In late April, the snow was off the ground at the Casa Berardi mine in northwestern Quebec. Temperatures hovered at a tolerable 12/7ch/C, and black flies and mosquitoes had yet to emerge from the vast muskeg plain. Nature had added a nice touch, sprinkling morning frost on the groundcover like a dusting of icing sugar. It was, in short, a pleasant time of year to visit the mine. The timing was fortunate in another respect: With commercial success at 1,200 tonnes per day, the mines and mill were being studied for a 50% capacity expansion.
The mines — there are two autonomous ramp-access mines sharing a common mill — are 100 km north of La Sarre, Que. The operation is owned by Inco Gold (a unit of Inco Ltd.) and Golden Knight Resources (a Teck Corp. affiliate). The combined “geological” ore reserve is 11.1 million tonnes grading 7.54 grams gold per tonne. The total minable (proven and probable) reserve is 5.5 million tonnes grading 7.2 grams per tonne. The East mine is currently extracting a lower grade of ore than the West mine, but according to Inco Gold president Martin Robinson, grades should be similar in the long run. At a mining rate of 400,000 tonnes per year, the operation has at least 14 years of productive life. But depth potential and a known gold-bearing zone between the two mines should guarantee a much longer life.
A recent re-evaluation of reserves at the West mine, which came into commercial production in April, prompted the decision to reassess the operation’s capacity. Current mill throughput is 1,200 tonnes per day. Once the owners finish crunching numbers by this fall, they may boost it to 1,800 tonnes. The mill currently operates the whole week through, 365 days per year. Miners work 10-hour shifts, two shifts a day, four days a week. Direct cash operating costs run approximately US$200 per oz., or $6.43 per gram. Operating costs (mine, mill and overhead) run C$63 per tonne. The 1990 production goal is 88,380 oz. (2,750 kg) of gold.
Up in this part of the country, the overburden can run as deep as 50 metres. Outcrops are sparse. As a result, sinking a shaft or driving a ramp is at first an earth-moving job. The East mine portal is protected from overburden inundation along the first 100 metres by an Armco corrugated steel dome and concrete floor. This producer, like others in the region, well remembers the crown pillar collapse at the Belmoral mine in 1980 near Val d’Or, which killed eight miners. Casa Berardi has been extremely cautious in defining the crown pillar. At the East mine, for example, the first level is 100 metres below the surface, well below the overburden-bedrock contact. Crown pillar recovery will come much later. The ramp measures 5×5 metres and inclines 15%. A low-profile, specially built Caterpillar grader grades the incline and the surface roads.
The ramp bottoms at the 250-metre level, currently the lowest development level. MacIsaac Mining & Tunnelling developed the mine. Further development now is being handled by Casa Berardi’s miners. The ramp is being driven to the 300-metre level. Two drifts have been advancing toward the ore zone, one to the west on the 250 level and one in the opposite direction on 275.
In the East mine, ore extraction is virtually split in two by a 7-to-12- metre-wide vertical pillar. To the west of the pillar, mechanized cut-and-fill is the sole mining method; to the east, vertical retreat mining (vrm), a bulk method perfected by Inco’s Sudbury mines, has been successfully adapted.
The decision to use either cut-and-fill or vrm is not an arbitrary one, explained Jean-Yves Cloutier, superintendent of technical services. “In competent terrain, where the geometry is subvertical and we have continuity of ore and a low grade, we use vrm,” he said. “We secure the back once and take out a 25-metre panel.” The eastern portion of the orebody requires a surgical technique. It tends to be narrower (an average of five metres) and the ground conditions are less than ideal because of the graphite-laden Casa Berardi Fault on the hangingwall. Once exposed, it deteriorates rapidly. “The graphite is not competent at all, so you end up with an unravelling wall,” Cloutier said. “We developed cut-and-fill to secure it.” In one stope, the graphite portion of the back almost immediately began decaying and what resulted was a kind of cantilevered back when the crumbling graphite section near the hangingwall advanced upwards. Swellex bolts, screening and shotcrete have secured the back for now, but further mining was halted. The ore will be taken later from above with the vrm method.
