FOLLOWING THE FAULT: The gold mines of northeastern Ontario and

AMERICAN BARRICK

When American Barrick’s Holt-McDermott mine came into the public eye in the late 1980s, the reserve was estimated at about 3.3 million tons grading nearly 0.19 oz. gold per ton (three million tonnes at 6.5 grams per tonne). After going underground and actually mining the deposit, Barrick downgraded the figure to 2.6 million tons of proven and probable ore at 0.14 oz. (2.3 million tonnes at 4.8 grams). It was an unpleasant surprise. But reality has sunk in. As Jeannot Boutin, technical supervisor, told The Northern Miner Magazine during an underground tour: “We’re not a 0.2 mine. We have to be rational and efficient with our mining.”

On a 7-day-per-week cycle, the mine department is hoisting between 1,400 and 1,450 tonnes per day to feed a modern and very hungry 1,500-tonne-per-day mill. The budgeted average millfeed grade for this year is 4.5 grams per tonne (0.13 oz. per ton). July was a good month in which millfeed ran an average 5.5 grams. (0.16 oz.). Cash production costs are US$284 per oz., while the mining and milling target cost for this year is C$40 per tonne. Mill recoveries are running 94.7%. The dilution problems reported last year were the result of, among other things, teething pains in developing the proper stope distances between pillars, according to Leonard Boulard, underground supervisor. “The first stope on the 100 level was opened 80 metres with no pillars. We discovered that was a bit long. We also discovered the hangingwall was peeling.” Bigger pillars are being left now and cable bolts are supporting the hangingwall where necessary. Stopes are opened at both ends and mined toward the middle. The Holt-McDermott shaft was originally sunk to 420 metres below surface. To gain access to new ore zones at depth, in-house shaft-sinking was begun this fall. The shaft will bottom at 550 metres. Mining has proceeded as deep as 350 metres near the shaft. However, to develop more stopes, Barrick started mining the Worvest zone, which is a kilometre and more from the shaft. Worvest is a lense-shaped deposit that reaches a maximum width of 15 metres. Barrick this year will develop another zone to the east, called the Mattawasaga property. The Holt-McDermott ore near the shaft is associated with the McKenna Fault, itself related to the Porcupine-Destor Fault of which it is an offshoot. The Mattawasaga zone might host the convergence of the McKenna Fault and a second break known as the Ghostmount Fault. B Brick plans to develop the known minable reserve and then carry on drifting toward what it hopes will be the fault convergence. The known zone carries a 4.2-gram grade.

The orebody in the main part of the mine dips between 65deg and 80deg and ranges in width from one or 2 metres to 15 metres. The 3-compartment shaft, which has a fourth, sinking compartment below the 300 level, features stations every 50 metres with a loading pocket for the two 9-tonne skips carved out of the rock at 330 metres below surface. Eight to nine stopes are being mined at any one time. Development involves driving cross-cuts south from the shaft into the ore and then drifting along strike. Development drifting is done with three rock drills mounted on a rail-equipped Long Tom. Development is occurring east on the 100 and 150 levels and both east and west on the 250 level. LM56 muckers load 5-ton Granby cars. Most of the haulage and mucking is achieved by track, although rubber-tired Cavos and load-haul-dump machines are used in mucking some stopes.

A Complex Orebody

Geological control is important in minimizing dilution. Chief geologist Murray McGill noted that “you’ve got to do a lot of drilling and you have to be careful in your analysis.” Boutin said that last year 208,000 ft. (60,000 metres) of diamond drilling were completed for delineation purposes. Development drifts are driven up to 200 or 300 metres in advance of mining so that drill core can be taken to fix the position and grade of the ore to be mined. Even then, keeping dilution down to the target 5% can be trying, because within an identified ore zone pockets of barren ground might occur. This internal dilution is just one more difficulty that this complex orebody poses to the Holt-McDermott mining team. To prevent sloughing, cable bolts secure the hangingwall. Mining is under contract by Boart. Longhole methods are employed, drilling 2 1/8-in. holes in 10- to 12-metre uppers and then drilling down from a drill sub 25 metres above the bottom opening. A 10-ft.-diameter borehole from surface to the 350 level provides downcast air and an escapeway, while the shaft and a smaller borehole provide upcast openings.

