Geochemical and pathfinder elements assessment in some mineralised regolith profiles in Bole-Nangodi gold belt in north-eastern Ghana

摘要

This study presents gold mineralisation and pathfinder elements characteristics in five surficial regolith profiles, with the aim of enhancing exploration strategies in the north-eastern Bole-Nangodi Gold Belt in Ghana. Samples were collected from mature soils and bedrocks in exploration pits and prepared for chemical and soil particle size analysis. 13 major elements, mineral forms and fifty-one trace elements were analysed using XRF, XRD and ICP-MS devices, respectively. SiO2, Fe2O3-MnO and Al2O3 are elevated in the A, B and C horizons, respectively, while Na2O-K2O-MgO-CaO-P2O5 systems dominate the bedrocks. Gold pathfinder element suites of As-Mo-Ag-Sn-Sb-Te-W-Hg-Bi are above Primitive Mantle values by a factor of5, while the mean chemical index of alteration (CIA) values are above 80%. Profiles contain70% quartz with stable mineral concentrations of 53, 18 and 29% in the A, B and C, horizons, respectively. The B horizon is the most altered horizonbased on CIA, loss on ignition and Fe/Al ratios; the horizon accounts for 52% of the material and 76% of elements in the2mm particle size. Mass balance and principal component analysis shows that Au exploration targets and the associated pathfinder element suites are the following: (1) horizon A with Sr-Ca-Ge-Sn-Th in the amphibolite and biotite gneiss profiles (2) horizons A and B with S-K-Zr-Tl-Ge in the volcaniclastic and (3) the bedrocks with Cu-Pb-Sb-Ag-Mo and Mn-Cr-Ba-V-Ce-Bi-Fe-Co-Sb-As-Se of the metavolcanic and phyllite profiles, respectively. The regolith models summarise the mineralogical and structural framework of the profiles and may largely influence exploration designs.