Genesis and Sulphur Source of Volcanic‐Hosted Carlin‐Type Gold Deposits in the Youjiang Basin, SW China: A Case Study of the Jiadi Deposit

The Youjiang Basin hosts more than 100 Carlin‐type gold deposits within the ‘Golden Triangle’ region in southwest China. The Jiadi deposit, a representative large‐scale Carlin‐type deposit in this basin, is hosted by volcanic rocks associated with the Permian Emeishan mantle plume. This study presents new mineral geochemical and S isotopic data for auriferous pyrite in the Jiadi deposit. Distinct generations of pyrite include a porous pre‐ore core (Py1) that is surrounded by “smooth” oscillatory overgrowths (Py2), representing the ore stage. Compositionally, Py2 contains higher concentrations of Au, As, Cu Co, Sb, Ni, and Ag than those in Py1. Both Py1 and Py2 likely contain Au as lattice‐bound Au + within both Py1 and Py2. In particular, As is concentrated in Py2 as several finer oscillatory zones. This ‘porous’ core–‘smooth’ rim texture and the geochemical data can be explained by a fluid‐driven dissolution–reprecipitation process. During this process, elements including Au were liberated from Py1 and incorporated by Py2. The elevated concentrations of Ti, Al, and P in both Py1 and Py2 are attributed to continuous interactions between ore fluids and Fe‐enriched basaltic wall‐rocks. Moreover, Py1 and Py2 share similar δ 34 S ranges of −1.92‰ to 1.72‰ and −2.20‰ to 3.23‰, respectively. This suggests that the sulfur in the ore fluids likely originated from a magmatic source. A magmatic–hydrothermal model that includes a genetic affinity for concealed granitoid plutons was proposed for the volcanic‐hosted Carlin‐type deposits. The volcanic rocks hosting the Jiadi deposit also played an important role in Au mineralisation by supplying reduced Fe for sulfidation.