Experts say heap leaching can work in sub-arctic climate

To the untrained observer they look more like unfinished parking lots than h low-cost mining operations.t With piles of ore fragments heaped on top of giant leach pads, it seems p Canada’s heap leach mining operators are paving the way for a new supermarket or a drive-in movie theatre rather than attempting to extract gold from low d grade ore.

But despite the success of a number of heap leaching operations in the southwestern U.S., these parking-lot-like operations have been slow to catch r on north of the 49th Parallel.

While three heap leach mines in Newfoundland, New Brunswick and Timmins, Ont., are in the late stages of development, Canadian mining companies have yet to prove they can operate the system successfully in this country. Poor weather conditions is the reason most experts give for the absence of heap leaching in Canada, but once the technology becomes familiar with Canadian gold miners, they all agree the concept could have a dramatic effect on the local mining industry.

First developed in Nevada during the l970s, heap leaching allows gold producers to mine gold at grades considered uneconomical under normal mining methods.

By foregoing the expensive milling process used in conventional mining methods, gold producers can use heap leaching to extract very fine grained gold from ore grading as low as 0.03 oz per ton and still make a reasonable profit.

After ore is taken from the mine it may be leached as run-of-mine material in pads constructed on an impermeable surface in flat-topped piles 10-2 0 ft high.

The piles are sprayed continuously with a dilute cyanide solution that p dissolves the gold out of the rock and passes it down through the rock where e the gold-rich fluid is collected on the leaching pad.

The cycle is repeated until the rate of gold extraction declines and the maximum practical recovery is achieved. Over a period of months, the a gold-rich fluid flows through a series of channels to a sump before being c pumped to a gold recovery plant nearby.

After the solution has percolated through the heap, gold is removed through a process involving activated carbon granules in a series of tanks. Gold adheres to the surface of the granules which are stripped of gold chemically and the gold is later removed from the fluid electrolytically.

Although this technique is usually applied to oxidized ores, it can be used on any ore in which the gold is readily accessible to the solution and where there are no minerals which react with the cyanide to prevent adequate gold dissolution.m

Heap leaching, combined with open pit mining, which allows mining companies to put a 5-million- ton-a-year operation on stream for about $10 million, came into its own in the l970s at the Cortez Gold mine in Nevada. Since then, seasonal operations like Sonora Gold Corp’s. Jameston, Ca., and Consolidated Goldfield’s Ortiz Mine in New Mexico, for example, have been operating successfully in the United States.

But despite the fact that some mining experts think heap leaching could change the complexion of gold mining across the Canadian Shield, Canada is still lagging well behind in its effort to bring the process on stream.

“The climate in this country has scared a lot of people off,” said Dennis McLeod, former president of Pamour Porcupine, the company which conducted the first ever heap leach test in Ontario.

Mr McLeod recently resigned from the company after Pamour’s Timmins mining operations in northern Ontario were acquired by Giant Yellowknife Mines.

A Scotsman and now president of Toronto based Doelcam Inc., he has made a career out of profitably mining low grade ore and recovering gold from a tailings. “There is absolutely no reason why we can’t do this anywhere in North America. We musn’t let climate cloud our judgment,” he said.

“It’s just a question of taking known ideas and technology and applying them in situations where people don’t think they can work.”

Last year Pamour achieved a 68.4% recovery rate over three monthsfrom a 10,000-ton heap averaging 0.037 oz per ton gold. The ore was mined from Pamour’s No 3 pit near Timmins, Ont.

Mine manager Peter Rowlandson says the company expects to begin commercial production later this year with between 200,000 and 500,000 tons of ore at a cost of $4-$5 per ton. He expects the company to heap leach about 2 million tons from pit 3 over the next five years.

While Mr Rowlandson is reluctant to be specific at this stage, he says much of Pamour’s heap leaching tonnage could come from the old Young Davidson mine the property h between l934 and l955, the operation closed down. “We will be doing some test work on the mine,” said Mr Rowlandson, who expects Pamour’s heap leaching operation to be profitable.

While Ontario’s initial heap leaching project should be operational by late l987, Atlantic Canada’s second heap leach operation at the Cape Spencer Gold mine near Saint John, N.B. is undergoing a number of changes. Canada’s first commercial gold heap leaching was conducted by Anaconda Caribou at its Bathurst, N.B. deposit in 1982.

