Petrogenetic and geochemical characteristics of some auriferous granitoids in the Kumasi Basin, Ghana: Implications for geodynamic settings and controls of orogenic gold mineralization in the Edikan Gold Mine

Abstract

The Edikan Mine, which consists of Fobinso and Esuajah gold deposits, lies within the Asankrangwa Gold Belt of the Birimian Supergroup in the Kumasi Basin. The metasedimentary rocks in the Basins and the faulted metavolcanic rocks in the Belts that make up the Birimian Supergroup were intruded by granitoids during the Eburnean Orogeny. This research aims to classify granitoids in the Edikan Mine and ascertain the petrogenetic and geochemical characteristics of some auriferous granitoids in the wider Kumasi Basin, Ghana, to understand the implications for geodynamic settings. A multi-methods approach involving field studies, petrographic studies, and whole-rock geochemical analysis was used to achieve the goal of the study. Petrographic studies revealed a relatively high abundance of plagioclase and a low percentage of K-feldspars (anorthoclase and orthoclase) in the Fobinso samples, suggesting that the samples are granodioritic in nature, while the Esuajah samples showed relatively low plagioclase abundance and a high percentage in K-feldspars, indicating that they are granitic. The granitoids from the study areas are co-magmatic. The granitoids in Esuajah and Fobinso are generally enriched in large ion lithophile elements and light rare earth elements than high field strength elements, middle rare earth elements, and heavy rare earth elements, indicating mixing with crustal sources during the evolution of the granitoids. The granitoids were tectonically formed in a syn-collisional+VAG setting, which implies that they were formed in the subduction zone setting. Fobinso granodiorites showed S-type signatures with evidence of extensive crustal contamination, while the Esuajah granites showed I-type signatures with little or no crustal contamination and are peraluminous. Gold mineralization in the study area is structurally and lithologically controlled with shear zones, faulting, and veining as the principal structures controlling the mineralization. The late-stage vein, V3, in the Edikan Mine is characterized by a low vein angle and is mineralized.

Keywords

Edikan Mine / geodynamic setting / granitoids / lithologically controlled / structurally controlled / subduction zone

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