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Vol. 16, No. 19 Week of May 08, 2011
Providing coverage of Alaska and northern Canada's oil and gas industry

Fortune Hunt Alaska: Gold’s allure draws fortune hunters

Source of much of the placer gold that beckoned Alaska’s early prospectors remains unfound

Shane Lasley

Mining News

Gold’s allure has beckoned fortune hunters to Alaska since the 1880 discovery of the yellow metal in the streams near what would later become Alaska’s capital of Juneau. Over the ensuing 130 years the glimmering commodity has been recovered in nearly every corner of the Far North state, leaving only the oil-rich plains of the North Slope without a discovery.

Most of the some 42 million ounces of gold found in Alaska has been in the form of placer, leaving the lode source of many of these alluvial producing streams yet unfound.

Over the past two decades enormous gold finds such as Pebble, Donlin Creek and Livengood have been unveiled in Alaska and geologists familiar with the state expect that more world-class 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,” Millrock Vice President of Exploration Phil St. George, who played a key role in the discovery of Pebble and expansion of Donlin. “I, and others, think there is a lot of potential to find other Pebbles, other Donlins, other huge gold systems.”

Tintina Gold Belt

The Tintina Gold Belt is a particularly rich and vast aurum province that hosts such large Alaskan gold deposits as Fort Knox, Pogo, Donlin Creek and Livengood. These world-class discoveries only begin to account for the source of more than 17 million ounces of placer gold recovered from the streams of the Golden Arc, as the gold belt is sometimes referred.

Bound on the north by the Tintina fault and on the south by the Denali fault, the Golden Arc cuts a swath about 850 miles, or 1,350 kilometers, long across the middle of the state, averaging more than 200 miles, or 320 kilometers, wide.

The gold mineralization of the Tintina Gold Belt in Alaska can be divided into two distinct groups: the eastern portion of the belt, running from the Alaska-Yukon border about 300 miles, or 484 kilometers, into the state; and the 74,000-square-mile, or 190,000-square-kilometer, Kuskokwim Gold Belt of Southwest Alaska.

In addition to hosting two of Alaska’s three operating gold mines, the eastern half of Alaska’s Golden Arch is home to International Tower Hill Mines Ltd.’s nearly 20-million-ounce Livengood gold project. The intrusion-related gold mineralization in all three deposits is estimated to be about 90 million to 100 million years old.

Over the past 125 years more than 12 million ounces of placer gold have been recovered from the eastern extent of the Tintina Gold Belt in Alaska, but the lode source of the alluvial deposits of prolific mining districts such as Fortymile and Circle have yet to be found.

Rolling Thunder, an intriguing program launched in 2010 by junior explorer Full Metal Minerals Ltd., is a staking and exploration initiative targeting the source of more than half a million ounces of placer gold recovered from the streams draining the rolling hills of the Fortymile Mining District.

Recognizing that the belt of Cretaceous-age deposits, prospects, and placer gold mines of Yukon Territory’s White Gold District trends northwest into Alaska – Full Metal geologists surmised that similar mineralization could be the undiscovered lode of the alluvial gold producing streams in the neighboring Fortymile district on the stateside of the border.

Applying a firsthand understanding of the geologic controls, geochemistry and targeting methods that led to discoveries at White Gold some 60 miles, or 100 kilometers, to the southeast Full Metal geologists canvassed Alaska’s Fortymile gold district.

This reconnaissance sampling and mapping has identified multiple areas of strong alteration and quartz veining reminiscent of White Gold. Discoveries made with Rolling Thunder may lead to the source of the Fortymile alluvial gold, and aid the search for the lodes that fed placer streams across Alaska’s Eastern Interior.

Further west, more than one million ounce of placer gold found in the streams of the Circle Mining District, but the hardrock sources have eluded explorers. Located about 100 miles, or 160 kilometers, northeast of Fairbanks — this historical district has been mined continuously since 1894.

Kinross Gold Corp.-subsidiary Fairbanks Gold Mining Inc. recently staked a group of claims over a placer producing area in the district.

At the western end of the Golden Arc lies the Kuskokwim Mineral Belt, a 400-mile- or 645-kilometer-long gold-rich terrain that runs northeast from the Goodnews Bay region of Southwest Alaska. The gold mineralization found in this province was deposited by a widespread pulse of magmatism and mineralization about 70 million years ago, making it about 20 million years younger than the Fort Knox-type mineralization to the northeast.

The nearly 40 million-ounce Donlin Creek gold deposit — being developed by Barrick Gold Corp. and NovaGold Resources — highlights the potential of this Southwest Alaska province.

