TRACE ELEMENT GEOCHEMISTRY OF SOUTH AFRICAN OILS AND CONDENSATES

Seven trace elements (Co, Cr, Cu, Fe, Mn,, Ni, and V ) were determined in 27 crude oils and condensates from Bredasdorp and Orange sedimentary basins, South Africa using inductively coupled plasma – optical emission spectrometry (ICP-OES). The trace element distribution patterns were used to determine the origin and thermal maturity of the oils and condensates and depositional environment of the organic matter from the oils were derived. The abundance of trace elements in the both Bredasdorp and Orange Basins are generally low. The abundance of trace elements in the oil samples is relatively higher that of the condensates. The metal ratios especially V/Ni indicate that the source rocks of most of samples from the two basins were deposited in reducing environments with a few samples deposited in oxidizing environments. The cross plot of nickel versus vanadium of samples from both Bredasdorp Basin and Orange Basin indicates the source rocks that yielded most of the samples had marine organic matter source input and were deposited under anoxic conditions. The distribution of the trace elements and the values of the ratios calculated from them indicate that the samples are thermally mature. Dendogram cluster analysis of the samples was able to discriminate between oils and condensates but did not discriminate between samples from different basins.