Fairfield underground at Siwash North

It isn’t often that a company can turn a profit from bulk sampling. But that’s exactly what happened last year when Fairfield Minerals (TSE) extracted 2,030 tons from its Siwash North gold deposit, near this interior community, for shipment by rail to Noranda, Que.

The program resulted in the sale of 8,700 oz. gold produced at a cost of about C$250 per oz. (The cost included corporate overhead, contract mining, shipment of the bulk-sample ore over 2,300 miles and related smelter charges.) It also resulted in the recovery of $3 million, now being used to offset the cost of ongoing programs aimed at both underground test mining and an expanded open pit to remove near-surface reserves.

Last year’s program was not only a financial success, as The Northern Miner learned when it drove into the property; it was also a technical success for both Fairfield and its consulting group, Cordilleran Engineering. Fairfield test-mined a narrow, high-grade ore shoot with minimal dilution, at a strip ratio of about 80-to-1 waste-to-ore. The average grade was found to be remarkably consistent and considerably higher than anticipated. The original grade estimate of 1.5 oz. per ton was based on a mining width of 3.3 ft. whereas the actual mining width was about 1.5 ft., averaging 4.25 oz. gold per ton.

“Last year’s program gave us a good handle on what we are dealing with, and increased our confidence and comfort in this project,” said President John Stollery. “One of the reasons we’ve been successful is that we have the same people on the project who made the original discovery in 1986.” Stollery concedes that narrow-vein deposits are often viewed as difficult to mine and as having limited reserve potential. He points out, however, that Siwash North is similar to several Canadian gold mines where narrow, high-grade veins have been profitably extracted. These include the Leitch mine in Ontario (which turned out more than 860,000 oz. gold from a 1-ft. vein with an average grade of 0.96 oz. gold per ton) and the Pickle Crow mine (which produced 1.5 million oz. from a 2-ft. vein averaging 0.47 oz. per ton). To date, Fairfield has focused mostly on the high-grade Mother Shoot within the Siwash North deposit. This shoot (which yielded last year’s bulk sample) has a 650-ft. surface exposure and has been traced by drilling to 1,000 ft. downdip where it remains open for expansion. The near-surface portion dips at about 25 for a distance of about 400 ft., where it steepens to 65. In 1991, Fairfield was of the view that the shoot contained 220,000 oz. gold in 340,000 tons averaging 0.65 oz. gold per ton. A revised drill-indicated reserve was recently published, based on more realistic open-pit and underground mining widths of 1.3 to 2.6 ft. (with a 0.6 oz. cutoff). That revised estimate is 135,000 tons averaging 1.59 oz. per ton. “This represents 215,000 oz. gold which can be increased by more exploration,” Stollery said, adding that a drill hole returned 11.61 oz. gold over a width of 2.9 ft., 835 ft. downdip in the main shoot.

Fairfield’s 1993 program will include an expanded open pit to remove more near-surface ore. This next phase will be focused on an additional 4,500 tons containing an estimated 10,000-12,000 oz. gold readily available for extraction along strike from the existing pit.

That work is being carried out by Kelowna, B.C.-based Wiltech, under supervision by Fairfield geologists. First, the waste rock overlying the zone is removed in 6.5-ft. benches to expose the narrow vein (the boundaries are well-defined and gold values do not typically extend into the wallrock). The ore is then carefully extracted into a “dust pan” to prevent loss of gold values from any portion of the rich vein, particularly areas where leaching of sulphides has taken place.

Siwash North is believed to be a deep-seated, mesothermal system. Gold mineralization is hosted by quartz veins and silicified granite containing 10-15% pyrite plus minor chalcopyrite and galena. The gold is fine and largely in the free state, and tests indicate 60-80% recoveries are possible with a gravity circuit. The project is environmentally safe because of the simple mineralogy and the lack of deleterious elements and acid-generating rock.

Mainstreet Mining, the underground contractor, was driving the underground decline that will accommodate trackless mining equipment. At the time of our visit, about 650 ft. of the 1,312-ft. decline had been completed. To allow for the start of test-mining, more than 600 ft. of drifting are planned along the vein.

“We will test-mine both areas of the vein,” Stollery explained. “We plan to use shrinkage on the steeper part of the vein and resuing on the flatter portions.”

Ground conditions are generally good, particularly in the granodiorite. However, support in the form of bolting and shotecreting was required in areas where dyking and alteration were encountered.

The test-mining, to take place this fall, is expected to yield about 4,000 tons of vein material which will be sampled and stockpiled for processing. Stollery said the program is aimed at determining which mining methods will be most suitable and economical. It will also help determine ground conditions and confirm grades indicated by surface drilling. “We particularly want to see what our grades and dilution will be,” Stollery said, adding that a further underground stage will likely be required before a production decision can be made. Another phase of open-pit mining is also planned, to focus on an area believed to host a further 15,000 to 20,000 oz. gold.

In the meantime, the debt-free company is involved in discussions to process stockpiled reserves at existing facilities, some of which are nearby. The possibility of building a plant, with a capacity of about 100 tons per day, on the property will also be examined. Capital costs would be modest. Fairfield will continue using a small plant built on-site for sample preparation; it has proved accurate for maintaining grade control and establishing the gold content of the stockpiled ore. As it turned out, the grade estimate based on last year’s bulk sample was 5% lower than the grade determined by the Quebec smelter.

Stollery had high praise for his team of geologists and mining professionals, several of whom are graduates of his Alma Mater, the Haileybury School of Mines. He particularly acknowledged their innovativeness in designing the mining dust pan and the on-site sampling plant. “This is what the Haileybury School of Mines is all about,” he declared.