Atna, Expatriate eye leaching processes for Wolverine

Partners Atna Resources (ATN-T) and Expatriate Resources (EXR-V) are considering which metal leaching process provides the best means of avoiding problems related to high levels of selenium at the Wolverine deposit in the Yukon.

Tests in 1997 identified an anomalously high amount of selenium in sulphide minerals. This raised concerns, as selenium is known to cause problems during smelting and refining, the reason being that it is not easily separated from the metal or sulphur products.

Initial copper and zinc concentrates were found to contain an average of 0.43% and 0.15% selenium, respectively, which is several times higher than normal. Lead sulphide and sulphosalt minerals accounted for half the selenium in the copper and zinc concentrates.

However, metal leaching will enable the partners to produce metals rather than concentrates. Not only will this offset the selenium problem; it will capture more of the value of the high-grade Wolverine deposit, the companies say.

Wolverine has a resource of about 6.2 million tonnes grading 12.66% zinc, 1.33% copper and 1.55% lead, plus 370.9 grams silver and 1.76 grams gold per tonne. This translates into 1.7 billion lbs. zinc and 72 million oz. silver (zinc and silver make up about 80% of the gross metal value).

A preliminary review indicates that the potential increase in revenues from on-site recovery of metals could pay for the increased capital and operating costs of a metallurgical plant in the Finlayson district, provided current reserves and resources in the region are processed in a common plant.

For some time now, Atna, Expatriate and Cominco (CLT-V) have been pondering consolidating the Wolverine and nearby Kudz Ze Kayah deposits under one entity in the hope of curtailing costs. If a common plant is deemed economic, a consolidation of interests could be the next step.

Kudz Ze Kayah, a zinc-lead-copper-gold-silver project owned by Cominco, is 24 km northwest of Wolverine and likewise is plagued by high selenium content.

Preliminary metallurgical studies are being conducted by a team of geoscientists hired by Atna and Expatriate, and a scoping study will attempt to evaluate the economics of various metal leach possibilities.

The study, to be managed by H.A. Simons, will consider the viability of various leach methods, including those used by Cominco at Trail, B.C., and by Falconbridge (FL-T) at Kidd Creek in Timmins, Ont.

Regardless of the process chosen, either solvent extraction-electrowinning (SX-EW) or electrolysis will be used to produce cathode copper and zinc. Cyanidation of residues is also being considered for the recovery of precious metals.

In related news, a second phase of drilling has been completed at Atna’s partially owned San Antonio volcanogenic massive sulphide (VMS) property in the Dominican Republic. Results from the 6-hole program are expected before mid-September. Atna stands to earn a 60% interest from Energold Mining (EGD-V).

Meanwhile, at the Dry Creek VMS property in Alaska, a 10,000-ft. drill program is entering the final stage, with assays expected sometime in the autumn. Atna is earning a 51% stake in the property from Grayd Resource (GYD-V).

In the same state, drilling is under way on Atna’s Caribou Dome property, which hosts stratiform copper mineralization geologically similar to the Kupferschiefer copper-shale deposits in Europe and the Zambian copper belt deposits in Africa. Atna stands to earn a 100% interest in the property.

At last report, the company had $13 million in its treasury and 23.6 million shares fully diluted.