PETROLOGY OF GOLD RICH SOIL AND IMPACT OF GOLD MINING ON SOILS IN MEIGANGA AREA (ADAMAOUA PLATEAU, CAMEROUN)

The soils of Meiganga, belonging to the lateritic domain of the intertropical regions, have significant mining resources that are exploited by artisanal and slightly mechanized methods, providing income to the government and local populations. However, this activity’s nature remains a source of insecurity and very serious environmental transformations. This study aims to contribute to the knowledge of the macromorphological, mineralogical, geochemical and physicochemical characteristics of these soils and to assess the level of physical degradation and metallic pollution of the soils of this locality following gold mining. For this purpose, field work during which observations were made in situ; pits were dug and described macroscopically; soil samples were taken for laboratory analysis.The in situ observations show that, depending on the gold mining techniques used, the sites are exposed to deforestation risks, erosion, collapses, soil and water pollution, etc.

Two aspects have been considered in this study: 1) petrological characteristics of weathering profile shows that it can be divided into three parts, from the bottom to the top which are: weathered and decayed rock; a nodular ferruginous relict of lateritic crust and surface clay-sand. We notice a homogenization and a wathering of the primary chemical signature more and more marked as we get towards the surface. Macromorphologically, they are generally of clay texture, lumpy, polyhedral, more or less compact, and porous. The major present mineral phases are quartz, kaolinite and muscovite. One notes the presence sometimes of hematite, gibbsite and orthoclase, and also albite and calcite but with low contents. 2) Trace elements contents (Cr, Ni, Cu, Zn, As, Pb, and Cu) are high, exceeding the maximum tolerated values in the soil, and the highest values are found in the clay mineral rich horizons. Microchemical analyses (SEM) and extraction tests are in process with a view to better understanding of the retention mechanisms and the risks of release of trace elements into the environment, and their transfer to the food chain. In order to ensure a sustainable management of mineral resources and protect humans from any risk.

Key words: soil petrology, lateritic soils, gold mining, metallic trace elements, metallic pollution.