1. Boreholes with good sampling devices (such as core drilling heads or sampling tubes) should be drilled at grid positions N0E4.8, S0.5E4.8, and S1E4.7 to investigate the high geomagnetic anomaly to determine if this is a gravel filled trench or a kimberlite body or some other intrusive.
2. After powerful dewatering systems have been established in the existing Deep Hole on Muirton, as well as in strategically placed wide-diameter borehole wellpoint screens, excavation of all the overburden between the existing water filled excavation (Deep Hole) and the western boundary of Muirton must be carried out in order to expose the basal gravel in this deep trench for the recovery of the large number of diamonds which have probably been trapped there.
3. The ridge of Dwyka Shale shown on the map by Mr Coen Visser will help to restrict inflow of water from the Vaal River into the workings, but the south eastern extension of the gravel filled trench or depression could be a problem. If, as expected, this trench extends into the channel of the Vaal River, it could provide a permeable conduit for flow of water from the river into the depression, and would therefore need to be sealed off from the river. The presence and width of such a deep gravel zone should be properly investigated by means of boreholes, its properties determined, and its areal extent clearly mapped, in order to do effective planning of protective measures for the area between the Dwyka Shale ridge and the Ventersdorp Lava hill, These could then entail the following:

Aerial photographs of the area show what appears do be a kimberlite fissure system running from the east across the farms Drooge Veldt and Klipfontein and eventually crossing the Vaal River and entering the southern part of Muirton. This would intersect a north-northeast trending fissure in the area of the high magnetic anomaly encountered by the geomagnetic survey.

The presence of so many grains of Chrome Diopside in the drilled samples (AAB56 Sample No's. 2 and 4, C.H.E. Visser) is of special significance. This mineral, found only in Kimberlite, is comparatively unstable, and would not remain unweathered over long distances in the fluvial environment of the Vaal River floodplains. Chrome Diopside present in fluvial gravels must therefore be taken as a good sign that these deposits are not far removed from some Kimberlitic source such as a pipe or a fissure.

Muirton Farm undoubtedly displays a very unique set of geological features encompassing both Primary Kimberlite and Secondary gravel Deposits which warrant further proper excavation and treatment for the recovery of diamonds.

G.J. Greeff (Ph.D.)

Stellenbosch

15 February 1997