Following the transfer of BHP Billiton’s interest in the Alto Cuilo joint venture exploration project in Angola to Petra Diamonds, Petra has taken full control of the project. It will fund and operate the project. Petra also acquired a 40% shareholding in Moyoweno, the Angolan commercial company which holds a 13% interest in the Alto Cuilo kimberlite project.
At Alto Cuilo, Petra is focusing its work programme on nearsurface crater rim resedimented volcaniclastic kimberlite deposits where encouraging exploration results were recorded. Petra believes that the crater rims have the potential for substantial deposits of economic diamond-bearing material, as is the case at other diamond mines with similar mineralisation, such as Catoca in Angola and Williamson in Tanzania.
An initial work programme budget of US$10 million for 2008 is being funded from Petra’s internal cash resources, and Petra expects to significantly accelerate the pace of exploration at Alto Cuilo.
Previously, the Alto Cuilo kimberlite exploration programme focused on delineating economically viable largetonnage kimberlite vents containing diatreme-facies volcaniclastic or tuffisitic kimberlite. The diamond bearing potential of crater-facies resedimented volcaniclastic kimberlite (RVK) was not the area of focus, and specifically not the RVK typically encountered along crater rims. Catoca successfully mines this crater facies RVK close to surface and Petra believes that by refocusing the exploration campaign on the crater facies RVK, the potential for finding a world-class kimberlite deposit at Alto Cuilo remains good.
From the entire Alto Cuilo area of 2,670 km², Petra identified 276 km² for its revised work programme. This smaller area hosts 51 kimberlites of which eight are being targeted. These kimberlites form a cluster and the possibility is one or more could be mined using a central process plant.
Mining of the Catoca pipe has shown that RVK can sustain a kimberlite mine that extends to depths in excess of 100 metres. Catoca, which recorded revenues of US$450 million for 2007, is approximately 60 hectares in surface area. The eight kimberlites targeted by Petra at Alto Cuilo range from an estimated 30 to 180 hectares in surface area.