Canadian Mining Journal

Feature

Getting Down and Dirty at Laronde

The deepest underground shaft in the Western Hemisphere is now complete--a 2,249-m-deep mine shaft, the third for the LaRonde mine, and the centrepiece of its major six-year-long mine and mill expansi...


The deepest underground shaft in the Western Hemisphere is now complete–a 2,249-m-deep mine shaft, the third for the LaRonde mine, and the centrepiece of its major six-year-long mine and mill expansion.

The Abitibi region of northwest Quebec has prospered for generations of miners, although the picture is no longer so rosy. Most of the major mining companies are closing their regional exploration offices.

However, the 100% owner of the LaRonde mine, Agnico-Eagle Mines Ltd. of Toronto, has bucked the tide with remarkable success. The company’s management group thinks the Abitibi’s long history of mining and infrastructure makes this a very good place to be building a mine. “I’d rather be going deep than remote,” says Ebe Scherkus, executive vice-president and COO.

In 1976 Dumagami Mines Ltd. began exploring the old Dumagami property, 56 km west of Val d’Or. The massive sulphide deposit had been found the previous decade using geophysics. Noranda Inc. was the main owner of Dumagami, but Agnico-Eagle was the operator. In 1986 Agnico-Eagle acquired Noranda’s interest.

The deposit was put into production in 1988 as a 1,360-tonnes/day gold- silver-zinc-copper open pit and underground mine and mill (CMJ July 1988). It was built at a cost of $32.5 million, and named the Donald J. Laronde mine after the first project manager. (It has since been renamed the “LaRonde mine”.) A second shaft was added in 1993-94, and a third one started in 1994 as an exploration shaft. The third shaft became the No.3 (or “Penna”) production shaft, named after Paul Penna, long-time president of the company.

It took dogged determination to find the additional ore that has turned the depleted mine into an ‘elephant’ deposit. The reserves and resources above the Penna shaft bottom will provide LaRonde with at least an 18-year life.

The cost of the expansion is ten times as much as the original mine, at about $320 million, financed by bank loans and equity. This has been done on a tight budget, according to Anton Adamcik, vice-president exploration and environment, with the design, engineering and construction management done in-house at LaRonde by people while they were doing their regular jobs.

The program target has been constantly shifting, with the latest change a year ago, increasing the production rate from 3,270 to 4,540 tonnes per day.

“This is a very key year in the schedule,” says Scherkus, with the bulk of the capital expenditures to be finished by year-end. The shaft was completed on March 31. The new hoist has been built and installed. Mining from the No.2 shaft was completed in April and from the No.1 shaft will be completed in September, so miners are moving over to the Penna shaft. All parts of the mill expansion are to be completed by the end of the third quarter, and the whole operation is expected to be running at capacity by the beginning of the fourth quarter.

The bulk mining methods and larger processing plant mean that the cash costs will be coming down as the production level rises. LaRonde is forecast to pour 300,000 ounces of gold in 2002, and 331,000 ounces in 2004, the latter at a cash cost of only US$97/ounce, including royalties. This compares with 90,035 ounces of gold poured in 1999 at a cash cost of US$274/ounce.

In addition, the plant extracts valuable amounts of silver in the bullion product, and zinc and copper in the flotation concentrates. This amounted to 277,327 ounces of silver, 4,435 tonnes of zinc and 1,489 tonnes of copper in 1999. These values will increase proportionately with the boost in production.

The non-unionized workforce at LaRonde numbered 307 people three years ago when the production rate was 1,820 tonnes/day. The number of workers has been increasing, and will reach and stay at about 390 at full capacity. Employees come from the surrounding communities of Val d’Or, Malartic, Rouyn-Noranda and Amos. Turnover and absenteeism have been low over the whole life of the mine. Last year LaRonde won the regional John T. Ryan safety award for metals mines in eastern Canada, for the second year in a row. This has been a remarkable achievement during a period of rapid expansion, with a growing workforce and lots of contractors on site.

Exploration Background

When LaRonde opened in 1988, it had humble reserves of 702,000 ounces of gold in relatively shallow deposits. An exploration drift was driven 2.4 km east from the No.1 shaft on level 20 (880 m below surface). Underground drilling encountered zinc-rich sulphide mineralization in two zones, the “20 North” and the “20 South”. Diamond drilling chased the sulphides downward, proving that the high zinc values gave way to high gold and copper values with increasing depth, as in the orebody at the No.1 shaft.

