Elizabeth Agyekum, PhD
E. Agyekum1, M. Van Lichtervelde2, K. Adomako-Ansah1, G. Mensah Tetteh1, J. Ganne2
1Department of Geological Engineering, University of Mines and Technology (UMaT), Tarkwa, Western Region Ghana
2Gèosciences Environnement Toulouse, Université Paul Sabatier, Toulouse, France
The study investigates the evolution, controls, and exploration significance of rare element mineralisation in granitic pegmatites within the Biriwa-Ewoyaa enclave of the Cape Coast Basin, southern Ghana. Motivated by increasing global demand for lithium and other critical metals, the study provides a comprehensive mineralogical and geochemical framework for understanding Li-Cs-Ta pegmatite systems in a Paleoproterozoic Birimian terrane. A methodology combining field mapping, petrography, whole-rock geochemistry, and in-situ mineral chemistry (EPMA and LA-ICP-MS) was used. The pegmatites are classified into barren, fertile, and mineralised types, reflecting progressive magmatic differentiation and rare-element enrichment. Mineralised pegmatites are distinguished by the occurrence of spodumene, Li-phosphates, and columbite-tantalite group minerals, which are absent in barren varieties. Geochemical data reveal strongly peraluminous compositions and systematic enrichment of incompatible elements (Li, Rb, Cs, Nb, Ta) from barren to mineralised pegmatites. Elemental ratios (e.g. K/Rb, K/Cs, Cs/La, Mg/Li) effectively discriminate pegmatite fertility and provide robust exploration vectors. Mineral chemistry records a clear magmatic-hydrothermal evolutionary continuum, expressed by compositional zoning in Nb-Ta oxides, fractionated zircon signatures, distinct generations of muscovite and spodumene, and evolving REE patterns in apatite and phosphates. The results establish the Cape Coast Basin as a highly prospective province for rare element pegmatites and provide a predictive framework for future exploration in Ghana and comparable Precambrian terranes.