Origin of the Keyue Pb-Zn polymetallic deposit in southern Xizang:Evidences from sulfur and lead isotopic compositions

The Keyue Pb-Zn polymetallic deposit in southern Xizang is located in the eastern part of the Tethys Himalayan Sb-Au-Pb-Zn metallogenic belt, in which the lenticular or vein ore bodies strictly controlled by the NE-trending faults occur in the carbon-bearing calcareous slates of the Lower Jurassic Ridang Formation. The δ³⁴S values of the sulfides from the ores range from 9.2‰ to 11.2‰, with an average of 9.85‰, similar to those of the Jurassic strata in the Ridang Formation, implying that S is mainly derived from the host strata. The sulfides from the ores give the lead isotopic ratios of 10.669-19.813 for ²⁰⁶Pb/²⁰⁴Pb, with an average of 19.740; 15.823-15.979 for ²⁰⁷Pb/²⁰⁴Pb, with an average of 15.902, and 40.104-40.687 for ²⁰⁸Pb/²⁰⁴Pb, with an average of 40.410. These higher lead isotopic ratios bear a striking resemblance to those of the Himalayan crystalline basement, possibly indicating that the lead in the ores comes from the Himalayan crystalline basement.