An assessment of soil pollution from artisanal gold mining in Wantia Area (Meiganga, Cameroon)

Cameroon has a strong geological potential for several mineral resources that, if well managed, could support economic growth through development of the mining sector. Wantia Area (Meiganga, Cameroon) is a “golden area” where gold is extracted by artisanal and slightly mechanized methods. Despite its economic contribution to the country's gross domestic product (GDP), gold mining is a source of environmental pollution, health hazards, deforestation and enhanced erosion that leads to the destruction of farmland. Unstable mine shafts, dumps and tailings, which are not monitored nor rehabilitated, cause environmental degradation. For example, where sulphides are in contact with water and air there is formation of acid mine drainage (AMD), polluting aquifers and surface water by heavy metals. In this study, we aim to assess the level of environmental degradation and metallic pollution of soil following gold mining to aid the preservation of environment and to promote a sustainable exploitation of mineral resources in mining sites. Macro-morphological characterization reveals that soils are clayey, slightly compacted and porous, with grain sizes in mainly clay to silt range. These soils are acidic with pH varies from 5.21 to 5.91, and consequently favorable to the solubilization of heavy metals [1].

The mineralogical assemblage of the soils obtained using x-ray diffraction (XRD) is mainly composed of quartz, kaolinite and muscovite, but also contains low concentrations of hematite, limonite, gibbsite, orthoclase, albite and calcite. This mineralogical assemblage is consistent with the region's geology, dominated by muscovite and biotite granites, orthogeiss and sandstones, and the weathering patterns [2]. The bulk chemistry of the soils and sediments obtained using x-ray fluorescence (XRF) showed high trace metal contents that exceed the maximum levels in upper continental crust [3]. Concentrations of trace metals (As, Cr, Cd, Fe, Ni, Pb, Sb, and Zn) in soil samples were analyzed using inductively coupled plasma mass spectrometry (ICP-MS) and the results were used to assess the pollution using an Enrichment Factor (EF) and geoaccumulation index (Igeo). Levels for all studied trace elements in soil samples greatly exceed those of the average continental crust and largely exceed those found in the control soil samples taken from areas distant from wind and/or water contamination by mining waste. EF revealed anthropogenic sources for Cd, As and Sb in these soils. Igeo indicates that Wantia soils are moderately to extremely polluted with As and Sb. Further studies are ongoing on the physico-chemical and microchemical analyses to determine the mineral phases that host and/or adsorb trace metallic elements (TME), the mechanisms of their retention and release into the environment, and transfer into the nutritional chain. Remediation methods can be suggested to overcome this situation and to ensure a sustainable use of mineral resources.

 

[1] Jung, M.C., & Thornton, I., (1996). Applied Geochemistry, 11, 53-9.

[2] Ganwa, A.A., et al., (2008). Comptes Rendus Geoscience, 340, 211-222.

[3] Rudnick R.L., & Gao, S., (2003). Composition of the Continental Crust. The Crust, Elsevier-Pergamon, Oxford, 1-64.

 

 

Keywords Wantia soils, Soil pollution, Artisanal gold mining, Heavy metal contamination.