The mill flowsheet includes one-stage crushing, semi-autogenous grinding followed by a ball mill, 2-stage cycloning forrclassification, 6-stage carbon-in-leach (CIL), pressure stripping, electrowinning and refining in an inducation furnace. CIL, rather than cyanide leach and carbon-in-pulp, was chosen because of the presence of gold-robbing graphite in the ore. The ore is leached during a 24-hour retention period with cyanide in an alkaline slurry in conjunction with activated carbon. Average mill recovery last year was 94.7%.

Occasionally, graphite in the ore impeded recoveries. However, because the graphite-bearing ore wws rich, in the neighborhood of 0.2 oz., management felt it was worth the drop in recoveries.

ST ANDREW GOLDFIELDS

The Porcupine-Destor Fault represents both blessing and at least mild curse to St Anddew Goldfields’ Stock Twp. mine 70 km east of Timmins, Ont. Were it not for the fault, there would be no gold ore to mine. But the fault also poses the biggest challenge to mining — ground control. St Andrew’s main N-2 zone lies between the major Porcupine-Destor Fault and a minor break associated with it. Actual mining does not extend into the major fault, although activity associated with the fault in the past has affected ground conditions in stopes. This requires caution by the miners and ground control methods that go beyond strategically placed mechanical bolts.

The major break crosses the shaft area below the fourth level, 575 ft. (175 metres) below surface. For now, a ramp provides access for Levels 5 and 6. Mine manager Bob Ritchie estimates that St Andrew can haul ore profitably by truck from as deep as the eighth level, but to reach mining areas below that level (should it become necessary), the company will need to consider solutions to ground conditions in and around the shaft area below Level 4 or develop an alternative to shaft-deepening. “We could go to the eighth level by haulage. That would give us 600 vertical feet for haulage. Past 600 ft, you’re getting a truck an hour on a return trip,” Ritchie told The Northern Miner Magazine on a tour late this summer. The two JCI 13-ton trucks hauling now between the fourth and sixth levels can each make the return trip in 30 minutes. Those concerns, however, are something that St Andrew can safely file away under “future considerations.” Currently, the Stock Twp. mine is operating well above capacity. The nameplate capacity in the mill is 500 tons per day. But as chief geologist Otto Zavesiczky noted, the mill has been running between 500 and 700 tons per day for the past few months. Indeed, during the mill tour, the meters that monitored both the ore conveyor leading to the crusher and the grinding circuit displayed current throughput at 30 tons (27 tonnes) per hour, which on a 24-hour cycle would mean daily throughput of at least 700 tons (635 tonnes).

The mine first attained commercial production in October, 1989. In the first six months of this year, it produced 14,726 oz. of gold. At an average processed grade of 0.14 oz. (4.8 grams) for the first six months of 1990 and a cost per ton of roughly C$50, mining and milling are profitable, having produced an operating profit of $1.3 million. After depreciation and depletion charges of $4.4 milion, the company reported a mine operating loss of $3.1 million for the period.

Cut-and-fill mining provides millfeed. The stopes are mined by contractor Mindecon Inc.in 8-ft. (2.4-metre) li
fts from level to level. The stopes are no wider than 25 ft. (7.5 metres). “When we tried to go to 40 ft. (12 metres), we had a fall of ground,” said Ritchhe. “The golden rule here is 25 ft. and leave a pillar.” Drilling is conventional, using Secan rock drills and JCI 2 1/2- and 1 1/4-cu.-yd. load-haul-dump machines for mucking. Occasionally, scrapers are used. The smaller machines remain captive until the cycle ends at the upper level. The orebody pinches and swells considerably so that long-hole mining methods cannot be incorporated.

Ground control in the stopes takes the form of 20-ft. (6-metre) Swellex bolts, cable bolts of up to 90 ft. (27 metres) long and screened backs. “I never had faith in Swellex bolts before. I didn’t have experience with them,” said Ritchie, a former Redpath employee who previously had been working at the Hemlo mines. “But they work. In our ground here, they really helped us.” So far, the first of six established levels has been mined out. The second level, which takes a small bite out of the top portion of the N-2 zone and a big piece of the M-1 zone, will be mined out within a year’s time. Ritchie hasn’t ruled out the potential for ore in the eastern and western extremities on that level. The lion’s share of mineable ore lies in the M-1, M-2 and N-2 zones, all to the west of the shaft.

