Mine Visit: A DIGNIFIED DECLINE; Operators are intent on securing

“We know the reserves aren’t as good as they were, so we’re upgrading our equipment and changing our mining methods,” Chief Engineer Brian Anderson told The Northern Miner Magazine on a visit to the mine. Mine Manager Frank Grebenc (who, soon after our visit, was appointed mine manager of the Golden Giant) estimated that, between 1989 and 1990, Noranda will have spent $20 million upgrading production machinery in the mill and underground. Higher production levels will offset a gradually diminishing grade, and thus extend mine life. Forecasts now suggest that in another eight years the ore will have run out.

The deposit first came to light in 1953 when Geco Mines staked an area near what was to become the Manitouwadge townsite in northern Ontario. In 1964, Geco amalgamated with Noranda. From the time of the first hoisted skip in 1957 to the present, Geco has produced 46.8 million tons grading 1.87% copper, 3.83% zinc and 1.68 oz silver per ton. By the middle of this year, the remaining reserve was 11,821,000 tons grading 1.61% copper, 2.9% zinc and 1.13 oz silver per ton.

Geco began as a 3,300-ton-per-day operator, peaked at 5,000 tons-per-day in the mid-1970s, and settled at the current mill production rate of 4,100 tons. Mine Superintendent Ken Byberg noted production costs for mine, mill, exploration, plant and administration are among the lowest in the Canadian industry. “We’re aiming for $30 per ton,” he added. The employee profit-sharing plan, to mid-year, added another $3.35 per ton to production costs, which indicates the financial health of this antique but not antiquated producer.

Geology

According to Chief Geologist Hugh Lockwood, the orebody is an easterly trending, sub-vertical zone occurring on the south limb of an easterly plunging folded sequence of highly metamorphosed Archean volcanics and sediments known as the Manitouwadge Synform. This, in turn, is part of a highly deformed and poorly understood section of metavolcanics and gneisses lying along the south side of the interface between the Quetico and Abitibi-Wawa Belts of the Superior Province.

The orebody is a lenticular, continuous zone of mineralization extending from surface to a vertical depth of 3,200 ft along an easterly 35/7ch/ plunge. The average strike length of the orebody is 2,400 ft. The width varies from 10 to 250 ft, with the average being 65 ft. The core consists of massive pyrite, pyrrhotite, sphalerite, chalcopyrite and galena. In addition to copper and zinc, the orebody carries silver and minor quantities of gold and tin. The massive core is surrounded by an envelope of disseminated and stringer pyrite, phyrrhotite and chalcopyrite in sericite schist. Several subsidiary lenses of mineralization are found in stacked form in the hangingwall and footwall of the main orebody.

The deposit has undergone multiple periods of deformation and has been subjected to regional metamorphism of up to almandine-amphibolite grade. It is stratigraphically underlain by anthophylite-cordierite-garnet gneisses (granite gneiss group), enveloped by ore-related sericite schist alteration (sericite schist group) and overlain by quartz-biotite-feldspar gneisses containing both silicate and oxide facies iron formations (grey gneiss group). In short, Geco is interpreted as an overturned, deformed, syngenetic, stratiform, volcanogenic massive sulphide deposit.

Mining

Access to the underground orebody was first provided by the No. 1 shaft, which bottomed at the 2450 level (2,450 ft below surface). An internal shaft, or winze, a few hundred feet east of No. 1, provided additional depth penetration as mining went deeper. Today, the No. 4 shaft, roughly 4,000 ft east of No. 1, is the sole production shaft. No. 4 was sunk in 1963 as mining moved eastward and rendered the earlier shaft and winze uneconomic from a haulage standpoint. Some workers still descend No. 1 to reach working areas, mostly pillars left from primary mining.

Geco has three distinct orebodies: the huge main zone, which has provided the bulk of the ore; and the 4/2 and 8/2 zones. Blasthole mining has been the major mining method at Geco, although cut-and-fill did play a role in some upper sections. It was discontinued in 1984. The lion’s share of production comes from remnant and pillar mining. Transverse pillars are 120 ft wide on each side of the stopes and every third pillar (a “boundary” pillar) is 150 ft wide. Transverse stopes and pillars are in the lower part of the ore and are 30 ft or thicker. Anything narrower than this is mined longitudinally.

The mining/backfill method sets this mine apart from most others in Canada. Geco’s backfill material is predominantly quarry rock, which is mined on surface and dumped down raises directly into stopes as they are mucked out, so that sloughing is restricted. (Leaving bigger stopes open for any length of time caused troublesome dilution levels.) In the Main zone, most of Geco’s mucking had been accomplished by 125-hp slushers positioned in scram drifts. But eventually, as more of the 4/2 ore zone is developed, the mine will have 14 load-haul-dump machines working underground in both development and drawpoint mucking. The load-haul-dump machines (LHDs) will eventually replace most scram, drifts and slusher mucking that typified the Geco mucking method. At the time of writing, mining was taking place throughout the workings. But a gradual focusing will occur in the 4/2 and 8/2 zones as pillar and remnant mining advances, said new Mine Manager John Keyes.

This system, called quarry fill blasthole, was devised in the early 1960s. Narrower stopes, usually not close to the existing orepass system, are mined by open blasthole stoping. The 4/2 (an average 12-ft-wide, copper orebody) and the 8/2 zinc zone are mined this way. As more and more of the Main zone becomes mined, production will increasingly rely on open stoping blasthole from the 4/2 and 8/2 zones to fill quotas. In mucking out the Main zone, Geco relies on slushers positioned in scram drifts. But eventually, as more of the 4/2 ore zone is developed, the mine will have 14 LHDs (all Eimco Jarvis Clark) working underground.

