Genesis and Magmatic-Hydrothermal Evolution of the Yangla Skarn Cu Deposit, Southwest China

摘要

The Yangla skarn Cu deposit (150 Mt at 1.03% Cu) is located in the central segment of the Jinshajiang metallogenic belt within the Sanjiang (Three Rivers) region, southwest China. Skarn orebodies are mainly developed between different units of Devonian carbonate and quartz sandstone rocks with stratiform-like shapes, or within the contact zone between granitoids and marbles. Re-Os dating of molybdenite intergrowth with chalcopyrite yielded a well-constrained Re-187-Os-187 isochron age of 232.0 +/- 1.5 Ma with a weighted average age of 231.8 +/- 1.3 Ma, both coeval with the related intrusions (233.1 +/- 1.4 and 231.0 +/- 1.6 Ma at 2 sigma by zircon U-Pb dating) from our previously published work. Field and textural relationships indicate three hydrothermal stages characterized by assemblages of prograde skarn (pre-ore stage), retrograde skarn and Cu-Fe-Mo-Bi sulfides (main ore stage), and Pb-Zn sulfides associated with calcite and quartz (late ore stage), as well as one supergene stage marked by secondary Cu mineralization (malachite and azurite). Skarns contain garnets with andraditic compositions (Ad(96) Gr(2 similar to 3)Py(0 similar to 1)) and clinopyroxene (two series: Hd(6)Di(94) and Hd(86)Di(13)Jo(1)) with low Mn/Fe ratios (<0.1), typical of Cu skarn deposits worldwide.