At the close of the 19th Century gold enticed fortune hunters from around the world to Alaska, a rugged and sometimes harsh land at the forefront of western expansion. Today, this Far North state, considered by many as the most mineralized province on Earth, continues to attract explorers seeking the yet to be discovered mineral riches of America’s Last Frontier.
The Arctic weather, rugged terrain, limited infrastructure and high exploration costs that challenged Alaska’s early gold seekers are still in – a situation that has helped keep the state’s vast mineral potential at the edge of exploratory expansion.
“Alaska hasn’t experienced near the amount of exploration that has taken place in British Columbia and the Yukon (Territory),” according to Millrock Resources Ltd. Vice President of Exploration Phil St. George.
Though the Far North state is regarded as largely unexplored, it has given up several world-class deposits over the past 20 years. Among these recent finds are two world-class deposits St. George was involved early on; Pebble, which is estimated to contain 80.6 billion pounds of copper, 107.4 million ounces of gold and 5.6 billion pounds of molybdenum, and the 40 million-ounce Donlin Creek gold project.
Geologists familiar with Alaska expect that more outstanding deposits lay hidden just below the surface of the vast and underexplored state.
“The thing about Alaska is there are a lot of low-lying areas out there that are covered with vegetation, glacial gravels and things that haven’t been explored thoroughly, or at all,” St. George explained. “I, and others, think there is a lot of potential to find other Pebbles, other Donlins, other huge gold systems.”
These huge systems are not just found in remote and logistically challenging regions of the state. A stone’s throw away from the road running north from Fairbanks to the oil fields of Alaska’s North Slope, International Tower Hill Mines Ltd.’s nearly 20-million-ounce gold deposit at Livengood is one such find.
First gold in Southeast
Alaska’s mineral potential was recognized in 1880 when Auk Chief Kowee, a Tlingit from Admiralty Island, led prospectors Joe Juneau and Richard Harris to the headwaters of the appropriately named Gold Creek. This find near what would later become the state’s capital brought a surge of gold seekers, who, over the following two decades, would make gold strikes over the entire state.
A year after the find by Juneau and Harris operations began at the Treadwell gold mine located southeast of Juneau. At its peak, Treadwell employed 2,000 Juneau residents and was the largest gold mine in the world. From 1881 to 1922, more than 3 million troy ounces of gold were extracted from the mine.
Following this initial discovery near Juneau, prospectors spread out over the entire length of the Southeast panhandle, finding not only rich deposits of gold, but also palladium, silver and copper. This heavily mineralized region of Alaska continues to give up significant deposits.
A 450-mile-, or 725-kilometer-, long belt of late-Triassic volcanogenic massive sulfide deposits stretches along the panhandle encompasses such metals-rich deposits as Niblack, Greens Creek, Palmer and, as the belt continues into British Columbia, Windy Craggy.
Anchored by Bokan Mountain to the south, 350-mile-, or 560-kilometer-, trend of more than two dozen rare earth element prospects covers much of the same area of Southeast Alaska.
Explorers find Tintina
Trekking into Alaska’s interior fortune hunters made the next big gold strike in the Fortymile District at the eastern extent of Alaska’s 109-million-acre portion of the Tintina Gold Belt, a rich gold province that arcs across the breadth of the state.
Two of the three operating gold mines in Alaska (Kinross Gold Corp.’s Fort Knox Mine and Sumitomo Metal Mining’s Pogo Mine) as well as International Tower Hill Mines’ Livengood project are all found in this eastern region of Interior Alaska.
Since the vastly rich deposits of placer gold were discovered on the gravel bars of the Fortymile River in 1886, more than 12 million ounces of alluvial gold have been recovered from the eastern half of the Tintina Belt, but the lode source of many of the historic mining districts has yet to be found.
Beyond Livengood, the Tintina Gold Belt arcs to the southwest. A 400-mile- or 645-kilometer-long belt of gold-rich terrain known as the Kuskokwim Gold Belt dominates this western extent of the Golden Arch.
Donlin Creek — being developed by Barrick Gold Corp. and NovaGold Resources Inc. — is the crown jewel of the Kuskokwim. Over the past several years, majors and junior explorers alike have scoured this region in search of other large intrusive-related gold deposits, uncovering several promising prospects.
