Host-rock compositions and fluid inclusion characteristics associated with epithermal Au–Ag mineralization at Galim-Legalgorou, Cameroon

The Galim-Legalgorou Au–Ag prospect in Northwestern Cameroon has been recently classified as epithermal based on the wall-rock alteration assemblages, ore mineralogy, and chemistry of electrum plus sphalerite. However, questions regarding the host-rock compositions and how these may have interacted with mineralizing fluids remained unanswered. This study presents the host-rock compositions as well as features of quartz-hosted fluid inclusions related to mineralization. Whole-rock major element data show a highly evolved magmatic rock series from basalt to rhyolite, with the latter being the major host to the mineralization. Rare-earth element data of the trachyte and rhyolites show a slight enrichment trend in LREE relative to HREE, with a negative europium anomaly ({Eu/Eu*}CN = 0.09 to 0.51), suggestive of plagioclase fractionation at the magma source. Coexisting liquid-rich and vapor-rich secondary fluid inclusions are consistent with boiling and vapor loss during the late stages of fluid evolution. LA-ICP-MS data show that Na and K are the dominant ions in fluid inclusions, suggesting that the fluid was in equilibrium with alkali-rich host rocks at the time of mineralization. Homogenization temperatures of 180–303 °C (average ~ 273 °C), with salinities around 2.2 wt% NaCleq., and Na–K geothermometry indicate trapping conditions near the base of the epithermal environment. The study further establishes the Galim‑Legalgorou prospect as the first well‑constrained low-sulfidation epithermal Au–Ag mineralization documented along the Cameroon Volcanic Line, and demonstrates that mantle‑derived magmatism in an intracontinental rift system can generate epithermal mineralization comparable to arc‑related systems, expanding global models of precious‑metal formation in volcanic terranes.