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Bureau of Mines / Minerals yearbook 1990
Year 1990, Volume 2 (1990)

Pittman, Tom L.
Alaska,   pp. [54]-70 ff. PDF (3.5 MB)


Page 65

ALASKA—1990  65States. The milling rate averaged 1 ,050 st per
day.
The silver was contained in the gravity and flotation concentrates from the
mill and recovered by smelting and refining. The Red Dog Mine was the other
major silver source in Alaska in 1990. An average of about 4,000 tons of
open pit ore per day was milled by selective flotation, producing lead, zinc
and bulk zinc-lead concentrates. Silver was recovered from each of the concentrates
by smelting and refining. The ore milled in 1990 was reported to have averaged
about 25.7 % zinc and 10.5 % lead, from a published reserve of 
85 million tons averaging 17. 1 % zinc, 
5.0 % lead and 2.4 troy ounces silver per st. Some of the ore exposed at
the surface of the deposit contained badly oxidized mineralization and was
stockpiled for later research and treatment. The moderately oxidized ore
yielded rather poor recoveries of lead and silver and required considerable
work on the grinding and flotation circuits to attain the expected metallurgical
results. Silver recovery was about proportional to the lead content of the
mill products. Elemental sulfur is present in the ore and requires preliminary
flotation to keep it from diluting the shipping concentrates. Anticipated
annual silver production is about 3.9 million troy ounces when milling 6,000
tons of ore per day. The silver would be recovered from smelting 560,000
st of zinc concentrates averaging 
3.0 troy ounces of silver per st, 120,000 st of lead concentrates at 16.5
troy ounces silver per st, and 50,000 St of bulk concentrates at 4.5 troy
ounces silver per st. Placer gold recovered in 1990 contained an unspecified
amount of silver. Refined gold yields the silver as metal, but the placer
gold used as nugget specimens and for nugget jewelry retains the silver in
the original alloy. Exploration for primary silver and silverbearing base
metal deposits did not attract much interest or monetary expenditure because
of the relatively low metal prices. 
Thz.—.The State survey reported 25.855 metric tons of tin, valued
at
about $200,000, was produced in Alaska in 
1992. The reported tin output in 1989 was 87.99 metric tons valued at $672,000.
Sphinx Mining Inc. recovered a byproduct placer tin concentrate at its placer
gold mine on Midnight Creek, in the Ruby-Poorman district, about 30 miles
south of the Yukon River, in the western region. Shoreham Resources Ltd.
also produced a placer tin concentrate from its gold placer on Cache Creek
in the Tofty district, in the eastern interior region. Kennecott Exploration
Inc. mapped 8 square miles, took soil and rock geochemical samples and drilled
two holes in a tin exploration program at Potato Mountain, on the Seward
Peninsula. There was little exploration effort and expenditure on tin in
1990 other than that necessary to hold several promising prospects justified
by previous work. 
Zinc and LeatL—The State survey reported 1990 zinc production at
164,350
metric tons valued at $253 ,680,000 and lead production at 40, 106 metric
tons valued at $30,954,000. This was an increase from 18,007 metric tons
of zinc and 8,698 metric tons of lead valued at $29,383,400 and $7,692,009
in 1989. The amounts and value of 1990 zinc,silver and lead production reported
to the Bureau of Mines has been withheld to avoid disclosing company proprietary
data. Alaska ranked first among the States in zinc production, second in
lead production and third in silver production. Nevada and Idaho silver output
topped Alaska in 1990. 
The Greens Creek Mine operated full time during its second year. The mine
is in a nonwilderness area east of Hawk Inlet, on Admiralty Island, about
18 miles southwest of Juneau. The underground mine supplied an average of
1 ,050 st per day of ore to the selective flotation mill, for a total of
382,574 tons. The State survey lists 1990 production at 7,636,501 troy ounces
of silver, 38, 103 troy ounces of gold, 33,457,804 pounds of lead and 74,006,086
pounds of zinc in concentrates. Copper and barium minerals in the ore were
not recovered. Startup problems in the mill were brought under control by
finer grinding and by 
modifications of the flotation circuits and reagents. Lead, zinc, and a bulk
lead-zinc concentrate were shipped to foreign smelters from the company's
Hawk Inlet storage and loading dock. The bulk concentrate goes to Imperial
Smelting Furnace (IFS) smelters for the recovery of the complex mixture of
contained metals. The known ore bodies have been described as volcanogenic
massive sulfide deposits in folded metaseditnentary rocks of late Triassic
age. The explored ore deposits are the north, central, and south zones. The
zones range from 6 to 80 feet thick, from 200 to 700 feet down dip and 1,200
to 2,000 feet long. Mining was by drift and fill methods in the narrower
parts of the deposits and by modified cut and fill methods in the wider stopes.
Much of the stope fill is deslimed and pressure-filtered mill tailings backhauled
into the mine. Jumbo drilling, loading, and hauling is accomplished by dieselpowered
equipment. There was an ambitious program of 61,500 feet of development and
exploration drilling in addition to 47,500 feet of production drilling. The
operating work force is about 265 people. The State believes this operation
adds about $30 million annually to the economy of Juneau in salaries, goods,
and services. Except for a few people, the operating crew lives in the Juneau
area and is transported by the Alaska Dream, a catamaran crew boat, from
Auke Bay to Youngs Bay on Admiralty Island and thence by buses to the mine
and mill sites on Greens Creek and the storage and shipping site on Hawk
Inlet. The company has a smaller standby catamaran based at its Auke Bay
dock. 
The Red Dog Mine is situated about 90 miles north of Kotzebue and 52 miles
inland, northeasterly, from the Chukchi Sea. The mine produced 1,318,200
tons of zinc-lead-silver ore during the first year of its open pit operation
in 1990, according to the State survey. Only 321,700 tons of lead, zinc,
and bulk (1SF) lead-zinc concentrates were shipped during the short open-water
season of about 100 days. The concentrates went to the Cominco Alaska Inc.
(Cominco) smelter at Trail, British Columbia, 


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