Cominco discovers large copper-gold porphyry in Alaska

Just when it seemed junior companies were stealing the limelight in making discoveries, a unit of Cominco (TSE) announced it had discovered a porphyry-style copper-gold deposit at its Pebble Beach property some 200 miles southwest of Anchorage, Alaska. The deposit was found by Cominco Alaska Exploration, a wholly owned subsidiary of Cominco, in a completely overburden-covered area without any previously known mineralized occurrences.

Cominco said results from an initial diamond drilling program carried out in 1990 suggest a preliminary reserve of about 200 million tons averaging 0.4% copper and 0.012 oz. gold per ton. Within this area, a 50 million ton portion is reported to average 0.5% copper and 0.015 oz. gold per ton.

Owen Owens, Cominco’s vice- president of exploration, stressed that although preliminary results are “most encouraging,” more detailed drilling and metallurgical work will be required to determine the economic potential of the project. Most drill holes are only 300-400 ft. deep and about 1,000 ft. apart.

The zone is open to depth and to the northeast, and Owens said the property still has “substantial exploration potential.” A follow-up program of extensive detailed diamond drilling is planned for the 1991 field season, but the budget for the program has not yet been determined.

It appears Cominco is encouraged by results to date from the Pebble Beach property, particularly in view of the fact it is in accessible and moderate terrain about 50 miles from Alaskan coastal waters. The project is on Alaska state claims held 100% by the company.

In contrast to some major companies which have in recent years tended to emphasize acquiring advanced properties, Owens said Cominco’s philosophy has always been to develop many of its projects internally from grassroots or early stage exploration prospects.

Some of its notable successes in this regard include the discovery of the huge Valley copper deposit in southern British Columbia (now part of Highland Valley Copper owned 50% by Cominco). The Red Dog zinc-lead-silver project in northern Alaska was taken on in the early stages of discovery, and it was recently developed into one of Cominco’s most important mining operations.

Owens said the Pebble Beach discovery was the result of careful geological observation, extensive soil sampling, discrimination and persistence by the team of geologists involved.

“This entirely new discovery was made through sound grassroots exploration and exploration geologists are to be congratulated for their efforts,” he stated.

Cominco was led to the area of interest by investigation of a gold- bearing quartz vein several miles away. The showing was drilled, but the drilling failed to establish continuity to the gold values.

In keeping with the company’s practice, geological examinations were carried outward from the project which located other areas of weak silicification and iron alteration to the north. Rock debris sampling and wide interval geochemical sampling for gold led to early diamond drilling, but results were deemed “discouraging.”

A review of regional geochemical results indicated nearby copper values in soils. Although no outcrops were found in the area of interest, sulphide mineralization was found in a few frost boils. In 1989, the last drill hole in the area intersected copper and gold mineralization.

In 1990, follow-up drilling confirmed the importance of the mineralization and a widely spaced drilling program was carried out to locate the limits of the mineralization and to determine the geology of the zone.

Some preliminary metallurgical work was also carried out last year. Owens said preliminary results indicate the mineralization is of the type that would be amenable to conventional flotation processing methods for sulphide deposits.

More metallurgical work will be carried out this year, along with further diamond drilling. The objective of the 1991 program will be to define the mineralized resource more completely, and to understand the nature of the deposit and its potential before considering any on-site construction or site disturbance.

In view of environmental considerations, the 1991 program will be helicopter-supported with all equipment and personnel moved by helicopter.