Metallogenesis of the Lanmuchang Gold–Mercury–Thallium Deposit, Guizhou, China: Insights from Alteration Styles and Geochemistry

The Lanmuchang deposit in Guizhou, China, represents a unique Carlin-type system characterized by the concurrent enrichment of gold (Au), mercury (Hg), and thallium (Tl). This study integrated mineralogical and geochemical analyses to reveal the alteration processes, ore-forming conditions, and metallogenic mechanisms of the deposit. The results demonstrate that the ore-related alterations in the Lanmuchang deposit were dominated by silicification, decarbonation, argillization, and sulfidation. Gold mineralization occurred under low-temperature (200–230 °C), weakly acidic pH (∼4), and reducing conditions (log fs2 = –11.4, log fo2 = –35.3––39.5). Gold-bearing pyrite formation was jointly controlled by silicification, decarbonation, and sulfidation processes. Mercury mineralization occurred at 126–195 °C, weakly acidic to near-neutral pH (4.4–7.8), and variable fugacity (log fs2 = –15.1––5.6, log fo2 = –45––28.9). Cinnabar, as the primary Hg-bearing mineral, was likely precipitated during cooling and oxidation of hydrothermal fluid. Thallium mineralization occurred at lower temperatures (113–137 °C), neutral-alkaline pH (6.9–9.1), and lower fugacity conditions (log fs2 = –18.8––15.1, log fo2 <–42.2). Argillization processes (including kaolinization and illitization) potentially facilitated the mobilization of Tl, which was subsequently enriched in lorandite and pyrite under a weakly alkaline and reducing environment. The systematic variations in alteration styles and ore-forming conditions of Au, Hg, and Tl mineralization are interpreted as the key controlling factors for their spatial association and separation patterns, providing new insights into multimetal enrichment in Carlin-type deposits.