Current reserves stand at 767,027 tons at a grade of 0.161 oz. per ton, equivalent to 697,300 tonnes at 5.5 grams per tonne.

The reserves do not include St Andrew’s properties nearby. For example, in neighboring Taylor Twp., the company has outlined reserves in two deposits. And it has also entered into a mining and milling contract on Goldpost Resources’ property in nearby Hislop Twp., which is readily accessible by Highway 101. Tests conducted by Lakefield Research have indicated that the highly siliceous Goldpost ore will require a finer grind (to 87% passing -200 mesh) than the Stock Twp. ore. As well, associated companies of St Andrew are involved in the development of the Garrison Creek property, in Garrison Twp. Here, a mineralized zone has been delineated by Falconbridge Ltd. and Garrison Creek.

Meanwhile, probing for more ore at the Stock Twp. mine, St Andrew has driven an exploration drift on the second level 600 ft. east. No economic mineralization had been encountered, but the target still lay 70 ft. (21 metres) out, where a diamond drill had intersected gold mineralization.

Mineral processing begins with a rockbreaker on the fourth level. Above ground, a Kemco 24 x 36-inch jaw crusher and a Symons 4 1/4-ft. shorthead cone crusher reduce the muck to minus 5/16 of an inch. With a work index of 16.2, the Stock Twp. rock is relatively soft. The Allis-Chalmer ball mill is charged with 2- to 2 1/2-inch balls. The ball mill product is then thickened to 59% solids, leached and then pumped through five carbon-in-pulp (CIP) tanks. A straight carbon-in-leach plant was not possible because of the pyrite content of the ore and the ore hardness, said Peter Massi, mill superintendent. The rated capacity of the leach and CIP circuits is 1,000 tons (909,000 tonnes) per day, while the grinding section has nameplate capacity of 500 tons (455 tonnes). After the CIP circuit, the carbon is stripped of gold and the gold is collected by an electrowinning process. Recoveries run slightly above 94%.

ROUYN RESOURCES

Rouyn Resources’ Francoeur mine on the outskirts of Rouyn-Noranda, Que., has proven reserves of 534,000 tons grading 0.22 oz. gold per ton (485,450 tonnes at 7.5 grams per tonne). It has another 618,100 tons (561,800 tonnes) in the probable category and one million tons (910,000 tonnes) is in the possible category. If, with current development work, 500,000 of those probable tons can be rendered into proven ore, Rouyn will push ahead with the building of a mill. And a former producer will once again be in business. Rouyn was mining the Francoeur orebody up until late June. It stopped, says Rouyn president Jean-Guy Rivard, because profits were being eaten up by the costs of truck haulage to LAC Minerals’ East Malartic mill in Malartic, Que. At between C$9 and $10 per ton, haulage and the resulting muck rehandling were making a money-loser out of the mine, he said. With custom milling taking another C$18 per ton and mining $50, Rouyn simply could not support the operation. Relative to other mines, total cash costs per ton were high, although Rivard points out that depletion and depreciation charges are low in relation to such charges at comparable mines.

In its current reincarnation (the property is the site of several past producers), the Francoeur mine is Rivard’s brainchild. It was Rivard, as the ambitious president of a junior, who bought a 50% interest and operator status from LAC Minerals for $8.5 million. (LAC still holds a 50% interest.) For a time, production was being hoisted up shaft No. 6, which bottoms at 1,535 ft. (460 metres) in ore zone 3. In June, 1989, a new shaft to 2,697 ft. (809 metres) was sunk a half-mile to the northeast of No. 6 shaft. Excessive water inflows at the 800 and 1200 levels during shaft-sinking delayed the project by four months. Grouting stanched the flow of water. The shaft has three compartments and is fitted with two 5-tonne skips. The mine has been developed on six levels below the 12th level. The Northern Miner Magazine toured the underground operation through the new shaft.

The mine sits about 2.5 km north of the Cadillac Break in an area known as the Francoeur-Wasa Fault. To the south of this local fault are mafic volcanics and to the north are mafics with intermediate to felsic rocks. The orebody dips to the north at 55deg and then begins levelling off to 30deg at depth. Where the dip of the orebody becomes shallow, Rouyn has reverted to a room-and-pillar configuration in the stopes. Nearer to surface, where the dip is closer to vertical, either long-hole or shrinkage is used. Ore width and ground conditions dictate which of the two methods are employed.

