For a project that was viewed as a modest underground producer three years ago, Mascot Gold Mines’ Nickel Plate mine has certainly come a long way. Perched high above the town of Hedley in southeastern B.C., the property now hosts a major open pit mining operation scheduled to produce 120,000- 150,000 oz per year — one of the largest gold producers in Canada. Besides putting British Columbia on North America’s gold mining map, the Nickel Plate mine has demonstrated the importance of flow- through financing to this country’s mining industry. Even President Henry Ewanchuk concedes: “there probably wouldn’t have been a mine there without it.”
Because of the subsequent dilution brought on by the flow-through- funded exploration programs, Mascot opted to debt-finance the project. A $70-million loan agreement was negotiated with the Canadian Imperial Bank of Commerce, part of which was converted into a gold loan.
Mascot borrowed 100,000 oz of gold from the bank and sold it at $409.80(US) per oz to net $56.9 million. (The gold must be returned by April 28, 1988.) In the meantime, a 3% interest charge will apply to the loan.
Now Mascot has to produce sufficient gold to cover the loan — something the company is well on its way to doing.
It has been said that mines are made, not found, which is probably as true today as it was decades ago. In Mascot’s case, the economics of an open pit operation remained largely unrecognized until Mr Ewanchuk and his exploration team took over the project in 1984. Several mining geologists had emphasized the open pit potential in various reports before although it was never seriously considered.
Following up on suggestions made by consulting geologist Martin Kierans, who worked at the property for a time, Bill Hainsworth (another consultant) also began pushing the open pit potential. Frank Holland, project manager for Mascot during the late 1970s and 1980s, has been involved with the project through both assessment phases, underground and open pit. He worked under Louis Starck who optioned the property in 1967 and is still a company director. Both men can take some of the credit for the fact that Mascot is producing for the third time since its discovery.
In 1984 a large surface program outlined about 3.1 million tons of open pit reserves which were confirmed and expanded a year later. Approval in principle was given in 1985 for an 1,800-ton-per-day milling operation which was bumped up to 2,700 tons the following year based on 8.3 million tons of reserves averaging 0.14 oz gold per ton.
Mine capacity is about 26,000 tons per day with an 8.6-to-1 strip ratio; a minimum 89% mill recovery rate is expected with annual gold production of 120,000-150,000 fine ounces based on the 2,700-ton-per-day milling rate. Site construction began in May, 1986; open pit mining the second week in October, and the first gold pour was made this April. The plant was completely operatio nal by the second quarter, coming in under budget and well ahead of schedule, according to Mascot.
The mine site is about two miles northeast of Hedley on Nickel Plate Mountain which, despite its name, never produced any nickel. Discovered by two prospectors in 1898, the gold deposit was first mined in 1904 when a 40-stamp mill was erected in the main valley. With a source of employment so near, a small community was born which was named after Robert Hedley, the manager of the Hall mines smelter at Nelson. The mine manager at Mascot is Jim Walmsley who came from the Highland Valley in B.C.
Remnants of an old tramline, which incidentally dropped some 3,400 ft to the mill and covered a slope distance of 10,000 ft, are still visible on the mountainside. Production ceased in 1955, and over the life of the mine six separate ore zones were developed: the Nickel Plate, the four Sunnyside zones and the Bulldog. At present, mining is confined to the South (Bulldog) and Central zones but work will get under way in the North pit (Nickel Plate) about a year from now, says Mr Walmsley.
Higher grade ore is being developed first in order to reduce the payback period, and the company is mining from two open pits of which the North and Central will join up eventually. There are roughly 1.5 million tons of reserves left in the two smaller pits and about six million tons in the larger. Reflecting their desire to optimize gold production at this early stage, the present cutoff grade is about 0.05 oz gold per ton, but it will eventually drop to 0.03 oz, says Al Bellamy, mine superintendent.
Mining must take into account underground workings beneath the open pit which require backfilling. Drop raises have been driven into old stopes which are then filled with low grade material. The low grade ore and old stope pillars are scheduled for recovery by open pit mining as benching proceeds downward in the pits.
