The origin of the Quemocuo carbonate-hosted Pb-Zn deposit in the Sanjiang Tethyan Belt, SW China: Constrained by Sm-Nd isochronic age and Sr-S-Pb isotope compositions

Abstract

The newly discovered Quemocuo Pb-Zn deposit (7.1 Mt of sulfide ores, grading 1.65–7.17 wt% Pb and 1.13–5.7 wt% Zn) is located in the Tuotuohe area of the Sanjiang Tethyan metallogenic belt, SW China. The stratiform and veined ore body is hosted in the limestone of the Upper Permian Labuchari Formation and occur along the NE-trending fault. Four main mineralization stages are distinguished as follows: (i) pyrite + calcite + quartz, (ii) sphalerite + galena + pyrite + calcite + barite + quartz, (iii) galena + sphalerite + pyrite + calcite + barite + quartz, and (iv) calcite + dolomite. Sm-Nd dating of five calcite samples in stage II yielded an isochronic age of 34.3 ± 2.2 Ma (MSWD = 7.1), possibly reflecting the formation age of the Quemocuo Pb-Zn deposit. In situ sulfur isotopic compositions of the sulfides in stages I, II and III range from −29.5‰ to −26.5‰, −4.7‰ to +6.0‰, and +1.7‰ to +6.9‰, respectively. Such sulfur isotope signatures indicate bacterial sulfate reduction (BSR) and thermochemical sulfate reduction (TSR) of seawater or sulfate minerals. In situ Pb isotopic ratios indicate a similar origin for the sulfides in stages I, II and III, which all are related to metamorphic basement rocks and ore-hosting sedimentary strata. Initial 87Sr/86Sr ratios of sphalerite are 0.7085–0.7117, indicating a mixed source as suggested by in situ Pb isotopes. The Quemocuo Pb-Zn deposit was proposed to be a strata-bound and normal fault-controlled epigenetic deposit, with a mixed source of basement and strata, and even volcanic rocks. Our study suggests that the formation of the Quemocuo Pb-Zn deposit is related to the Cenozoic collision event between the Indian and Eurasian plates.