Sulfur isotopic characteristics of the Zhaxikang Sb–Pb–Zn–Ag deposit in southern Tibet

Abstract

The Zhaxikang Sb–Pb–Zn–Ag deposit is the only super-large deposit in the North Himalayan Metallogenic Belt, but its genesis is debated. Genetic models include hot springs, magmatic-hydrothermal fluids and sedimentary exhalative overprinted by hydrothermal fluids. Here, we present sulfur isotopic data to constrain the genetic models for this deposit. The δ 34SV-CDT values of sulfides in the first pulse of mineralisation range from 7.8 to 12.2‰ (average = 10.7‰), and in the second pulse of mineralisation have lower δ 34S values of 4.5–11.3‰ (average = 8.5‰), suggesting the sulfur source for the first pulse of mineralisation is mainly seawater sulfur mixed with some mantle-derived sulfur, whereas the second pulse of mineralisation originated from mantle-derived sulfur and sulfur from earlier formed sulfides and wall rocks. Together with previously published Fe–Zn–Cd isotope evidence for the Zhaxikang deposit and regional S isotopic and geochronological data, the new data suggest that the first pulse of mineralisation is related to multiple seafloor volcanic events during the synsedimentary period (220–130 Ma) with submarine hydrothermal sedimentation (metasomatism) genesis that is overprinted by the second pulse of mineralisation associated with the magmatic-hydrothermal activity during the post-collision period (25 Ma to now). KEY POINTS The Zhaxikang Sb–Pb–Zn–Ag deposit, a super-large deposit in the North Himalayan Metallogenic Belt, is the product of overprinting hydrothermal events. The first pulse of mineralisation is related to multiple seafloor volcanic events and is overprinted by a second pulse of mineralisation associated with the magmatic-hydrothermal activity. Sulfur isotope analyses show the first pulse achieved equilibrium during sulfide crystallisation, but kinetic Rayleigh fractionation induced sulfur isotope variations for the second pulse of mineralisation.