Golden beaches of Nome
By the turn of the 20th Century fortune seekers had reached the gold-rich beaches of the Seward Peninsula of western Alaska, touching off Alaska’s best known gold rush. Over the ensuing century, some 10 million ounces of placer gold has been recovered there, while only 30,000 ounces of lode gold has been mined, making the region a prime target for modern explorers.
Though made famous by gold, the 20,600-square-mile, or 53,350-square-kilometer, Seward Peninsula is host to tungsten-enriched tin deposits at its western tip and rare earth element prospects to the east.
The tin-tungsten potential of the western Alaska isthmus is highlighted by the Lost River Mine, located on Cassiterite Creek about 6 miles, or 10 kilometers from the Bering Sea. Lode production from a historical mine here is said to include 5.6 tons of concentrate containing 3.5 tons of tin and 0.6 tons of tungsten in 1913 and 309 tons of tin in concentrate produced between 1952 and 1955.
In the 1960s two resources were calculated for the Lost River property; 200,500 tons grading 1.3 percent tin and 0.125 percent tungsten oxide (WO3) and 105,000 tons grading 0.76 percent tin and 0.6 percent WO3. Cape Mountain and Potato Mountain are two similar prospects in the region.
The Seward Peninsula’s rare earth potential is highlighted by a 50-mile-, or 80-kilometer- long trend of REE occurrences found were the isthmus connects to the rest of Alaska. In addition to REEs turning up in samples, this area hosts the right geology for deposits of these increasingly important metals.
“It is the same sort of geology as far as we know right now. It is one of those unusual type granites that tend to have these types of elements in them – uranium, thorium and the rare earths,” explained Alaska Department of Natural Resources Division of Geological & Geophysical Surveys Senior Minerals Geologist Dave Szumigala.
This is a high priority target for state geologists charged with assessing Alaska’s REE potential.
Bold explorers explore Brooks
At the height of the Nome Gold Rush adventurous prospectors were seeking gold along the southern slopes of the Brooks Range, a 600-mile-long chain of mountains dividing the oil-rich North Slope from the rest of Alaska.
By 1901 these bold explorers were finding gold in the cold streams of the Chandalar and Koyukuk-Nolan districts, north of the Arctic Circle. High-grade orogenic veins are the suspected source of the rich alluvial deposits and large gold nuggets found by the early fortune hunters of this region.
The western reaches of the Brooks Range is home to several high-grade sedimentary exhalative deposits. The most notable of these SEDEX deposits is Red Dog, being mined by partners Teck Resources Ltd. and NANA Regional Corp.
While extremely high zinc grades give Red Dog its distinction, the mine produced more than 6 million ounces of silver as a byproduct in 2010.
“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 there are Paleozoic rocks that are similar to Red Dog,” St. George said.
Anarraaq and Lik, located 7 miles, or 9 kilometers, and 14 miles, or 17.5 kilometers, respectively, from Red Dog, are two other known high-grade SEDEX deposits in the area.
The western half of the Brooks Range is also home to a belt of precious metals-enriched volcanogenic massive sulfide deposits. Arctic, being advanced by NovaGold Resources Inc., is the best known of these 400-million-year-old deposits.
Arctic is located in the Ambler District, a belt of VMS deposits that stretches at least 70 miles, or 115 kilometers, east-west. Similar Devonian-age VMS mineralization has been discovered as far as 140 miles, or 230 kilometers, east of the deposit. Hints of this Devonian age mineralization have also been found on the Seward Peninsula, about 200 miles, or 320 kilometers, to the southwest.
Though much of the VMS mineralization discovered in northern Alaska is very high grade, explorers have only scratched the surface due to its remoteness.
“It hasn’t been drilled off very well because it is so remote. People have just worked on the very near-surface mineralization, so there is a lot of potential at depth. There is potential for other Arctics. If there was some infrastructure or development starting to occur at Arctic, the (Ambler) district would probably get another generation of deeper, more thorough drilling,” St. George observed.
Building infrastructure to access Alaska’s natural resources is a priority for Alaska Gov. Sean Parnell and a road to the Ambler district is high on his to-do list.
