Campbell digs down: new shaft to reach deeper mineralization

Northern Ontario is well-known for its lode gold mines, but few can claim as illustrious a career as Campbell of Placer Dome (PDG-T).

Developed in the 1940s, at the height of the Red Lake staking rush, the mine has gone on to celebrate 50 years of continuous operations. Along the way, it has poured an astonishing 11,995 dor bars, accounting for more than half the camp’s historical output.

But old-timers might be hard-pressed to recognize Campbell these days — it sports a new headframe and the latest in processing technology. The change reflects a modernization program begun 12 years ago, after operator Campbell Red Lake Mines merged with Placer Development and Dome Mines to form Placer Dome. More recently, these efforts culminated in the commissioning of the Reid shaft, named after mine manager Stuart Reid, now deceased.

“The Reid shaft represents the biggest investment in the future of Campbell we have yet made,” Joc O’Rourke, current mine manager, told a group of analysts who, along with The Northern Miner, recently toured the mine. “Realistically, it offers us the infrastructure for excess hoisting capacity for a long time to come, gives us 1,500 ft. for new levels and allows us to move men and material down in a way we’ve never been able to do before.”

Costing $80 million to construct, the Reid shaft extends 6,000 ft. below surface, or 1,800 ft. beyond the original shaft. Supporting it is the largest hoist ever constructed in North America, which is capable of transporting 50 men 1,800 ft. per minute, compared with the standard 15-man capability. Moreover, noted O’Rourke, its 11.5-ton skips will haul 2,750 tons of material to surface each day, boosting production by nearly a third.

“We expect to exceed this very comfortably, and in commissioning we are doing just that.”

Facilitating this will be a ramp system between levels 27 and 39 — a first at Campbell. In higher levels, equipment must be disassembled, transported via the shaft and then reassembled when moved between levels. The ramp had reached level 30 by the time of The Miner’s visit.

Another facet of Campbell’s evolution is the switch to longhole stoping from cut-and-fill methods, which accounted for only 3.5% of 1998 production.

“As long as we keep sub-levels at 50-ft. intervals and control [dilution] from the walls, there is not a very big increment in terms of grade,” said O’Rourke. “But there is a huge difference in tonnage: the same block of ore mined by cut-and-fill gives a quarter of the tonnage as longhole, and the actual mining costs are one-third less with the latter method.”

Surface retouching is likewise helping. Today, the mill sports column flotation cells, an autoclave and carbon-in-pulp plant, simplifying pre-1991 roasting techniques for that portion of the ore that is refractory. (The mill continues to recover 50% of mined gold in a gravity circuit.)

The various changes have seen cash costs per tonne milled fall to $108 (on 545,000 tonnes) in 1998 from $126 (on 460,000 tonnes) in 1992. Concurrently, annual output has remained relatively unchanged, in the 300,000-oz. range, though head grades have declined 22%. This translates into a savings of US$32 per oz. over that period, with 1998 costs at US$127 per oz. However, future years, including 1999, are expected to top 280,000 oz. at US$138-140 per oz.

Geologically, Campbell exploits a series of zones sitting in the eastern portion of the Red Lake greenstone belt. Mineralization is structurally controlled, hosted by basalt and ultramafic flows, with gold occurring freely in quartz-carbonate veins or encapsulated by sulphides, mainly in the form of arsenopyrite, pyrite and pyrrhotite.

Proven and probable reserves stand at more than 4 million tons grading 0.43 oz. per ton. Of that, 598,104 tons grading 0.56 oz. are blocked out between the 27 and 30 Levels.

Key to replacing those reserves are the deeper, untapped areas. Near-term plans call for 4,500 ft. of exploration drilling and 75,000 ft. of drilling from levels 27 and 30, as well as from the shaft where levels 33 and 39 will eventually branch off.

“On 39 Level, we are a good 1,500 ft. from anywhere we’ve mined before,” noted O’Rourke, “so we are not so much interested in outlining reserves as in understanding what it looks like down there — that is, the geology and where this mine is going.”

Campbell’s measured and indicated resources stand at 1.6 million tons grading 0.27 oz. per ton, with another 1.25 million tons grading 0.39 oz. in the inferred category. Historically, the geometrical complexity and erratic nature inherent to the system has seen only 50% of resources converted to reserves, underscoring the need for conservatism.

Nevertheless, newly adopted paste backfill will assist future miners in exploiting those stopes with even greater efficiency and productivity. The added bonus: a good portion of mill tailings will go back where they came from, reducing reclamation costs and appeasing any environmental concerns.

But after all is said and done, said O’Rourke, “the reason we are all here is to pour gold.” And it is that philosophy that has taken Campbell from an operation earning $37.4 million in 1992 to one recording $54.9 million in 1998. Not bad for a 50th anniversary.