S-Pb isotope characteristics and prospecting model of the Nagengkangqieer silver deposit in the eastern segment of East Kunlun Mountain

The Nagengkangqieer silver deposit is a large-sized hydrothermal vein-type independent deposit expected to become a superlarge silver deposit.Based on the study of geological characteristics of the mining area, the authors investigated the ore-forming material source and the relationship between the two types of magmatic rock and mineralization by studying the S-Pb isotopes of the ore sulfide and the Pb isotope of the monzonitic granite and granodiorite.The δ³⁴S values of the sulfide samples(pyrite, galena and sphalerite)range from -6.1‰ to 3.9‰, mainly from -4‰ to 2.1‰.The concentrated values suggest that the ore-forming material(sulfur source)had the characteristics of deep source magma sulfur.The ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb values of sulfides range from 18.28 to 18.62, 15.6 to 15.73 and 38.38 to 39.1, respectively.The LA-ICP-MS zircon U-Pb age of the monzonitic granite in the mining area is 239±1 Ma, and the (²⁰⁶Pb/²⁰⁴Pb)_i, (²⁰⁷Pb/²⁰⁴Pb)_i, (²⁰⁸Pb/²⁰⁴Pb)_i values of the monzonitic granite range from 18.389 to 18.585, 15.638 to 15.648 and 38.288 to 38.558, respectively.The LA-ICP-MS zircon U-Pb age of granodiorite is 252±1 Ma, and the (²⁰⁶Pb/²⁰⁴Pb)_i, (²⁰⁷Pb/²⁰⁴Pb)_i, (²⁰⁸Pb/²⁰⁴Pb)_i values of the granodiorite range from 18.348 to 18.447, 15.625 to 15.629 and 38.394 to 38.412, respectively.The lead isotope composition plot shows that the ore-forming process had weak relationship with the two types of magmatic rocks, and it had obvious linear correlation with the volcanic rocks of the Erlashan Formation in this area.A comparative analysis of the neighboring Harzhaz lead-zinc-silver deposit which had similar sources of ore-forming materials shows that the sulfur source was identical, and the Pb isotopic composition of the ore exhibits a distinct linear relationship, indicating that the ore-forming materials of the two deposits had the similar source region or evolution process.The ore-forming geological conditions, ore-forming material sources and fluid characteristics of the two deposits indicate that the two deposits are both medium and low temperature hydrothermal vein deposits.On the basis of the research conducted by the authors and previous researchers, the metallogenic model and prospecting model were constructed to provide guidance in search for the same type of silver deposits in this area.