Robert Nshimirimana

The late Middle Pleistocene upper third molar from Florisbad : metrics and morphology

In the early 1930s an upper right third molar (M3) together with a calotte and fragmented facial bones of an adult fossil hominin was recovered during excavations at Florisbad. The M3 is one of the few well-dated teeth associated with cranial remains from the late Mid-Pleistocene in southern Africa and as such provides a valuable addition to the fossil dental record of this region. Here we provide a detailed description of the tooth based on standard measurements and 3D images derived from high resolution micro-high resolution micro-focus X-ray tomography. Our results show that the Florisbad M3 falls within the size range of African Homo erectus. It is slightly larger than other peri-contemporary M3s known from Africa that date from the Middle to Late Pleistocene. Like them, however, it also falls within the size range of recent, large-toothed African populations. These results suggest the maintenance of selective pressures favouring large teeth in some African populations until the present.

The Use of 3D X-Ray Computed Tomography for Gold Location in Exploration Drill Cores

Three-dimensional computed tomography (3DCT) is a non-destructive characterisation technique that was applied to the study of gold-bearing ore from the Witwatersrand Deposit, South Africa. The ability to pinpoint gold occurrence prior to downstream comminution and leaching would potentially reduce processing costs. The aim of the study was therefore to determine to what extent gold, typically fine-grained in occurrence, could be identified in situ. Two gold-bearing drill core pieces were investigated using 1-mm focal spot X-ray tomography and micro-focus X-ray tomography (μXCT). Using the derived data, the cores were physically cut and polished for examination by conventional automated scanning electron microscopy (SEM) to detect gold grains. The SEM results were then compared against the μXCT data. Gold was, to an extent, located by μXCT and validated against SEM data. These first findings suggest that areas rich in gold can be pinpointed by 3DCT prior to conventional assessment, hence potentially reducing processing costs.