Nearly a year after Gordex Minerals poured the first dore gold bar from the Cape Spencer property, the operation is being converted from a heap to a vat leaching mode.

“Back in January we came to the conclusion that heavy rains were making it difficult to control the water balance,” explained Gordex president Hal Pawson. “The vast amounts of water (caused by heavy rainfall in the area) made treatment costs extremely expensive for us.”y

While weather conditions put a seasonal limit on the operation, simply covering the ore pile with a light nylon tarpaulin (similar to tarpaulin used to cover infields in baseball) means that Gordex can operate both 24 hours a day and year round.

The $2.5-million expansion, which involves constructing two 50,000-ton vats, will allow Gordex to process 100,000 tons of gold bearing rock this w year and double that amount in l988.0

Reserves currently stand at 500,000 tons grading 0.1 oz gold per ton; the e mine life is expected to be around three years.n

“We can still use the sprinkler system and we don’t have to put the cover a down all the time,” said Mr Pawson. To stop high winds from blowing the cover away, the company simply holds it down with rubber tires.

While vat leaching makes the Gordex operation unique, Hope Brook Gold’s heap leaching project on the remote south coast of Newfoundland has some characteristics which make it stand out.

Scheduled to be operational by mid-August, l987, the company will heap leach 750,000 tons of ore from the open pit mine to provide cash flow for a conventional underground mining operation in l988.

By earning $21 million between August, l987, and October, l988, the company can help offset the $150 million capital cost of developing a conventional underground operation.

With an expected recovery rate of 126,000 oz of gold annually, Newfoundland’s only gold mine will be the 6th largest gold producer in Canada.

Open pit reserves currently stand at 754,000 tons grading 0.13 oz gold per ton. The company is predicting a 70% recovery rate. Some 75,420 oz gold will be recovered (28,070 in l987 and 47,350 oz by October, l988).

Although Arctic conditions on the south coast of Newfoundland are unlikely to prevent a mid- August production date, Nordac Mining Corp.’s heap leaching ambitions are likely to take much longer than that.i

During the next two years Nordac president James Stephen will explore three properties in the Dawson Range Gold Belt in the Yukon Territory in anattempt to prove 7 million tons of grades 0.035 to 0.04 oz gold. “Geologically, we have inferred that the ore is there, it’s just a question now of going out

To achieve this, Nordac will spend $750,000 this year to explore the Antoniak and Revenue properties which lie near the southeast end of the belt and are accessible by road. Located 60 km northeast of Carmacks, Yukon, the Antoniak property appears to contain three potential ore bodies within a larger area of weak mineralization. Using a cutoff grade of 0.85
oz gold per ton, reserves indicated to depth of 60 m are 2.2 million tonnes with an average grade of 0.06 oz and a stripping ratio of 3.9:1.

“It’s just a question of building up our reserves,” said Mr Stephen, who ‘ thinks his company could operate for 6-8 months a year if and when they locate the required grades and tonnage.

“We would be looking at the same weather conditions as Pegasus Gold Corp.’s heap leaching operation in Montana where precipitation levels are approximately 14 inches per year,” he said.

Since the southwest Yukon remained unglaciated during the past ice-age, the region is ideal for heap leaching. As a result, oxidization has increased porosity and permeability and destroyed many of the minerals that might have encapsulated the gold, or could condume reagents.

“Ore doesn’t have to be crushed to the same extent as other heap leaching operations.” said Mr Stephen. Leached caps over highly fractured porphyry deposits reach thicknesses up to 160 m and gold mineralization within them appears to be well suited for heap leaching.

“We are looking for a mine,” added Mr Stephen, who claims his company will a take any future heap leaching project to the feasibility stage.

Despite the region’s suitability for heap leaching, he isn’t sure why the process hasn’t been attempted before in that area. “It’s just something that other people haven’t gone after,” he said. However, as his company begins a drilling program on the Antoniak property this month, Mr Stephen is certain that travellers on the road north from Carmacks will be seeing some broad a expanses of heaped gravel springing up in the area. And not one of them will be a parking lot.