Fingerprinting Pb-Zn mineralization events in the SW Yangtze Block, South China: A case from Yuanbaoshan deposit

The southwestern Yangtze Block represents one of the world's largest lead-zinc provinces, comprises more than 400 known carbonate-hosted Pb-Zn deposits and contains over 30 million tons (Mt) of total Pb + Zn reserves. The Pb-Zn deposits in this area have been studied extensively by economic geologists, but the origin and mineralization processes of these deposits are still controversial. The Yuanbaoshan deposit is a typical carbonate-hosted Pb-Zn deposit of medium scale (0.19 Mt P + Zn reserves @ 0.7-26.31 wt%), which is in the northern part of the Pb-Zn mineral belt in the southwest margin of the Yangtze Block. In this study, we have conducted LA-ICP-MS sulfides trace elements, S isotope analyses, together with gangue carbonate C-O stable isotope analyses and pyrite Rb-Sr dating. We present Rb-Sr isotopic data on the pyrite that yields an isochron age of 196.4 +/- 2.3 Ma. The mineralization temperature at Yuanbaoshan, as determined by the Ga, Ge, In, Mn and Fe (GGIMF) in sphalerite geothermometer, ranges from 161 to 264 degrees C (Sp1) and 141 to 246 degrees C (Sp2). The 813CPDB values range from -0.66 to 0.61 %o, 818OSMOW values range from 15.6 to 17.3 %o. In situ S isotopes show that the 834S values of sulfides range from -1.4 to 17.73 %o. The field, petrologic, geochemical and isotopic data from our study lead to the following salient findings. (1) The dissolved carbon and oxygen of ore forming-fluids of these Pb-Zn deposits were mainly derived from sedimentary carbonate dissolution. (2) The reduced S in the sulfide of the Yuanbaoshan Pb-Zn deposit is mainly derived from the thermochemical sulfate reduction (TRS) and the reduced S produced by the pyrolysis of S-containing organic matter in the carbonaceous mudstone of the Ebian Group. (3) The large-scale Pb-Zn mineralization in the southwest margin of the Yangtze Block was influenced by the postcollision extension between the Indosinian Block and the South China Block during ca. 200 Ma.