|
Fortune Hunt Alaska 2012: Alaska reigns as top silver producer Poor man’s gold enhances luster of a number of deposits in Far North state Shane Lasley Mining News
Thanks largely to the 6.5 million ounces of silver produced at Hecla Mining Co.'s Greens Creek Mine in 2011, Alaska remains the United States' top producer of "poor man's gold."
The nation’s top silver-producing mine is situated in the middle of a 450-mile-long belt of late-Triassic VMS deposits that spans the Southeast Alaska panhandle and extends to the north, encompassing the Windy Craggy deposit in British Columbia.
Volcanogenic massive sulfide deposits similar to Greens Creek hold great promise for fortune hunters seeking the white metal in Alaska.
At some 8 million tons of reserves averaging 421 grams per metric ton silver, 3.2 grams per metric ton gold, 9.2 percent zinc and 3.5 percent lead, Greens Creek is by far the most silver-enriched of the known deposits along this trend.
Woewodski Island is one Southeast Alaska prospect that demonstrates promise to be a Greens Creek contemporary. A hole drilled by Bravo Ventures Group Inc. in 2003 cut 1.8 meters grading 222 g/t silver, 6.34 percent lead and 16.15 percent zinc and underscores the potential of the prospect. But limited drilling has uncovered no signs of thick zones of high-grade massive sulfides there.
Prince of Wales Island, found at the southern tip of the Southeast Alaska panhandle, is home to several promising silver-rich VMS prospects. The best known of these is Heatherdale Resources Ltd.’s Niblack project, which contains has an indicated resource of 5.65 million metric tons of ore averaging 29.52 g/t silver — along with 1.75 g/t gold, 0.95 percent copper and 1.73 percent zinc.
The ore at Constantine Metal Resources Ltd.’s Palmer Project at the north end of Alaska’s portion of the VMS belt contains about 31 g/t silver — accompanied by 2 percent copper, 4.8 percent zinc, and 0.30 g/t gold.
More VMS deposits Southeast Alaska is not the only place to find silver-rich VMS deposits in the state.
Andover Ventures Inc.’s Sun deposit in the Ambler Mining District of Northwest Alaska, for example, has a resource, calculated for the project in 1977, of 20.3 million metric tons averaging 74 g/t silver, 1.9 percent copper, 4.5 percent zinc and 1.2 percent lead.
Sun is located at the eastern extent of a belt of VMS deposits that stretch some 70 miles along the southern slopes of the Brooks Range.
Arctic — the most advanced deposit along this belt — has an indicated resource of 19.45 million metric tons averaging 4.05 percent copper, 5.8 percent zinc, 59.55 g/t silver and 0.97 g/t gold.
In the Alaska Range about 36 miles southwest of the crossroads town of Tok, Heatherdale Resources is also exploring the silver-rich Delta Property in an emerging VMS region in Interior Alaska. An inferred resource of 15.4 million metric tons grading 62 g/t silver, along with 0.6 percent copper, 1.7 percent lead, 3.8 percent zinc and 1.7 g/t gold, has been calculated for Delta.
Two holes drilled by Heatherdale in 2011 reaffirmed the presence of precious metals-rich VMS mineralization on the property. Hole 2011-154 cut 13.4 meters averaging 85 g/t silver, 0.56 percent copper, 5.2 percent zinc, 2.4 percent lead and 1.56 g/t gold.
“Initial drilling has more than justified our belief that Heatherdale’s extensive land position at Delta presents tremendous opportunities for delineating sizable deposits of high-grade, precious metals-enriched VMS mineralization,” said Heatherdale President and CEO Patrick Smith.
Northwest SEDEX Although the value of the silver pales in comparison to the spectacular zinc grades, Teck Resources’ Red Dog Mine in Northwest Alaska produced a whopping 7 million ounces of silver in 2010.The silver-enriched ore at Red Dog is part of a high-grade sedimentary exhalative, or SEDEX, body.
Exhalative deposits are formed over millennia when the earth “exhales” mineral-rich brine onto the ocean floor, creating layers of sulfide ore.
Northwest Alaska is home to several other SEDEX deposits and is prospective for others. These include Teck’s Anarraaq and Zazu Metals Corp.’s Lik deposits.
“Red Dog is one of the greater lead-zinc deposits in the world, and there is more potential for those in Northwest Alaska as well as other places (where) there are Paleozoic rocks that are similar to Red Dog,” observed Millrock Resources Inc. Vice President of Exploration Phil St. George.
According to a 2004 report written for the Society of Economic Geologists, the Anarraaq deposit consists of a barite body estimated to be as big as 1 billion metric tons and a zinc-lead-silver zone with a resource of about 18 million metric tons grading 18 percent zinc, 5.4 percent lead, and 85 g/t silver.
Lik is estimated to contain about 4.6 billion pounds of zinc, 1.5 billion pounds of lead and 41 million troy ounces of silver and its grade averages about 8 percent zinc, 2.6 percent lead and 47 g/t silver.
Statewide potential In addition to SEDEX- and VMS-style mineralization that host Alaska’s two silver-producing mines, several other types of ore found across the state are known to contain rich stores of the white metal.
When mineral-laden brine is not exhaled, but instead is trapped in ocean-floor sediments, it forms replacement-style deposits. Full Metal Minerals Ltd. is exploring one such deposit at its Fortymile project in eastern Alaska.
Hole LWM10-64 drilled at Fortymile last year cut 5.89 meters averaging 198 g/t silver, 7.4 percent zinc, 13.8 percent lead. LWM10-68 intersected 4.4 meters averaging 314 g/t silver, 23.7 percent zinc and 23.6 percent lead
Epithermal gold prospects found along the Alaska Peninsula and the Aleutian Islands typically contain high concentrations of silver, but are relatively unexplored.
Shumagin and Apollo, two such epithermal gold deposits being explored by Full Metal on Unga Island, contain a combined historical resource of 280,000 metric tons averaging 27.7 g/t gold and 92.6 g/t silver.
Next Gen Metals Inc.’s Silver Chalice prospect — found on the banks of the Yukon River about 330 miles west of Fairbanks — reflects Interior Alaska’s potential for silver-rich epithermal deposits. Rock chip samples from the property returned assays up to 462 g/t silver. The average silver-gold ratio of these samples is about 40:1.
Most of Alaska’s tin prospects such as Kougarok, Sleitat, Win, Won and Coal Creek also contain silver, and the precious metal is typically a significant by-product in porphyry copper deposits such as Pebble.
With silver prices remaining strong, the white metal continues to enhance the luster of mineral deposits across Alaska.
| 