“Another roads-to-resources goal is to complete environmental permitting, public process, and ultimately access the Ambler Mining District and its rich mineral deposits within five years. The Legislature and I joined forces on this piece with US$4 million during the 2010 session, and I’ve included US$1.25 million more in this proposed budget,” Parnell said.
Utilizing these funds, State of Alaska Department of Transportation & Public Facilities is studying potential transportation corridors connecting Ambler to Alaska’s contiguous infrastructure.
Though an exact route has yet to be determined, it would likely follow the footsteps of Alaska’s early gold seekers, taking off from the Dalton Highway about 200 miles, or 320 kilometers, north of Fairbanks and heading west along the southern slopes of the Brooks Range.
Hints of rare earth elements have also been found along the southern slopes of this mountain chain north of the Arctic Circle.
Porphyry belt, more
South of the Tintina Belt lies a band of mineral-rich terranes, or series of related rock formations, drawing the attention of modern day fortune hunters. This arc consists of the Wrangellia Composite and Kahiltna terranes, two interrelated but distinct assemblages.
The Kahiltna assemblage was formed when the Wrangellia Composite Terrane — which consists of three related terranes (Wrangellia, Peninsular and Alexander) — thrust up the ocean floor as it collided with Alaska.
Pumped with copper and gold-bearing fluids at least twice, the more than 400-mile-, or 650-kilometer-, long Kahiltna Terrane in Southwest Alaska is home to the Pebble deposit and is highly prospective for other world-class porphyry copper-gold and intrusive gold deposits. This region
“There are great indications of mineralization all around this Kahiltna Terrane, and I think an area play could really break out here,” Millrock President and CEO Greg Beischer told Mining News.
Though the Kahiltna assemblage is best known for its porphyry and other intrusive related copper and gold projects, the region also is highly prospective for other styles of mineralization.
“All over the Kahiltna Terrane keep your mind open to any style of mineralization — it could be VMS (volcanic massive sulfide), a skarn or a great big vein,” Beischer advised.
The Kemuk iron-titanium property, located about 100 miles, or 160 kilometers, west of the Pebble project, is one such project.
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. The deposit, hosted in magnetite-bearing ultramafic rocks, also is prospective for platinum group elements.
The Wrangellia Terrane, a subset of the larger composite terrane, stretches east from Southcentral Alaska through southern Yukon Territory and along the coast of British Columbia. This island arc is prospective for nickel, platinum group elements and copper-gold porphyries.
A 175-mile, or 280-kilometer, long area of rare earth element soil anomalies has also been outlined in this region along the southern slopes of the Alaska Range.
Yet another belt of young porphyries runs the length of the nearly 1,000-mile- or 1,600-kilometer-long Alaska Peninsula southwest of the Pebble deposit. The mineralization in this geologically active section of the “Ring of Fire” is much younger than the others, ranging from 10 million years to current.
Full Metal’s Pyramid project, on this island arc formed by the Pacific Ocean plate diving under the North American plate, hosts 125 million tons of near-surface copper mineralization grading 0.403 percent copper and 0.025 percent molybdenum. Exploration in the late 1980s identified associated gold values that have greatly improved the potential at the project.
Terrane wreck
Alaska can attribute its mineral wealth to multiple terranes dumping their payloads over its landscape. Geologists are still sifting through the wreckage of this terrane wreck — a task not always easily accomplished as pileups have resulted, in many cases, from multiple mineralization events intertangled in the same geographical regions over time.
“We have got all these mineral deposits and mining districts because the geology of Alaska is composed of rocks of multiple ages, formed by a wide variety of geological processes, arranged in these various terranes that slammed into each other in what is present-day Alaska,” explains Alaska Division of Geological & Geophysical Surveys geologist David Szumigala.
Coal, rare earth elements, tungsten, uranium, niobium and diamonds have been found amongst the gold, zinc, copper and other commodities that have spilled across the Far North landscape.
As economic deposits in other politically-stable parts of the world become harder to come by, fortune hunters will continue to follow the footsteps of Alaska’s early gold seekers in order to discover the unfound riches hidden in the terrane wreckage that makes up the Last Frontier.
