The bedrock of the region is covered by at least a thin veneer of wind-blown Kalahari sand and exposure is very poor. Rocks close to surface are often extensively calcretised and silcretised due to prolonged exposure on a late Tertiary erosion surface (the African Surface) which approximates to the present day land surface.
The country rock at the Karowe Mine site is sub-outcropping flood basalt of the Stormberg Lava Group which is underlain by a condensed sequence of Upper Carboniferous to Triassic sedimentary rocks of the Karoo Supergroup. The basalts, which are very extensive and underlie much of central Botswana, are Jurassic (180 Ma) and lie unconformably on the sedimentary succession, but are traditionally regarded as part of the Karoo Supergroup.
There are few outcrops in the Letlhakane area, as the bedrock is concealed by several metres of aeolian sand of the Kalahari Group, reflecting the area's position on the edge of the Tertiary Kalahari Basin. To the south and west of the Orapa Kimberlite Field, the bedrock may be overlain by up to 40 m of Kalahari Group sediments.
The Orapa Kimberlite Field lies on the northern edge of the Central Kalahari Karoo Basin along which the Karoo succession dips very gently to the south-southwest and off-laps against the Precambrian rocks which occur at shallow depth (although they are seldom actually exposed) within the Makgadikgadi Depression. The Karoo succession is condensed, with a total thickness of around 600m and is best preserved in west-northwest/east-southeast oriented grabens. The large AK1 Kimberlite lies within such a graben (Coates et al. 1979).
The Orapa Kimberlite Field includes at least 83 Kimberlite bodies, varying in size from insignificant dykes to the 110 ha AK1 Kimberlite which is Debswana's Orapa Mine. All are of post-Karoo age. Of the 83 known Kimberlite intrusions, four (AK1, BK9, DK1 and DK2) have been or are currently being mined, and a further five (AK6, BK1, BK11, BK12 and BK15) are recognized as potentially economic deposits.
Drilling has shown country rock succession at the property. The volcanic and sedimentary units are almost flat lying.
Bedrock is covered by a reddish brown top soil layer 1.0 - 1.5m thick made up largely of aeolian sand. There is a discontinuous thin gravel layer or 'stone line', <0.6m thick, at the base of the soil with clasts from 20 - 50mm in size. The gravel is partly calcretised. Testing by De Beers has shown it to be barren of diamonds. The soil and gravel are underlain by a friable calcrete to a depth of 3 - 4m, below which is a massive silcrete horizon, often densely veined by calcite. Over the Kimberlite, the silcrete grades downwards into highly weathered and partially silcretised Kimberlite with extensive calcite veining. Indicator minerals and vaguely preserved macrocrystic Kimberlite texture can be seen in places. Kimberlite can be clearly identified below about 8 - 10m depth.
The geology of the AK6 Kimberlite has been deduced from geophysics, drilling and trenching.
Below the highly weathered layer, generally at a depth of 8 to 12m below surface, the Kimberlite is reddish brown to grey, soft and friable, and intensely veined. The Kimberlite tends to become softer with depth, although large lenses of calcrete and silcrete occur up to 15m below surface.
The Kimberlite is pinched at surface, and its sub-outcrop consists of a core covering 4.2 ha of Kimberlite surrounded by an area where the Kimberlite is capped by basalt or basalt breccia. The peripheral basalt breccias are not included as Kimberlite in the geological model, and are thus excluded from the resource.
The AK6 Kimberlite is regarded as a volcaniclastic Kimberlite, possibly pyroclastic, showing various degrees of welding. Better exposure following the start of mining operations may revise this interpretation.
The information in this section which is of a scientific or technical nature has been derived from the following technical report:
AK6 Kimberlite Project, NI 43-101 Technical Report revision and update on the AK6 Kimberlite Mine, Botswana", dated December 31, 2010 prepared by MSA Geoservices (Pty) Ltd. and authored by Messrs. Ian McGeorge, Consulting Geologist (BSc (Hons), Geol. MSc, CGeol, FGS), Mike Lynn, Senior Project Manager (BSc (Hons), Geol, MSc), Johannes Ferreira, Consulting Geostatistician (MSc, DEA Geostatistics, PrSciNat) and Rob Croll, Consulting Engineer (BSc (Min Eng)), Dave Blair, Consulting Environmental Scientist (BSc (Hons) Zool., Pri.Sci.Nat) and Dr. Kym Morton, Consulting Hydrogeologist (PhD FGS FSAIMM, Pri.Sci.Nat), each of whom is a "qualified person" within the meaning of this term in National Instrument 43-101 (the "AK6 Kimberlite Technical Report").
Copies of the above-mentioned technical reports are available under the Company's profile on SEDAR at www.sedar.com.