With the Sullivan and Polaris mines scheduled to close in the next two years,
The go-ahead to rebuild the existing mill and reopen the underground mine comes on the heels of a recently completed positive feasibility study. Pend Oreille is a mere 50 road miles south of Cominco’s smelting and refining operations at Trail, in neighboring British Columbia. Minable ore reserves are currently estimated at 6 million tonnes grading 7.2% zinc and 1.3% lead, based on 30% dilution and 80% recovery. The project also hosts inferred resources of about 500,000 tonnes grading 4.4% zinc and 0.7% lead.
A two-year construction program is slated to begin in October. It will involve the refurbishment of the existing concentrator and the sinking of a 1,250-ft. internal shaft.
Scheduled to begin production in the fall of 2002 at a rate of 2,200 tons per day, Pend Oreille is expected to produce 92,600 tons of zinc concentrate at a grade of 60% zinc and 14,300 tons of lead concentrate annually. The concentrates will be shipped to the Trail smelting complex. Mining will be carried out by room-and-pillar methods. The project has an expected mine life of at least 10 years and will employ about 170 people.
Cominco has already completed an Environmental Impact Statement (EIS) and now awaits final permitting approval from the state. David Godlewski, environmental manager for Cominco American (a wholly owned subsidiary), says the EIS results, which suggest that the project should move forward, are “strong evidence” that permits will be granted. A waste permit for the tailings is already in hand, and other permits are expected while the mine is being developed.
“We’re staging the permits as the project moves forward so we don’t have them too far in advance because bonding goes along with a lot of these permits,” Godlewski said.
Godlewski told The Northern Miner that “incredible local support” is one of the strengths of the project. Cominco has put together a committee of local stakeholders to address both the social impacts of the mine, as well as the environmental impacts.
“It has been a very successful program,” Godlewski explained. “The thrust of our permitting effort is to pre-emptively deal with the issues so that we don’t run into a brick wall sometime down the road. We’re also working with the environmental groups that have in the past opposed mining in that part of Washington state. We will address their concerns in such a way that they will feel more confident about the project moving forward.”
The first recorded shipment of ore from the Pend Oreille property dates back to 1906. Production was sporadic until 1930 when a 300-ton-per-day flotation mill was built on site. In 1937 the mill was expanded to 700 tons per day and, in 1951, the existing 2,400-ton-per day mill was constructed.
The Bunker Hill Company, which had acquired the project from mine founder Pend Oreille Mines & Metals in 1974, closed the mine in September 1977 following a labour dispute at its electrolytic plant in Idaho that forced the company into bankruptcy. At the time of Pend Oreille’s closure, mine staff had estimated the geological resources at 6.5 million tonnes grading 6.2% zinc and 1.5% lead.
From 1906 to 1977, the Pend Oreille mines produced a total 345,761 tons of zinc and 166,985 tons of lead from approximately 14.8 million tons of ore averaging a grade of 2.34% zinc and 1.13% lead.
Other mines in the district included the Grandview mine (production was 4 million tonnes grading 3.01% zinc and 1.16% lead) adjoining the Pend Oreille East Side mine to the south, and the Metaline mines (431,480 tonnes grading 4.28% zinc and 1.2% lead) about 2 miles to the southwest. These were operated by American Zinc Lead and Smelting Co. The Grandview mine closed in 1964.
Pintlar Corp., a wholly-owned subsidiary of Gulf Resources & Chemical, acquired Pend Oreille and optioned the property to Resource Finance Corp. (RFC) in 1988. RFC later purchased the property and associated infrastructure for US$1.25 million. With the financial backing of Kerr Addison Mines, and later, Inmet Mining, RFC completed an extensive development program that included dewatering the mine, drilling, underground drifting, plus engineering and feasibility studies.
In 1996, Cominco launched a $31.3-million takeover of RFC to acquire the past-producing mine as a new source of feed for its Trail metallurgical complex.
Pend Oreille is a Mississippi Valley-type, carbonate-hosted, pyritic zinc-lead deposit, with similarities to Nanisvik in the Northwest Territories and to zinc deposits in Ireland.
Current reserves occur in the Yellowhead dolomitic rocks in the middle part of the 3,300-ft. thick Cambro-Ordovician Metaline Formation. The bulk of the past ore production from the Pend Oreille mines came from the overlying Josephine dolostone unit at the top of the upper Metaline Formation, which consists primarily of subtidal carbonate facies overlain by black graptolitic slate of the Ordovician Ledbetter Formation.
The Josephine ore averaged a grade of 2.5%-3% combined zinc-lead at a ratio of about 2.25-to-1.
The Yellowhead ore occurs in the Bedded Dolomite unit, 800 to 900 ft. below the Josephine unit. The mineralization is stratabound and consists of massive and colloform-textured pyrite averaging 20%-30%, with varying amounts of pale tan to yellow sphalerite and coarse galena. Gangue minerals include mainly calcite and dolomite, but small amounts of quartz, talc, tremolite, barite and palygorskite may be present.
The Yellowhead zone consists of four flat-lying, northeast-striking en-echelon lenses that vary from 500 to 1,900 ft. long and average 20 ft. in thickness. Overall the zone is 6,900 ft. long and ranges from 330 to 650 ft. wide. Towards the end of Pend Oreille’s production history, previous operators created ramp access to the Yellowhead zone and did some mining at the southern end of the deposit.
Since acquiring Pend Oreille, Cominco has carried out extensive metallurgical and engineering studies and conducted infill drilling campaigns to upgrade and boost reserves. Exploration drilling in 1997 located a low-grade extension to the north, and three widely-spaced holes intersected a new zone several hundred metres east of Yellowhead. Last year’s program of limited drilling and geophysics developed several potential targets for follow-up work.
“We’re quite optimistic that we will be able to increase the reserves and therefore increase the life of the mine,” said Godlewski.
Production from Pend Oreille, along with a US$100-million mill optimization program now under way at the Red Dog mine in Alaska, will effectively offset the loss of production from the Sullivan and Polaris base-metal mines in Canada. Both are scheduled for closure by the end of 2001.
Pend Oreille is anticipated to replace approximately 60% of Sullivan’s current production.
Meanwhile, the Red Dog expansion will increase production of zinc concentrate to 1.1 million tonnes annually at a grade of 56% zinc from about 970,000 tonnes in 2000.
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