Genesis and ore-forming process of the Daping gold deposit in the central Jiangnan Orogen, South China

The Daping gold deposit is one of the largest gold deposits in the Xuefeng tectonic belt, central Jiangnan Orogen. The orebody occurs as auriferous quartz-ankerite-pyrite-arsenopyrite veins hosted by NW-striking and NE- to NNE-striking faults. This study presents in situ trace elements and sulfur isotopic compositions of pyrite, as well as H-O-Pb isotopic compositions of the mineralization veins, to constrain the genesis and ore-forming process of this deposit. Two generations of pyrite were identified in the mineralization veins: pyrite 1 (Py1) occurs as dark and polycrystalline cores, and pyrite 2 (Py2) occurs as bright rims overgrown Py1, or as discrete grains with porous textures containing abundant micro- to nano-inclusions (e.g., arsenopyrite). Py1 has low concentrations of As and Au, and high concentrations of Co, Ni, Cu, Bi, Te, Pb, and Sb, while Py2 has relatively higher Au and As contents and lower Co and Ni than Py1. Py 1 and Py2 yielded δ 34 S range of –11.34 to –4.89 ‰ (avg. = –7.09 ‰, n = 11) and –6.16 to –2.71 ‰ (avg. = –4.03 ‰, n = 21), respectively. The wide and negative δ 34 S range of Py1 may resulted from fluid-rock reaction that affected fluid redox conditions and caused significantly negative δ 34 S values in the sulfides. The porous textures, higher As and Au, lower Co and Ni of Py2 suggest that formation of this pyrite generation was related to phase separation due to rapid decompression. This process caused H 2 S to partition preferentially into the vapor phase, resulting in destabilization of Au(HS) 2 − .The δ 18 O and δD values of the fluids in the mineralization veins fluids are 5.24–6.14 ‰ and –60.6 to –59.1 ‰, respectively. The 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208 Pb/ 204 Pb ratios of the auriferous sulfides are 17.08–17.63, 15.48–15.54, and 37.64–37.94, respectively. Geological and H-O-S-Pb isotopic evidence indicates that mineralization is linked to crustal metamorphism, a signature common to most orogenic gold systems. The ore-forming fluids were likely sourced from the Neoproterozoic metasedimentary basement, probably through metamorphic devolatilization of underlying greenschist- to amphibolite-facies metasediments. Accordingly, the Daping deposit is best classified as an orogenic gold system.