Whitehorse, Yukon — The old saying that “mines are not found, but made” doesn’t always hold true, and can be wishful thinking in cases where deposits have too many flaws for engineers to overcome. While the silver-rich Wolverine zinc-copper-lead deposit being developed by
Yukon Zinc is nearing completion of a $17-million underground test-mining program and bankable feasibility study at the massive sulphide project in the Finlayson district of eastern Yukon. When The Northern Miner visited the picturesque site, the company had just broken into massive sulphide mineralization within the Lynx zone, about 225 metres underground.
Harlan Meade, president of Yukon Zinc, noted that the first sulphide rock come to surface “ten years plus one week from the discovery date of the deposit.” The moment was personally gratifying, he added, as he had been part of the (Westmin) discovery team before Wolverine was acquired by Expatriate Resources, a predecessor of Yukon Zinc.
The test-mining program under way will extract about 2,500 tonnes of ore, plus about 350 tonnes of waste to define mining conditions for the feasibility study scheduled for completion early next year. A production decision will follow.
The Wolverine deposit hosts resources of 6.23 million tonnes grading 12.66% zinc, 1.33% copper, 1.44% lead, 371 grams silver and 1.76 grams gold per tonne (with 4.5 million tonnes deemed minable). An updated reserve and resource estimate compliant with National Instrument 43-101 reporting standards is expected shortly, and will incorporate more than 55 new drill holes.
The proposed mine plan makes use of selective mining techniques to address the deposit’s challenging ground conditions, while on the processing side, dense media separation (DMS) will be used as a pre-concentration step to improve head grades and overall recoveries.
“The combination of DMS and the new mine plan makes for a perfect marriage here,” Meade says. “They’re the keys to the project, which frankly, had a few hurdles and some black history to overcome.”
The project started with high hopes after the first discovery was made, sparking the biggest staking rush in Yukon history. A string of new discoveries followed, and before long the region was expected to become Canada’s newest massive sulphide district with one or more mines.
Weak metal prices and the lack of infrastructure helped dash those dreams, and anti-development sentiments of the late 1990s didn’t help either. In the case of Wolverine, poor ground conditions and the presence of selenium (then a deleterious element penalized by smelters) also hindered financing efforts. When
Price boom
Yukon Zinc kept the faith and the project alive on a shoestring until China’s economic boom gave zinc prices an upward jolt not seen for decades. The nation used to be a net exporter of zinc, but is now a net importer, and demand is expected to remain strong as long as the nation’s economy maintains even modest growth. The supply gap pushed prices to US65 per lb. from below US45 per lb. just last fall.
“Zinc was a star metal in China last year,” Meade says. “We believe the supply deficit underpinning the prices we’re seeing now is here to stay. A number of mines are nearing the ends of their lives, and there aren’t many new mines in the pipeline.”
Yukon Zinc views the Wolverine deposit as a flagship asset in the district, where it has consolidated ground previously held by others to become the largest landholder. The company has other resources on its land package, but rather than spread itself too thin, has focused its efforts on developing Wolverine as a stand-alone mine.
“We’re looking at a variety of ways to optimize the deposit,” Meade says. “One goal is to get payback as quickly as possible, and we have the grades to do it. Yes, we have ground-control issues, but we have solutions to deal with that, and still get maximum recovery with minimal dilution.”
Dream team
Richard Goodwin, vice-president of mining, says the company assembled a dream team of mining engineers to devise a mine plan suited to the deposit, which consists of two lenses, Lynx and Wolverine, hosted within felsic volcanic rocks and argillaceous sedimentary rocks. Each lens has a thick core ranging from 6-25 metres (true thickness), flanked by thinner massive-sulphide mineralization.
The hangingwall and footwall are generally weak, but the massive-sulphide ore is competent, so access is located in the footwall to the ore, with a herringbone pattern of stopes. This provides a strong hangingwall-in-ore for stope development, and allows mining to progress with multiple faces sequentially up the dip of the mineralization.
“This way we don’t have to fight the (weak) hangingwall,” Goodwin says. “Men and equipment are always under solid backs.”
