The Red Lake gold mine and mill in Balmertown, northwest Ontario, opened in 1948, and has operated at between 150 and 800 tonnes per day. The mine was closed in June 1996 by a strike that only ended in April of this year. Until its closure, the mine had produced 3.1 million ounces (96,000 kg) of gold, but by 1996 was operating at a loss, with cash costs of US$360 per ounce.
The mine’s 100%-owner, Goldcorp Inc., pursued a major exploration program during the ensuing four-year shutdown, that has resulted in the delineation of the High Grade Zone (HGZ), a new orebody with latest reserves of 2.3 million ounces (71,000 kg) gold. The average cut grade of this deposit, at 1.37 oz/ton (47.0 grams/tonne) gold, makes it one of the highest grade deposits in the world.
The September 1998 results of an independent feasibility study undertaken by Watts, Griffis and McOuat led to a go-ahead decision: to spend US$56 million to expand the mine and mill to 545 tonnes of ore per day. This will yield 240,000 ounces (7,465 kg) of gold per year over the life of the mine, at a cash cost of US$88 per ounce, amongst the lowest in the world. A refractory concentrate will be stockpiled. This forms Phase I of the current project, and it was 90% complete when CMJ visited the property in early August. Commercial production is expected to begin this November, on schedule and on budget.
Phase II, scheduled in the next two years, will be the design and construction of a plant to treat the refractory concentrate, at an estimated cost of US$20 million.
Underground development and surface construction began in May 1999. As the union was still on strike, contractors and consultants were brought in to do the work, under project management by Merit Consultants International. Merit and the contractors are still doing most of the work on the site, although Goldcorp is now building up its own team to manage the operation.
The surface facilities have changed considerably during the project. Older buildings including the old mill, roaster/ baghouse and stack were demolished. Construction included a new mill, an office and security building, a warehouse, new compressors and a backfill plant, as well as improvements to the dry.
“The new design brings the key departments together–Administration, Engineering, Geology and Mining–and close to the headframe as well,” says Claude Lemasson, who became Goldcorp’s general manager in August after two years as construction manager of the site for Merit. “There’s been a significant improvement in communications as a result of that.”
Plans are already underway to expand the mine production rate. Wherever possible, equipment and buildings were sized to facilitate up to 900 tonnes per day of production. Feasibility studies for mine and mill expansion and refractory gold treatment will be started as soon as the mine reaches its initial design capacity of 545 tonnes per day.
Geology and Exploration
A two-year exploration program was announced in 1995, and almost immediately began to report intersections in the HGZ.
The HGZ lies in the nose of a steeply plunging fold east of the No.2 shaft. The zone, consisting of many en echelon veins, extends at least 500 m vertically from 30 to 40 level (and is still open at depth) and 180 m along strike, with each vein up to 6 m wide. The gold occurs with pyrite, arsenopyrite, quartz and carbonate.
The veins follow fairly continuous structures. Where the structures intersect are “pods” of ore with greater widths and higher grade; some faces assay up to 70 oz/ton (2,400 g/tonne) gold.
“We see spectacular high grade here, like I’ve seen nowhere else,” says Mark Tessier, Goldcorp’s underground manager. “They’ve hit this type of mineralization in the past, but never in the quantities that we’ve now got.”
There are at least six different zones within the HGZ, including the Hanging Wall Zone in the south limb of the fold, and the Main Zone in the north limb. Current reserves in the HGZ stand at 1.5 million tonnes grading 47.0 g/tonne (1.37 oz/t) gold, sufficient for eight years of production, based on a gold price of US$300/oz, external dilution of 22%, and the cutting of higher grades to 10, 5 or 2 oz/ton. The Sulphide Zone contains an additional reserve of 1.4 million tonnes grading 12.3 g/tonne (0.36 oz/t) gold. Goldcorp plans to resume mining there at a later date.
There is an intensive grade control program involving a senior geologist and eight production geologists, one on each mining level on every work shift. Good communications between the geologists, the underground manager and superintendent, and the miners have kept the dilution factor to a minimum.
During development, the production geologist’s workload is heavy. This involves mapping every active face (up to eight) on a level, and taking high-quality digital photographs that can be used for geotechnical mapping and for future reference. The sampling regime is thorough. Each face is double-channel-sampled. (This will later be reduced to single channels.) The general mine plan is based on the delineation drilling, but may be altered daily depending on the face sampling. Chief geologist Steve McGibbon has found the correlation between reserves and actual ore generally good, although some lucrative pods were found where waste had been expected.
After blasting, the muck piles are sampled at the face. The muck is again sampled along the tramway. Then the surface stockpile is sampled. At the beginning of August, there was a surface stockpile of almost 25,000 tonnes of HGZ ore from silling on 32-1 sublevel and 34 level. Assaying of 2,300 samples from this stockpile yielded a gold grade of 63.8 g/tonne (1.86 oz/ton), considerably higher than the forecast 47.0 g/tonne (1.37 oz/ton).
