Trevali began commissioning the 3,000-mt/d Caribou mill, shown here, in May. (Photo: Trevali Mining)

When Caribou reaches design capacity, its annual payable production of metals in concentrates will average approximately 93 million lb of zinc, 32.5 million lb of lead, 3.1 million lb of copper, 730,000 oz of silver, and 1,500 oz of gold over a planned mine life of 6.3 years. Direct life-of-mine cash costs are estimated at $0.46/lb of zinc equivalent. Total site operating costs are estimated at $74.77/mt milled, including mining, milling, general and administrative, and environmental.

Trevali acquired the inactive Caribou operation from Maple Minerals in November 2012. The mine and mill had operated for approximately 13 months prior to going into receivership in 2008 due to depressed commodity prices. Trevali replaced, refurbished, or repaired all of the key mill operating units, including crushing, grinding, flotation, concentrate filters, metallurgical and geochemical laboratories, and concentrate handling facilities.

As of mid-August, troubleshooting of ramp-up issues was ongoing. A new SAG mill and the two existing ball mills and three IsaMills were all operational. Ongoing initiatives were focused on optimizing charge rates, grind characteristics, and media composition.

Underground mine production was continuing according to plan at approximately 1,500 mt/d, sufficient to maintain the approximately 100,000-mt surface mill feed stock pile being utilized during mill commissioning.