Canteen Koppie at Barkly West: South Africa's first diamond mine

Canteen Koppie, a nationla monument of historical value, occurs next to Barkly West on the north bank of the Vall River. Diamonds wer discovered there in 1869 and it becamme the first alluvial diamond diggings in South Afric. The digging continued, albeit on and off in the yers leading kup to 1948 when the site was proclaimed a national monument. The sediments occur in a structurally controlled and glacially modified depression within the andesitic lavas of the Archaean Ventersdorp supergroup. The fluvial gravels were deposited, and locally modified depression within the colluvium, in the downstream end of a palaeo-loop of the Vall River as a splay deposit where the channel abruptly abruptly widenes as it exits this narrow loop. The gravel accumulation has been described as the 12 m to 16 m terrace package linked to the Younger Gravelsels of the Vaal Basin and correlated with the Pleistocene Rietputs Formation. There are two gravel facies associations and one sand facies within the splay unit. Colluvial facies are dominant particularly in the upper part and are composed of large andesite fragments which are mostly sub-angular and lacking obvious abrasion features suggesting that these are of local derivation. The gravel of the flyvial facies are crudely cross-bedded and consist of small to medium sized exotic sun-rounded pebbles that have been mixed with the local andesite boulders in the toes of the scree doposits. These facies are more prominent in the lower part of the succession. The red sand facies occurs as thin cover particularly in the distal part of the gravel units and increases in thickness in the lee of the gravel splay. The exotic clasts in the fluvial gravel are derived from the palaeo-Vaal, erosion of nearby Dwyka sediments which can still be found along the north bank of the loop[, and by reworking of higher level and older gravels, remnants of which are still present on top of the loop by the palaeo-Vaal and its inability to remove the coarse collurium during those latter states of its occupatio of this palaeo-loop. A climatic change to more arid periods might have had some influence. Canteen Koppie has also produced an abundance of Acheulian Stone Age artefacts. These are present in both sedimentary facies suggesting that this splay deposit is at lest Late Pleistocene to Lower and Middle Pleistocence in age. Recent dating of the overlying sands indicates that these are at least 125 000 years old. Finally an analysis of the mini8ng records suggests that this splay deposit might have produced between 10 000 carats and 15 000 carats of diamonds which would have expressed itself in the region of three of five carats per hundred tonnes. The oversized clasts of the scree deposits would have acted as important traps for the diamond s.