Wharf set for record output

Wharf is aiming at 1989 output of 71,000 oz of gold. By early July, when The Northern Miner visited the operation, the mine was halfway to the goal. Last year, output climbed to 59,500 oz. In fact, in every year since 1985, production has risen by between 10,000 and 15,000 oz.

The expansion last year included a new crushing system, construction of a fourth leach pad and additional mill capacity, which boosted annual production to 2.3 million tons of ore from the previous 1.3 million tons.

From the start in 1983, this mine has grappled with clay problems — the bane of the heap leachers. An overabundance of clay in the ore often leads to cyanide percolation problems on the leach pads. Wharf’s clay posed a different challenge.

It clogged the crushers to the point where “it was just like bubblegum,” said mine manager Robert Barnes. During the first two years of operation, clay was especially troublesome as mining into the north end of the Annie Creek pit, picked up as much as 180-ft clay thicknesses. In 1984, a wobbler was installed at the crushing plant to pull out the clays, but it was costly to maintain.

The new crushing system, with a bigger jaw crusher (a 48-inch Nordberg for the primary crush), a secondary Omni core crusher and two tertiary crushers, has solved the problem to a large extent. And whereas before the final product was 1 1/4 inch, it is now a nominal 1/2 inch, which improves recoveries and speeds the leach cycle. The clay-rich ore, mostly stockpiled material from earlier mining, is sent through the old crusher. It has a capacity of 1.4 million tons per year, although Barnes said it was a fight pushing even a million tons through it. High-clay ore is mixed two-to-one with less mucky material from the Foley Ridge pit.

“We’ll continue having clay problems and we’re still modifying the system to handle the muddy materials,” Barnes said. “But we should be out of the muckier sections by next year.”

The capacity expansion also included additions to the fleet of 50-ton Caterpillar haul trucks and the purchase of a Demag H85 7 1/2- cu -yd hydraulic shovel. The Demag shovel is ordinarily used in the pit, but it can also be found unloading the leach pads because of its faster cycle time. When pad off-loading speed is of the essence, the front- end loaders go to the pit.

As with all low grade heap leach operations, grade control is a priority at this operation. The orebody lies within the Deadwood Formation, an intertidal sequence of sandstone, quartzite, siltstone and mixed calcareous rocks intruded by northeast trending, steeply dipping fractures (or verticals, as they are called). Gold mineralization occurs within these fractures and spreads horizontally where ore mineralization replaced impure dolomite beds. The ore zones often overlap horizontally where the verticals are closely spaced.

“When we have a bench with shales or shaly material we don’t have much ore,” said Dan Dorfschmidt, grade control engineer “But when we have the sandstones and siltstones we have lots of ore.” Grade control research aims to minimize ground movement, and thus dilution, during a blast.

When blast monitoring first began in 1987, Wharf found that the material sometimes moved as much as 16 ft. Now, the maximum allowable movement is 5 ft and always in the direction of other ore, not into waste.

Mining began here with the Annie Creek deposit. Wharf has since begun mining a second deposit, the Foley Ridge, and is carving one more slice out of the east side of the Annie Creek pit, where the stability of the walls has allowed for 40-ft benches. In the Annie Arm Extension just behind the Annie Creek pit, benches are 20 ft because the ground is less stable. General mine foreman Mike Caretto said Annie Arm and Foley Ridge will eventually be linked as one large pit.

The heap leach segment consists of four pads. Initially, off-loading had not been planned. But now that off-loading has become part of the cycle, pad No 1 has been re-lined to facilitate the load/unload cycle and pad No 2 will be re-lined this summer. Each pad is huge, capable of holding about 1.3 million tons. Sprinklers, not drip-lines which seem to be developing into the preferred cyanide delivery system elsewhere, spray the ore with cyanide solution. Drip-lines are used in the cold winter weather (the cyanide solution is heated to 60 degrees F).

The current proven and probable reserve as of Dec 31, was 24.3 million tons grading 0.037 oz per ton. Exploration targets are plentiful in the immediate area of the workings. Cash operating costs are $178(US) per oz of gold produced.

At the corporate level, a controlling 38.9% interest in Wharf Resources was acquired by Dickenson Mines (TSE) in late 1987. However, that was soon followed by a bid from Corona Corp. (TSE) to wrest control of Dickenson itself. The Corona bid failed after Goldcorp Investments Ltd., acting as a “white knight” (a friendly suitor), stepped in and gained control of Dickenson and a sister company, Kam-Kotia Mines.

Dickenson management did not change after the takeover, although the Dickenson board of directors added two Goldcorp representatives. The final chapter in this fight for control may yet be penned by a judge. Corona has filed a lawsuit against Dickenson, Kam-Kotia, Goldcorp and others. As well, Goldcorp is being sued by a shareholder who alleges misrepresentation by the gold fund’s officers.

Corona holds a 7.6% interest in Wharf.

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