Geochemistry of sulfide minerals from skarn Cu (Au) deposits in the Fenghuangshan ore field, Tongling, eastern China: Insights into ore-forming process

Abstract

In situ elemental compositions of sulfide minerals have been widely applied to trace ore-forming processes of magmatic-hydrothermal ore systems, yet the application of elemental compositions of the sulfide minerals in skarn ore deposits is still restricted by the lack of understanding of their behaviors during the skarn formation processes. In this study, in situ (LA-ICP-MS and EPMA) elemental compositions of medium- to coarse-grained euhedral pyrite and xenomorphic granular chalcopyrite are investigated for the Fenghuangshan and Baoshantao skarn Cu (Au) deposits in the Tongling region, eastern China. The results show that the studied pyrite samples have relatively consistent trace element composition characteristics, while the chalcopyrite studied displays high Zn, Ag and Pb contents, and relatively high Bi content. Au, Ag, Cu, Pb, Bi, Sb and Tl are mainly of lattice bound appearance in the pyrite structure. The Au, Ag, Sb, Pb and Bi are mainly incorporated into the chalcopyrite structure as coupled substitutions. Low Au (mainly < 0.1 ppm), Se (<3 ppm) and As (<100 ppm) contents, and high Co/Ni (mainly >1) and Se/Tl (mainly >10) ratios of the pyrite studied, and high Sn (>10 ppm) and low Tl (<1 ppm) contents of the chalcopyrite imply a high temperature, high oxygen fugacity and acidic pH magmatic-hydrothermal fluid for the Tongling skarn Cu (Au) mineralization. High Zn and Bi contents in the pyrite and chalcopyrite studied, and low Co/Ni ratios (<0.1) of the pyrite from quartz monzodiorite probably indicate a sedimentary component from subducted slab contribution to the magmatic-hydrothermal system.