The Boseto copper mine is situated in Ngamiland in the Kalahari copper belt of north-west Botswana. The mine is 100% owned by Australia-based Discovery Metals and is being developed using open cut methods.
Results of a pre-feasibility study of the mine announced by Discovery Metals in July 2008 confirmed the economic viability of the project. A bankable feasibility study (BFS) completed in August 2010 further confirmed these results.
Botswana’s Government gave the final environmental approval for the project in June 2010. The mining license was awarded in December 2010 for 15 years.
Commissioning of the concentrator is currently underway. Milling, flotation and production of the first concentrate is expected in June 2012 with annual production of 36,000t of copper and 1Moz of silver. Production is expected to cease in 2026.
The project is expected to create direct employment for about 250 people and additional indirect and contractor jobs.
Geology and mineralisation at Botswana’s mine
The Boseto copper mine consists of three main prospects – Zeta, Plutus and Petra. The mine is part of the Ghanzi-Chobe fold belt, which is a 140km-wide zone of deformation.
The mine is found to contain copper mainly in the form of chalcocite. Minor amounts of bornite and other copper sulphides are also found. The copper occurs in steeply dipping areas with a width of two metres to 20m.
Malachite and chrysocolla mineralisation is also found at shallow depths. It will be stockpiled and will not be processed for the first 15 years.
Reserves, mining method and ore processing at Boseto copper mine
Mineral resources at Boseto are estimated at 131Mt graded at 1.3% Cu and 16.2g/t Ag. Measured resources are estimated at 15.7Mt graded at 1.4% Cu and 16.7g/t Ag.
Indicated resources are estimated at 20.5Mt graded at 1.5% Cu and 21g/t Ag. Inferred resources are estimated at 94.8Mt graded at 1.3% Cu and 16.2g/t Ag.
An open cut method will be used for the first three years of mining. Mining at the Zeta prospect is currently ongoing with 500,000t of ore being mined and stockpiled by the end of May 2012. Crushing of ore was also completed during the month.
Underground mining is expected to start from the Zeta prospect in the last quarter of 2013, with production expected in 2015.
A 3mtpa conventional copper silver concentrator has been constructed for processing the minerals. The concentrator includes a comminution circuit wherein the ore undergoes a three stage crushing followed by ball milling and grinding.
The ore will then be converted into slurry and processed through a sulphide flotation circuit and an oxide flotation circuit. The slurry processed through the sulphide and oxide circuits will be blended and dewatered using a press filter to develop the copper-silver concentrate. Commissioning tests are currently ongoing at the mill.
Costs and financial support for the African mine project
As per the BFS, the mining costs are estimated at $3/lb of copper and $28/oz of silver.
A syndicate of banks including Standard Chartered Bank, Standard Bank, Credit Suisse and Caterpillar Financial are providing a debt finance of $180m for the project as the lead financial arrangers. Caterpillar joined the syndicate in March 2011 to provide finance and equipment for the project.
The funds will be used for the construction of the copper silver concentrator ($105m) and for the mobile mining fleet ($75m). Caterpillar will supply the majority of the fleet for the mining operations. In addition, the syndicate will provide $25m towards cost overruns, working capital and hedge lines.
Transportation and handling of concentrate
Concentrate produced at the plant will be packed into 1t-2t bags and transported to African smelters or an international shipping port.
Discovery Metals signed a five year agreement with Transamine in March 2010 for 100% offtake of the Boseto concentrate. The agreement will reduce Discovery Metal’s risk exposure and improve its working capital.
Contractors and environmental studies at the Boseto deposit
In June 2010 Sedgman was awarded an engineering, procurement and construction contract worth $85m for the project. The scope of work includes design and construction of the copper silver concentrator and borefield development. GRD Minproc carried out the BFS for the project.
The environmental studies carried out for the project concluded that there were no negative environmental and social impacts. Surface water resources were also not expected to be impacted by the project.
Any potential impacts were termed as manageable and Discovery Metals is expected to undertake several mitigation strategies to deal with such impacts.