Geochemical Dispersion of Elements and Their Correlation with Gold in the Regolith at the Tetteh Prospect of the Chirano Gold Mines in the Sefwi Belt of the Birimian, Southwestern Ghana

Abstract

The processes controlling gold (Au) mineralization in Chirano, a gold prospect in south-western Ghana have been investigated using a detailed geochemical dataset of 45 variables from 197 sampling locations. The data were subjected to advanced statistical analyses and bivariate graphical interpretations in the light of the underlying lithology. Four processes of significance have been identified from the multivariate analysis in terms of the geochemistry of the soil in the area. The most important process accounts for almost half of the total variance in the dataset and also correlates strongly with Au. Although Arsenic (As) registers the highest loading under this factor, Aluminium (Al), Silver (Ag), Manganese (Mn), Copper (Cu), and Iron (Fe) record higher correlations and could serve as better pathfinders than As in the study area. This study also shows that there is a second, less prominent process contributing to the availability of Au in the area. This process ranks third amongst the processes of significance in terms of the geochemistry, and correlates negatively with As, suggesting that the latter is not suitable as a pathfinder for Au in the traditional sense. However, since this third process is weaker compared to the first, the implication of this interpretation may be limited to only some locations in the study area. In addition to the revelations from the multivariate statistics, the regolith in the study area has evolved over the years and therefore the changes in regolith should be factored into the exploration protocols. The pre-existing preserved surfaces were found to be masked predominantly by transported materials consisting of ferruginized and exotic sediments. Within the surficial regolith and especially in the Fe-oxyhydroxide rich horizons, Au concentrations increase to significant values that are higher than those of the bedrock or saprolite thereby showing the significant Au re-distribution within the regolith. This study also highlights the apparent Au depletion in the mottled clay zones and in the saprolite and the enrichment of the metal in lateritic residuum and the topsoil. The high Au expressions in the upper parts of the regolith generally are transported whereas the residual soil anomalies have low Au concentrations and do not merit further exploration follow up.

Keywords: Regolith, Gold mineralization, Pathfinder elements, Chirano mine, Sefwi belt, southwestern Ghana.