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Fortune Hunt Alaska: Wrangellia, prime PGM hunting ground A belt spanning Alaska hosts promising platinum prospects; intriguing sniffs around state Shane Lasley Mining News
For the explorer seeking platinum group metals — platinum, palladium, rhodium, iridium, osmium, and ruthenium — starting at a community that bears the name of the elusive element seems a good choice.
Platinum was founded shortly after the 1926 discovery of the rare metal that inspired the towns name by Yup’ik residents Walter Smith and Henry Wuya in the streams of the Goodnews Bay region of Southwest Alaska.
Anchored by Platinum in the west a 1,250-mile-, or 2,000-kilometer-, long series of associated terranes — dubbed the Wrangellia Composite Terrane — is prime hunting ground for platinum group metals.
“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,” explains Alaska Department of Natural Resources Division of Geological & Geophysical Surveys Senior Minerals Geologist Dave Szumigala.
Though an economic PGM lode-source has yet to be discovered in the Goodnews Bay region, about 650,000 ounces of the extremely rare metals were recovered from the placers of the Salmon River drainage. An Ural-Alaska type ultramafic complex is believed to be the lode source of this alluvial platinum.
Rock samples taken from an outcrop on Red Mountain at the head of a stream 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.
Following up on these finds, Pacific North West Capital and Stillwater Mining Co. undertook a 3,000-meter drill program in the uplands of the placer producing streams in 2008, but failed to pierce the platinum-bearing ultramafic body they were seeking.
Other Wrangellia discoveries Some 600 miles, or 1,000 kilometers, northwest of Platinum is Pure Nickel Inc.’s Man project, a prospect that is showing promise as a primary source of PGMs.
Though nickel was previously the primary target at Man, platinum and palladium grabbed the spotlight during Pure Nickel’s 2010 exploration of the Interior Alaska project.
The final hole of the 2010 season cut 165.9 meters averaging 253 parts per billion (0.253 grams per metric ton) platinum plus palladium. Horizon 2, included in this intercept, returned assays of 318 parts per billion (0.318 g/t) platinum and palladium over 24 meters.
A hole drilled in 2003 cut 2.7 meters of a little more than 1.1 g/t platinum and 1 g/t palladium. The significance of this intercept was fully recognized on the back of the 2010 results when the company realized these layers of PGM-enrichment share characteristics with Western Bushveld, a region of South Africa that produces some 70 percent of the world’s platinum and palladium.
Pure Nickel Chief Consulting Geologist Larry Hulbert, who studied in the Bushveld complex for five years, said, “The geochemistry of the drill core is starting to reveal that PGE mineralized horizons are present and that they are remarkably similar to that of the PGE-bearing reef environments seen elsewhere in the world,”
About 200 miles, or 320 kilometers, southwest of Man explorers are also finding platinum in the Wrangellia Terrane as it crosses into the Yukon Territory, adding to the potential of this belt.
Salt Chuck, another property owned by Pure Nickel, marks the southeast extent of Alaska’s PGM-prospective belt. This Prince of Wales Island property is adjacent to the historical Salt Chuck palladium-copper mine and covers a northwest-trending mafic-ultramafic igneous complex.
Salt Chuck palladium-copper mine is reported to have recovered 290,000 ounces of palladium and 6.2 million pounds of copper from 296,000 tons of ore mined between 1916 and 1941. The mine also produced significant credits of gold and silver.
More recently rare earth elements have also been discovered at Pure Nickel’s Salt Chuck property.
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.
According to a report by U.S. Geological Survey geologist Robert Kelley, late Triassic flood basalts characteristic of the Wrangellia Terrane have been found at least 50 miles, or 80 kilometers, southwest from the southern Alaska Range through the Talkeetna Mountains.
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.
The Kemuk iron-titanium property is another PGM prospect beyond the bounds of Wrangellia.
The U.S. Geological Survey estimated reserves on the project at 2.2 billion tons grading 15 percent to 17 percent iron and 2 percent to 3 percent titanium. Hints of the platinum metals have also been found in the magnetite-bearing ultramafic rocks at Kemuk.
From the Seward Peninsula in far west Alaska to the Fortymile district at the state’s eastern border, small amounts of placer platinum have been recovered as a byproduct of gold mining. These anomalous occurrences underscore the potential of discovering PGMs across the Last Frontier’s vast gold producing districts.
Linux Gold Corp. reports that soils samples collected near Dime Creek on the Seward Peninsula contain up to 174 ppb platinum, 144 ppb palladium and 160 parts per billion gold.
“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,” Szumigala explained. “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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