Morphological and chemical assessment of alluvial gold grains from Ako'ozam and Njabilobe, southwestern Cameroon

Abstract

Placer gold is widely distributed in southwestern Cameroon but no known lode sources have been uncovered possibly because of intense weathering. In this study, the morphology and microchemistry of alluvial gold from Ako'ozam and Njabilobe were investigated to understand the nature of the source mineralization. SEM, QEMSCAN and EMPA methods were employed to characterize morphology, mineral associations, alloy composition and mineral inclusions of placer gold in both localities. The gold grains exhibited angular to sub-rounded shapes, complex outlines and possessed surface textures such as striations, pits and cavities. These morphological parameters indicated a close source. Major mineral associations included clays and quartz with minor monazite, zircon, pyrite, ilmenite, rutile, chlorite and Fe oxide minerals. Gold in the area is essentially alloyed with Ag. Mineral inclusions included quartz, rutile, Fe-oxide and mica. Gold chemistry indicates interaction of the mineralization with basic rocks notably amphibolite and metadolerite in the area. The wide compositional span of Ag indicated that gold mineralization in the area resulted from multiple source deposit. Similarity in chemical character of gold from Ako'ozam and Njabilobe pointed to the same mineralizing event that sourced the placers in both localities. Gold chemistry suggested an orogenic style of mineralization in which gold occur as free gold in quartz veins. Liberation properties of gold within the Ako'ozam-Njabilobe area weighed in favor of physical gravity-based ore recovery methods which are environmentally friendly.