Alteration and lithogeochemical characterisation of the Esaase gold deposit in the Paleoproterozoic Birimian Terrane of Ghana

Abstract

The Esaase gold deposit is located in the Asankrangwa gold belt and within the Paleoproterozoic Birimian Supergroup of the Kumasi basin. The deposit represents an important example of a structurally controlled turbidite-hosted gold system. Despite its economic significance, the geochemical processes controlling the element mobility during mineralisation remain poorly understood. This study presents an integrated petrographic and mass balance investigation of the Esaase gold deposit to characterise alteration processes and quantify the elemental mass transfer associated with the hydrothermal mineralisation. Petrographic studies revealed two major stages: (I) metamorphic and (II) hydrothermal. Stage II is associated with gold mineralisation. Metamorphic alteration is characterised by fine-grained sericite, chlorite, paragonite, and albite, while hydrothermal alteration is characterised by coarse-grained sericite, chlorite, carbonates, quartz, albite, paragonite, pyrite, arsenopyrite, and traces of chalcopyrite and gold. (Na₂O/Al₃O₂ vs. K₂O/Al₃O₂) Isocon-based mass balance calculations reveal a net mass gain of 16.67%, with significant enrichment in Au, As, Sb, Bi, Pb, Te, Se, Sb, Cr, Ni, and Cu, and marked depletion in Cao without significant changes in K₂O and Na₂O. These geochemical trends reflect localised but efficient fluid-rock interaction along structurally controlled hydrothermal pathways. The alteration assemblages are dominated by sericite-chlorite over sericite-albite, as supported by alkali-alumina molar ratios (Na₂O/Al₃O₂ vs. K₂O/Al₃O₂), consistent with alteration haloes surrounding sheeted quartz-carbonate veins. The deposit geology, alteration mineralogy, and lithogeochemistry of the Esaase turbidite-hosted gold deposit are similar to other world-class turbidite-hosted gold deposits, such as Bendigo in Australia, Meguma in Canada, Reefton in New Zealand, and Shangxu in China. This study establishes the quantitative mass balance assessment of the hydrothermal alteration at Esaase, demonstrating how moderate net mass gains reflect structurally controlled fluid flow and mineralisation. The findings provide new constraints on the genetic interpretations and support targeted exploration strategies in the Kumasi basin and similar geological settings.