Genesis of carbonate-hosted Zn-Pb deposits in the Late Indosinian thrust and fold systems: An example of the newly discovered giant Zhugongtang deposit, South China

• Published in: Journal of Asian earth sciences 2021-10, Vol.220, p.104914, Article 104914
• Main Authors: Wei, Chen, Huang, Zhilong, Ye, Lin, Hu, Yusi, Santosh, M., Wu, Tao, He, Lianglun, Zhang, Jiawei, He, Zhiwei, Xiang, Zhenzhong, Chen, Da, Zhu, Chuanwei, Jin, Zhongguo
• Format: Article
• Language: English
• Subjects: Bulk C-O isotopes; In-situ S-Pb isotopes; In-situ trace elements in pyrite; MVT deposit in thrust belt; Sources of metal elements and associated fluid
• ISSN: 1367-9120; 1878-5786
• DOI: 10.1016/j.jseaes.2021.104914

[Display omitted] •The Zhugongtang deposit belongs to MVT deposits formed in an orogenic thrust belt.•Ores were deposited from low-temperature, low fO2 and weakly acidic basinal brine.•H2S was sourced from synchronous seawater sulfates in ore-hosting sedimentary rocks.•Metals were derived from a mixed source of basement and country rocks.•Sulfide precipitation was triggered by mixing between two different fluids. The Sichuan-Yunan-Guizhou triangle region contains numerous economically important carbonate-hosted Zn-Pb deposits that occur in the Late Indosinian thrust and fold system rather than foreland basin. In this paper, we investigate the thrust-controlled Zhugongtang deposit (>30.0 Mt ores @ 6.76 wt% Zn and 2.27 wt% Pb) as a case study, using ore deposit geology, in-situ trace elements and isotopes in sulfides, to provide new insights into the ore genesis of the MVT deposits in the thrust belts. The sulfide orebody is structurally controlled by a kilometer-scale thrust system and occurs as open-space fillings, vein or replacement structures. Trace elements in pyrite show a low concentration of Co, Ni, Tl and Se, suggesting that the sulfides were formed under low-temperature (100–250 °C) and slightly reduced conditions. The δ13CPDB values (−7.53 to +1.73‰) in calcite lie between the marine carbonate rocks and sedimentary organic matter, and the calculated δ18Ofluid values (+3.40 to +13.36‰) are different from that of marine carbonate rocks but partly overlap with the basinal brines. Such C-O isotope signature indicates that the carbon was mainly derived from the host rocks (limestone) with additional contribution from organic carbon. The oxygen isotope values suggest mixing of the basinal brine and the limestone. The δ34S values of sulfides within Permian strata (+12.2 to +15.3‰) and Devonian strata (+18.5 to +23.8‰) are similar to the coeval seawater sulfate within the ore-hosting strata, respectively. This indicates that the reduced sulfur is originated from evaporative sulfate within host rocks by thermo-chemical reduction in the near-close system. In-situ Pb isotopic ratios of galena (206Pb/204Pb = 18.566–18.758, 207Pb/204Pb = 15.757–15.769 and 208Pb/204Pb = 39.061–39.366) are comparable with the Proterozoic basement and the country rocks, indicating the mineralizing metals were mainly derived from basement rocks and partly extracted from country rocks via fluid-rock interaction. Regional geological evidence indicates the timing of Zn-Pb mineraliza