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Fortune Hunt Alaska 2012: Goodnews beckons with PGM prospects From placer streams to historical mines, hints of elusive metal span Alaska Shane Lasley Mining News
Hints of the enigmatic platinum group metals — platinum, palladium, rhodium, iridium, osmium, and ruthenium — have been found across Alaska.
“You have Goodnews Bay sitting there, and from Salt Chuck through Goodnews Bay, there is a whole belt of those Ural-Alaska types that could be explored,” said Dave Szumigala, former senior minerals geologist at the Alaska Department of Natural Resources Division of Geological & Geophysical Surveys.
For the fortune hunter seeking platinum, a town named after the elusive metal seems to be an obvious choice.
The Goodnews Bay district of Southwest Alaska, where the town of Platinum is located, is the only current platinum-producing region in the state. Though an economic PGM lode-source has yet to be found there, about 650,000 ounces of the rare metals have been recovered from placers of the Salmon River drainage. XS Platinum — an unlisted public company — is using modern gravity separation techniques to recover fine-grained platinum, palladium and gold left in the tailings of dredge operations of days gone by.
An Ural-Alaska-type ultramafic complex is believed to be the lode source of this historical placer production. Claims held by XS Platinum cover hardrock prospects that are believed to be the source of the precious metals found in the alluvial deposits.
Rock samples taken from an outcrop on Red Mountain at the head streams feeding the Salmon River returned assay results up to 2.27 grams per metric ton platinum. Geologists also discovered platinum and palladium enriched magnetite clinopyroxene veins in the area.
Prime hunting grounds The Wrangellia Composite Terrane — a series of associated assemblages that span some 1,250 miles from Southeast Alaska through Southwest Alaska is prime PGM hunting grounds.
During its heyday, the Salt Chuck Mine located on Prince of Wales Island in Southeast Alaska was the top palladium producer in the United States. From 1915 to 1941, this Southeast Alaska operation produced some 300,000 metric tons of ore averaging 0.95 percent copper, 1.96 g/t palladium, 1.12 g/t gold and 5.29 g/t silver, according to U.S. government summaries (1948).
Though Salt Chuck was never put back into production after its wartime shutdown, a 7,000-meter-by-1,600-meter mafic-ultramafic igneous complex is prospective for the metals recovered at the bygone operation.
Pure Nickel plans to test this prospective geology with a drill program scheduled for the last half of 2012.
From Salt Chuck to Brady Glacier, located some 300 miles to the northwest, a number of PGM prospects have been discovered along the entire Southeast Alaska Panhandle.
The Wrangellia Composite Terrane continues northward into Yukon Territory before arcing back into Alaska. Prophecy Platinum Corp.’s Wellgreen PGM-nickel-copper project is found in the assemblage as it sweeps through southwestern Yukon.
Pure Nickel Inc. is seeking similar ultramafic-associated mineralization at Man, a PGM-nickel-copper project located in Alaska’s Wrangellia Terrane about 250 miles northwest of Wellgreen.
In 2010 Pure Nickel discovered two horizons at Man reminiscent of the PGM-layered intrusions found at the Bushveld Complex of South Africa. One hole drilled that year cut 165.9 meters averaging 0.253 g/t platinum plus palladium. Horizon 2, included in this intercept, cut 0.318 g/t platinum and palladium over 24 meters.
Chip-Loy, located some 250 miles southwest of Man, is a cobalt-copper-nickel prospect that has geochemical markers associated with platinum metals.
Chip sample intervals from the deposit run up to 3.3 percent nickel, 0.25 percent cobalt, 2.1percent copper, 12.1 g/t silver, and 43.2 percent iron.
Tetradymite was found in the samples taken from Chip-Loy in the 1980s. Though this bismuth-tellurium-sulfide mineral is commonly associated with platinum, PGM have yet to be discovered at this prospect.
Intriguing sniffs While the Wrangellia Composite Terrane is considered the best place in Alaska to hunt for platinum, a number of prospects exist beyond this belt.
From the Seward Peninsula in western Alaska to the Fortymile district adjacent to the Yukon border, small amounts of alluvial platinum have been recovered as a by-product of gold mining. These anomalous occurrences underscore the potential of discovering PGMs across Alaska’s vast gold-producing districts.
The Valdez Creek Mining District, located about 65 miles southeast of Fairbanks, is one such region. According to a 1988 U.S. Bureau of Mines report, concentrates from 52 alluvial samples collected from placer gold streams in the district contained measurable quantities of PGM elements.
One sample from Gold Creek contained 3,100 parts-per-billion platinum; another sample from Tyone Creek measured 4,100 ppb platinum and 280 ppb palladium, while a sample from Fourth of July Creek returned 2,500 ppb platinum.
Late Triassic flood basalts characteristic of the Wrangellia Terrane have been found through the Talkeetna Mountains some 50 miles southwest of the known extent of the assemblage, according to a report by U.S. Geological Survey geologist Robert Kelley.
No ultramafic rocks have been mapped to date in this possible extension of the Wrangellia, but field geophysical data suggest the possibility of buried ultramafic bodies, and nickel-copper-PGM stream sediment geochemical anomalies occur in close proximity to the basalts.
“What’s intriguing is there are sniffs in a number of places. All it takes is for someone to come up with a model that makes sense, which could lead to a lot of exploration and/or discoveries,” observed Szumigala, who now works for Kinross Gold Corp. “But, with the conventional models, these little hits here and there have not evoked an exploration target looking totally at platinum.”
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