HOPE BROOK REVIVAL

Royal Oak Mines acquired the Hope Brook mine in southwestern Newfoundland last year and by July 1, 1992, had begun commerical production. Total output for the year was 50,693 oz.

The mine is running now at 105,000 tons on an average month and the gold production target for 1993 is 129,000 oz. Average cash costs for last year were US$254 per oz. The former owner, BP-Selco, sold the mine after several years of unprofitable operations. To achieve financial success, Royal Oak overcame several bottlenecks that had previously affected throughput. These included the inability to destroy cyanide in the tailings, SAG mill downtime because of mafic pebbles, winter ore-handling problems from portal to mill and ore haulage to surface.

For having solved the key bottlenecks, Hope Brook’s young (30-something), aggressive management team deserves full marks. Kevin Weston became mine manager, replacing General Manager Mike Werner, who saw the mine through re-commissioning and now heads up the Yellowknife division. At Hope Brook, the focus now is on hitting its stated production target for 1993. In the six months of 1992, Hope Brook produced 50,673 oz. The March figure should reach about 9,500 oz.

The mine began as an open pit and is currently being developed on four levels underground, the bottom-most being the 4900 level.

Hope Brook is a ramp access mine, the ramp running along the footwall side of the orebody. The portal surfaces at the 5120-m. level. The ramp has a 12% grade and, to date, runs 7,000 m. in length and 220 vertical m.

When re-development first began, the mine was flooded to the 5060 level. As Royal Oak proceeded with the de-watering, four major falls of ground were encountered in the ramp. The most severe cave-in required the driving of a 180-m. bypass.

“This (the discovery of falls of ground) caused some alarm because, as de-watering progressed, we couldn’t verify the length of the bad ground,” recalls Lance Flewelling, Mine Superintendent.

Apparently, the ground falls were caused when water, combined with fine colloidal material in this heavily jointed and stratified ground, turned the material (mainly pyrophyllites) into the consistency of toothpaste. Unflooded, the mine offers good ground conditions.

From the ramp, cross-cuts are driven into the ore and a sill is blasted out in ore. This will become the drawpoint and haulage level. On the 4900 level two parallel drill drifts are being driven. This will be both haulage and drill drift because Hope Brook drills both upholes and downholes.

After sublevels have been driven, a slot raise is then blasted out by Canadian Mine Developments, which has been contracted to do all the raises.

Production drilling is accomplished with Cubex in-the-hole drills incorporating a 3.5-m burden and 4-m. spacing. The 3.5-inch-diameter bits, specially made for the highly siliceous Hope Brook ground, is manufactured by Torcal in Saskatchewan. They are diamond-enhanced to withstand the “incredibly abrasive” ore. “Without these bits we’d burn out a regular carbide bit in 20 ft.,” Flewelling said. At about three times the price of regular bits, they’re expensive, but necessary.

The stopes are mined longitudinally, rather than in a transverse configuration as BP had done. Flewelling said the longitudinal system creates a funnel-shaped drawpoint, thus reducing the amount of remote-controlled mucking by LHD. Remote mucking

is slower, by as much as 50%, as compared with conventional means.

Cable-bolt holes are drilled from production drifts within ore, not from drifts in the largely barren hangingwall. This obviously reduces waste material. There was a second reason for avoiding a hangingwall drift, Flewelling said. “It is a weak structure, unstable, unpredictable.”

Grouted, double-strand cable bolts (5/8 inch) support the hangingwall. The bolts are unusually long, on average about 100 ft.

The explosive used earlier was ANFO, but Hope Brook is relying now on emulsion explosives manufactured by ICI. In this mine, it is cheaper, offers better energy delivery and improved fragmentation.

For ore haulage to surface, the mine depends on 50-tonne-capacity, trolley-driven electric trucks manufactured by Kiruna. Conventional diesel trucks and LHDs haul ore from drawpoints to two chutes specially equipped to load Kiruna trucks.

The trucks are fast — at full load up a 12% grade they hit speeds of about 12 km. per hour vs. a diesel truck speed of about 3 km. They run quietly and smoke-free. Unfortunately, the electronic circuitry that keeps them moving is vulnerable.

On a late-March visit by The Northern Miner Magazine to the facility, one of the three trucks was down for repairs. Availabilities are currently about 70%, but when mining descends to the 4900 level, Mine Superintendent Lance Flewelling says this is sufficient for producing to the 4900 level.

Royal Oak is still mining stopes in the two upper levels, mostly remnant rib pillars. Development on the new, deeper 4900 level was in mid-March. Two stopes were providing millfeed. By this fall, all production will come from 4900. By the end of April four stopes had been developed.

Monthly production reaches about 110,000 tonnes, though February proved a poor month with 90,000 tons.

This was caused by sloughing from adjacent backfilled stopes that were structurally less competent than predicted. The mining stopes were rib pillars left over from BP’s ownership.

“We have two stopes running good grade and no dilution. That will sustain us until we get production from 4900 by mid-April,” Weston said. Development muck on 4900 is running a healthy 0.15 oz. per ton.