Nevsun Resources joined the ranks of producing mining companies in early January when it poured the first gold at its Bisha mine 150 km west of Asmara, Eritrea, East Africa. The first pour was part of the plant commissioning process and rendered two doré bars totaling 26 kg (approximately 920 oz). Nevsun, which is headquartered in Vancouver, British Columbia, anticipates ramp-up to full commercial production will be completed during the first quarter of 2011, and said Bisha came in under its budgeted cost of $260 million.
The Bisha deposit is configured in three distinct layered zones, a 35-m-thick surface oxide cap having a high gold and silver content immediately overlying a 30-m-thick, copper-enriched supergene zone, which itself overlies a deeper primary sulphide zone containing both zinc and copper, which is open at depth. The open-pit Bisha mine will produce about 430,000 oz/y of gold from the oxide cap during its first two years of operation. During the following three years, it will produce high-grade copper concentrate from the deposit’s supergene zone, and thereafter it will produce separate zinc and copper concentrates from the primary zone.
Contained metal production over Bisha’s projected 10-year mine life is expected to total 1.06 million oz of gold, 9.4 million oz of silver, 734 million lb of copper, and more than 1 billion lb of zinc. Operating costs, including all royalties and credits are expected to be under $250/oz of gold, in the range of $0.54 to $0.67/lb for copper, and $0.50/lb for zinc.
The Bisha mine is based on conventional open-pit mining methods, using heavy-duty highway trucks loaded by excavator/loader. The milling rate will be 5,500 mt/d of ore. The oxide ore is being processed by cyanide leaching and carbon in pulp recovery; the supergene and primary ores will be processed by flotation. Production of copper concentrate will begin at a minor amount during year two, increase to significant quantities during years three to five, and reduce to smaller quantities during years six to 10. Zinc concentrate production will occur only during years six to 10.
The state of Eritrea has a free carried 10% interest in the Bisha project, plus an additional 30% paid participating interest, for a total of 40%.