On the formation conditions of porphyry Cu-Mo polymetallic deposits in the Xiaosigou district
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The host mass consists of quartz diorite-porphyry (marginal facies), granodiorite porphry (intermediate facies) and granite porphry (central facies). The petrographical facies are asymmetrically spread. The formation temperature of the rock mass ranges from 890 to 800°C, the pressure from 330 to 380 bars and the depth from about 1.5 to 2 km. Mineralization is controlled by the N-E contact zone and adjacent fault structures. Mo-mineralization occurs in the granite porphyry with strong potash metasomatism. Cu-Mo-mineralization is distributed in the inner contact zone of the rock mass, and the wallrock is K-silicified granite porphyry. Cu-pyrite-mineralization is recognized in skarn and serpentinite. Pb-Zn ore veins occur in marbleized limestones. Rock and mineral analyses, fluid inclusion studies and highT-P experiments indicate that extensive precipitation of Cu-bearing pyrite took place atT = 290–250°C, andP = 330–380 bars and that of copper atT = 400–310°C andP = 330–380 bars. Precipitation of Pb and Zn was followed by the transformation of hydrothermal solutions from alkaline to intermediate with decreasing temperature.
KeywordsPyrite Rock Mass Quartz Vein Hydrothermal Solution Granite Porphyry
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