Nevsun Resources’ copper expansion project at its Bisha mine in Eritrea reached commercial production in early December, following successful commissioning of a new copper flotation plant. Nevsun began producing gold at Bisha in December 2011, processing ore from the project’s oxide cap. The new flotation plant initially processed pyrite sand through the rougher flotation circuit to produce a precious metals concentrate. Production of copper concentrate began in August 2013.
Transportation logistics from the Bisha mine site to Massawa port were performing as expected, and three ocean shipments of copper concentrate totaling approximately $60 million in value had been made as of early December.
The build cost of the Bisha copper concentrator and infrastructure totaled approximately $110 million, 12% under the budget of $125 million. The concentrator is expected to reach its design production rate of 200 million lb/y of copper in concentrate in the first quarter of 2014 at cash costs of less than $1/lb.
The Bisha mine is located 150 km west of Asmara, the capital of Eritrea. The state of Eritrea has a free carried 10% interest in the project, plus an additional 30% paid participating interest for a total 40% interest.
The Bisha mine is based on a high-grade volcanogenic massive sulphide deposit that was configured in three distinct, layered zones: a 35-m-thick surface gold-silver oxide zone that is now mined out; an underlying, 30-m-thick copper-enriched supergene zone; and, beneath the supergene zone, a primary sulphide zone containing both zinc and copper, which is open to depth.
Probable supergene zone reserves total 6.42 million mt, grading 4.09% copper, 0.67 g/mt gold, and 28 g/mt silver. Con- tained supergene-zone copper is estimated at about 579,000 million lb. Probable primary zone reserves total 17.66 million mt, grading 1.13% copper, 6.54% zinc, 0.74 g/mt gold, and 49 g/mt silver. Contained primary-zone copper and zinc are estimated at 439 million lb and 2.5 billion lb, respectively.
Current planning calls for the addition of a zinc flotation circuit to the Bisha concentrator when mining reaches the primary sulphide zone.
Bisha is mined using conventional drill-and-blast, open-pit mining techniques. Comminution is through a conventional, single-stage crushing/SAG/ball mill circuit. Flotation is based on conventional rougher, cleaner and regrind circuits. Copper concentrate is thickened, dewatered and stock- piled for shipment. Tailings are stored wet in a lined tailings management facility.
Power is provided by dedicated diesel generators. Water is sourced from pit de-watering and from local well fields.