LA-ICP-MS analysis of sulfides from the Sinongduo Ag-Pb-Zn deposit, Tibet: Insights into element incorporation mechanisms and ore genesis

Abstract

As one of the most significant Ag-Pb-Zn deposits in the northern Gangdese polymetallic belt, the Sinongduo has been widely concerned since its discovery and hosts proven reserves of 148,136 t Pb (1.95 %), 205,722 t Zn (2.70 %), and 400 t Ag (52.33 g/t). Despite its economic importance, the mechanisms of Ag incorporation in sulfides and deposit genetic type remain debated. This study mainly employs in situ LA-ICP-MS trace element analysis of sulfides (sphalerite, pyrite, and galena) to address the above issues. Three mineralization stages are identified: (Ⅰ) pre-ore pyrite + quartz stage, (Ⅱ) sphalerite + galena + pyrite + minor chalcopyrite + Ag-bearing minerals main stage, and (Ⅲ) post-ore calcite + quartz stage. LA-ICP-MS depth profiles and multivariate statistical analysis reveal trace elements are primarily hosted as lattice-bound solid solutions and nanoscale inclusions, with limited micro-inclusion formation. In the Sinongduo deposit, where silver is the most critical element, its substitution mechanisms exhibit significant differences among sphalerite, pyrite, and galena. In sphalerite, silver incorporates into the crystal lattice via coupled substitutions involving the replacement of Zn by Fe, Cu, Sb, Ga, and Sn. In pyrite, silver enters the lattice through coupled substitutions where Fe is replaced by As, Sb, and Co. In galena, silver is incorporated into the lattice through coupled substitutions where Pb is replaced by Sb and As. Trace element thermometry (GGIMFis geothermometer) yields ore-stage temperatures of 226.0–288.0 °C (mean = 256.8 °C), consistent with fluid inclusion data. The trace element distributions in the Sinongduo sulfides, such as Fe, Mn, Cu, Ag, Sn, and Pb enrichment and Ga, Ge, In, and Co depletion in sphalerite, together with the supports from the host rock, alteration, texture and mineral assemblages, suggest that the Sinongduo deposit is a typical epithermal deposit. This study establishes the Sinongduo deposit as a typical epithermal system and demonstrates that in situ LA-ICP-MS analysis of sulfide trace elements provides robust constraints on deposit genesis.