The drive to increase proven reserves has focused on two ore zones below the 11th level. In both zones, the deposit tends to pinch and swell anywhere up to 25 ft. (7.5 metres). The minimum mining width is 5.5 ft. (1.6 metres) and the average is 10 ft. (three metres) wide. All mining to date has been under geological control. “We could do it visually, but we might end up with more dilution,” said Chief Geologist Alain Vachon. The bread-and-butter of the orebody is a band of highly deformed, neutral milonite dubbed the Band Beige (for its color). “It varies from a few inches to four to five feet,” Vachon said. “When we lose it (in a stope), it doesn’t mean the gold disappears, but the grade will go down, because this is our high grade.” Gold is either free (i.e. caught between fractures in the pyrite grains) or enclosed within pyrite grains. For this reason, the ore requires an extremely fine grind, said Vachon.

In the long-hole stopes that are relatively flat-lying (between 40deg and 30deg), bar-and-arm rigs support the Atlas Copco BBC 120 rock drills. The flat-lying stopes represent about 90% of mineable ore. Rouyn is working with the Industry Research Centre of Quebec to modify the long-hole method. The company is spending C$200,000 on this project. Drill wagons, rather than bar-and-arm rigs, would be preferable, and the company is researching this option now, said underground superintendent Rene Brunet. “We have looked for smaller buggies and one manufacturer is helping us with the problem,” he said. Because the bar-and-arm rigs can drill only two holes at each set-up, the best performance is about 170 ft. (50 metres) per shift. A drill wagon would nearly double that, Brunet estimated.

Dilution is a key concern at this mine. Initially, Rouyn studied positioning the first hole in the drill ring in the long-hole stopes flush to the hanging wall contact (gabbro). The result would have been dilution of between 20% to 25%. So, that first hole near the hanging wall is started 2.5 ft. (76 cm) from the contact. Dilution is roughly 5%. Pillars are positioned in staggered, or en echelon, fashion rough
ly 15 metres apart in room-and-pillar stopes. Apart from actual mining for bulk tests and so on, all the attention underground is focused on hitting that 1-million-ton (909,000-tonne) figure in the proven category. Above surface, Rivard is rationing the cash in his treasury (C$5.4 million in cash and short-trm securities) so that the bills can be paid up until a milling decision is made. An on-site mill, he estimates, would cost about C$14 million. He admits he doesn’t have all the answers, but “I want to be milling in our mill by March, 1992,” he said.

RADISSON

Radisson Mining Resources has, for the past three years, patiently nursed toward commercial production the old Duquesne mine, 32 km north of Rouyn-Noranda, Que. Several financings led to underground development and bulk samples that continue to point to real potential as a small-ton, relatively high-grade producer. At the time of our visit in late August, commercial viability still had not been declared. But President Guy Bourassa predicted that, by the time the ink dries on the pages of this October issue, commercial production would be a reality.

Be that as it may, the mine is interesting from the purely technical point-of-view. Our visit began near the shaft on the bottom, or ninth, level. Curiously, the loading pocket has been excavated just above this level. Ore from the bottom level is hauled by ore car to the shaft and then dumped directly into skips. In the old days, there were no waste or ore passes. The loaded cars were pushed on to the cage and hoisted to surface. Now, passes have been installed. Haulageways are very narrow, providing passage for 1-ton cars and not much more. The orebody is about 180 metres west of the shaft. The shaft in not ideally positioned, said Bourassa. Stopes are being developed from the third to the ninth levels.

Because of the competency of the rock, rockbolts are almost completely absent, not only in stopes but also in the more permanent installations of the mine, such as haulageways and drifts. Bourassa recalls that one mined-out stope from the earlier days hadn’t been rockbolted at all and that hardly any sloughing had occurred from the walls of the mine.

The known gold deposit strikes roughly east to west for approximately 500 metres along the Porcupine-Destor Fault. Ore zones are generally lense-shaped and they pinch and swell from as little as half a meter wide to as much as 10 metres. The average width is two metres. Gold-bearing mineralization is generally associated with felsic porphyritic intrusives and is locally related to silicified zones close to the subsidiary fractures of the main break.

