Discovery of the large-scale Eocene Xiwu Pb-Zn-Ag deposit in the Tethyan Himalaya: Geochronology, geochemistry, and C-H-O-S-Pb-Sr- Nd isotopes

The known Pb-Zn-Sb-Au polymetallic deposits in the Himalaya mainly formed during the main-collisional convergence (65-41 Ma) and post-collisional crustal extension (25-0 Ma) tectonic settings. Here, we report the discovery and genesis of the large-scale Eocene Xiwu Pb-Zn-Ag deposit that formed during the late-collisional tectonic transition stage (40-26 Ma) in the eastern Himalaya. The surrounding ore-hosting rocks are mainly low-grade metamorphosed Jurassic clastic rocks and Early Cretaceous dia-base. The most important ore-controlling structures are NE-SW thrust faults. The ore minerals include large amounts of galena, sphalerite, tetrahedrite and siderite, with minor chalcopyrite, pyrite, arsenopy-rite, calcite and quartz. In this contribution, we analyzed the S-Pb isotopes of sulfides, fluid inclusions and the C-H-O-Pb-Sr-Nd isotopes of nonmetallic minerals. The results indicate that the ore-forming mate-rials originated from deeper metamorphic rocks of the Greater Himalayan Crystalline Complex. This study infer that the source of ore-forming fluids was mainly metamorphic fluids with moderate temper-atures and salinities, and S and C were mainly derived from microbial sulfate reduction and the decar-boxylation of organic matter, respectively. The main ore-forming mechanism is fluid mixing between the deep ore-bearing metamorphic fluids and shallow formation waters. The Sm-Nd isotopic age of side-rite is 37.4 & PLUSMN; 1.1 Ma, which is slightly younger than the zircon U-Pb age of the Zhunba leucogranite (38. 9 & PLUSMN; 0.4 Ma) but is consistent with the main epoch of early prograde metamorphism (43-36 Ma) in the Himalaya. We propose a new metallogenic model for Himalayan Pb-Zn-Ag deposits that can greatly pro-mote ore prospecting. The genetic type of the Xiwu deposit is a clastic-dominated subtype of sediment-hosted Pb-Zn deposits.& COPY; 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.