TECH CORP. A Twist of Fate

People often assume porphyry copper deposits in British Columbia average less than half a percent copper. They sometimes throw in a little bit of molybdenum just for good measure. The situation is different, however, at Teck Corporation’s Afton mine, near Kamloops. The occurrence of supergene alteration at Afton made native copper of primary economic significance and chalcocite secondary. The latter is the highest grade copper mineral, 80% copper, commercially mined. At Afton about 70% of the copper occurs as native, 25% as chalcocite and 5% as chalcopyrite with bornite and covellite. The deposit has averaged 1% copper with about 0.02 oz of gold per ton of ore. The gold by-product is about equal in value to the copper produced.

Last year Afton produced about 58,000 oz of gold. Concentrates averaged 0.8 oz of gold and about 40% copper. Gold is associated with the copper. Silver is relatively unimportant and is usually 10 times the gold grade.

John Lovering, mine manager, readily admits that just being in the pit is “a bit of a bonus.” However, ground instability has become a problem and two major slides have occurred during the last year. The first slide occurred on the south wall and the second on the north. The areas in question were carefully monitored and crews were removed well in advance of the failure. The monitoring system used to detect ground movement will remain in place until mining has been completed.

Describing the present mining scheme as a salvage operation, Mr Lovering said the company is using a 4-cu-yd clam to mine 50 ft below the present pit floor. “We feel confident that we will be able to get ore out that way,” he says, although productivity will be low. Afton is aiming for a production rate of 2,500 tons per day from the clam. This salvaging operation may take 5-6 months. About one million tons of ore are available for milling from stockpiles. The combination of ore salvaged from the pit and ore from stockpiles will provide mill feed until mid-summer.

Blasting has generally been done into a free face, but this technique is now impossible because of limited space in the bottom of the pit and this is affecting ground conditions.

An innovative dewatering system has been developed for the pit. George Sutherland, pit superintendent, describes the unit as a “super sucker.” A haulage truck has been converted to transport water from the pit. The truck is equipped to load to capacity (10,000 gallons) in about 15 minutes and empty in fewer than two. The pump used to load the truck can handle up to one inch solids, he notes.

The company has also devised a simple but effective dispatching system which he claims has improved productivity by about 25%. It is inexpensive and involves placing three different lights at the pit crest with colors matching those on the shovels. The dispatcher tells the truck operator which shovel is ready for loading to visit by turning on the proper light at the pit crest.

Once mining in the Afton pit has been completed, a new pit will be developed on the Pothook deposit. This deposit has a lower copper grade, 0.39%, but it contains significant amounts of gold.

This new pit will provide mill feed for about one year. Afton will evaluate the Ajax property which is about six miles from the mine, while mining at Pothook. The evaluation may cost upwards to $1 million. If a decision is made to proceed with Ajax, Ajax ore would be trucked to the Afton concentrator. The grade at Ajax is about half the ore grade in the Afton pit. The ore at Ajax, however, would have a much lower stripping ratio and this will partly compensate for the lower grade.

Higher grade mineralization, averaging about 1.5% copper and 0.03 oz of gold per ton, exists below the Afton pit. This mineralization is uneconomic at present metal prices. Mike Lipkewich, general manager of metal operations for Teck, does not rule out the possibility of an underground mine being developed at some future date.

Although copper mineralization was first discovered in the Kamloops district 90 years ago, serious exploration began in the 1950s. Five decades earlier, a prospector had put down a 300 ft shaft on the Pothook claim which later proved to be 2,000 ft south of the main Afton orebody.

This is almost an exact parallel to the Kidd Creek mine discovery at Timmins, where a shallow exploration shaft had been sunk in pyrite several hundred feet from what later proved to be the largest base metal discovery in Canadian history.

There’s an axiom in the exploration business: if three majors have looked at a property, it is probably a good bet. On that basis, the Afton property qualified around 1960; by that time Kennco Explorations, Noranda and New Jersey Zinc had all looked at it with only marginal success. Chester Millar, now chairman of Glamis Gold, gets full credit for the Afton discovery. His interest in the claims heightened in 1964 when he was working on a nearby property as a drill contractor.

He persuaded Colonial Mines to drill some percussion holes around the old Pothook shaft, but the program was stopped after 11 holes. Shortly thereafter, he formed a private syndicate which staked more claims adjacent to the Trans Canada Highway and completed a 30-hole drill program plus an induced polarization (ip) survey.

Drilling revealed an east-west trending zone of copper mineralization extending to the west and presumably to depth. These results were coincident with an ip survey that showed a large anomaly trending in the same direction and centred several hundred feet from the Pothook shaft.

An underwriting was completed in 1969 which allowed the syndicate to proceed with a follow-up program that included more drilling on several week anomalies. The ip anomaly passing through the Pothook zone was found to be caused by disseminated pyrite in the intrusive rocks. Typical of most porphyry copper deposits in British Columbia, one of the first holes in the zone graded 0.4% copper over 170 ft.

Two companies, Duval Corp. and Quintana Minerals, looked at the property over the next two years, but both dropped out. Afton Mines refused to give up and with $70,000 in its treasury the company mounted a percussion drilling program in 1971 where copper mineralization had been intersected.

Development of the property was suspended for a time pending clarification of an agreement signed in May, 1972, between Canex Placer and Afton Mines. Teck had entered the picture by purchasing 51% of the outstanding Afton shares on the open market and claimed to have control. The company argued that the subsequent deal between Afton and Canex Placer was invalid because it had not approved the agreement.

The matter was settled in 1973 when Teck and its subsidiary, Iso Mines, agreed to pay Canex Placer $4 million to relinquish its rights to the property. The stage was set to resume work on the property and Teck later went on to define a viable orebody.

Reserves at feasibility study time were 34 million tons grading 1% copper plus a $2-per-ton credit for gold and silver. The mine was brought into production at 7,000 tons per day in early 1978 and the project included a copper-smelting complex, the first of its kind in the province. Capital costs for the mine were about $85 million.

The smelter qualified for benefits under British Columbia’s Copper Smelting and Refining Incentive Act which provided for payments of up to 2.27 cents cents per lb for blister and refined copper produced in the province. Payments were limited to 10 years, a maximum of $500,000 per year. The incentive had a favorable impact on the economics of the smelter. The smelter has not been operating in the past few years because the economics of shipping concentrates to Japan for processing are much better, says Afton. The facility cannot handle high-sulphide ore because it does not have the scrubbing capacity. The sulphur content increases with pit depth. The company has attempted to sell the facility, but only a few items have been sold.

Land initially purchased by Afton for mining purposes necessitated acquisition of agricultural land that was incidental to mining requirements. This land, including attendant grazing leases and licenses, has been developed into a productive cow-calf ranching operation. The Sugarloaf Ranch runs a herd of 300. The ranch produces its winter feed by growing hay on 100 acres of irrigated farmland. It is truly a western ranch. Cowboys still saddle up and head for the high country.