Standard mining techniques are utilized at Mascot where about eight million tons of ore and waste rock will be removed each year. Haulage distances are being optimized and 20-ft benches excluding subgrade are taken to maintain a 60 degrees pit slope. Almost 2,600 ft of drilling has to be completed each day, seven days per week, to maintain production, he said.
“Safety and production are a priority,” he added, noting that Mascot pays extremely close attention to wall scaling. This scaling is done with the shovel or else the wall is dragged with a large truck tire. Shovel operators are cautioned not to overdig when they loosen the wall rock.
Rotary down-the-hole hammers and 6-in button bits are used for production drilling because the rock is often hard and abrasive. Tri-cone roller bits have been known to self- destruct after a few hundred feet, mostly because of bearing problems. A staggered 10×10-ft blast pattern is employed in ore.
Grade control is extremely important at Mascot and more than 550 assay determinations are done by atomic adsorption each day. Drillers gather cuttings in a sample device at the collar of the hole and good correlation has been reported between operators’ results and bulk-sampling. The results are often cross-checked with independent assay facilities as well.
The Ingersoll Rand dm 45E blast hole drills are equipped with high- pressure, screw-type compressors which deliver 900 cu ft per min of air at about 350 lb per sq in for increased penetration. Twenty-foot holes can be drilled in a single pass and deeper ones can be drilled by adding another 20-ft length of steel. Two 1600 E refitted P&H shovels with 7.5-cu-yd buckets are used to load six 60-ton Wabco haul trucks. Additional pit equipment includes a 992 Caterpillar front-end loader with a 13-cu-yd bucket, a 16G Caterpillar grader, a Komatsu 155 angle dozer, service vehicles and a sand truck. At the time of our visit, maintenance superintendent Bob Trent noted t hat a Mascot crew was “stripping down a shovel in Nevada.” He also said the company was able to hire “excellent trades people” and was helping some of them through trade school.
Emulsion-type explosives are used to load holes because of their high detonation velocity and good breaking characteristics in hard rock. The mine has been experimenting with different blasting techniques including pre-shearing and cushion blasting for wall control. Rock hardness varies and the bedding planes of the various rock units are taken into account before blasting. In general they load to an 8-ft collar to avoid excessive fly rock.
The Nickel Plate orebodies contain fine-grained gold and large amounts of arsenopyrite and pyrrhotite. But Bill Wilkinson, chief geologist, admitted the association with arsenopyrite is not always “a strict rule.” The ore, which has a bond work index of 19 kW-hr per ton, exhibits a blocky nature suited to autogenous grinding or pebble mill grinding. Studies by Mascot show a gold recovery of 89% at a grind of 80% passing 400 mesh (0.038mm). Kilborn Engineering of Vancouver was responsible for all engineering work on the concentrator and crusher, working in close consultation with Mascot.
Mill superintendent Don Ingram says some of the
equipment in the mill was purchased from Esso’s Granduc mine at Stewart, B.C., which is now dismantled. Pebbles are used as grinding media and requirements are estimated to be 75 tons per day for mill throughputs of 2,700 tons per day. Most of the equipment in the crushing and grinding circuits is second-hand, but it was refurbished prior to installation. Mascot readily concedes that a substantial cost saving was realized in some areas by refurbishing used equipment. But the major advantage was actually reduced delivery time, which allowed for tighter scheduling of plant construction.
Comparative testing of carbon-in- pulp or carbon-in-leach gold recovery versus zinc precipitation indicated advantages in conventional precipitation methods at the Nickel Plate mine. Influential factors included: requirements for treatment of either total tailings volume or some barren bleed stream to comply with requirements of a zero discharge operation; decreased carbon activities caused by scaling of carbon surfaces due to fine product grind; and variable solution soluble copper content adversely affecting gold adsorption on carbon. Hydrogen peroxide has been chosen for cyanide destruction initially, he says.
Tailings are discharged to an impondment area some 4,500 ft away and the difference in head totals about 1,350 ft. As a result, nine velocity- reducing plates are required at three stations along with two drop boxes to adequately handle solution in an 8-in uninsulated, sclairpipe line. This same system has been installed at Placer Development’s Golden Sunlight operation in Montana and is working well, Mascot says.
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