Provenance, depositional process, and tectonic setting of gold placer from the Bétaré-Oya Gold District (East-Cameroon, Central Africa) along the Precambrian Sanaga fault

Abstract

The Bétaré-Oya Gold District is one of the three gold districts in East Cameroon with varied types of mining. The study site is an open-cast mine located in an alluvial plain. The strata succession globally consists of two positive sequences represented by three facies associations and seven lithofacies: massive clast-supported (Gcm), massive trough-cross bedded (Gtm), and massive matrix-supported (Gmm) conglomerates; massive sands (Sm); and massive (Fm), heterolothic (Fhl), and convolute and heterolithic (Fhlc) clays. The facies analysis indicates deposition after a recent tectonic event creating a depression, followed by a rapid deposition of varied facies and energies of sedimentation with fluvial and gravity inputs. The deposits come from proximal to distal sources but more proximal. The identified heavy mineral or accompanying minerals reveal a plutonic source (tourmaline sometimes folded), a volcanic source (olivine or clino-pyroxene with cracks), and a metamorphic source (sillimanite, andalusite, and staurolite). In the pan concentrates of placer with high silver (Ag) concentration (100 ppm) are also associated with relative abundance of lead (Pb) (17.8 ppm), zinc (Zn) (27 ppm), and low levels of copper (Cu) (3.1 ppm). The concentration and distribution of some element ratios, such as thorium/scandium (Th/Sc), chromium/thorium (Cr/Th), and europium anomaly (Eu/Eu∗), rare earth elements (REEs) and aluminum oxide/titanium dioxide (Al2O3/TiO2) vs. silicon dioxide (SiO2) plots for the studied sediment indicate heterogeneous sources of rocks with dominance of felsic sources. The discriminant diagram reveals a recycled or sedimentary provenance of the deposited sediments. The tectonic setting plot indicates a collision tectonic setting which is consistent with the Precambrian history of the study area which belongs to the Pan-African North-Equatorial fold Belt. The gold deposits in the Bétaré-Oya area probably derive from several sources, such as a vein source (from magmatic and metamorphic processes of the Neoproterozoic age) and a sedimentary source (from remobilization of ante-Neoproterozoic rocks of Archean and Paleoproterozoic age), deposited during the Cenozoic period linked to the reactivation of the Precambrian Sanaga fault. These are likely associated with a supergene source as indicated by the presence of dissolution microstructures. The cases of detrital gold deposits from several sources has been reported for the Serpont gold deposits in South-East Belgium, and those associated with authigenic forms are known in Poland, New Zealand, and Tanzania.