LaRonde Extension

The LARONDE MINE began life in 1988 as the DUMAGAMI open pit and underground mine, before Agnico-Eagle Mines acquired 100% interest in 1992. Over the last two decades, the complex and rich mine has become a “company-maker”, turning Agnico- Eagle from a small silver and gold miner into a cash-rich intermediate gold producer.

The mine can be found in a very good neighbourhood for large, deep, long-life gold mines–in the Abitibi greenstone belt of northwest Quebec, mid-way between Rouyn- Noranda and Val d’Or.To date LaRonde has produced 3 million oz of gold; its healthy silver, zinc and copper credits make it one of the lowest cost gold operations anywhere. In 2007 the mine produced 230,992 oz of gold at a total cash cost of -US$365/oz (net of byproduct credits); those byproducts were 4.92 million oz of silver, 71,600 tonnes (t) of zinc and 7,500 t of copper. The minesite costs last year were Cdn$65/t.

Payable gold is expected to dip to 215,000 oz this year, as gold grades are scheduled to be lower, with the other metals staying about the same. Total cash costs for gold are expected to be approximately -$189/oz in 2008.

The non-unionized LaRonde operation employs about 650 people, and serves as the company’s training ground for technical people and project specialists. Annual contract negotiations are handled by an employee committee. In 2007, LaRonde mine had a lost time injury rate of 3.83 per 200,000 hours worked.

The big change at LaRonde right now is the US$293-million development of the mine at depth. A new winze is being sunk to reach the ore below level 245 (2,450-m depth), called LARONDE EXTENSION, which contains another 5.0 million oz Au in reserves. This project cost includes an expansion of the mill facilities, and will extend the mine life by nine years to 2021. LaRonde is expected to average 340,000 oz of gold annually over the rest of its life, at total cash costs of US$150/oz. CMJ toured the facility in mid-May.

Going Down

Dumagami/LaRonde has been mined using a succession of shafts plus a ramp from surface. The first two shafts are now closed. The third one–the Penna shaft–was completed in 2003 from surface to 2,250-m deep. The deepest mining to date is on level 233 (2,330 m below surface), and the decline has reached level 242.

LaRonde uses two mining methods: longitudinal retreat in 15-m sections with cemented rockfill or cemented pastefill, as well as transverse open stoping with both cemented and unconsolidated rockfill as well as cemented pastefill. Sublevels are driven every 30 or 40 m, depending on depth. Production equipment is all Sandvik Tamrock and includes 16 6.1-m3 load-haul-dumpers (LHDs), six 4.6-m3 LHDs (all remote-control enabled) and six 50-tonne haul trucks. Production drills are Sandvik Tamrock Solo and Data Solo drills. The older and new equipment are all the same make and models, for ease of maintenance.

Since deep mining (below level 194) began five years ago, LaRonde’s rock mechanics team has continually updated its methods for areas of higher rock pressures and more seismic activity, according to mine superintendent Marc Ruel. Almost all the seismic activity is generated by the mining, so re-entry is delayed 12-24 hours after certain production blasts. The team tinkers with the mining sequence in the primary and secondary stopes, and is involved in various research initiatives in Canada and abroad, mainly with the Australian-based Centre for Geomechanics.

Rock support typically consists of Split Sets in the walls and resin-grouted rebar in the back in the upper parts of the mine. However, in the deeper levels the rock is highly stressed and fractured, requiring a more robust ground support system. For these deeper workings, LaRonde engineers have developed the Hybrid bolt (patent pending) to reinforce the broken rock mass–a 1.8-mlong rebar with resin is inserted into a 2.0-mlong Split Set, which gives elongation plus rigidity. Miners inspect and report daily on the ground support in the working area.

The LaRonde mine is a busy place, with about 225 people underground on a midweek day shift. The underground diesel mechanical equipment is large, and is mainly responsible for the high underground temperatures of 20-30C. The mine has a 37,000-m3/min ventilation system. There is currently a 12-MW cooling station on surface and a 3.5-MW one on level 146.A 7-MW cooler is being built on level 170. Ultimately there will be 30-MW of cooling equipment.

The building of LaRonde Extension is described by Martin Krisko, the assistant mine superintendent assigned to the expansion, as the company’s biggest project, and it’s going on inside an operating mine, which makes it more challenging, especially since the mine is served by just one shaft plus a ramp.

Construction of the internal shaft (No. 4) has recently begun. It will be an 835-m-long, 5.5-m (inside diameter) concrete-lined circular winze from 2,030-m (level 203) to 2,865-m depth. The services in No. 4 shaft will be nearly identical to the Penna shaft: two 25-t skips in counter-balance with a double-deck cage accommodating 54 people. The only difference lies in the fact that the new shaft will be equipped with a 10-person maryanne cage that will enable personnel to travel via the shaft at will.

In the level 203 service hoistroom now are four small winches that support the galloway that is being used for sinking; once shaftsinking is complete, these will be replaced by the Davy Markham 3.35-m-diam singledrum service hoist. For production there will be a Davy Markham 4.88-m-diam doubledrum hoist with two 1,490-kW engines supplied by ABB. The two large hoists are essentiall new. As well, there will be a 1.8-m-diam auxiliary hoist for the maryanne, purchased from the Kidd mine in Timmins, Ont. The production hoist will use 5-cm-diam wire rope and a fully hydraulic braking system. Each of the four brakes on each drum can brake independently. The automated hoist system is almost the same as for the Penna shaft; the hoists for both shafts will be operated from the control room on surface, which also controls ventilation and cooling.

