
Institution:1. Czech Geological Survey, Klárov 131/3, 118 21, Prague 1, Czech Republic
2. Institute of Geography and Geology, University of Würzburg, Am Hubland, D-97074, Würzburg, Germany
3. Department of Geological Sciences, University of Cape Town, Rondebosch, 7701, South Africa
4. National University of Uzbekistan, Vuzgorodok, 700174, Tashkent, Uzbekistan
Abstract:A lithogeochemical, mineral chemical, isotopic, and fluid inclusion study of barren, low-, and high-grade Au-mineralized samples from the shear zone-hosted Amantaytau gold deposit, Uzbekistan, shows that the local host rocks, Late Ordovician–Earlz Silurian carbonacous shales, are likely to have been an important source of Au, As, Ni, and S in the formation of the deposit. Syn-depositional pyrite in these shales contains on average 0.23 ppm Au, 1,083 ppm As, and 861 ppm Ni. The distribution of rare earth elements (REE) indicates a homogeneous source of light REE, whereas the heavy REE distribution reflects most likely primary variations in the sediments. The mineralized zone is marked by a positive Eu anomaly, which supports reducing conditions during the mineralization. A hydrothermal overprint by an aqueous–carbonic fluid is reflected in a high-grade Au-mineralized sample by δ13C values of ?13.0?‰ (V-PDB). The δ 34S values in pyrite (?0.13 to +7.30?‰ CDT) from barren and mineralized samples are consistent with marine sulfate being the principal source of the ore sulfur. Assuming a formation temperature of between 300 and 400 °C for the main stage of mineralization, as indicated by the alteration mineral assemblage, the calculated δ 18Ofluid is between 9.5 and 13.4?‰ V-SMOW, which points at a metamorphic origin of the ore fluid.
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