Trevali Mining has announced the results of a preliminary economic assessment (PEA) for restarting production at its Caribou underground zinc-lead-silver mine and mill complex in the Bathurst mining camp of northern New Brunswick, Canada. 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.

The base case PEA for reactivation of the 3,000-metric-ton-per-day (mt/d) Caribou operation indicates positive economics at a pre-production capital expenditure of $36.3 million to produce approximately 93 million lb/y of zinc, 32.5 million lb/y of lead, 3.1 million lb/y of copper, 730,000 oz/y of silver, and 1,500 oz/y of gold in concentrates. Life-of-mine cash costs are estimated at $0.46/lb of zinc equivalent over a mine life of 6.3 years.

“We welcome this preliminary economic assessment for our Caribou mine, with scheduled commissioning of operations in the first half of 2015,” Trevali President and CEO Mark Cruise said. “These results model a respectable return based on this initial base-case model, and we believe that there is excellent potential for additional optimization given that approximately 3 million mt of mineralized material is presently not included in the mine plan and the deposit remains open for expansion.”

The base case Caribou PEA uses price assumptions of $1/lb zinc, $1/lb lead, $3/lb copper, $21/oz silver, and $1,200/oz gold. Underground operations will take advantage of in-place development and infrastructure, with a centralized ramp trucking system serving as the main access for the mine. Mining will primarily be conducted using the Modified Avoca method with waste-rock backfill, with the exception of a longhole retreat mining method for partial sill pillar recovery near the end of mine life.

The processing plant’s milling circuits will include fine-grinding using IsaMills to optimize metallurgical recovery of the fine-grained sulphide mineralization in the district, followed by standard sulphide flotation recovery circuits to produce three concentrates: zinc, lead-silver and copper-gold. The average life-of-mine modeled head grade for mill feed is 6.11% zinc, 2.49% lead, 0.34% copper, 67.9 g/mt silver, and 0.86 g/mt gold.

The restart of Caribou operations represents the initial development phase of Trevali’s longer-term plans for its Bathurst camp properties. Subject to ongoing technical studies, the company is looking at the potential for a second stand-alone milling facility to support development of its fully permitted Halfmile mine and the Stratmat deposit, where drilling and baseline permitting programs are in progress.