Choice orebody split between two premier gold producers

It’s a mere printed line on a claims map and no more than a surveyed picket line in the bush, yet it represents the division between the Bousquet No. 2 mine of LAC Minerals (TSE) and the LaRonde mine of Agnico Eagle (TSE).

The boundary line slices one of Canada’s choice gold orebodies east of here into two parts. Who has got the best of it remains for history to confirm. Currently quoted ore reserves clearly favor LAC with 55% more ounces, but mining has been under way for only a short time. Then there is the Cadillac phenomenon known as “upgrading” to be taken into account. There is time for the numbers to modify.

Reserves at Bousquet No. 2 to January, 1991, are quoted at 8.7 million tons grading 0.2 oz. gold per ton for a total of 1.736 million contained ounces. LaRonde’s reserves to January, 1990, are 7.3 million tons grading 0.154 oz. for a total of 1.122 million contained ounces. In each case, tonnage is for all designations of ore, dilution has been added and all high values have been cut. In fact, the procedures for calculating reserves are practically identical for both companies.

The phenomenon of “upgrading” first came to light at the Doyon mine, owned jointly by LAC and Cambior (TSE). Doyon shares similar geology to the LaRonde and Bousquet No. 2 mines.

It was evident from early on that Doyon mill head grades were consistently higher than calculated grades. The cause is essentially conservative grade estimation; that is, high assays are cut and dilution is added at a lower grade than actually realized. At Bousquet No. 2 and LaRonde there is an unpredictable degree of natural sweetening; the ore zone is intersected by numerous, vertically dipping joints, or tight fractures, the plane of which is frequently shot with coarse gold.

In addition to being no more than cracks, the fractures have a north-south orientation and they are rarely if ever intersected by diamond drilling which runs in the same direction. They are generous sweeteners but there is no way of estimating their value by conventional sampling. They only register is the mill return.

The orebody is a lensing body of massive sulphides with accompaniments of disseminated breccia and stringer sulphides. The principal mineral is iron pyrite with minor copper sulphides, chalcopyrite, chalcocite and bornite and traces of lead and zinc. Copper content of the ore is 0.45% for Bousquet and is similar at LaRonde. Zinc can reach nuisance concentrations in some areas of LaRonde; it co-precipitates with the gold in the milling process and fouls both the precipitating carbon and the final bullion.

The main lens tops out at about 600 ft. below surface at LaRonde and can be traced to a depth of 3,600 ft. at Bousquet. The lens plunges at about 55 degrees to the west and the upper margin of the massive sulphide enters Bousquet ground 1,400 ft. below surface (stringer and disseminated ore have a greater spatial extent and consequently cross the boundary at a shallower level). Dip varies from 80 degrees to vertical, both to the north and to the south.

The strike length on LaRonde’s upper levels reaches 1,100 ft. but tapers with depth as is expected with a lensing body.

Normal ore widths range from 10-50 ft., and, as might have been predicted, some of the richest ore and the best mining widths straddle the boundary. Mining the boundary pillar in a systematic manner requires the close co-ordination of mining practices by both companies if all of the ore is to be extracted with the least amount of unbalanced rock stresses. Both LaRonde and Bousquet are starting at the bottom of the ore and mining upwards and outwards in lock step. In this manner the overall mining face will form an upside down “V” with the apex of the V gradually moving upward. The mined out area is backfilled with extra-strength cemented rock fill. (The sequence has already begun.)

Milling at LaRonde started in May, 1988. Throughput is currently 1,600 tons per day and the mill is scheduled to reach its rated capacity of 2,000 tons in October of this year. Estimated gold production for 1991 is 120,000 oz. Bousquet’s ore is trucked 23 miles to LAC’s East Malartic mill; commercial production started in October, 1990, at 1,000 tons per day. Throughput is now approaching 1,500 tons. (Since the site visit, LAC announced a mill expansion to 2,000 tons per day.) Estimated gold production for 1991 is 169,000 oz. If Bousquet was able to move from greenfield in 1986 to production in 1990 (a remarkably short period of time), it was because the target had been spotlighted by LaRonde. But the history of LaRonde, the pioneer, was otherwise and comprised a dogged two decades of stop-and-go exploration until the discovery hole hit ore at 2,800 ft. in 1986.

Dumagami Mines was the original owner of the LaRonde property and Agnico Eagle was Dumagami’s main financial backer. The two companies were amalgamated in 1989.

LaRonde’s main shaft was sunk to 1,420 ft. in 1983 giving access to four levels. The work was exploratory with the purpose of investigating a drill-indicated reserve of 2.7 million tons grading 0.094 oz. Detailed evaluation indicated that the deposit was not economic.

In 1986, after the main orebody had been delineated by drilling, the shaft was sunk to its present depth of 3,185 ft. and intensive development started.