Abstract
Western Tianshan along the southwestern margin of the Central Asian Orogenic Belt is well-endowed with epithermal and porphyry Au deposits. The Kuruer Cu-Au deposit, recently discovered in the eastern part of Western Tianshan, was considered as a high sulfidation epithermal deposit. However, our geological, fluid inclusion and stable isotopic studies indicate that it actually formed in transition from high sulfidation to porphyry. The host rocks include the Dahalajunshan Formation volcanic and volcano-sedimentary rocks such as andesite, rhyolite, ignimbrite and tuff. Cu-Au mineralization mainly occurs as quartz-dominated stockworks or disseminations, with abundant pyrite and chalcopyrite and minor galena and sphalerite. Gold occurs as invisible phase in sulfides. Hydrothermal alteration includes a silicic core, surrounded by phyllic alteration and peripheral propylitic alteration. Based on field observations, paragenetic and crosscutting relationship, the mineralization process can be roughly divided into three stages. The early stage is characterized by the assemblage of quartz+pyrite+chalcopyrite while the middle stage contains quartz and chalcopyrite at absence of pyrite. The late stage is characterized by calcite±quartz±chlorite±chalcopyrite veins.Fluid inclusions at the early stage are mainly liquid-rich aqueous and CO2-rich inclusions and minor vapor-rich aqueous and solid-bearing inclusions. Their homogenization temperatures and salinities can be up to 420°C and 39wt.% NaCl eq., respectively, indicating that the initial ore-forming fluids are high temperature, high salinity, H2O-CO2-NaCl systems. In the middle stage, there are only liquid-rich aqueous inclusions, with homogenization temperatures and salinities of 130–190°C and 0.18 to 10.7wt.% NaCl eq., respectively. Liquid-rich aqueous inclusions in the late stage display much lower temperatures and salinities, ranging from 110 to 130°C and 0.18–2.7wt.% NaCl eq., respectively. Obtained δDH2O and δ18OH2O values of quartz from the middle stage are −98 to −107‰ and −2.1 to 0.74‰, respectively. The δ34S values of 9 chalcopyrite samples range from −10.2 to −2.4‰, with an average of −4.1‰. We conclude that the initial ore-forming fluids are magmatic in origin, and further cooled and diluted by mixing with meteoric water. Intensive fluid boiling and mixing facilitated hydrothermal alteration and mineralization.
Published Version
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