Abstract
Gold mineralization in Mintom area, south Cameroon was studied in a tropical forest setting using X-ray diffraction, inductively coupled plasma-atomic emission spectrometry (ICP/AES) and inductively coupled plasma-mass spectrometry (ICP/MS) respectively for the mineralogical and chemical data. The mineralization occurs in quartz veins in the archean Ntem complex of the vast Congo Craton in Central Africa. Gold distribution patterns were vertically studied in the different horizons of the weathering profile and in the different grain-size fractions of the materials sampled in the pit on down slope of the interfluve where the mineralization exists. The weathering profile consists of an upper, thin loose sandy-clayey horizon (P6) covered by a light humic horizon, a nodular horizon with lateritic nodules or blocks (P5), a gravel horizon (P4), a thin spotted horizon (P3) and a saprolite (P2) up to 1.4 m thick. The specific geochemical signature of the bedrock is not recognized in each horizon of the weathering profile. Some groups of elements, e.g., high SiO2 and low REE characterize quartz vein while Cr-Ni characterizes a basic rock like gabbro. The residual gold is concentrated at the base of weathering profile. Its concentration increases from the saprolite up to the gravel horizon and decreases in the surface horizons. However, the evolution of visible Au distribution is not the same for all grain-size fractions: 1) in the finest fraction, the Au content is only regular in spotted and gravel horizons; 2) in the medium size fractions, the Au is in high content and greatly decreases from saprolite up to the spotted horizon and disappears in the upper horizons; 3) in the coarsest fraction, Au content is found in the saprolite and the maximum Au content of the weathering profile is found in this layer just above the mineralized quartz vein. This observation shows that the Mintom residual gold comes from the quartz vein.
Highlights
The supergene mobility of gold in weathering profiles has been well documented in different parts of the world [1,2]
The study of supergene distribution of metal patterns in tropical weathering profile has to integrate a series of complex processes, recent or former, making it difficult to understand [9]; and the behavior of various elements terrains is usual to refer to the general lateritic weathering model composed of three main units [5]
The close structural and chemical filiations between the different units and components of a lateritic weathering profile model in dry climate zones, in tropical rainforest, and more in Central Africa were described in detail [20,21], such examples are known in Cameroon [20,21,22]
Summary
The supergene mobility of gold in weathering profiles has been well documented in different parts of the world [1,2]. The gold-bearing quartz veins and their behavior in weathering profiles of laterites are widely studied [3,4]. Many vast tropical areas are widely covered by a lateritic weathering mantle. In the Ity gold area, Ivory Coast, the Au contents of the laterite profiles are variable (8 - 25 g·t−1) and are strongly depleted at the surface (around 1 g·t−1) [6]. They noticed that Au particles are fine (
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