Multivariate cluster analysis of some major and trace elements distribution in an unsaturated zone profile, Densu river basin, Ghana

This study comprises soils formed on Paleoproterozoic Birimian Basement rocks (poorly graded silty sand, gravely sand and silty clays) from the unsaturated zone of the Densu River Basin, taken from a five meter depth. Elemental analysis of the soils samples were carried out by Energy Dispersive X-ray Fluorescence (EDXRF) to ascertain the levels of major and trace elements (K, Ca, Ti, Fe, Mn, Zn, Cu, Zr, Sr, Y, Pb, V, Cr, Ga, Ni and Rb) and to determine by statistical analysis the soil components which control the vertical distribution and the geochemical processes associated with the migration of the elements. The results indicated that there was general leaching of the base cations (K and Ca) near the surface 25 to 75cm depth while Fe and Ti concentrations remained fairly constant. Iron was the most abundant element found in the soil with concentrations ranging from 23.84g/kg to 143.70g/kg. The physicochemical analysis on soils shows moderately acidic to alkaline (pHH2O range 5.6 to 8.3) and reducing properties, Eh (mV) ranged from -107.1 to +50.2. Enrichment factor calculations show the metals were depleted or of minimal enrichment (EF values between 0 to 12.14) due to human activities. Cluster analysis of the samples shows only one sample is needed from depths characterised by similar physical properties of texture and colour.Key words: Unsaturated zone, energy dispersive x-ray fluorescence, vertical distribution, enrichment factor, cluster analysis

Geochemistry of Pegmatites associated with the cape coast granite complex in the Egyaa and Akim Oda areas of southern Ghana

The Cape Coast granite complex, which is associated with  metasedimentary rocks of the Birirmian in Ghana, is characterised by various minor intrusions that include pegmatites. The pegmatites, which are feldspar-rich, occur within, and at the margins of the granite batholiths and the surrounding schists. The major and trace element compositions of the pegmatites sampled from Egyaa and Akim Oda areas have been determined. The data indicates that the pegmatites from these areas have granitic compositions. The rocks are medium-K to high-K, calc-alkaline, S-type granitoids that are peraluminous and magnesian. Lower values of molar CaO/ (MgO + FeO <sub>tot</tot>) coupled with higher values of molar Al<sub>2</sub>O<sub>3</sub>/(MgO + FeO<sub>tot</sup>) suggest their derivation from partial melting from metapelitic sources, with the Birimian metasedimentary rocks being the likely source material. The rocks are depleted in Rb, Ba, Nb, Ce and Ti but rich in U, K, La, Hf and Y relative to primitive mantle. The data suggest that the pegmatites from these areas are late orogenic, and were emplaced at upper to middle crustal levels in a volcanic arc geotectonic environment