Abstract
The Springbok Flats Coalfield (SFC) is situated in a c. 60 km wide, 200 km long, SW-NE trending basin that stretches from c. 50 km N of Pretoria to 50 km S of Polokwane in the Limpopo Province. In this study, the distribution, nature and origins of uranium (U) mineralisation in the Karoo Supergroup of the SFC were investigated by a variety of methods, which includes; 1) facies analysis on borehole cores to understand the depositional environments, 2) geochemistry and mineralogical composition of the sedimentary rocks to understand the elemental concentrations and distributions (including uranium) and 3) provenance studies using U-Pb detrital zircon geochronology to indicate potential source areas of the clastic sediments. The geology of the SFC is largely known from borehole cores, as the Karoo Supergroup succession in the coalfield is poorly exposed. A total of five boreholes were drilled for this study, from the northeast (NE) to the central (C) and the southwest (SW) sectors of the SFC. The stratigraphy of the Karoo Supergroup in the SFC spans the Late Carboniferous to Early Jurassic. It is broadly similar to that of the main Karoo Basin (MKB), as well as to the Waterberg and Tshipise coalfields to the north of the MKB, and the Kalahari Karoo Basin (KKB) in Botswana, even though some units are absent. The basal part of the SFC consists of the fluvial-dominated lower Vryheid Formation (Fm), which is associated with swamp deposits of the lower Coal Zone (LCZ). The LCZ is only developed in the SW sector of the SFC and reaches a thickness of about 10 m. The lower Vryheid Fm is conformably overlain by a coarsening-upward successions of the upper Vryheid Fm, representing deltaic deposits, which are in turn overlain by the upper Coal Zone (UCZ). The LCZ and UCZ are cyclic deposits in the swamp characterised by a number of coal seams, alternating with in part carbonaceous as well as noncarbonaceous mudstones. The coal seams are dominated by alternating bands of bright to moderately bright coals and carbonaceous mudstones. The UCZ is conformably overlain by thick massive mudstones of the Beaufort Group equivalent, believed to represent deposits from suspension in a lacustrine environment. The Beaufort Group equivalent is unconformably overlain by the Molteno Fm, interpreted to have been deposited in fluvial environments under oxidising conditions. The Molteno Fm is in turn overlain by the Elliot Fm, which is dominated by very dusky red oxidised mudstones and siltstones, sandstones and conglomerates with fossil bone fragments occurring towards the NE sector of the SFC. The uppermost part of the Karoo Supergroup is represented by the Clarens Fm, consisting predominantly of aeolian sandstones. The Karoo sedimentation in the SFC was terminated by the extrusion of the Letaba Fm basalts, which are equivalent to those of the Drakensberg Group in the MKB.
Ph.D. (Geology)