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Sulfide Zonal Texture and Its Geological Significance of Ores from the Hongshan Copper Deposit in Shangri-La, Yunnan Province, China
详细信息   
摘要
The Hongshan copper deposit, located in Shangri-la, Yunnan, China, is tectonically situated in the southern part of Sanjiang Tethyan Zhongdian island arc. It is one of the most significant deposits in this district and gets very popular concerned since its discovery with hotly debated about the genesis. It occurs slate, metaclastics and limestone interbedding with medium-basic volcanic rock and volcanoclastic rock and intruded by intermediate-acidity and ultrabasic dykes or stocks. Lenticular copper sulfide ore-bodies occur in bedded skarn bodies or adjacent to it, and is disrupted by post-metallogenic faults. The copper ores develop sulfide zonal texture with pyrite as nuclear, chalcopyrite as intermediate zone and pyrrhotite as external zone. Pyrite in the core is usually euhedral or subhedral crystal while the coating chalcopyrite and pyrrhotite are anhedral. Chalcopyrite precipitate around the early-formed pyrite, pyrrhotite which acted as the main body of the sulfide zonal texture grows around the chalcopyrite. The inner sulfide is generally replaced by the outer one. The sulfide zonal texture precipitates from the inside out as the following order: pyrite-chalcopyrite-pyrrhotite. Analysis of trace elements and S isotopes exhibit similar characteristics from different sulfides of the zonal texture, for example, moderate REE and strong Eu depletion with a gentle seagull REE pattern; riched in HFSE as U, Th, Zr, Hf and depleted in LILE as Rb, Sr and Ba; both the REE and TE distribution patterns of sulfides are similar to those of ultrabasic rocks in Hongshan area; whereas from nuclear pyrite to intermediate chalcopyrite and to external pyrrhotite, the total trace elements and REEs (∑REE 0.17371×10-6, 1.22626×10-6 and 5.25925×10-6) shows gradually increasing meanwhile Co/Ni and Se/Te gradually decreasing pattern. The above features indicate the mineralizing fluid trapping more crustal component during evolution. The δ34SV-CDT of 24 sulfides have a magmatic feature ranging from 3.81‰ and 5.23‰, and an order as δ34SV-CDT(Po)<δ34SV-CDT(Ccp)<δ34SV-CDT(Py), indicating that the sulfur fractionation hadn’t reached an thermodynamic equilibrium. The sulfide zonal texture of ores from Hongshan deposit is formed by a magmatic-dominated mineralizing fluid precipitating as the order pyrite-chalcopyrite-pyrrhotite, and accompanied with the decreasing of H2S and O2 fugacity or arising of pH value from the earlier to later.

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