The primary stope areas will then be filled with paste backfill and mine materials, followed by pillar recovery on retreat. The idea is to get as much ore as possible while leaving the least behind.
Meade says the mine plan “assumes the worst ground conditions,” which weren’t as bad as expected and improved as the decline advanced toward ore. Bolting, screening and shotcrete sufficed in some weak areas, though steel-sets were needed in the weakest areas of the production-sized, 4 by 5-metre decline ramp, particularly near the portal.
“When our contractor (Procon Mining and Tunnelling) says we need extra support, we don’t argue,” Meade adds.
Infill drilling also took place this year and results will be incorporated into the feasibility study. The Hatch study will also incorporate results from DMS test work, along with other metallurgical information. The proposed mill is conventional, with 3-stage flotation to make zinc, copper and lead concentrates.
The mine plan calls for the extraction of an estimated 1,500-1,750 tonnes of ore and waste daily, with run-of-mine material processed through the DMS plant after primary crushing to remove waste and internal barren argillites within ore, resulting in 1,250 tonnes per day of high-quality ore for milling.
DMS revival
DMS is old technology, recently modernized by the coal industry and used with good results at several base metal mines, including Nanisivik in the High Arctic. It essentially “cuts waste off at the pass,” using basic gravity, and upgrades ore going into the mill, resulting in better recoveries and, by extension, lower production costs.
“It doesn’t work on every deposit,” Meade says, “but it works well at Wolverine, where the heavier ore sinks and the lighter waste floats.”
The DMS plant is expected to cost $1-1.5 million to install, but is expected to provide numerous benefits, including greater mining flexibility, better recovery of thinner, high-grade mineralization, and more complete pillar recovery.
The final feasibility study will better determine capital costs for the mine and mill complex, but previous studies include an estimate of $127 million, which includes a $15-million contingency. The previously estimated operating cost of $80 per tonne reflects the high costs of selective mining under difficult ground conditions, as well as dilution, then predicted to average about 28%.
With zinc prices expected to remain high, Yukon Zinc has already received expressions of interest from smelters seeking zinc concentrates. Zinc is expected to account for 54% of payable metal values, with silver next at 26%, and copper at 12%.
New selenium markets
Without lifting a finger, the company has licked another problem — the presence of selenium in Wolverine ores — which, a few years ago, would have meant penalties and reduced payments for concen
trates.
Selenium is essential to human health, with deficiencies linked to birth defects. To remedy the problem, selenium is added to fertilizers in areas where soils are overworked and selenium-deficient, notably in the populous nations of China and India. Prices have risen to US$60 per lb. from US$4 two years ago, which means selenium is no longer a liability at smelters that have circuits to recover it.
Looking ahead to a possible production decision next year, Yukon Zinc has proposed to build a 20-km access road connecting the site to the Robert Campbell Highway so concentrates can be hauled by truck to Stewart, B.C., for ocean transport to Asian smelters. Diesel fuel will be backhauled by the concentrate trucks.
The company already has some permits in hand and will be applying for the remainder next year. A project co-ordinator has been appointed by the Yukon government to assist with the permitting and environmental review process, and related issues that may arise.
With no mines operating in the Yukon, the company hopes to draw former mining personnel from the nearest communities of Ross River and Watson Lake. It also hopes to recruit miners from operations scheduled for closure, such as Eskay Creek in northwestern B.C.
The company already has a socioeconomic agreement with Ross River Dena Council, which represents the Kaska Nation, for their participation in the project and others in the region. The agreement provides the Kaska with employment, training, and service contract opportunities, and also includes a $400,000 payment that will be used by the Council to buy shares of the company.
If all goes as planned, Yukon Zinc expects to apply the infrastructure and operating experience it gains at Wolverine for future development in the region. The company has several nearby deposits and exploration targets that could provide additional development opportunities. Furthermore, as underground workings at Wolverine are constrained by a claim boundary with Teck Cominco’s Kudz Ze Kayah deposit, it seems logical that Yukon Zinc could one day seal a deal to mine that well-defined deposit too. The Finlayson district would then become the mining camp that its early believers predicted it would be.
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