Shrinkage stoping is the sole extraction method. Establishing the geometry of any given stope begins with the sub-level dimensions and careful sampling and visual control as mining proceeds upward in 2.4-metre (8-ft.) lifts using conventional Secan jacklegs. The ore is mucked out to chutes in the haulageways. “To control dilution requires that a geologist eyeball, sample and do test holes,” said Chief Geologist Guy Parent. “This is the kind of mine where bonuses (for miners) could work against you because miners might go after the tons,” he added. The orebody dips between 65deg and 70deg, which also obviates the need for extensive bolting.

While the main orebody runs east-west, intermittent north-south fractures occur. These fractures, which tend to displace the east/west-trending ore, still carry gold values. “We’re starting to find more of these fractures,” said Bourassa. A much longer north-south fracture has been identified on the fourth level, where Radisson’s miners have drifted for 25 metres. “It’s very narrow, but high-grade. We feel we can mine it over five feet (1.5 metres) with a 10-gram-per-ton grade,” said Parent. He is also heartened by diamond drill cores that have intersected ore-grade mineralization in porphyries 300 metres north of the main east-west orebody. In addition, the property held by Radisson follows the Destor-Porcupine Fault for five kilometres.

Until November, the Duquesne mine ore will be treated at Aurizon Resources’ Sleeping Giant mill. In preparation for that mill’s closing, Radisson has been negotiating with the owners of the Kerr Addison mill. The current underground reserve at the Duquesne mine is 565,330 tons (513,936 tonnes) of proven and probable ore at a grade of 0.26 oz. per ton (8.9 grams per tonne). A new reserve calculations is under way. Bulk samples have revealed a head grade of 0.29 oz. (9.9 grams) and recoveries of 96.5%. Radisson is planning a 300-tonne-per-day producer.

DUMAGAMI

Exploration geologists can drive themselves batty deciding when to call it quits on a drill program. At Dumagami Mines’ La Ronde project in early 1986, the do-or-die decision involved Hole 86-3. Planned to deviate by 1deg or 2deg every 100 ft. (30 metres), the hole carried on “straight to China,” recalls mine manager Eberhard Scherkus. The La Ronde at that point was little more than a promising low-grade play. But when Sherkus decided to let Hole 86-3 continue on its merry but deviated way, he had no inkling that two mines (the La Ronde and LAC Minerals’ adjoining property called Bousquet No. 2) would be the ultimate prize. “I remember the morning in February, which was my birthday. I looked at the core and it looked great, all in massive pyrite.” The assay office reported a 125-ft. intersection grading 0.14 oz. gold per ton (4.8 grams per tonne) — and mineable copper grades. A 59-ft. (17.7-metre) section of the core graded 0.23 oz. (7.8 grams) at a vertical depth of 2,650 ft., or 800 metres.

The La Ronde deposit consists of one distinct orebody. On the mine scale, the original known zone was named the East zone, which extended to the eighth level. Composed of several sulphide lenses, it is being mined by open pit and underground methods. Another zone, known as the West zone, is the westerly down-plunge extension of the same orebody. This zone becomes richer with depth. For example, between the 1,000- and 2,230-ft. (300- and 670-mmtre) levels, the grade is 0.17 oz. gold per ton (5.8 grams per tonne). Between the 2,230- and 3,280-ft. (670- and 985-metre) levels, the deposit averages 0.19 oz. (6.5 grams). The South zone is the only other known economic ore zone. It is a rich but small deposit (40,000 tons of 0.50 oz. material, or 36,350 tonnes at 17.1 grams) that has been extracted by shallow open pit. From all zones, current proven and probable reserves total 7.3 million tons grading 0.15 oz. gold per ton (6.6 million tonnes grading 5.1 grams per tonne). The West zone, discovered by Hole 86-3 which changed all the thinking about ore potential at depth, remains open at depth. Exploration this year will include diamond drilling to assess depth potential and a 6,000-ft. (1,800-metre) drift on the 20th level that will be driven east.

