Constraints on the Origin of Sulfur-Related Ore Deposits in NW Tarim Basin, China: Integration of Petrology and C-O-Sr-S Isotopic Geochemistry

Many small-size ore deposits occur in the Lower Paleozoic strata along the ENE-trending imbricate thrust fault in NW Tarim Basin. Based on field investigations and petrographic examinations, sulfur-related deposits mainly occur within the paleo-karst cavities and are composed of elemental sulfur and anhydrite. Elemental sulfur is extensively present, whereas anhydrite is limited to the Topulang area. The over-dispersed δ34S values (−25.2 to +7.4‰ VCDT) suggest that elemental sulfur and anhydrite typically originate from a multi-phase process involving bacterial sulfate reduction (BSR) superimposed stepwise sulfur disproportionation. The source of sulfate most likely derived from the subsurface Cambrian evaporites. The lower δ13C (−6.43 to −3.10‰ VPDB) and δ18O values (−13.49 to −10.30‰ VPDB) and the higher 87Sr/86Sr ratios (>0.7105) further suggest that the calcite cements precipitated from near surface aquifer with significant meteoric water influx and were associated with southeastward propagation since the Cenozoic in response to the remote effects of the India–Eurasia collision. This regional tectonic uplift and meteoric water influx created favorable anoxic environments (“sulfur springs”) for subsequent BSR and sulfur disproportionation along the Kepingtage overthrust fault front, resulting in the mineralization of sulfur-bearing species. This study provides a useful example for understanding the repeated processes of BSR and sulfur disproportionation for deep-buried evaporites associated with tectonic-driven mineralization within the Tarim Basin and elsewhere.