Geology and geochemistry of listwaenite-related gold mineralization in the Sayi gold deposit, Xinjiang, NW China

The Sayi gold deposit is part of the Sartohay ophiolitic melange in west Junggar, Xinjiang, China, and is hosted by listwaenite, which was transformed from serpentinite in a shear zone via fluid-rock reaction. Gold mineralization is hosted by mylonitized listwaenites and quartz veins within listwaenite lenses, formed during shearing. Our study demonstrates that fluid concentrated Au, Ag, As, Sb, Cu, Cr, Ni, and Co during transformation from serpentinite to listwaenite and ductile deformation. Deformation due to shearing played an important role in focusing ore-forming fluid along the shear zone. Gold mineralization accompanied formation of hydrothermal minerals in the following stages: carbonate-quartz-pyrite (CQP, stage I), mariposite-gersdorffite-gold (MGG, II), quartz-carbonate-pyrite (QCP, III), gold-bearing quartz (IV) and dolomite-calcite stage (V). Geological characteristics of MGG in mylonitized listwaenite demonstrate that gold mineralization formed during the transition from ductile to brittle deformation, which was followed by gold-bearing quartz veins filling brittle fractures. The Au contents show a positive correlation with Ag, As, Cu, and Sb contents in mylonitized listwaenite samples, consistent with the coexistence of native gold, gersdorffite, arsenian pyrite, and chalcopyrite in mylonitized listwaenite. Pressure decrease due to hydraulic fracturing during the transition from ductile to brittle deformation induced gold deposition in the Say! deposit. (C) 2015 Elsevier B.V. All rights reserved.