Sulphur and lead isotopic compositions of the Pb-Zn polymetallic deposits in the Linzizong volcanic area, Gangdese belt, Tibet: Implications for variation characteristics of ore-forming material sources and exploration targeting

Relatively little attention has been given to variations in ore-forming metal sources of Pb-Zn polymetallic deposits hosted in or near the Linzizong volcanic rocks from the eastern to western Gangdese belt. Based on the S and Pb isotopic data of typical Pb-Zn polymetallic deposits from the eastern to western Gangdese, the ore-forming sources are discerned. The delta S-34(V-CDT) values of the typical Pb-Zn polymetallic deposits in the Gangdese metallogenic belt have a relatively large range of -11.6 parts per thousand to 6.0 parts per thousand, different from those of the porphyry Cu +/- Mo +/- Au deposits (mainly vary from -2.0 parts per thousand to 1.0 parts per thousand) in the Gangdese metallogenic belt, indicating that the sulphur in the ore-forming fluid of Pb-Zn polymetallic deposits was dominantly of magmatic origin, but also influenced by strata nearby. The Nuocang and Beina deposits in the western Gangdese have a predominantly upper crustal source of Pb (average values: Pb-207/Pb-204 = 15.705, Pb-208/Pb-204 = 39.102), while the Narusongduo and Dexin deposits in the central Gangdese and the Leqingla and Xingaguo deposits in the eastern Gangdese are characterized by a mixed source in which Pb was derived from both the subducted slab and the ancient Lhasa basement. From the eastern to western Gangdese, Pb isotopic data show a gradually increasing scale of crustal materials from the Lhasa terrane basement. Combined with the geochemical data of the ore-related intrusions and Linzizong volcanic rocks from the six deposits, or nearby, we proposed that the heterogeneity of Lhasa terrane crust resulted in more ancient Lhasa basement components contributing to ore-forming sources from the eastern to western Gangdese. Moreover, relatively higher contents of Au, Ag elements could be identified in the Linzizong volcanic rocks of the western Gangdese than those of in the central and eastern Gangdese. Therefore, in addition to finding the cryptoexplosive breccia, epithermal, skarn, hydrothermal vein-type Pb-Zn polymetallic deposits, there is exploration potential for epithermal Au-Ag deposits associated with the Linzizong volcanic rocks, western Gangdese.