Property Geology and Geological Model
On De Bad, diamondiferous gravels are found within the Rietputs C, B and A terraces and Rooikoppie Gravels.
The Rietputs C fluvial alluvial gravels are found adjacent to the present-day Vaal River (1 – 5m above the river) which has a total length of 3,5km within the De Bad Ox-bow. The extent of the gravels along the river within the De Bad exploration right is 1.9km (figure 15). The gravels are generally found in the deeper sections of the channel and may be locally very rich.
Areas of enrichment are usually associated with alluvial traps such as bedrock irregularities, rock bars, plunge pools and the presence of large boulders. This gravel has a bimodal nature to it and consists of angular to well-rounded cobbles and boulders of lava together with rounded to well-rounded pebbles and cobbles of quartzite, agate and chert.
Many years ago, adjacent to the river a pit was made in the Rietputs C gravels, where a few cobbles and boulders can still be found, whilst a small portion of the same gravels were mined by Sonop mining on the adjacent property. A bulk sample was also excavated during the same period on the lower terrace (figure 15).
The Rietputs B fluvial alluvial gravels are found some 800m away from the river, located on elevated terraces, 16 – 18m above the present river. The clast supported, pebble-cobble gravels are 1 – 2 m thick and slightly to massively calcretised, showing weak imbrication. The gravels are overlain by a thin layer of Rooikoppie gravel with an average thickness of 0.5m. The ‘rolling’ bedrock consists of soft Dwyka tillite. Thicker gravel deposits are found in the deeper, low lying areas on the bedrock (figure 15 and photo 4).
The Rooikoppie Gravels occur as a thin layer covering the Rietputs B fluvial alluvial gravels and extend further away from the terrace to the southeast, up to a height of roughly 21m above the present-day Vaal River (figure 15). Rooikoppie gravels consist of sub-rounded to well-rounded of the most durable lithologies, such as quartz, quartzite, agate, jasper, chalcedony, fossilized wood and minor BIF. In places Red Hutton sands and soils covers the Rooikoppie gravels.