Where quarry fill blasthole is not used, the backfill comes from the mill’s flotation tailings. The coarse fraction is used in backfill, while the fines are sent to the tailings impoundment area. The backfill plant provides 300,000 tons of backfill sand per year in both cemented and uncemented form.

Geco aims to reduce the number of development sublevels by drilling off the 200 ft between main levels. This would eliminate 100-ft sub-levels. Production machines will either drill the 190 ft between levels or will drill down 120 ft and then be repositioned in the main level, 200 ft below, to drill off the remaining 80-ft uppers. Engineers are evaluating the performance of a Tamrock Solo 3/1/2/-inch production drill. It was being evaluated, during our tour of the underground, for drilling into 4/2 ore. So far, the machine has drilled holes as deep as 180 ft. “It has to do that accurately,” said Ken Byberg, mine superintendent. “We know it can drill 190 ft, but there is deviation.” Geco is working with rod makers Secoroc, Kenroc, Atlas Copco and Sandvik in an attempt to find the most accurate rods. Larger diameter Atlas Copco 3-wheel wagons with COP or BULROC hammers have been the mainstay of production drilling.

Innovation is also being sought in slot raising. Rather than conventional slot raising, Geco is experimenting with electric/hydraulic down-the-hole drills, such as those manufactured by Cube
x Ltd. and Continuous Mining Systems. It would drill out an 8-inch hole and then be fitted with an 18-inch reamer bit manufactured by National Compressed Air Canada Ltd. The point is to develop underground machinery that can fit in the cage. This is necessary because the mine does not have an extensive ramping system. In addition, the friction hoist makes slinging difficult. For the same reason, engineers have developed a 3-wheeled completely cageable truck that can carry 550 lb of ANFO (ammonium nitrate and fuel oil) and can serve as a platform for development drilling. Geco and one of its explosives suppliers, Northlands Explosives of Thunder Bay, Ont., have also helped develop a bulk ANFO mover and pneumatic loader capable of handling 1,000-lb bags. “In one blast recently we had to break 428,000 tons of ore,” said Byberg. “We could have used as much as 200,000 lb of ANFO. Delivery methods of this amount of explosives are important.”

Milling

Ore dressing begins at crushers underground. There had been three crushers in years past, but Geco has installed a system of orepasses that allows for a central crusher just above the 3850 level, to comminute mine-run material to minus six inches. During our visit, Geco was in the midst of building a new crusher installation below 3850.

All the ore is skipped up No. 4 shaft and then conveyed to the mill by an underground belt. Secondary crushing is performed by three 4/1/4/-ft Symons cone crushers in parallel. Four Dominion Engineering 12×14-ft mills do the grinding. Primary grinding is accomplished by 3/1/2/-inch rods, secondary with 2-inch-diameter forged steel balls and tertiary with 2-inch cast slugs. The final grind produces 60% minus 200 mesh. Cyanide is added to grinding to depress iron sulphides and active sphalerite.

Differential flotation recovers copper and zinc. The ore first reports to the copper circuit at a nominal 8.8 ph. After a regrind and a cleaning flotation circuit, cleaner tails are thickened and processed through a scavenger circuit. Final copper grade averages 29% with 18 oz silver per ton.

Copper tails are then processed through the zinc circuit at a nominal ph of 9.3 with copper sulphate activating the sphalerite. To concentrate the zinc to 53%-54%, two stages of cleaning are incorporated. The first zinc cleaner tails have a scavenger circuit. Outokumpu Courier 30 on-stream x-ray analyzers and a Foxboro Spectrum Multistation System computer handle process control requirements. “Our computers have increased recoveries by half a standard deviation, which here is 1%,” said Mill Superintendent Dave Hendriks.

Dewatering was a 3-step process in the past, but Geco recently installed two Verti-Press pressure filters to replace vacuum filters and rotary kiln dryers and produce a filter cake with 7% moisture at 15 tons per hour. Relatively new to the industry, Verti-Press pressure filters have been successfully incorporated into mills at Falconbridge Ltd’s Sudbury operations. Geco’s pressure filters and the structures and ancillary equipment built around them cost about $2.5 million. Other mill capital expenditures include $5.2 million to replace flotation cells. This work was done in 1988.

Mill head grades average between 1% and 3% copper and between 2% and 5% zinc. “We do have pods of 6% or 7% or 8% copper and sometimes we get a slug of this stuff,” Hendriks said. Copper recoveries run 92% to 93% and zinc hovers between 82% and 88%. Copper concentrates are shipped to Noranda’s Horne smelter and to Hudson Bay Mining & Smelting’s Manitoba complex. Zinc concentrates are processed at Noranda’s Valleyfield, Que., plant. Since startup in 1957, Geco has produced enough concentrates to fill a train 1,220 km long. By the time the last concentrate car is topped up eight years from now, this imaginary train will have added another 300 or so kilometres.

THE RESERVE PICTURE

Geco’s reserves of 11.8 million tons grading 1.61% copper, 2.9% zinc and 1.13 oz silver per ton are adequate for about eight years of mine life. Failing the discovery of new mineralization, a shutdown is inevitable. But nobody has given up hope yet.

Airborne electromagnetic and magnetometer surveys were run this year. Quite a few anomalies have shown up from that work. Next year, diamond drills will probe the most promising. Says Chief Geologist Hugh Lockwood: “We’re looking for good, high-grade sources of ore to feed the mill. Any orebody found within a 40-mile radius would suffice.”

Meanwhile, Hucamp Mines holds ground adjoining Geco to the east. Underground diamond drilling in Hucamp territory has not been particularly promising. But where there’s proximity to a producer, there’s hope. An exploration drift continues to be driven into the Hucamp ground.

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