Geometallurgical and Kinetic Controls on Cyanidation of a Mildly Refractory Low-Sulfidation Epithermal Gold Ore: Insights from the Mount Muro System, Indonesia

Gold (Au) and silver (Ag) are commonly co-extracted from low-sulphidation epithermal (LSE) ores by alkaline cyanidation, yet their dissolution behaviors often diverge despite close mineralogical association. This study investigates Au–Ag cyanidation in ore from the Mount Muro LSE deposit, Central Kalimantan, Indonesia, through integrated mineralogical characterization, diagnostic leaching, time-resolved cyanidation, residue analysis, and kinetic modeling. Diagnostic leaching indicates that ~80% of Au is cyanide-accessible at P₈₀ ≈ 75 μm, whereas only ~54% of Ag occurs in free-milling domains, with the remainder hosted in sulfide and Cu–Ag sulfosalt phases. Continuous cyanidation confirms this contrast: Au dissolves rapidly and reaches a plateau of ~87% recovery, while Ag extraction proceeds more gradually to ~78%. Residue analysis shows that unrecovered Au and Ag are concentrated in fine fractions (<38 μm), demonstrating control by mineralogical locking, partial passivation, and micro-scale diffusional barriers rather than reagent insufficiency. Shrinking Core Model diagnosis identifies mixed kinetic control for Au and diffusion-dominated control for Ag. Despite differing dominant mechanisms, kinetic model discrimination shows that both metals are best described by the Ling model, capturing non-linear, accessibility-controlled dissolution. These results highlight evolving surface accessibility as the primary control on cyanidation performance in mildly refractory LSE ores.