Goldcorp’s four-person exploration team is conducting a large and aggressive exploration program that is expected to add considerably to the reserves. Diamond drill contractor Major Dominik will pull 54,000 m of core from underground drifts this year. The intent of the program is not just to replace the annual mine production, but to find another orebody like the HGZ, according to McGibbon.
Currently there are three main exploration targets. One of these is testing mineralization along high-angle ultramafic-mafic rock contacts in the west Hanging Wall Zone on 17 level, which may be similar to the nearby G and L Zones in the Campbell mine, and may also tie in with exploration targets on 34 level west. Another target is lower grade sulphide mineralization on the east side of the mine between 13 and 21 levels, along-strike from the East South C Zone. A third target is an extension of the Hanging Wall 5 Zone.
The well-publicized “Goldcorp Challenge”, an internet-based contest launched in March 2000, invited non-employees around the world to suggest where to explore for the next six-million-ounce orebody, near the current underground workings. By the time the competition closed the end of July, 1,400 had registered and received the data. Submissions are being judged on their merit by an outside panel for the awarding of the US$500,000 in prize money. The submissions will be sent to McGibbon who says, “We are hoping for some good, off-the-wall ideas, maybe from Asia or Australia where they do exploration differently.”
Through land purchases, Goldcorp has increased its property holdings in the district to 18,400 hectares. The company’s regional exploration is not confined to gold. In July, it announced the discovery of significant palladium and nickel values on the Trout Bay property, Goldcorp’s other high-profile program in the camp, 34 km west of the mine site.
The mine development project includes refurbishing the existing two-shaft system (which was built between 1946 and 1980) and the tramming system between the two shafts on 23 level. As well, there is development of four new mining horizons below the previously-mined orebodies. Levels are 45 m (150 feet) apart, so 30 level is about 1,300 m below surface, and the loading pocket at 38 level is 1,700 m below surface.
The mine contractor Dynatec Corp. began underground development and construction in May 1999 and should complete Phase I of the project by November of this year. This includes four new mining levels in the HGZ: 31-1 sub, 32-1 sub, 34 level and 37 level. It also includes a new haulage system on 37 level, and new ventilation and ore and waste handling systems between 30 and 37 levels. By that time, the mine should be producing 545 tonnes of ore per day.
All of the mining initially will be by ramp-access cut-and-fill, although there may be a small amount of captive cut-and-fill in the future. In later stages, the sill pillars will be removed by longhole mining.
The mining is very selective. Jacklegs drill 2.4-m rounds or 3.0-m breasts, while the jumbos drill 3.0-3.4-m rounds. The height of the rounds is 3.0 m, and the standard width is from 1.2 to 6.1 m, depending on the ore zone. The ground is dry, so blasting is done primarily with Anfo and also with emulsion explosives. The ore is mucked with 0.6-m- to 1.0-m-wide slusher/scrapers and 0.7-m3 to 2.3-m3 load-haul-dumpers.
“Because of the high-grade nature of the zone, when we’ve completed mining from a sublevel, we will clean the floor all the way back to the ore pass, so that we recover all the gold,” says Tessier. “We also collect all our spill in the bottom of the shaft and send it for ore.”
Swellex and Split Set friction bolts from 1.8 m to 3.7 m long (one-third the span of the heading) support the backs and walls in the ore; cable bolts are used in the rare headings that are wider than nine metres across. “When the ground works (minor surface strain bursting is common), the friction bolt will yield with the rock and not break,” says Tessier. “We also use a fine mesh screen that catches any loose coming off the back.” He says this follows similar concepts designed for Kinross Gold Corp.’s Macassa mine in Kirkland Lake, Ont., a much deeper mine that had to overcome adverse ground conditions.
Two Alimak raises were driven for ore and waste passes from 30 level to 34 level, where a temporary haulage system has been set up. These two passes will be extended to 37 level by the end of this year, where the permanent haulage will be built. This will consist of a 500-m-long tracked haulage drift. Cars on 37 level will drop the ore and waste through grizzlies equipped with rockbreakers into passes that supply the loading pocket on 38 level. This ore is then skipped to 23 level where it is transferred via rail haulage to the No.1 shaft for skipping to surface. The two hoists that serve the No.1 shaft and the hoist for No.2 shaft have been automated by ABB. As well, the trains, rockbreakers, and loading pockets will all be fully automated, allowing one operator to run the 37 level haulage system remotely. This will be especially useful during shift changes and post-blast periods.
All stopes will be filled with paste fill beginning in mid-September, using a system designed by Golder PasteTec. Paste fill consists of tails from the mill mixed with cement (up to 10%) and water in the new backfill plant on surface. This slurry is distributed to the stopes via a series of 12.7-cm-diameter boreholes and pipes.