Quebec regulations demand regular testing and surveying of the cable for the production, service and auxiliary hoists, but LaRonde is the only mine in Canada that uses a safety factor of 4 (Quebec regulations require a minimum safety factor of 5), according to the LaRonde general manager Christian Provencher. A magnetometer surveyor can inspect the cable while it is running at full speed of 914 m/min.

Both the Penna shaft and No. 4 shaft are in the footwall north of the orebody, where the ground is more stable. The shafts are about 50 m apart; personnel will be transferred from one to the other on level 206 and materials on level 215, to avoid congestion. The muck from level 245 and below will be hoisted in the winze to level 206 where it will be dumped in an ore chute and transferred to the Penna shaft ore-handling system via a conveyor and then skipped to surface. The normal production rate will be 6,000 t of ore with 1,500 t of waste generated per day. Maximum hoisting capacity in the winze on a weekday will be almost 10,000 t, most of which will be ore, as the waste will be used in backfill.

Construction of the infrastructure for LaRonde Extension began in Q2 2006. The crew of the shaft-sinking contractor, Dumas Contracting, began to mobilize to the site in October, after completing Agnico-Eagle’s Lapa and Goldex shafts. Meanwhile, LaRonde has been preparing the underground infrastructure, including a major maintenance shop and warehouse on level 206 and a shop for the sinking on 215 level, which will become the future skip maintenance shop. Steel and other materials are brought to the site numbered to avoid confusion and loss. A Manulift truck that can reach up to 13.7 m high is being used to install steel on high backs without scaffolding, saving considerable time.

During the last qua
rter of 2007, the focus was on underground infrastructure construction and detailed engineering. The galloway was delivered and installed in January 2008, and conventional sinking of the No. 4 shaft has begun. The first bench in the shaft was blasted in March 2008. The blasting of the waste silo collar and the installation of the steel, including liners of the silo, were completed in March. The shaft had reached level 218 by mid-May. Construction of the cooling facility and electrical substation on level 170 are ongoing. Once the initial “break-in” period is over, the rate of sinking will be 2.1 m per day; the sinking should be complete by the end of 2009.

Mill expansion

The LaRonde mill is the result of a series of expansions, starting from the 1,630-t/d Dumagami mill in 1988.The last expansion in 2006 simplified the process, resulting in fewer products but adding stability and robustness, with a nameplate capacity of 7,000 t/d. This $9-million increase to the copper flotation circuit consisted of adding Outotec mechanical-and tank-flotation cells. An Outotec continuous X-ray system has also been added. The plant averaged 7,324 t/d throughput last year. Starting in 2011, the plant will receive ore from LaRonde Extension, which will be very similar to the current mill feed, with slightly lower copper, lead and zinc grades.

The LaRonde mine produces ore for a number of stockpiles that can be mixed, stabilizing the mill feed grade. Following grinding come the copper and zinc flotation circuits. In 2007, the copper concentrate product contained 11% Cu plus most of the gold and silver, and was sold to Xstrata’s Horne smelter in Rouyn-Noranda. The zinc concentrate contained 54% Zn plus a little gold, and was sold to Xstrata’s Kidd smelter in Timmins, Ont. About 14% of the gold is recovered by a precious metals circuit including a Merrill-Crowe process refinery producing dor bars. Metal recoveries last year were 91% for gold, 88% for silver, 86% for copper and 87% for zinc.

A pilot plant is currently investigating the economics of making a separate lead concentrate. Mill superintendent Jean Cayouette said the plant could continuously produce lead concentrate by the end of this year.

At the beginning of May, LaRonde received its first sulphide concentrate from the GOLDEX MINE, and it will receive all of LAPA’s ore once that mine opens, thereby eliminating certain environmental risks from both those mines. This has resulted in a lot of infill construction within and between LaRonde’s mill buildings.

The Goldex sulphide concentrate is received by a $3.5-million, 150-t/day dedicated facility at LaRonde. This uses cyanide leach to dissolve the gold with a vacuum conveyor to remove solids. The clarified pregnant solution from the Goldex concentrate is added to LaRonde preg before proceeding to the rest of the precious metal circuit.

The new Lapa plant is described on p. 31.

Cyanide in the process and tailings water at LaRonde are destroyed using various methods:

Inco SO2/^air destruction, natural degradation and peroxy-silica secondary treatment. The water is treated in the lime plant to remove metals before discharge.

The high-sulphide content of the LaRonde ore and 80% recirculation of the process water led to a buildup of thiocyanate causing a toxicity problem in the late 1990s. In response, a biological treatment plant was put in service in 2004, which has been undergoing adjustments and improvements ever since. Its operation has stabilized since 2006.

The manager of environmental services at the site, Sylvain Boily, says there are two major projects at the water treatment plant right now. In the tanks where the thiocyanate is oxidized, the medium for bacterial growth has been changed from filter cloth to honeycomb-shaped plastic pieces, which don’t get clogged and double the surface area compared with the cloth. As well, dephosphation is proving to be an effective solution to the serious problem of algal overgrowth in Dominac Creek and Black River, which receive the discharged water. This involves adding alum to the water to bind with phosphate, followed by Magnaphox 10 to precipitate it. As a result of these and other improvements, the capacity of the water plant has almost doubled in the last year to 194 m3/h of water treated for discharge.

Over US$3.6 million will be spent this year on exploration in an attempt to secure a future for LaRonde beyond its current reserves. Properties that Agnico-Eagle controls– EL COCO, TERREX and SPHINX immediately to the east, and BOUSQUET and ELLISON immediately west–are already showing promise. The focus in 2008 will be on drilling the massive sulphide structure below the Bousquet infrastructure from the 1.6-km-long level 215 exploration drift. Additionally, a geophysical target will be drilled from level 86 as a resumption of work on the El Coco property.

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