South Africa – The purpose of this first phase of drilling was to increase the geological confidence in the c. 6 km long kimberlite dyke/blow system, which is east of, and on strike with, the former De Beers / Southern Era operated Marsfontein mine.
Marsfontein was operated for two years in the late 1990s with economics which allowed the entire capital cost to be recouped in under four days. Marsfontein’s run of mine grade was 172 cpht at a bottom cut off of +1.2 mm.
34 percussion holes (totalling 1 459 m) and nine diamond drill holes (totalling 432 m) have been drilled along a 1 580 m strike length of the c. 6 km dyke/blow complex. The width of the kimberlite dyke/blow system is between 1 and 2.7 m with two wider areas or ‘blow’ identified.
To test the vertical continuity of the system, a single 104 m hole was drilled chiefly in kimberlite. Petrographic analysis of the samples has resulted in classification of the dyke as a Group 2 Olivine Phlogopite rich magmatic kimberlite with the blows being volcanoclastic kimberlite. The size and abundance of olivines which are diamond indicator minerals is very positive.
A population of over 200 garnets have been microprobed with 38 probed as G10 (Harzburgitic paragenesis) and 17 as G10D (diamond inclusion garnets). A total of 18 garnets have been probed as Group 1 Eclogitic type which suggests a strong Eclogitic diamond paragenesis.
The remaining garnets are high interest G9 along with some megacrysts. These G10 and G9 garnets are important diamond indicators and have similar mineral chemistry to the nearby Marsfontein mine. A 200 kg core sample has been consigned for microdiamond analyses with results available within two months.
In previous work, 467 diamonds yielding 247 carats were recovered from the processing of surface material. The largest diamond was 3.66 carats and the parcel had an average size of 0.53cts/stone. The sale of these diamonds achieved a rough diamond value of US$180/ct and a modelled value of US$259/ct at a bottom cut off of +2mm.
Detailed ground geophysical test work has also been undertaken by Geofocus to determine the most effective technique to delineate the further lateral extension of the system. This work will select targets to be drilled during April and May. The results of the next drilling phase will determine the areas of Frischgewaagt, which will be subject to bulk sampling.
“Frischgewaagt is turning into a very exciting project. To date we have discovered two ‘blows’ on the kimberlite dyke system. We are moving to delineate the size of each one. The drilling samples contain high quantities of diamond indicator minerals of similar profile to the highly profitable Marsfontein mine some 20 km away,” says John Teeling, chairman of Botswana Diamonds.
“In the next two months we should have results from the microdiamond analyses and further information on the size and composition of the kimberlite dykes.”