Gold deposit type and implication for exploration in the Abiete-Toko Gold District, South Cameroon: constraint from morphology and microchemistry of alluvial gold grains

Abstract

The morphology and quantitative chemical analyses of fifty alluvial gold grains from fourteen studied sites were used to constraint gold deposit type and its implications to exploration in the Abiete-Toko Gold District in South Cameroon. The main results revealed that the gold grains show a core-rim zonation marked by Ag depleted rims as a result of leaching during transportation. The fineness of grains ranges from 826 to 1000 and their composition is almost binary gold-silver. Gold fineness refers to the relative amounts of Ag and Au present, given as a number out of 1000 and defined by Au/(Ag þ Au)*1000. The chemical composition of the gold grains are range as thus: 83.40-100 wt.% Au, 0.07-17.45 wt.% Ag, 0-0.96 wt.% Cu, 0-0.01 wt.% As, 0-0.02 wt.% Ni, 0-0.02 wt.% Co, 0-0.01 wt.% Se, 0-0.08 wt.% Hg and 0.003-0.03 wt.% S. The high sulphur concentrations of the gold grains probably imply primary deposition of gold by sulphidation; The ranges of Ni and Co concentrations suggest an interaction with greenstones. Such findings indicate that the Abiete-Toko area hosts a mesothermal-orogenic gold deposit. Exploration operations must target fractures and contact zones between ironstones, felsic gneiss and greenstones. Soil sampling is not recommended in this orogenic gold district due to the very thick and transported nature of the weathering mantle. Detailed mapping coupled to geophysical surveys are the recommended key exploration methods prior to drilling program.

Geochemistry of stream sediments from Eséka area (SW Cameroon): implications for surface process assessment and precious metals (Au, Pd, and Pt) exploration

“…Moreover, Pd, Pt, V, and Cu show similar behavior in stream sediments of Eséka area. The comparison of Au, Pt, and Pd contents in stream sediment of this study compared to other studies shows that these elements are lower than those recorded in Abiete-Toko Gold District, South Cameroon (Nono et al, 2021) and in Giyani area, South Africa (Sadeghi et al, 2015) with recorded content in percentage values. It should recalled that concentrations of precious metals (e.g., Au, Pd, and Pt) in stream sediments are below the detection limit in general (Bellehumeur & Jébrak, 1993;Bellehumeur et al, 1994) and even low contents in stream sediments can reveal the presence of valuable ore in their sources (Bonham-Carter et al, 1987;Parsa et al, 2017;Shahrestani & Mokhtari, 2017).…”

Petrology and geochemistry of metamorphosed rocks associated with iron formations of the Toko‐Nlokeng iron deposit, (Southern Cameroon): Implications for geodynamic evolution and mineralization

“…The depositional setting processes of Toko‐Nlokeng IFs have been associated with the rifting of an intra‐oceanic island arc, an interpretation supported by the bimodal nature and geochemistry of the mafic‐ultramafic in the Nyong Complex as highlighted by Soh Tamehe et al (2022); Moudioh et al (2020); and Swiffa Fajong et al (2022). This extensional basin contains both IFs and Au‐rich volcanogenic sulfide deposits (Binam et al, 2018, Binam et al, 2019; Fuanya et al, 2019; Kouankap Nono et al, 2021), with a series of sulfide and oxidized mineral phases acting as high‐ and low‐temperature end‐members in the submarine hydrothermal systems (Binam et al, 2018). Therefore, the spatial relationship between mafic‐ultramafic and IFs is probably controlled by the thermal history of the hydrothermal system in the basin.…”

“…The depositional setting processes of Toko-Nlokeng IFs have been associated with the rifting of an intra-oceanic island arc, an (2022). This extensional basin contains both IFs and Au-rich volcanogenic sulfide deposits (Binam et al, 2018, Binam et al, 2019Fuanya et al, 2019;Kouankap Nono et al, 2021), with a series of sulfide and oxidized mineral phases acting as high-and low-temperature endmembers in the submarine hydrothermal systems (Binam et al, 2018). and Lecolle (1989).…”

Tourmaline occurrence and gold mineralization at a granitoid-metasediment contact in the Upper Lom Basin, east Cameroon

“…The irregular and beanshaped gold grains with rough outlines and cavities suggest recently dislodged grains from the bedrock into the saprock with limited weathering effect. The microchemical classification of alluvial and eluvial gold grains is a technique that has been applied by many authors to provide information on the type, source and mode of primary gold mineralization in an area [21,30,34,36,39,62]. Primary mineralization studies and source deposit type can be investigated using Au-alloy composition and gold grain geochemical variation [76].…”

“…The identification of primary gold deposits in the eastern, southern, and northern goldfields in Cameroon, on the basis of gold microchemistry, has yielded pertinent information concerning primary gold mineralization. Orogenic primary gold mineralization is suggested in the southern goldfield of Cameroon [21,[37][38][39], based on placer gold studies. Hydrothermal quartz vein style of mineralization is common in the eastern and northern gold terrane as the possible primary source of gold [21,22,34,40].…”