Exploration activity up at Greens Creek

Operators of the Greens Creek polymetallic mine started surface core drilling in late April, the beginning of a summer long program designed to complete 40,000 feet of drilling at several targets surrounding the underground mine near Juneau, Alaska.

The $1.9 million budgeted for surface drilling work this year is the largest surface exploration program at the mine since production began in 1989 at Greens Creek, said Bill Oelklaus, environmental manager. "There are eight different areas around the mine" that will be explored this summer, he said in a telephone interview on April 30.

Greens Creek, one of the world's largest silver producers, also extracts gold, zinc, lead and copper from its ore mined from underground workings on the northern end of Admiralty Island, 18 miles from Juneau. Most of the surface exploration activity will be to the west of the existing mine workings, but there are targets in all different directions, Oelklaus said.

"We have high expectations to find more of this kind of (mineralized) material."

The increased surface exploration will be completed in addition to an underground exploration program, Oelklaus said. Another 40,000 feet of core drilling will be completed in the underground workings, work expected to cost $2 million, which is the company's typical annual investment for the underground work, he said.

"We've been active a lot of years (on the surface) but not near at this level. We're putting a lot more effort towards it," Oelklaus said.

Extending mine life

Oelklaus credits an increase in metal prices for the boost in the surface exploration program.

"A lot of it is metal prices. We're making good money and are interested in recycling it back into extending the mine life," he said.

Existing mineral reserves at Greens Creek provide an estimated mine life of 10 to 12 years. "We're hoping to extend that some more," he said.

Last year's exploration found significant polymetallic mineralization across a fault thought to truncate the large ore body, according to a summary of the Alaska's Mineral Industry 2003 report.

"Drilling of exploration targets on the west side of the Gallagher fault produced interesting results," the state report said. "The most significant find was a 10.3 foot drill interval that assayed more than 45 ounces of silver per ton. The intercept is across the Gallagher fault, an area that has never been mined or explored before. "This intercept increases the probability of finding a continuation of the ore body on the other side of the fault, which could add significant mine life to this already long-lived resource," the state report said.

Tailings expansion work begins

In conjunction with the additional exploration work, Greens Creek has also started a construction project needed to accommodate tailings created by future production. The mine's operator, Kennecott Greens Creek Mining Co., received final regulatory approval in early February to begin construction of a tailings disposal expansion project. Ground clearing and rock quarry work began in late April, Oelklaus said.

Construction costs for the tailings expansion project are estimated at $2 million to $3 million. The tailings storage footprint will expand from 29 acres allowed under old permits to 62.2 acres. Total land leased to the company after the expansion is 123 acres, up from 56 acres under the existing permit.

Kennecott will also be required to add carbon to tailings to enhance sulfate reduction, following a 30-month study to determine how much carbon should be added, what form will be most effective and how to incorporate the material in tailings.

The expansion will allow for another 20 years of production at Greens Creek. At its current production rate and with no expanded tailings disposal, Greens Creek would have run out of space in February 2005.

Greens Creek currently employs 260 workers and in 2003, milled a record 782,100 tons of material, according to the state report. Greens Creek metal production in 2003 includes 11.7 million ounces of silver, 99,500 ounces of gold, 76,700 tons of zinc, 27,900 tons of lead and an estimated 1,500 tons of copper.