Nevsun’s Copper Expansion Reaches Commercial Production
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. Contained 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 drilland-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 stockpiled for shipment. Tailings are stored wet in a lined tailings management facility.
Power is provided by dedicated diesel generators. Water is sourced from pit dewatering and from local well fields.