Geology and geochemical aspects of lode gold mineralization at Dimako–Mboscorro, SE Cameroon

Abstract

The Dimako–Mboscorro lode gold deposit has two styles of mineralization: quartz veins (4.5–54 ppm Au) and altered wallrock (up to 2.6 ppm Au). The veins occur in steeply dipping brittle–ductile shear zones in a foliated biotite metagranite. The alteration envelop around the gold-bearing quartz veins shows lateral zoning comprising a silicified/ ferruginized and mylonitic zone (SFZ) at the centre, through a transitional sericite zone (SZ), to an outer, slightly sheared, but mineralogically less altered, though bleached, metagranite zone (BZ) at the shear zone boundaries. Hydrothermal alteration in these zones is characterized by silicification (SFZ, SZ), hematite formation (SFZ), alkali metasomatism with muscovite/sericite formation (SFZ, SZ, to a much lesser extent BZ), and pyritization (SFZ, SZ). The auriferous quartz veins are concordant to the host structure but discordant to the foliation in the metagranite. The main ore minerals in the veins and in the SFZ and SZ zones are gold, hydrothermal hematite, sphalerite, galena, pyrite, chalcopyrite, arsenopyrite, chalcocite, covellite and colloidal supergene hematite. Gold occurs as inclusions in sphalerite (15.7±0.4 wt% Ag; 83.6±0.2 wt% Au), as coarse grains associated with euhedral hematite pseudomorphs (18.5±1.0 wt% Ag; 82.0±1.1 wt% Au), as stringers within fractures in quartz (13.3±0.1 wt% Ag; 87.1±0.5 wt% Au), as well as fine to coarse grains related to limonite, goethite and colloidal hematite (8.1±1.8 wt% Ag; 92.1±2.2 wt% Au). A hydrothermal metal association of Ag, Au, As, Ba, Pb, V, W, and Zn is identified in the wallrock and quartz veins. These metals, together with K-enrichment, are potential pathfinder elements for wider lithogeochemical exploration in this region, especially when combined with the lateral wallrock zonation pattern. Preliminary fluid inclusion data from the auriferous quartz vein samples indicate that gold was probably deposited from low salinity (<1 to 8 wt% eq. NaCl, with mean at 5.52 wt% eq. NaCl) H 2 O–CO 2 fluids that have total homogenization temperatures of 263–335°C.

Characterization of Alluvial Gold Bearing Sediments of Betare Oya District-East Cameroon, Implication for Gold Exploration and Recovery

“…This structure is transtentional situated within grabens and horsts formed during sinistral shearing, displaying features similar to those of pull-apart basins [7] [8]. This basin was probably filled by eroded and transported materials from N30 E-N40-E striking gold bearing quartz veins [4] and slightly metamorphosed quartzites and granitoids [9]. Alluvial gold is remobilsed in the metasediments hosted in biotite-, sericite-and chlorite-schists as well as in quartzites and shales [10] [11].…”

“…It has several tributaries and intermittent run-offs that actively denudate the surrounding highlands. Primary gold bearing quartz veins [4] including other intrusions are of common occurrence on these surrounding highlands. Huge amounts of eroded debris is thus washed down from these highlands and collected into the Lom River for onward transportation and deposition along its channel and over the floodplain.…”

“…Secondary alluvial gold is generally found in Proterozoic metasediments of the Lom Series [3]. The gold potential is relatively high: 0.39 -4.5 g/ton after [4] but the gold recovery methods based on combined traditional (separation of heavy mineral fractions from the light ones using manual gravity shaking tables or by washing and panning the alluvial materials carried from streams) and much modern techniques (use of electric shaking tables, classifiers and separators) are not appropriate and need to be improved. Gold exploration should be intensified and research methods diversified.…”

Artisanal gold mining in Batouri area, East Cameroon: Impacts on the mining population and their environment

“…This domain is characterized by multiple major strike slip faults and the wide distributed syn-to post-tectonic granitoids (Djouka-Fonkoué et al, 2008;Njiekak et al, 2008;Kouankap Nono et al, 2010;Nzina Nchare et al, 2010;Chebeu et al, 2011). Those granitoids of Panafrican ages are the gold host rocks, the mineralization is diffused within the rock masses and in some place carried by hydrothermal quartz veins (Suh et al, 2006). The main rock type in Batouri is Granitoids which include porphyritic biotite-amphibolite granites and granodiorites cross-cut by numerous quartz veins bearing localized gold mineralization.…”

Environmental Geochemistry of Mine Tailings Soils in the Artisanal Gold Mining District of Betare -Oya, Cameroon

“…Previous researchers have highlighted the potentially negative environmental impacts of these processes on biodiversity, ecosystem function and ecosystem services (Malaviya, Munsi, Oinam & Joshi, 2010;Simmons et al 2008). Amonoo-Neizer, Nyamah, & Bakiamoh (1995) reported the significant distribution of As and Hg in the top soils, plantain, water fern, elephant grass, (Suh et al, 2006). Although Vairon (1986) attributed a Proterozoic age (2100-2200 Ma, Birrimian) to the Lom series, recent data (Soba et al 1991) provide evidence of inherited Archaean ages (c. 2500 Ma) and Neoproterozoic ages (700-1100 Ma) on zircons from detrital material and Neoproterozoic ages (c. 700 Ma) from metavolcanic rocks in this district.…”