By the end of 1999, exploration of these two zones had defined proven and probable reserves of 3.0 million ounces and a resource of additional 3.0 million ounces of gold.

The two zones are very tabular, continuous bodies that dip steeply to the south.

The bulk of the Penna shaft reserves are in the 20 North zone. This consists mainly of massive sulphide and some stringer ore, with a strike length of 490 m; the zone has been followed to a depth of 2,962 m below surface, the deepest drill hole to date.

The 20 South zone has only 10% of the Penna shaft reserves tonnage, but 15% of its gold. The zone is 250 m long, 500 m high, and 5-10 m thick. Its upper portion is on the El Coco property. There are two sets of fractures–a vertical set striking north, and another that is subhorizontal. In mid-June, visible gold was found for the first time on the vertical north-south fractures in the 20 South zone, replicating the pattern of gold on these fractures at the No.1 shaft.

Agnico-Eagle now controls a 19-km-long continuous stretch of the northern splay of the Cadillac-Larder Break, the prolific regional structure that hosts the LaRonde mine as well as Barrick’s Bousquet No.1 and No.2 gold mines and Cambior Inc.’s Doyon and Mouska gold mines, all immediately west of LaRonde. Agnico-Eagle bought 100% interest in the El Coco property from Barrick Gold Corp. in 1999, and a 50% interest in Barrick’s Bruce Property early this year. The El Coco agreement includes a royalty payment to Barrick.

An aggressive exploration program will look for more reserves from a drift that will be driven east from the Penna shaft on the 215 level. (The levels are numbered in tens of metres, so the 215 level is at 2,150 m below surface.) “We want to find out what we have within two years,” says Scherkus. “We don’t want to leave 2.5 or 3 million ounces of gold in situ.” He adds the company probably would not extend the mine life, but would mine new discoveries simultaneously with the current reserves.

A Very Deep Shaft

When underground drilling had outlined 20 million tonnes of ore in the 20 North and 20 South deposits, the company hired MacIsaac Mining & Tunnelling Co. to construct a circular, 5.5-m-diameter, 1,737-m-deep concrete-lined exploration shaft. Shaft-sinking commenced in January 1996. Industries Beroma was the shaft steel supplier. L. Fournier & Fils Inc. supplied the concrete for the shaft, and is the shotcrete supplier. In fact, Fournier has built a concrete plant on the site.

Underground diamond drilling continued to find reserves downward, so the shaft was extended to a 2,259-m depth. “Even though the shaft is deeper than any other in this belt, sinking was remarkably trouble-free with respect to ground control,” says MacIsaac’s Karel Pieterse, project engineer. “No doubt this is true, in large respect, to certain sinking techniques that have been adopted.”

The first 333 m of shaft was sunk with pluggers using conventional benching techniques, with an average advance of 2.71 m per sinking day. MacIsaac then changed to a mechanized full face sinking technique, and developed innovative approaches to maintain the concrete within 3.5 m of the shaft face at all times, a new requirement of provincial regulations (CSST). The advance improved to an average of 3.14 m per sinking day with the jumbos.

The innovative explosives loading system, consisting of a pumping unit and bulk emulsion, resulted in several improvements–at least 10% reduction in the number of holes drilled, 50% reduction in the explosives loading time (from two hours to one hour), and improvements in the toe break.

A temporary bulkhead was installed over the cage hoisting compartment when the shaft reached a depth of 1,420 m, and temporary loading facilities were installed below the 134 level. This allowed mine development to start at this and higher elevations. Sinking continued until the shaft reached the 1,610-m depth. The bulkhead was relocated to a lower elevation and a mid-shaft loading pocket was installed. Then an accelerated mine development program was implemented, while sinking and shaft construction continued below the bulkhead.

The $29.4-million ventilation system for the Penna shaft has an air capacity of up to 36,800 m3/minute with a heating capacity of 1.27 million kJ (120 million BTU). The fresh air is drawn down through the No.3 shaft as well as a 6.7-m-diameter ventilation shaft, and conducted to all working areas via raises. An additional 6,510 m3/min of fresh air capacity arrives from the No.1 shaft via the exploration drift and a ramp. Exhaust air is gathered into 137-cm-diameter ducts that exit to surface through a separate 6.7-m-diameter exhaust raise.

