Genesis of the Yawan Sb deposit, West Qinling Orogen, Central China: Constraints from S–Pb–C–O isotopes and Sm[sbnd]Nd geochronology

Abstract

The Yawan Sb deposit is a large deposit located in the Xihe County, Gansu, northwestern China. Ore bodies are hosted in the Triassic limestone and are controlled by the NE- trending faults, occurring as lamellar, lenticular, veined, and lentil. Based on the cutting relationship between veins and mineral assemblages, the ore-forming process can be divided into four stages: I) pyrite + stibnite + milky quartz stage, II) stibnite + pyrite + gray-black cryptocrystalline quartz stage, III) stibnite + calcite + fluorite stage, and IV) clear and colorless calcite stage. The δ34S values (−2.5 ‰ to 5.8 ‰) of sulfides from stage II are similar to those associated with magmatic systems, but significantly different from the values (δ34S = −12.8 ‰ to 18.8 ‰) of pyrites from strata, suggesting that magmatic sulfur was the source for S2− in stage II. The δ34S values (−9.5 ‰ to −7.5 ‰) of stibnites from stage III are depleted in 34S relative to those of stage II, probably due to the increasingly mixing of meteoric water and SO42− from the strata. The Pb isotopes of sulfides from stage II and III (206Pb/204Pb = 17.745–19.176, 207Pb/204Pb = 15.478–15.711, 208Pb/204Pb = 37.7–38.742) show a mixed source of crust and mantle. The δ13C and δ18O values of calcites range from −0.84 ‰ to 3.94 ‰ and from 4.74 ‰ to 13.24 ‰, respectively, indicating that the ore-forming fluids originated from magmatic water, but influenced by water-rock interaction and meteoric water in the late stage. The SmNd isochron age of five calcite simples from stage III is 199.9 ± 1.7 Ma (MSWD = 1.6) with initial εNd values of −8.4, indicating that Yawan Sb deposit formed in the Late Triassic to Early Jurassic. On the basis of the data obtained in this paper, we consider that the Yawan Sb deposit is a distal magmatic-hydrothermal deposit formed during the transitional tectonic regime from the syn-collision to post-collision. Combined with previous studies, future exploration should focus on the distal magmatic-hydrothermal Sb deposits controlled by faults around concealed granites, and skarn-type deposits also need attention in Yawan-Daqiao district.