A Review of Granitoid-Related Gold Mineralization Styles and Characteristics of the Neoproterozoic Eastern Gold Districts, Cameroon and the Role of Fluid Inclusion Studies in Elucidating the Genesis

Abstract

Geophysical, structural and geochemical data have been used to study the relationships between magmatism, tectonics, fluid circulation and gold mineralization in eastern Cameroon, and to provide pressure-temperature-composition-time paths constrained by the available dating. Primary gold mineralization displays spatial and temporal relationship with felsic to intermediate I-type granitoids emplaced in the 620-635 Ma period, in a volcanic arc setting at 625°C to 775°C. These granitoids were probably generated by partial melting of hydrated lower mafic crustal rocks, under oxidizing to moderately reduced conditions, where global permeability and tectonic regime allowed vertical fluid exchanges to be established. Mantle-derived, gold-enriched alkalic magmas are postulated as the ultimate source of gold enrichment in the crust. The Pan-African orogeny, and associated regional metamorphism and magmatism, generated large-scale movements of gold- and base metal-bearing fluids in the crust, channelized along complex fractures into regional NE-trending shear zones in Cameroon (e.g. Central Cameroon Shear Zone). However, these gold-rich alkalic magmas are so modified by crustal processes that evidence of their genetic relationship with gold become obscured. The primary ore mineral assemblage of quartz veins and veinlets within these shear zones consists of pyrite, galena, chalcopyrite, specular haematite, and gold. Preliminary fluid inclusion data from these auriferous quartz vein indicate that gold was probably transported predominantly as a bisulfide (HS¯) complex and deposited from low salinity (2O–CO2 (±CH4±N2) fluids that have total homogenization temperatures of 245-355°C. Desulfidation of hydrothermal fluids by Fe-bearing minerals in the wall-rock triggered the main gold precipitation phase. The major and trace element composition of ore-forming fluids from the mineralized vein, barren and granitic intrusion is still largely unknown, yet could provide important and more direct evidence for the fluid source(s). This is vital in establishing a direct genetic link between granitoids and gold mineralization.