“Along the system we will have pressure transducers and video sensors so we can see what’s going on in real time,” says the chief engineer, Pierre Rocque. “If we see there’s a build-up of pressure, we can act on it right away, as opposed to plugging the hole and finding out about it six hours later.”
Goldcorp’s underground superintendent, Ted Okell, describes how a stope will be backfilled. “Before we put the sill mat in, we clean the floor with water and compressed air. The geologist then maps the ore on the floor. Then we place screen mesh on the floor of the stope, and anchor the screen to the walls with rebars. The hanging wall of the stope is also doweled with rebars to anchor the fill. Then we pour the cemented paste fill up to within 0.3 m of the back, like filling up a lake underground.” The paste fill takes about one shift to set; the adjacent lift can be blasted after one day.
The ambient temperature underground increases with the depth of the mine. The ventilation system brings 60 m3/second of fresh air to 30 level through the old mine workings, which heats the air naturally. The auxiliary ventilation system supplies 12-15 m3/second of fresh air to the working faces, which Tessier says is sufficient because of the small size of the equipment. Ultimately the fresh air will be distributed down the stope air raise to 34 and 37 levels and below, and will exhaust up the main ramp to 30 level and then to surface through another series of raises and drifts.
To enhance safety and understanding of the ground reaction, the mine has implemented a state-of-the-art, digital micro-seismic monitoring system supplied by ESG of Kingston, Ont. This can pinpoint seismic activity in the active areas between 30 and 34 levels. When it is extended down to 37 level next year, the system will cover a volume of rock 300 m by 460 m by 150 m.
Communications have been greatly enhanced by the addition of fibre optic cabling, which currently has 24 fibres and can transmit video, voice and data. On surface the cable links the administration building with the mill and headframe, maintenance and the backfill plant. The cable extends underground to various locations throughout the HGZ. “Fibre optic is much better than traditional copper communication cable because it is faster, more reliable and has a greater capacity,” says Rocque. As an example, the surveyors, geologists and front-line supervisors underground will carry Psion collectors for inputting data. These can be docked at stations hardwired to the fibre optic cable, so that data can be sent to surface, and vice versa.
New Processing Plant
The 545-tonne/day Red Lake mill was designed by Hatch-Rescan Engineering and built at a cost of US$20.5 million by various contractors managed by Merit. In 1998, Cameco Corp.’s Contact Lake mill in Laronge, Sask., was purchased by Goldcorp for its equipment. Some of the key components were dismantled, shipped, refurbished and installed in the new mill. These include the jaw and cone crushers, the ball mill, the leach and CIP tanks, and various other small pumps and equipment.
Two new pre-engineered buildings house the crusher plant and mill. All operations can be monitored and controlled from the central control room in the mill, with the help of a PLC system and an extensive camera network.
The technology in the plant is standard and proven, but the flowsheet is different with the CIP circuit before the flotation circuit. Studies at Lakefield Research had shown that this flowsheet would give better gold recoveries than if flotation came first.
The ore storage capacity is 2,700 tonnes in passes underground and 1,400 tonnes in two bins on surface. A bypass conveyor also allows crushed ore to be taken out of the circuit and stockpiled on surface, to later be refed into the system through the reclaim hopper and conveyor.
The most unique aspect of the Red Lake mill is the very high grade of the ore, according to Klaus Tietz, Merit’s plant commissioning manager. “A large portion of the gold (50-60%) is directly recovered through the gravity circuit. Of course, the security is high, and rightfully so.”
Tietz describes how the plant will operate.
Ore is crushed by jaw and cone crushers in two stages to -1 cm and ground to -80% passing 74 microns in a 3.5-m-diameter by 4.9-m-long, 8.9-kW ball mill. Part of this slurry feeds the Knelson centrifugal concentrator and Deister shaking table below, which recovers the gravity portion of the gold. Table product is direct-smelted into dor.
The grinding circuit product is thickened to 50% solids and pumped to the leach circuit, which has a retention time of 2.5 days in a series of four leach tanks.
There are six carbon-in-pulp tanks in series. When the loaded carbon grades 10,300 g/tonne gold, it is removed from the No.1 CIP tank and acid-washed. The gold is stripped from the carbon using a caustic solution, with a little cyanide added to improve recovery, in two 3.6-tonne vessels.
The eluate is pumped into the refinery where the gold plates onto stainless steel wool in the 3.5-m3 electrowinning cells, and the 79.8-dm3 induction furnace smelts it to dor.
Tails from the CIP circuit report to a two-stage INCO SO2/air unit, which transforms the cyanide to ammonia (for environmentally benign long-term storage at the tailings facility) and also precipitates out heavy metals, before the slurry goes to flotation. Also, if the cyanide were not destroyed, it would depress the gold-containing pyrite and arsenopyrite, which need to float in the next stage.
