Genesis of the Zhaxikang Pb-Zn-Sb-Ag-Au deposit, southern Tibet: insights from stibnite trace elements and S-Pb isotopes

The Zhaxikang Pb-Zn-Sb-Ag-Au deposit is situated in the North Himalaya Metallogenic Belt (NHMB), southern Tibet, and is unique due to its diverse metal resources. Two mineralization events (early Pb-Zn and late Sb) in Zhaxikang are controlled by the complex Cenozoic tectonic evolution in the Himalaya. The ore bodies occur as veins and are hosted primarily by shale interbedded with sandstone and limestone. Stibnite is the dominant Sb-bearing mineral in antimony mineralization. The LA-ICP-MS trace element analyses show that stibnite is characterized by high Cu, As, and Pb contents and low Co, Ni, and Te contents, and most elements occur as solid solutions. In addition, the analytical data indicate that several elemental coupled substitution mechanisms present as (Cu⁺ + Ag⁺) + (Mn²⁺ + Pb²⁺) ↔ 2Sb³⁺ + 2□ and Cu⁺ + Zn²⁺ ↔ Sb³⁺ + □. In situ S isotope analyses of stibnite (δ³⁴S = 4.2 to 6.2‰, mean = 5.7‰) indicate a dominant sedimentary rock-sourced sulfur, which suggests leaching of slate and limestone in the Ridang Formation by the ore-forming fluid. The newly obtained stibnite Pb isotopic ratios (²⁰⁶Pb/²⁰⁴Pb = 19.55 to 19.83, ²⁰⁷Pb/²⁰⁴Pb = 15.85 to 15.89, and ²⁰⁸Pb/²⁰⁴Pb = 40.38 to 40.76) indicate that the underlying Precambrian metamorphic basement and Mesozoic sedimentary rocks both supplied substantial metals for Sb mineralization. Combined with previous studies, our new isotopic results suggest that the two mineralizing events in Zhaxikang shared similar metal sources, i.e., sedimentary and basement rocks. Both mineralization events, under compressional and extensional tectonic settings, respectively, are closely linked to coeval felsic magmatic events. Finally, trace element data were investigated using PCA which allows the identification of geochemical parameters for predicting metal associations (single Sb or Sb polymetallic deposits) in a Sb ore district, supporting the potential use of stibnite trace elements as promising indicators for exploration targeting.