Development, Mining and Hoisting

MacIsaac excavated and did the concrete work in the 15 shaft stations (all of which will be linked by ramps), as well as the two loading pockets, on the 152 and 220 levels. Scherkus is impressed with the high backs and size of the excavations in the stations. Mechanical rock bolts were used to support the concrete-lined shaft walls, and steel sets were used to support the guides, services, etc., while the stations, pockets and drifts are supported with rockbolts, cablebolts, Swellex bolts, screen and shotcrete. “The secret in this ground is to get in, put in the support and secure it,” says Scherkus. He adds, “We haven’t noticed any creep or displacement yet, but it’s all very new.”

An El-Equip leaky feeder radio system supplies the underground communication.

The rock in the Penna shaft workings is not particularly hot; the highest temperature measured has been 27*C. No seismic activity has been recorded, which is surprising considering the large size of the stations. The local rock strength is fairly low at 150-200 MPa for basalt and 90-120 MPa for felsic rocks, so the rock would tend to fail by plastic deformation rather than faulting.

A consultant was brought in to measure in situ stress. By projecting from the 60 MPa stress at the 21 level (about 910 m below surface) at the No.1 shaft, the consultant expected to find rock stress of 70-80 MPa. However, the measured north-south stress at the 152 level (1,520 m below surface) was only 64 MPa. This appears to be due to less shearing and deformation and therefore less accumulated stress at the Penna shaft. This is good news, in that the low stress should result in a low dilution factor (waste falling into the ore).

During sinking, there was about 10,000 m of drifting and 3,000 m of raising above the bulkhead using the Penna shaft for access. MacIsaac excavated the main, 6.7-m diameter raises, while Montali excavated the smaller Alimak raises. The development between the 118 and 152 levels was all done using ramp access from the No.1 shaft at the 122 level. Ross-Finlay 2000 Inc. did the horizontal development on three of the lower levels. The rest of the underground development has been done by LaRonde employees.

All level development has been completed above the 152 level, and miners are now driving the sublevels and undercutting the stopes. About 7.0 million tonnes of ore has already been developed from the upper part access.

Production mining at the Penna shaft uses transverse open stoping, with blocks 30 m high, 15 m in strike length and up to 30 m thick. Tamrock Solo H1006 drills are used for production, and the main production machines are Tamrock Toro 1400 load-haul-dumpers. By the end of June, 11 ore blocks had already been mined. Scherkus says that he has been pleased with the dilution factor of generally less than 10%.

This spring the underground exploration team began to use computerized notepads for recording samples, observations and data electronically. They are using Mapper software by Century Systems, which includes handwriting recognition.

The ore handling system on the 152 level is fully automated, from the rockbreaker through the jaw crusher and conveyor system to the coarse ore storage bin (4,540-tonne-capacity) to the loading pocket at the shaft. As well, the cable bolting and rock bolting are mechanized, and the ventilation system is fully automated. “With a mine at that depth, you have to automate,” says Scherkus. “There is no choice.”

The $14-million paste backfill system will be able to deliver 180 tonnes of backfill per hour to the mined-out stopes via two parallel 15-cm-diameter holes. The pipes lead from surface to the 20th exploration drift via a steep borehole. There they separate, with one following the drift to the Penna shaft, and the other following another borehole to the 122 level ramp. From here the pipes follow raises to bring the paste backfill where needed.

The decision to move to a larger production rate meant that the hoisting capacity had to increase. The hoist drum diameter was changed from 4.9 m to 5.8 m, and the skips were made as long as possible (increasing from 14.5 to 24.5 tonnes capacity). This required a 10-m extension to the top of the headframe building (now 60 m tall) plus the additional set of backlegs for support. Cook Engineering designed the headframe and hoist room, and ABB Inc. supplied the new drives for the hoist.

The hoist rope has a diameter of 57.2 mm. In order to expand the capacity at minimal cost, Agnico-Eagle successfully lobbied the Quebec government to reduce the required safety factor of the hoist rope from 5.0 to 4.0, bringing the Quebec regulations in line with South African standards. Because of this, the new hoist cost $6 million, rather than the anticipated $35 million. Scherkus believes it is acceptable to change Quebec’s standards because of the significant improvement in rope technology as well as in rope monitoring methods.

The new hoist was delivered May 15 and was working 38 days later. The mine now has a hoisting capacity of 9,082 tonnes of ore and waste per day, sufficient headroom to produce the desired 4,535 tonnes of ore.

Mill Expansion and Metallurgy

The original 1,360-tonne/day concentrator had grinding and copper flotation followed by a carbon-in-pulp (CIP) circuit to recover gold. Through additions to the existing plant over three years, the capacity was up to 3,265 tonnes/day in January, and is expected to reach the 4,535 tonnes/day level by the beginning of the fourth quarter.