Refractory concentrate from the flotation cells is thickened and drum-filtered to 90% solids, and then stockpiled for future treatment. Autoclaving is under consideration for this concentrate, but other processes will also be tested. A decision should be made by mid-2001, and the system should be in place a year later.
Tailings from flotation are thickened to 55% solids. About 65% of the tails will be used as paste fill, and the rest will go to the tailings impoundment.
The 1998 feasibility study predicted that 40% of the gold would come off through gravity separation. (Initial production shows higher gravity recovery.) Another 43% of the gold is expected to be captured by the CIP circuit. About 12% of the gold will be tied up in the refractory concentrate. Therefore, when the latter is treated, the gold recovery is expected to be at least 95%.
The crushing, milling and gravity circuits were commissioned in July, and the first gold was poured from a gravity concentrate on August 1. The gravity circuit captured 55% of the gold in the ore, and the dor assayed 83% gold and 7-9% silver, compared with an expected 80% gold and 7-10% silver content. The commissioning of the mill is to be complete by October.
Kerry McNamara, the manager of environmental services, describes how the new tailings disposal system will differ from the old one.
“We will definitely produce much cleaner effluent than before,” says McNamara. The effluent treatment system in the mill will destroy cyanide and precipitate heavy metals including arsenic, before the tails can be used as backfill or sent to the tailings pond. Over 65% of the tails will be used in paste backfill, greatly reducing the amount of solids for disposal. Additionally, two containment dams bordering Balmer Lake, the historic polishing pond, have been raised 1.2 m and a tailings blanket on the upstream side has made the dams less permeable, to increase retention time.
“Our intention is to make the current secondary pond into a polishing pond, so that we can move the final control point to the effluent entering Balmer Lake,” says McNamara. “We are not quite there yet.” She is also considering building a wetlands area within the current tailings system, to reduce concentrations of ammonia (from the breakdown of cyanide).
However, the tailings from the first five decades of mining still pose hazards, especially in Balmer Lake. “Arsenic is a big issue with us,” says McNamara. After almost 50 years of tailings from two mines, the lake had serious environmental impacts. But with treated effluent from Placer Dome Inc.’s Campbell mine starting in 1993, and the shutdown of the Red Lake mine in 1996, Balmer Lake quickly recovered to the point of being hypereutrophic (making more food than the fauna could consume). In 1998, thrice-weekly sampling of water from Balmer Lake began to pick up elevated arsenic values. Increased biological activity at the sediment/water interface had created a redox condition that is releasing arsenic from the sediments into the water column.
To date, Goldcorp and Placer Dome have spent more than $500,000 on research to address the elevated arsenic in Balmer Lake. One of the studies included a test in which 19 walleye weighing 1.8 kg, marked with acoustic radio tags, were transferred into the lake in May 1999. There was an initial mortality of eight fish, probably due to post-surgical stress. Nine walleye were found the next spring, two of which were harvested in July 2000, and each had gained 0.9 kg, so there was no shortage of food. The federal Department of Fisheries and Oceans (DFO) is analyzing the fish for bio-accumulation of heavy metals, and was to release its results in September. The DFO is also looking at several methods of dealing with arsenic, including seeing if it will bond with the iron and silica in zeolites.
Mark Tessier has been managing the underground work at the Red Lake mine for Merit Consultants since April 1999, the month that Dynatec began to mobilize to the site. In mid-August he was hired by Goldcorp as underground manager. He summarizes his experience, and projects into the mine’s future.
“This was a difficult project. We had a very old mine in which we had to rebuild a lot of the main infrastructure, and were doing major development work at the same time.
“Now that the new infrastructure is coming online, you get the benefit of these things being completed. The project really did a dramatic surge at the beginning of April this year. Through the summer months things have been really progressing well. Development has recently been ahead of schedule.
“Dynatec has been doing quality work and I’ve been reasonably satisfied with their effort to date. We’ve had our problems, but we’ve got a pretty good working relationship established.
“The ore is turning out to be better than what we’d expected in most respects, and that’s always a plus. The ramp is through [from 30 level to 34 level], which is a real good shot for morale, and it’s also increasing our operating efficiencies. So I would say that we’re in good shape going into the fall.
“The next big push is to get the backfill system up and running. You can only mine for so long before starting to put fill in the ground. We’ll also be finishing off the track haulage on 37 level this fall, and that will be another big milestone.
“Going ahead, the development will never end at this mine until the mine ends, there are just so many good exploration targets at depth, along strike, and in the upper parts of the mine. We want to get the ramp down to 40 level in the future. We also want to get the new fresh air ventilation system in operation next year. Someday, we may consider a shaft-deepening, depending on exploration results. If we find enough ore in other parts of the mine, we might even look at sinking a new shaft.”