Casa Berardi on line for 90,000 oz.

To judge by results at the Casa Berardi mine more than 100 km. north of here, Inco the nickel miner makes the grade as a gold miner too. The Casa Berardi East mine has been profitably producing gold for more than a year now and the West mine, four kilometres away, entered commercial production April 1. Combined targeted production for 1990 is 90,000 oz. at a 1,200- tonne-per-day production rate.

And recently Golden Knight Resources (TSE), which owns 40%, and Inco Gold, a unit of Inco Ltd. (TSE), which holds the remaining 60%, announced they may increase the daily production rate to 1,800 tonnes. A decision on the expansion could come this fall.

Currently, gold is recovered from separate ore zones along the Casa Berardi Break, a graphite-rich mudstone fault that strikes approximately east-west across the property. A third area of gold mineralization known as the Major zone or zone Principale, sits midway between the two mines and may offer new ore in the future.

Inco Gold President Martin Robinson said the biggest challenge faced by the Casa Berardi operations people, the senior ranks of which were seasoned nickel and chromite operators, has been understanding the nature of the mineralization.

“It amazes me that there’s no visible gold. It’s very difficult to tell whether you’re in gold or not (as mining proceeds),” he said. However, strict sampling has ensured adequate grade control. Direct cash operating costs are approximately US$200 per oz.

Inco’s acknowledged expertise in bulk mining, refined over decades of operations in the Sudbury basin of northern Ontario, has been adapted at Casa Berardi. One such method, vertical retreat mining (VRM), accounts for roughly half the mined ore in the East mine.

“We use VRM wherever possible because it’s much cheaper,” said mine manager Bob Lepage, a 23-year Inco veteran whose previous assignment was as superintendent of the McCreedy West operations in the Sudbury area. Some modifications to the mining scheme will be necessary if an expansion gets the green light.

Generally, where widths are narrower and grades lower, mechanized cut-and-fill is the preferred extractive process in the East mine. At the West mine, mechanized cut- and-fill and a bulk blasthole method account for production.

Other features common to both mines include ramp access, diesel truck haulage, and a backfill product of cemented sand and waste rock. The two mines also share a 1,200- tonne-per-day carbon-in-leach mill. Only minor changes to the crushing and grinding circuits will be required if the expansion is approved.

They differ in terms of ground control, however. This was immediately evident during the later tour of the West mine, where water continually drips from the back in the ramp leading to the workings. The East mine is far drier. The blockier, heavily deformed West mine ground requires more bolting — both mechanical and Swellex bolts — and screening than does the East.

Screening in the East mine is required only in a stope where mining has exposed the graphite fault, which quickly degenerates when exposed. To prevent excessive spalling from the sides and back, Casa Berardi’s miners steer clear of the graphite if at all possible.

Fortunately, the ore runs parallel to, and south of, the graphitic fault in the East mine; mining seldom intrudes into the less competent ground. In the West mine, the ore sometimes crosses the fault. Where this has occurred, the drift through the fault is timber-supported.

Gold mineralization is also somewhat less predictable, though higher in grade, in the West mine.

“In the West mine we are accessing a higher-grade pod,” Robinson said. But eventually both mines should display similar grades, he added.

The current minable (proven and probable) reserve in the East mine is roughly two million tonnes grading 7.2 grams per tonne. The West mine has a slightly higher tonnage at 3.5 million tonnes, but a similar grade. The West mine reserve represents a 44% increase over an earlier reserve estimate. It was this upward revision that has prompted Inco and Golden Knight to explore the possibility of an expansion.

The total geological reserve when the Major zone is factored in is 11.1 million tonnes, grading 7.5 grams per tonne. At an annual production rate of 400,000 tonnes per year, the mine has at least 14 years of minable reserves.

But since both the East and West mine reserves are open at depth, a longer life can be expected. As well, exploration along strike of the Casa Berardi Fault, which for miles is Inco-held ground, could well unearth additional deposits.