The Zone 5 underground mine within the Khoemacau copper project in Botswana is accessed via the north, central and south boxcut portals. Credit: Khoemacau Copper Mining.
Ore is processed at the Boseto processing complex, located 35km from the mine site. Credit: Khoemacau Copper Mining.
Power is supplied by the Botswana power grid to a 132kV substation at the Khoemacau copper project site. Credit: Khoemacau Copper Mining.

The Khoemacau copper project is an underground mine being developed by American private equity firm Cupric Canyon Capital’s subsidiary Khoemacau Copper Mining in Botswana.

Khoemacau Copper signed a $565m project funding package deal with Cupric Canyon Capital for the development of the high-grade Khoemacau copper project in February 2019. The funding package was increased to $650m in July 2019. Underground development at the Zone 5 mine within the project commenced in early-2020 with more than 350,000t of high-grade sulphide stockpiled on the surface to date.

The production of the first copper and silver concentrate from the Khoemacau project was achieved in June 2021. The project is expected to have a life of mine (LOM) of 22 years.

An expansion project to increase the production at Zone 5 from its existing 3.65 million tonnes per annum (Mtpa) to 4.5Mtpa is also currently underway. The expansion project is expected to produce more than 125,000t of copper and 4.5 million ounces (Moz) of silver a year at full-scale production.

Khoemacau copper project location, geology, and mineralisation

The Khoemacau copper project is located in a 4,040km² land package within the Kalahari Copper Belt in north-west Botswana. The underground mine development is currently focused on the Zone 5 deposit with a strike length of 4.2km and south-east dipping mineralisation with an average thickness of 10m.

The deposit is situated between two sandstone units, the hanging wall Marker sandstone and the footwall Ngwako Pan quartzite sandstone. It remains open at depth and partially along strike.

The mineralised zone is situated in the hanging wall sequence, approximately 30m above the contact between the Ngwako Pan and D’Kar formations. It cross-cuts host units from the lower D’Kar limestone unit in the south-west to the interbedded alternating siltstone and sandstone unit and carbon-rich siltstone unit in the north-east.

Mineralisation near the surface occurs as a transitional sulphide zone containing both oxide and sulphide minerals including malachite, chalcopyrite, bornite, native copper and minor chrysocolla. Located in the centre portion of the deposit, a small zone that extends to depths of 400m below the surface is dominated by native copper with strong brecciation.

Khoemacau copper project reserves

The proven and probable mineral reserves at the Khoemacau copper project (Zone 5) were estimated at 33.96 million tonnes (Mt) grading 2.03% copper (Cu) and 19.66g/t silver (Ag), as of June 2020.

Mining operations at Khoemacau copper project

The Zone 5 mine is a bulk mechanised underground mining operation based on the long hole open stoping (LHOS) mining method. The mine is expected to have a production capacity of 3.65Mtpa via three mining corridors, with production ranging between 1Mtpa and 2Mtpa from a single mining corridor. Stope production is performed using 9m³ (21t) loaders and 60t haul trucks to transport the run of mine (ROM) ore to the surface.

The first section of the mine uses pillars with no paste fill. Paste filling will be incorporated as the mining depth increases to improve overall resource recovery.

The orebody with more than 4km strike length made it necessary to split the strike into mining corridors with twin decline systems servicing each corridor with exception of the North Corridor that starts as a single decline. The design provides surface access to each of the three corridor decline systems through three boxcuts.

The 6mx6m decline allows the passage of the largest fleet item, the haulage trucks while also meeting the ventilation requirements. The declines have a minimum radius of 25m to provide optimal access to levels that are spaced 25 vertical metres apart.

The downward gradient of 1:7 maximises the capability of the haulage fleet and minimises the decline length per vertical metre. Level accesses between floors are at 50m vertical intervals, which increase to 60m when passing the sill pillar locations.

Mineral processing

The Boseto sulphide concentrator, located 35km from the mine site, is being upgraded from its original nameplate capacity of 3Mtpa to 3.65Mtpa to treat the Zone 5 ores. The project is estimated to produce up to 155,000t of high-grade copper concentrate at 40% Cu and 375g/t Ag.

The ROM ore undergoes a three-stage crushing in a primary jaw crusher followed by secondary and tertiary cone crushers before being passed on to a crushed product screener. The fine crushed ore undergoes grinding in a ball mill with a cyclone separator, while the cyclone oversize undergoes regrinding and separation in a secondary cyclone.

A linear screen sorter transfers the fine ground material to the rougher flotation circuit to produce the rougher concentrate, while the tailings flow to a tailings thickener and are stored in the tailings storage facility to be later used as backfill.

The rougher concentrate undergoes two-stage cleaning to produce a concentrate that is thickened and filtered to produce the final concentrate which is stockpiled before being bagged for shipping.

Project infrastructure

The power demand for the project is being met by the Botswana power grid via a 50km-long overhead transmission line connected to a 132kV substation. Backup power is supplied by existing diesel generators from the previous Boseto operations.

The process water requirement is met from two wellfields, at Boseto and Haka including a new 40km-long underground pipeline from Haka to Zone 5. Additional water supply is secured from the dewatering of boreholes from the Zone 5 mine.

Contractors involved in the copper-silver mine

Khoemacau Copper Mining awarded Australian mining services provider Barminco a five-year underground mining services contract for the Zone 5 mine in June 2019.