The Mobilong alluvial diamond field of southeast Cameroon: Revised economic potential and sedimentological attributes

Abstract

Since they were first discovered in the 1930s, the diamond placers that are dispersed intermittently along Cameroon's eastern frontier with the Central African Republic have been the subject of numerous exploration campaigns. These small placers, mainly confined to Quaternary sediments, have never been mined on a large and commercial scale, but have instead been, and continue to be, exploited by the artisanal mining sector. From exploration in the 1980s, the Mobilong alluvial field was recognised to have economic potential based on a manually directed exploration campaign, but gravel sample volumes used for grade estimation are considered to be unrepresentatively small in this study. Recent mechanical mining and bulk trench sampling of this alluvial field, however, yielded greater gravel volumes, which allowed for a modern reassessment of the placer's sedimentology and diamond potential. It demonstrated that this alluvial field is overall a low-volume, small-diamond and uneconomic placer, with higher diamond concentrations in localised areas. The low potential is attributed to the limited availability of diamonds from secondary detrital sources, coupled with the inefficiency of fluvial mechanisms to promote diamond concentration. With unknown kimberlite occurrences in Cameroon and the neighbouring Central African Republic, Proterozoic and Cretaceous successions are considered to be detrital hosts of diamonds; a re-evaluation of these provide insight into their diamond contribution to the Mobilong alluvial field.