Heavy mineral samples were taken from a vertical reverse-circulation drill hole, which cut weathered kimberlite from 34 metres down-hole to the end of the hole at 116 metres. The hole was stopped while still in kimberlite, owing to technical problems caused by groundwater.
Heavy minerals were extracted and representative samples of kimberlitic indicator minerals were tested by electron microprobe analysis. One sample contained 40 garnet, 12 chrome diopside and 50 ilmenite grains, while another contained 106 garnets and 21 chrome diopside grains.
Fifty-eight per cent of the chrome diopside plot within the diamond stability field. Garnet composition indicates that just over half of the peridotitic garnets are in the diamond stability field, whereas 40% of the eclogitic garnets plot in the diamond inclusion field. The ilmenite chemistry is indicative of an environment where diamonds could be preserved.
The A15 kimberlite is one of 23 kimberlites found in the Nxau Nxau kimberlite field. It has an indicated diameter of 800-1,000 metres and contains abundant coarse-grained ilmenite, garnet and chrome diopside grains (up to 5 mm in size).
A15 does not contain crater sediments and is deeply weathered, suggesting the upper portion of the crater was eroded. The drill hole cut tuffisitic kimberlite breccia containing xenoliths of shale, quartzite, granite and basalt. The kimberlite contains more chrome diopside and garnet than other kimberlites found in the area.
The company plans to drill more holes into A15 this month in order to extract a larger, representative sample for microdiamond analysis.
The project is held by Newdico, which in turn is owned by Tsodilo (81%) and South African-based
Gcwihaba Resources, a unit of Tsodilo, is exploring its wholly owned Gcwihaba property in Botswana. Ground gravity and magnetic surveys have identified targets for drilling.
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