130 / 2016-12-15 10:10:11

Metamorphic overprint on the Ashele Cu-Zn deposit in Altay, Xinjiang: Evdences from geology and inclusions

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The Ashele Cu-Zn deposit is located in the Ashele Devonian volcanic-sedimentary basin to the south of the Altay accretionary orogenic belt. The deformation and metamorphic textures are well developed in wall rock such as asymmetric and symmetry pyrite pressure shadows, zonal extinction of quartz, undulatory extinction of quartz, and altered quartz edge. Three kinds of different occurrence vein-type quartz can be distinguished in the Ashele Cu-Zn deposit, i.e., the veins-type quartz in the volcanic layers (Q1), the lentoid quartz veins (Q2) in metamorphic volcanic rock and the sulfide quartz veins (Q3) cutting across the mylonitized tuff with disseminated pyrite and chalcopyrite. There are H2O-CO2 fluid inclusions in Q1, Q3, and barite. Those characteristics disagree with the feature of fluids in VMS deposits, and are typical of metamorphic fluids. The calculated δ18OH2O values of parent fluids of Q1, Q2 and Q3 quartz veins respectively range from 4.1‰ to 6.8‰ (SMOW), 6.2‰, and 5.5‰ to 7.4‰ (SMOW), and the measured δD values of fluid inclusions range from -97.3‰ to -104.5‰ (SMOW), -92.8‰, and -98.7‰ to -109.6‰ (SMOW) respectively. The deformation and metamorphic textures of wall rocks in Ashele deposit and the existence of H2O-CO2 fluid inclusions in quartz and barite can be evidences to explain that metamorphic fluids participate in the superimposed reformation and possess of multi-stage.