Galena geochemistry as recorder of and pathfinder for volcanogenic massive sulfide deposits: A case study of the Keketale volcanogenic massive sulfide−type Pb-Zn deposit, Altai Mountains

Galena is a common economic mineral, but galena geochemistry remains poorly understood in volcanogenic massive sulfide (VMS) deposits. This contribution attempts to characterize galena geochemistry and its controlling parameters, as well as assess its utility as an exploration indicator. Two generations of galena have been recognized in the Keketale VMS-type Pb-Zn deposit, Altai Mountains, i.e., syngenetic galena in massive sulfide mineralization and epigenetic galena in epigenetic superimposed mineralization. Syngenetic galena exhibits broad trace-element variations, whereas epigenetic galena compositions consistently overlap the syngenetic range. Despite metamorphism and remobilization, galena’s structural elements remain largely unmodified. It is inferred that almost all elements (Sb, Ag, As, Cu, Tl, etc.) are incorporated into galena by direct and/or coupled substitutions, though some elements (Zn, Cu, As, etc.) constitute the components of micro-inclusions. The trace-element composition of galena is principally governed by temperature and coexisting minerals (notably sphalerite and sulfosalts). The Pb isotopes of syngenetic and epigenetic galena define a mixing line between host sequences and concealed old crustal materials, indicating that metals were derived from strata that were successively leached by evolved seawater-derived and later metamorphic fluids, leading to syngenetic and epigenetic mineralization, respectively. Notably, galena proximal to the hydrothermal vent exhibits elevated Tl, Cd, and Sn contents, likely due to higher temperatures and fluid fluxes, and this trend potentially serves as a vectoring tool for locating mineralization centers. By integrating compiled galena datasets (n = 1066) with a random forest algorithm, different types of Pb-Zn deposits derived from contrasting fluids can likely be distinguished by galena geochemistry. Accordingly, both trained classifiers and the discrimination diagram (log[Tl] vs. log[Sn]) are proposed to facilitate the classification of unassigned Pb-Zn deposits. Briefly, this study refines current understanding of galena geochemical systematics in VMS deposits, providing insights that enhance both genetic interpretation and exploration strategies for VMS deposits.