Tsodilo Resources Limited, the international metals explorer said Bosoto (Pty) Ltd, its Botswana subsidiary has completed core drilling programme on BK16. According to the company, the main objective of this stage of the evaluation programme of this 5 hectare kimberlite pipe and satellite is to upgrade the geological model.
It said a robust model is required to optimise the outlay of the large diameter drill (LDD) holes for the forthcoming bulk sampling programme.
“In total, 20 core holes (NQ) were drilled over various part of the intrusion. Three of these holes were re-drilled due to drilling difficulties for improved core recoveries in difficult ground conditions and hence there are 17 boreholes which will be used in the geological model. Five of these were vertical holes and 12 were inclined also to intersect the kimberlite contact with the country rock. In total 3,662.2 meters were drilled,” the company said in an update.
Tsodilo said the core has been moved to the company’s facility in Maun where detailed geological (kimberlite facies and estimates of dilution by country rock fragments) and geotechnical (density, fracturing and joint patterns) studies are conducted. All cores have been photographed, logged and magnetic susceptibility readings taken every 20 cm. Samples from selected kimberlite phases have been submitted for petrographic analysis.
The core was examined by kimberlite specialist, Dr Jock Robey, macroscopically and microscopically using a binocular microscope. Five different phases of kimberlite were identified: Red volcaniclastic kimberlite VK1, Black VK2, Grey VK3, VKXXX and coherent kimberlite CK1.
According to Tsodilo, the Red VK1 occurs as thin irregular skins at the pipe contact, has both basalt and sandstone xenoliths and may have been the earliest kimberlite phase while the Black VK2 occupies most of the eastern part of the Main pipe and consists of pale green to white altered olivine macrocrysts that reach 10 mm in size but which are typically 3 mm in size.
It said the most distinctive feature of the Grey VK3 are the common relatively small (<10 cm) basalt Xenoliths that are totally altered to a grey colour. “This VK occupies the western part of the Main pipe and is seen to contain large brown olivine macrocrysts typically 5 mm in size (max. 10 mm).”
It added that the VKxxx was isolated as it is only seen in some parts of the upper pipe and is dominated by basalt xenoliths up to 8 m in size, with many of the large blocks showing evidence of brecciation. “This brecciation is thought to be related to sub-surface explosive activity during the embryonic stages of pipe formation while the CK1 was intersected between the Main pipe and the Satellite, has high angle contacts to the wall rock sediments and has been interpreted as a dyke.”
Kimberlite phases VK2 and VK3 are volumetrically the most important and will be the focus of the LDD programme. However, this programme will only be finalised once the geological model has been completed.
The BK16 kimberlite project is located within the Orapa Kimberlite Field (OKF) in Botswana. Botswana diamond mines have produced an average of 27 million carats annually in the last 10 years and Botswana is the world’s largest producer of diamonds by value. In 2014, the OKF area produced 13,355,292 carats.