Could one hole in Cranbrook, B.C. kill Red Dog?

To an untrained eye it’s an ordinary zigzag on a piece of paper filled with zigzagging lines.

But to Paul Cartwright, a geophysicist whose company, Pacific Geophysical, conducted the Controlled Source Audio Magnetotelluric or csamt survey for short, it’s two anomalous zones of enhanced conductivity deep under the Paleozoic cover rocks of southwestern British Columbia.

And to enthusiastic B.C. prospector John M. Leask it’s a “Sullivan target,” which, if a 5,000-ft hole he plans to sink this spring clicks, could “kill Red Dog,” Cominco Ltd.’s huge zinc project in Alaska.

Leask is not alone in his enthusiasm. Henry Ewanchuk, past president of Mascot Gold Mines, supports the idea based on what he knows about the Willyama Basin in Australia, home of the famous Broken Hill mining area where a number of monster orebodies have been found. Many geologists like Ewanchuk have wondered why, in the rifted marine sediment of the Purcell Group in southeastern British Columbia, which is so similar to the Willyama Basin down under, only one major lead-zinc mine has been found.

That single mine, the Sullivan, has been in production since 1909. Now, with 15 years of reserves left, it’s on its last legs and owner Cominco is well on its way to developing another rich lead-zinc deposit, the Red Dog, to replace it. That far northern mine could be in production by 1991.

But Leask has not given up on the Purcell rocks. His bull’s-eye target measures one kilometre wide, four kilometres long and 200 m thick. Now that’s a monster orebody. Financially, Leask is being backed up by industry heavyweight Dynamic Capital, run by Mr Dynamic himself, Ned Goodman. Goldpac resurrected

They have resurrected a Vancouver shell called Goldpac Investments (trading this week in Vancouver at $1.10) and plan to merge this company with Tectono Resources as a vehicle for the exploration program. Ewanchuk will serve on the board of directors and cmp Investment will buy some 500,000 flow-through shares to net the new company $1 million. There are currently 3,859,000 Goldpac shares issued. Three million are in the company’s safety deposit box and 859,000 are “on the street.”

The target Leask is so enthusiastic about is an anomalous conductor above the Precambrian basement buried under 4,000 ft of sediments. Leask likens the structure to a buried canyon or graben. This down-faulted block of rock, located about 20 km south of the Sullivan mine, at one time in the very distant past (anywhere from 800 million to 1.7 billion years ago) was submerged below sea water on what was then the west coast of the continent.

According to his geological reconstruction of the area, based on four years of hard, determined work, this part of the basin was just part of a major zone of weakness in the crust along a major spreading centre between the Pacific and North American tectonic plates, much like the Gulf of California is today.

This zone of weakness is marked by numerous faults in the Precambrian basement rocks of the basin, providing passageways for hot, mineralized fluids driven by seawater, to circulate in what is known as a thermal convection cell.

Lead- and zinc-bearing sulphides produced at such a hot spot would tend to spread out in a thin, unmineable, fan-like pattern over the sea floor if there were no traps to contain it. Leading them in

Drilling in the area by Cominco over the years has delineated such a sulphide fan south of the Sullivan mine. Owen Owens, vice president exploration for Cominco, tells The Northern Miner there have been two small zones, separate from the Sullivan, of less than one million tons each, which have been mined over the years. But his company’s work has found nothing big.

“Leask has a reasonably located property,” Owens says of the Cranbrook property. He would not comment on Leask’s chances of finding a major orebody there. Geophysicist Cartwright emphasizes the depth of the conductor and the inherent risks of interpreting such an event.

To Leask, Cominco’s work indicated there was a thickening trend leading to a potential source in the direction of ground he staked in 1983. So Leask convinced Noranda to drill a hole on the 104-claim property where he thought such a trap existed.

“That hole changed our entire view of what was going on here,” Leask told a gathering of investment analysts in Toronto this week. “Instead of a trough, we saw it as a canyon, which has a lot more potential to act as a trap.”

The hole returned the type of litho-geochemical results a geologist would expect to find in an alteration pattern 500 m from the Sullivan orebody — high mercury, barite, hemititic chert and a mineral called dalmationite.

Instead of drilling $350,000 holes to delineate the structure, Leask then hit on a rare opportunity to co-operate with an oil and gas company that was exploring for petroleum in the same area.

They wanted to look at Leask’s core, so in exchange, he got a chance to look at the results of a new type of geophysical survey. It was like nothing he had seen before. Geophysics

That geophysical method is csamt. It was brought to its present state of development by Phoenix Geophysics in Markham, Ont., which has sold the system to several contractors including Pacific Geophysical in Vancouver. What it eventually led to was the discovery of Leask’s “Sullivan target.”

Leask finished his csamt survey last August, delineating what looks like an ideal place to restrict the flow of sulphides — even deeper than the Sullivan trap.

“At these depths, we need to find 40 million tons of Sullivan-grade material to make it economic to mine,” Leask says. The Sullivan has 29 million tons grading 5.5% zinc, 5.3% lead and 1.4 oz silver per ton.

“And I think we have a 25% chance of hitting something big on our first hole,” Leask says.

“I would hope he has at least that chance,” Cartwright says.

Cominco, and some Goldpac investors, will be holding onto their hats if that 25% is enough.