The expansions have brought about numerous changes and improvements to the flowsheet, which was conceived and designed primarily by LaRonde staff. The staff also supervised the construction, so no general contractor was hired.

A 5,000-tonne surface ore storage bin has been built as well as a zinc concentrate loadout. A new Svedala 7.3-m by 4.1-m primary SAG mill has been added, with a 4,500-horsepower variable speed drive. The copper flotation circuit has been expanded, and a new zinc recovery circuit added. The CIP circuit is being replaced by counter-current decantation (CCD) and Merrill-Crowe gold and silver recovery, because the high silver values would have resulted in too large a material-handling job in the carbon-in-leach tanks. A new shop and offices have also been built.

A large number of contractors were used, most of which employed local Abitibi residents. SNC-Lavalin Inc. designed the SAG mill, leaching /CCD/ refinery and cyanide destruction/paste backfill circuits. Leslie Engineering designed the civil parts of the copper and zinc circuits, and the office, shop and laboratories. Construction Promec as well as Moreau and R. Blais & Fils were the electrical contractors. Construction Talbon Inc. has worked with Ppin Fortin, Laval Fortin and Citek on the surface foundations and buildings, Structures GB and Structures Donald Morin were the steel erectors, and R. Blais & Fils did the mechanical installation. L. Fournier & Fils Inc. supplied the concrete.

The three campaigns of metallurgical testing were done in-house on bulk samples between 9,775 and 50,963 tonnes each, from mid-December 1999 until the end of March. Grades and recoveries achieved the target levels during the last campaign. The copper concentrate had 150 g/t Au, 1,165 g/t Ag and 16% Cu, while the zinc concentrate contained 11 g/t Au, 224 g/t Ag and 52% Zn. The overall recoveries were 92.37% for Au, 62.15% for Ag, 73.93% for Cu and 76.57% for Zn.

Stope reconciliation showed that there had been an underestimate of the ore’s grade–there is significantly more gold than the expected 3.0 grams/tonne–because the specific gravity was found to be too conservative.

LaRonde uses modern practices to reduce environmental impact. All process water is recycled, so only 15% make-up water is required. From half to 60% of the tailings will be used as paste backfill underground.

An Inco SO2-air cyanide destruction system is completed and operational; it removes cyanide at the plant, before the tails are pumped underground as backfill, and before the waste water enters the polishing pond.

The plant produces sulphide-rich waste, which is deposited underwater in the tailings pond. At capacity the plant will be disposing of 1,815-2,270 tonnes of tailings per day. Phase I of construction for the new 20-hectare tailings impoundment area, was completed in the autumn of 1999. The dams are being raised this year and should be complete by October.

Corporate Plans

Over its 40-year history, Agnico-Eagle has mined silver in Cobalt, Ont., and gold at the Eagle mine near Joutel, Que., but LaRonde is the company’s only producing mine at this time.

With continual good news on the exploration front, and all the pieces falling neatly in place in the mine and plant, LaRonde looks like a healthy part of the company’s future. “We view this as a company-maker,” Scherkus grins. “This puts us on the map.”

The company hedges none of its future production, as it believes that this gives away the price upside. With the cash operating costs at LaRonde coming down, Agnico-Eagle will continue to make money even if metal prices drop.

LaRonde is expected to generate a large cash flow, which will support more exploration by the company as well as its two exploration arms, Sudbury Contact Mines Ltd. and Mentor Exploration and Development Co. Ltd. The target will continue to be economically sound gold deposits. “We are in a good position to pick up good properties, in that Agnico is one of the few remaining major mining companies still actively exploring in northwest Quebec,” says Alain Blackburn, manager of corporate development. “Our focus is to find another LaRonde mine up north, but we won’t forget Nevada.”

Would Agnico-Eagle be an attractive take-over target? Scherkus says it could happen, but he’s not worried. The shares are widely held and widely spread. The company has developed a following of more than 18,000 shareholders (13,000 in the United States), many of them long-term. Retail clients hold 65% of the shares and institutions only 35%. He adds: “We believe there is room for a premier intermediate pure gold play that produces at the lowest possible cost.”


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1 Comment » for Getting Down and Dirty at Laronde
  1. ashley macisaac says:

    in tasmania where people are griping about minng- im so proud to see my relatives still digging deep!There is a mine called kangarooflats for sale over here for as little as 15 million- which will give way to more gold inthe future- any takers:)?
    ashey macisaac

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