PYRITE TYPOMORPHISM AND ORE FORMING SIGNIFICANCE IN YANGSHAN GOLD DEPOSIT,WEST QINLING
Yangshan gold deposit is located in the middle of the reluctant-lipped suture zone of the West Qinling orogenic belt,and the ore body is mainly endowed in the carbonaceous clastic-carbonatite strata of the Middle Devonian.In this paper,based on detailed field investigations and petrography,gold-loaded pyrite in mineralized kilomagnetite and mineralized plagioclase granodiorite porphyry were analyzed in situ using electron microprobe EMPA,respectively.Both types of pyrite were found to have obvious core-mantle-edge tri-generation ring structures in backscatter(BSE)images,corresponding to early mineralization(py1),main mineralization(py2),and late mineralization(py3),respectively.The S and Fe percentages from the core to the rim(py1～py3)show a decreasing and then increasing trend,while As and Au show the opposite characteristics;pyrite w(S)/w(Fe)＜1.148,atomic number S/Fe＜2,pyrite in Yangshan gold mine is sulfur-poor and iron-poor pyrite with sulfur loss;δFe-δS and(Fe+S)-As graphs show that Yangshan gold mine is a magmatic hydrothermal linked type of pyrite.The δFe-δS and(Fe+S)-As diagrams indicate that the Yangshan gold ore is a Carlin-like gold deposit closely associated with magmatic hydrothermal fluids;As enters the pyrite as As-to replace S,and is accompanied by the substitution of other elements for Fe2+;the gold in the pyrite ore is mainly in the form of lattice gold(Au+),and a small amount of nano-sized gold particles exists at the same time;the mineralization of the Yangshan gold ore is closely related to the Late Triassic magma,and the deep underground magma room may provide a large amount of mineralization materials.
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