Joe Mann’s reserves on the rise

The Joe Mann mine, 40 miles south of here, has taken fortune’s buffets and rewards over its 40-year career. Now, under the management of Campbell Resources (CCH-T), it has enjoyed almost a decade of stability and has bright prospects for the future.

History has given the mine a thrill ride few people would envy. Discovered in 1950, it was put into production in 1956 by Chibougamau Explorers (Chibex), an M.J. Boylen company that was ultimately absorbed by his Key Anacon Mines. Production reached 686,000 tons of ore, grading 0.5% copper and 0.22 oz. gold per ton by 1960; then cash got tight and production was suspended. A fire in August of 1963 wiped out the 500-ton-per-day mill.

The mine was resurrected in 1971 by Chibex, which began dewatering and underground development; in the process, it proved up 1.2 million tons of ore grading 0.5% copper and 0.22 oz. gold per ton. Production started again in November 1974, using a shiny new 750-ton-per-day mill, but metallurgical problems forced the mine to close in 1975.

Chibex had its own difficulties with red ink, and the property passed to Falconbridge Copper and NBU Mines, whose 1976 feasibility study found that a gold price of US$160 per oz. — about US$30 higher than the price that then prevailed — could render the operation profitable. In September of that year, Meston Lake Resources took over the property, and the company began rehabilitation in the early 1980s when the gold price spiked.

Money troubles intervened again, and, in 1983, Campbell financed another feasibility study. Dewatering and underground exploration were successful and Campbell took over Meston in 1985. Commercial production resumed in 1987.

Shear zones

The Joe Mann mine exploits a set of shear zones that strikes east-west and dips almost vertically, in Archean-aged gabbro and volcanic rocks.

Underground, the shear zones stand out sharply from the enclosing rocks and can be contorted and tightly folded.

The mineralogy of the veins is simple, with free gold, chalcopyrite, pyrite, pyrrhotite and magnetite in a quartz gangue. “It’s a nice product to work on,” said mill superintendent Germain Naud, who spoke to The Northern Miner on a recent site visit.

The mine’s biggest success has been in replacing mined tonnage. Even though the mine has produced an average of 68,000 oz. per year since 1990, proven and probable reserves stand at about 1.2 million tons grading 0.28% copper and 0.26 oz. gold per ton, with possible reserves of 2.4 million tons grading 0.27% copper and 0.26 oz. gold — higher than at any time since the mine reopened.

Campbell has continued to renew reserves by exploring at deeper levels on the Main and South zones, which are now developed to the 2,650-ft. level.

Possible reserves have been drilled as far down as 3,750 ft. on the Main zone. Historically, the mine has been able to count on about 2,000 tons of ore per vertical foot of development.

Surface exploration west of the shaft, which began in 1994, has encountered some shallow mineralization on the same shear structures. Later drilling confirmed that the gold was present at depth, so an exploration drift was started in 1995 on the 1,650-ft. level. The drift intersected mineralization directly down-plunge from the near-surface showings, and drilling from stations and crosscuts along the drift has since indicated that the new “West zone” could extend to 3,450 ft.

In September, Campbell’s board of directors approved plans to deepen the shaft to 3,780 ft. from the present 2,680 ft., and to drift into deep ore east of the shaft.

The deeper shaft will allow six more levels to be developed on the Main and South zones, and will also allow for further exploration and, ultimately, definition drilling on the West zone. Campbell will finance the $14.5-million project from cash on hand.

Shrinkage stopes

Ore is mined principally from shrinkage stopes; longhole stoping becomes economic once stopes reach widths of 7.5 ft. and lengths of 100 ft. The bonus structure recognizes the importance of limiting dilution, with rates that increase in narrower stopes.

At present, the mine hoists about 1,200 tons per day; the shaft’s capacity is around 2,000 tons and, if stopes are developed in the West zone, some increases could be made to the production rate.

Cash production costs are projected to be US$275 per oz., and higher production could offset some fixed costs and bring down that figure.

Campbell’s 1,500-ton-per-day mill in Chibougamau has given the company a significant advantage over former operators of the mine. The mill was originally built to handle 3,500 tons of copper-gold ore per day from the nearby Chibougamau and Merrill Island mines, which have long been closed. It now operates at about 1,200 tons per day, processing gold ore from Joe Mann.

Whatever metallurgical problems earlier operators had experienced are no longer apparent; the mill recovers about 93% of the gold and 96% of the copper in the ore. Roughly 42% of the gold is recovered in a gravity circuit, including two Knelson concentrating tables. The mill sends a chalcopyrite flotation concentrate, which contains the copper and 39% of the gold, to the Horne smelter in Rouyn-Noranda, Que.

Tailings from the flotation circuit go to a direct-cyanidation circuit to leach the rest of the gold; the cyanidation process is essentially complete after 28-30 hours, and the material then joins the gravity concentrate in the mill’s furnace.

Another benefit of the simple metallurgy is environmental control. Mill effluent goes into two settling ponds and then to a polishing pond, over a 6-month cycle. By the time it is released, its cyanide content is well below the discharge limit of 0.1 part per million; most often it is below the limit of analytical detection. The tailings solids meet the criteria for an inert fill, and the disposal areas have plenty of capacity. “The ore from Joe Mann is an easy one,” says mill metallurgist Jacqueline Leroux, who oversees environmental compliance. “It’s not acid-generating; on the contrary, it’s alkaline-generating.” Solid tailings are revegetated and usually are taken over by native plants in about five years.

Exploration

The key to mine life in the medium term will be to find and develop new ore on the structures now being mined. Over the longer term, there is potential for more mineralization in the immediate area. Soquem, Quebec’s provincially owned mineral exploration company, is earning a half interest in Campbell’s 112 claims surrounding the mine property. Under the option agreement, the Crown company must spend $4.2 million on exploration, with Campbell retaining the right to operate any developed property.

To date, Soquem has spent $1.7 million on geophysical surveys, mapping, trenching and 42,500 ft. of diamond drilling. Showings appear to cluster in a corridor about 2 km wide around the main east-west deformation zone.

The West zone, which extends off the Campbell-Soquem property, has been drilled and appears to be a strike extension of the mine’s West zone. The Rohault showing, extending east from the mine property, has been tested only on surface so far, but it shows widths of 1 to 3 metres.