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

Bayari, Eric E., Foli, Gordon, Gawu, Simon K. Y.
Environmental earth sciences 2019 v.78 no.9 pp. 268
B horizons, C horizons, X-ray diffraction, X-ray fluorescence spectroscopy, aluminum, aluminum oxide, biotite, gneiss, gold, iron, mineralization, models, particle size, principal component analysis, quartz, regolith, Ghana
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 of > 5, while the mean chemical index of alteration (CIA) values are above 80%. Profiles contain > 70% 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 horizon based on CIA, loss on ignition and Fe/Al ratios; the horizon accounts for 52% of the material and 76% of elements in the > 2 mm 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.