Howard’s Pass has sat undeveloped since 1982, when Placer concluded that an underground mining operation was uneconomic. The decision was based on lack of infrastructure and the high cost of shipping concentrates.
“Placer was looking at a fairly high-cost, underground operation running at somewhere between 2,500 and 3,000 tonnes per day,” Copper Ridge President Gerald Carlson tells The Northern Miner. “We’re now looking at a minimum of 15,000 tonnes per day, or some larger number equivalent to a small porphyry deposit . . . but it would be strictly open-pit.”
Copper Ridge has made an initial payment of $10,000, which entitles it to a 150-day period to conduct due diligence. The company can then elect to buy the property by initially paying $1 million (75% cash and 25% shares) as part of the $10-million total payment, to be made over four years. A further $5 million will be payable when a production decision is made.
Discovered by Placer in 1972, Howard’s Pass was explored by means of diamond drilling and underground development through to 1981. At the time it was staked, mineralization reportedly had been traced on surface for a strike length of 5 km and widths of up to 46 metres. Individual 1.5-metre samples assayed as high as 40-50% combined zinc-lead. U.S. Steel acquired an option on the project in 1975 and earned a 49% interest by spending $10 million. In total, about $15 million was spent on the property.
Howard’s Pass is in the Selwyn-Mackenzie zinc-lead province and centres on two shale-hosted, stratiform sulphide deposits: XY and Anniv. Placer estimated that the sedex deposits contained indicated reserves of 113.4 million tonnes grading 5.4% zinc and 2.1% lead, including a higher-grade core of 8.2 million tonnes grading 10.6% zinc and 5.5% lead in XY. Additional inferred resources for both deposits were pegged at 363 million tonnes.
North of Anniv, drilling has tested the OP zone, which geologists now believe may be part of the Anniv zone.
Mineralization occurs in the shales of the Road River Formation and consists mainly of bedded to massive zones of sphalerite, with lesser amounts of galena and minor framboidal pyrite. Exposed outcrop is strongly oxidized and leached.
The lens-shaped deposits are folded and faulted, so there are thickenings of the deposit, particularly at the fold noses. It is mostly synclinal, with a few anticlinal places.
Issues affecting metallurgy include the presence of graphite, which serves to dilute the grade of the concentrate, and the fine-grained size of mineralization, which makes it difficult to separate the lead from the zinc for the purpose of producing concentrates. At the end of the day, Placer opted to produce a bulk concentrate that contained few impurities and little iron.
Copper Ridge will next examine metallurgy and power options, with the aim of reducing capital and operating costs.
A combination of mining and hydrometallurgical technology is expected to allow for the production of zinc metal near the mine site. Toward this end, Copper Ridge is in discussions with a major mining company that holds proprietary rights to new hydrometallurgical technology. In the long term, this new technology holds the potential for:
simplifying the metallurgical process and improving zinc recoveries;
reducing transportation costs by eliminating the need to ship concentrates to smelters; and therefore
eliminating smelter charges.
“Our concept is to maximize the zinc recovery,” says Carlson. “We’re not interested in the lead, so a rough flotation, or maybe even a gravity separation, will do. We don’t care half as much about the grade of the concentrate, because we’re not going to move it anywhere.”
Carlson adds that his company is considering processing the concentrate on site using the proven technology of pressure oxidation to produce zinc metal.
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