In 1989, 693,825 tons of ore were milled at a grade of 0.136 oz (630,750 tonnes at 4.7 grams). The mill production rate was 2,000 tons, or 1,820 tonnes, per day. To test the mill’s capabilities, it has been run up to 2,600 tons, or 2,360 tonnes, per day. Gold production last year was a few ounces short of 85,000. This year, Scherkus predicts, the mine will yield 94,000 to 96,000 oz. (or up to 3,000 kg) of gold and 1.8 million lb. (810,000 kg) of by-product copper. Ore is coming from the West zone above the 10th level and at the 20th and 21st levels. The open pit has been mined out, although a 250,000-ton (227,000-tonne), open-pit stockpile has yet to be processed. Mining is progressing from the third level up to the sill pillar of the pit floor. Transverse open stoping with delayed cemented backfill is the method of choice above the third level, where the orebody is wide (between 10.5 and 12 metres) and the ground relatively competent. The cemented rockfill consists of waste rock, 5% to 6% cement, and 2.5% flyash. After a 20-day cure, secondary stopes are taken out from between the backfilled stopes. Unconsolidated rock fill provides support in the mined-out stopes between cemented backfill stopes.

Sub-level retreat is used in the narrower portion
s of the orebody below the third level. However, when mining begins in the richer ore on the bottom-most levels, transverse open stoping will again be used. And that suits Scherkus just fine. Sub-level retreat, he said, “is a 7-days-per-week, 24-hr.-per-day method. You’re blasting against fill and you’re never certain of the toe. When you’re drilling uppers 80deg, you could be ripping the hangingwall.” The transverse method incorporates an Ingersoll-Rand CMM2 in-the-hole hammer, which drills 4-inch holes in rings six feet (1.8 metres) apart and toe spacings of six to eight feet (1.8 to 2.4 metres). Dumagami is evaluating an Atlas Copco Simba 279 top hammer. Primary transverse stopes are about 30 ft. wide and 100 ft. high (nine metres wide and 30 metres high) from sub-level to sub-level. The secondary stopes are 60 ft. (18 metres) wide. In sub-level terrain, an electric-hydraulic Atlas Copco Simba 254C drills 3-inch holes at a rate of 400 to 450 ft. (120 to 135 metres) each 8-hour shift. The Simba is mounted on a Getman carrier and drills 35- to 45-ft. (10.5- to 13.5-metre) uppers to the floor of the sub-level above. There are two stopes per sub-level horizon. The distance between sub-levels is 13.7 metres. (45 ft.). For development work, Dumagami employs three 2-boom electric-hydraulic Atlas Copco jumbos with 1238 rock drills. Slot raises in sub-level retreat stopes are driven by conventional open raises. In transverse stopes, the services of Machine Roger raise are employed.

Ground control in haulageways and sub-level drifts is confined to rock bolts, Swellex bolts and screens. “When we have a wider part of the ore, we put in 10-ft. (3-metre) Swellex with screens and 7-ft. (2.1-metre) rock bolts,” said mine superintendent Paul Henri Girard during our underground tour. “On the wall, we put split sets and straps.” A Normet scissor lift truck accommodates bolting and screening, while another Normet truck provides services. During the tour, we were shown a particularly difficult ground problem in the 1040 sub-level. The walls here were schistose and required straps, split sets and cable lacing. Because of the experience gained in this stope, Girard will change the access to the north, footwall side on the 10th level rather than the south (hangingwall) side, which had resulted in the deterioration evident in 1040. This schistose material extends to the 12th level and no farther. Below that, ground conditions improve markedly, because the rock is highly silicified.

That is why Scherkus is eager to begin mining at depth (20th level and below). Grades are also higher. Scherkus predicts average grades of about 0.30 oz. gold per ton (10.3 grams per tonne). And the orebody, while it pinches and swells, ranges from 20 to 40 ft. (8.4 to 14.4 metres) wide. Although our tour did not include a sidetrip down the shaft to the bottom-most levels, Scherkus said the 21st level is ready for mining now. Level 20 will be ready by year-end, when production drilling will begin.

Haulage to ore and waste asses is a track operation on Levels 10, 20 and 21. Elsewhere, load-haul-dump machines do the trick and this mine has a variety of older and newer Eimco Jarvis Clark units, as well as a remote-control Wagner scoop and a Toro.

