African A-Type granites: A geochemical review on metallogenic potential

Abstract Tin and other high-field-strength (HFS) elements are becoming increasingly significant, driven by technological advancements and a global effort to develop alternative energy solutions. A-type granites are associated with the mineralisation of these critical metals and therefore, investigating the influences on their metallogenic potential is essential for future exploration. The geochemical comparison between selected mineralised and unmineralised African A-Type granites, highlights the importance and implications of fractionation, crustal contamination, crustal emplacement and the composition and evolution of the magmatic-hydrothermal fluid in the development of endogranitic Sn mineralisation. Trace elemental ratios such as Zr/Hf, Nb/Ta and Y/Ho demonstrate the relationship between the degree of fractionation and interaction with acidic, F- and Cl-rich magmatic-hydrothermal fluids in these mineralised and barren African examples. Circumstantial differences in magmatic origin, not only directly influence the metallogenic budget of a granite but also influence the F and B content of the later stages of felsic magmatism. These volatiles prolong fractionation, consequently facilitating the likelihood of HFS element saturation and the development of an economic deposit. Moreover, the combination of continental setting and the enrichment of HFS and volatile elements by the assimilation of fortuitous crustal lithologies can upgrade an originally unfavourable magma composition, to one with a potential for mineralisation. It is therefore shown that mineralisation is ultimately achieved through a series of sequential, incompatible and HFS element, enrichment stages that culminate in the accumulation of sufficient metals to produce economically significant mineralisation.