In the cut-and-fill portion of the mine, an attack ramp affords access. Each horizontal bench in the cut-and-fill stopes is 3.5 metres, and six such benches can be taken with the same attack ramp. As mining advances vertically, the ramp backs are taken down so that equipment can move into the next level. The stopes run as wide as 11 metres. But, because of ground conditions, that width has been set as a maximum for now, said George Darling, mine superintendent. “If we find we can take more, we will. But we won’t do it until we’ve gained that experience over the next couple of years.” The average width is five metres. Atlas Copco 1 and 2-boom jumbos drill off the rounds and, with a dolly attached, they torque the 7-ft. mechanical rockbolts. Wagner 426 (24-tonne) and 440 (39-tonne) trucks haul the muck to surface. Eimco Jarvis Clark 350 and 600 load-haul-dump machines do the mucking. With the attack ramps, the equipment can move freely into and out of the stopes as mining advances vertically.
The blasthole method was demonstrated on our tour at the 200 level. An electric-hydraulic longhole machine with a rod carousel, made by Continuous Mining Systems, was drilling 85-ft. (26-metre) uppers. The machine is capable of 120-ft. (37-metre) uppers, but deviation begins between 85 and 90 ft. (or 26 and 27 metres), Darling said.
Where mechanized cut-and-fill is used in the West mine, equipment is captive as mining advances upwards. Services are provided through a raise at one end of the stope, while workers climb a manway excavated at the other. Tight fill secures the ground after each 4-metre cut. Equipment similar to that in the East mine is used in this mine: jci lhds, Atlas Copco jumbos and Wagner trucks. The West mine also relies on a blasthole method to extract parts of the orebody. As Gerry Lafantaisie, West mine superintendent, explained, the undercut is drilled with a longhole machine, while the top of the stope is taken with an in-the-hole drill. Some stopes in this mine are as wide as 12 metres and as narrow as three metres. Where ground conditions are more difficult, cut-and-fill is used. “We have very little dilution because we’ve been very selective,” said Lafantaisie, an Inco veteran who was project supervisor on the East mine development. The deepest level of the West mine is 300 metres. Mining takes place on the 200-and 250-metre levels.
Unlike mining at its eastern counterpart, mining in the West sector requires that occasional crosscuts be driven across the graphitic fault. When that does occur, the drift is heavily bolted, screened and timbered. Water intake and ground control are also a bigger concern in this mine, because the blocky, heavily sheared ground is less competent than that of the East mine. This mine has an underground service garage, while all mining equipment in the East mine is serviced and repaired on surface.
Inco the operator hasn’t yet given serious thought to mining below 300 metres in the East mine. But, given current truck haulage technology, it appears that a shaft from surface (or more likely because of the thick overburden, a winze from the 100-metre level) will be required in the near future. Mine manager Robert Lepage said Inco considers the vertical depth limit of truck haulage to be 330 metres (1,000 ft.). Beyond that, haulage is not economically feasible. Ore could be skipped up the production winze on the 100 level and transported by conveyor or truck to the surface crusher.
Currently, mine planners are
developing more stopes in the East mine, where development is lagging somewhat. “For a period, we did go after the ounces,” Lepage said.
Geology
Casa Berardi was first discovered by an airborne electromagnetic survey, which picked up the graphite anomaly. Inco staked 13 claims in 1974. The discovery hole came later, in the spring of 1981. It did not intersect mineralization in what was to become the East or West mine. Rather, the drill cut gold values in the Main zone, or Zone Principale, which sits between the orebodies. This zone will eventually be mined.
In the two known orebodies, gold occurs in three types of mineralization: quartz veining, which carries gold most of the time; silicified material, where the quartz component is more than 20% but less than 60%; and mineralized rock, which contains higher amounts of arsenopyrite and pyrite and is usually in tuffaceous rock. Gold in this nearly vertical deposit is finely disseminated and grade control requires constant diamond drill information ahead of mining. Mineralization is more consistent and continuous vertically than it is horizontally, production geologist Gilles Labelle told The Northern Miner Magazine.
Practically all ore in the East mine lies south of the graphitic Casa Berardi Fault. Both the East and the West mines are open at depth.
Management
Lepage came on board from Inco’s Levack operation in March. He is focusing his attention on establishing a preventive maintenance program and generally filling in the pieces of a maturing management structure. For example, a full-time environmentalist has been hired, as has a preventive maintenance planner. And Lepage is beginning to institute a loss control program. This is a safety and accident prevention program based on the International Safety Rating System. “Part of our plan is that we’ll make this a 5-star operation,” he said. A 5-Star designation is the highest rating achievable under the system. The total salaried and hourly-paid workforce at the mine and mill is 163, ninety of whom work for the mine department.
Be the first to comment on "On Site At Casa Beradi"