The mine also has two 15-ton Dux trucks. There are two underground crushers — one at the 11th level, where the workings down to the 10th are accessed by a ramp from surface, and the second at the bottom of the shaft below the 21st level, about 3,200 ft. (960 metres) below surface. Both are Buchanan 36 x 48-inch jaw crushers.

The 3-compartment shaft is about 195 metres south of the ore zone near surface and as much as 450 metres from it at depth. There are eight levels. Ore and waste passes were excavated with Alimak raise climbers. The main sumps on Levels eight and 22 are each outfitted with two Mather & Platt pumps.

Milling is a straight carbon-in-pulp (C-I-P) process with flotation cells to concentrate the copper ore. Surface crushing circuit consists of a Nordbery Symons standard cone crusher (to minus two inches) and a Nordberg Symons shorthead (to minus 3/8 inch). The grinding circuit features two Nordberg ball mills (11 x 17 ft.) and a 7 x 10 regrind mill. “If we want to go over 2,000 tons (1,800 tonnes) per day, we use the regrind mill,” said Jean Robitaille. The ground product is 70% to 80% minus 200 mesh. The gold ore is then thickened, pre-aerated leached and put through the C-I-P circuit. The carbon is then stripped and the gold recovered through the electrowinning process. Of special note here is that Robitaille believes the La Ronde might be the sole mill in Canada using a carbon called Norits R3515. This type is especially abrasion-resistant to combat the abrasiveness of the ore.

The copper flotation circuit consists of one Maxwell and one Minpro rougher, five 600 cu.-ft. Dorr-Oliver scavengers and 10 Denver cleaners. The gold grade in the copper concentrate, which is shipped to Noranda’s Horne smelter is 400 grams per ton. The overall (flotation and c-i-p) recovery of gold is 92%.

On the corporate side, Dumagami was recently amalgamated with Agnico-Eagle Mines. As well, Noranda, formerly a part-owner in the property through a shareholding in Dumagami when La Ronde was an exploration play, is suing Agnico for failing to make full and timely disclosure to Noranda before it sold its Dumagami stake in early 1986. Soon afterward, Hole 86-3 came in.

SIDEBAR

STOCK OR LIVESTOCK?

A chicken coop in the shadow of a headframe. Barnyard noises competing with the rumbling of a mine surface plant. The farm and the mine seldom share acreage. But they do at St Andrew Goldfields’ Stock Twp. mine.

Mine manager Bob Ritchie and other senior staff who live on the property have developed quite a knack for animal husbandry. They can boast of a regular little farm with about 50 ducks, 15 chickens, four pigs, and several sheep, goats and pheasants. And on the acreage acquired by St Andrew around the mine, you can find Ritchie or other staffers on a tractor aftee work mowing hay or baling it. By the way, the animals in the vicinity of the Stock Twp. mine site are a far cry from pets. They are destined for eventual slaughter. But according to one farm enthusiast, Henning “Kilowatt” Lederer, chief electrician and Mindecon vice-president, these hardened mining men are a bit squeamish.

“We haven’t the heart to do it. We’ll have to get someone else to do it.”

SIDEBAR

DUMAGAMI GEOLOGY

The regional geology is described as an assemblage of Precambrian volcanic and sedimentary rocks rending westerly from the Grenville Front across northwestern Quebec and into Ontario. The Blake River Group, a unit of mafic to felsic volcaniclastic rocks within the assemblage, has played host to the economic gold deposits in the area. Within hailing distance of La Ronde are LAC Mineral’s Bousquet Nos. 1 and 2 and the Doyon mine, owned by LAC and Cambior. The Blake River Group has been intruded by the granite to granodiorite Mooshla stock to the west and has been metamorphosed to a regional greenschist facies. Prominent structureal features of the arera are the east-west striking Larder Lake/Cadillac Fault to the south and the roughly parallel Parfouru Lake Fault bounding on the north.

On the Dumagami property, an east-west-striking and sub-vertical dipping shear zone in felsic pyroclastics hosts the known gold sulphide zones. These are conformable to the shear and are separated only by low-grade mineralization.

The main orebody, the West zone, tops out about 180 metres below surface. It dips steeply north in the upper section to steeply south at depth. In the West zone, the sulphides appear more massive in form than in the smaller East zone (the open pit) and there is greater continuity of sulphide lenses. Diamond drilling at depth indicates a significant increase in copper and gold content, suggesting a depositional relationship.