Over the past several years, majors and junior explorers alike have scoured the region in search of other large intrusive-related gold deposits, uncovering several promising prospects.

With more than 1.5 million ounces of alluvial gold recovered from its streams, Iditarod is the most productive placer producing district in the Kuskokwim Mineral Belt, yet only about 3,000 ounce of hard rock gold has been found here.

Famed for its enormous gold nuggets – including the 5th- and 13th-largest found in Alaska, at 122 and 62.5 troy ounces respectively – Ganes Creek is another example of the potential of this mineralized region of the Tintina Gold Belt.

Found in the Ophir Mining District about 25 miles, or 40 kilometers, west of McGrath, some 250,000 ounces of placer gold has been mined from Ganes Creek and an estimated 734,000 ounces of the alluvial aurum still remains. The coarse nature of the gold eludes to a nearby lode source.

Besides Donlin Creek-style mineralization, the Kuskokwim belt also hosts Nixon Fork, a carbonate skarn deposit rich in copper, silver and high-grade gold; several mercury-antimony deposits; and a large past-producing placer platinum deposit.

10-million-ounce peninsula

Since the 1898 gold strike made by the “Three Lucky Swedes” on Anvil Creek, just a few miles from present day Nome, an estimated 10 million ounces of gold has been recovered from the Seward Peninsula in Northwest Alaska. Though this 20,600-square-mile, or 53,350-square-kilometer, isthmus is one of the world’s most prolific placer producing regions, only about 30,000 ounces of lode gold has been mined there.

The rivers and beaches of the Nome Mining District itself produced more than half of the placer gold that lured tens of thousands of fortune hunters to this far western region of Alaska at the turn of the 20th Century.

“The (Nome) district has produced some 5 million ounces of alluvial gold. We certainly see the potential for additional targets there,” NovaGold Resources Inc. President Rick Van Nieuwenhuyse said.

NovaGold’s Rock Creek Mine, which was put on care and maintenance before reaching commercial production, is the only modern hardrock mine on the peninsula. The company has put the mine and the nearby Big Hurrah gold deposit up for sale.

With drills turning on two Seward Peninsula gold properties, Millrock Resources Inc. is amongst the most tenacious of the contemporary explorers in the region. This junior, in partnership with Kinross, completed around 2,500 meters of reverse circulation drilling at the Council project northeast of Nome last year. Following the Council program, Ryan Gold Corp., a Toronto-based junior then known as Valdez Gold Corp., funded a 5,000-meter drill program at Millrock’s Bluff property east of the famous mining town.

TintinaGold Resources Inc., a company formed as a spin-out vehicle for NovaGold’s exploration properties, completed 1,750 meters of drilling at Kugruk, a property about 70 miles north of Nome that hosts copper-iron skarns, silver-lead-zinc prospects and placer gold rich drainages. This program is the first drilling completed on the project since the late 1970s.

Further north still, Cedar Mountain Exploration Inc. is focused on seeking a near-surface, bulk tonnage sedimentary gold deposit at its Kelly Creek gold project.

Northern nugget country

Placer deposits in the Chandalar and Koyukuk-Nolan districts along the southern Brooks Range also drew fortune seekers at the turn of the 20th Century. High-grade orogenic veins are the suspected source of the rich alluvial deposits and large gold nuggets found in these placer districts located above the Arctic Circle about 200 miles, or 320 kilometers, north of Fairbanks.

An estimated 84,000 ounces of gold has been recovered from the Chandalar district. About 76,000 ounces of the yellow metal, or about 90 percent of the total, was alluvial gold found in the stream beds and frozen bench gravels. Most of the remaining 10 percent of the total was recovered from the Mikado Lode.

Goldrich Mining Co., a junior mining company that has claims over most of the Chandalar district, said Mikado is one of about 30 auriferous quartz-sulfide veins that are now documented on the property. Very little modern exploration work has been completed at Chandalar.

The Koyukuk-Nolan district, which lies directly west of Chandalar, has produced about 350,000 ounces of placer gold. The region is well-known for producing large nuggets. The third (146 troy ounces), fourth (137 troy ounces), 14th (61 troy ounces) and 17th (55 troy ounces) largest gold nuggets in Alaska were found on the Hammond River, a tributary to the Koyukuk River.

A lode source for these big nugget producing placers has yet to be discovered. Silverado Gold Mines Ltd., though, is drilling what it believes to be the source of the placer gold found in Nolan Creek, another large nugget producing drainage in the district.

World-class porphyries

At the largest known gold deposit in Alaska, the precious metal is actually a byproduct in a porphyry copper-gold-molybdenum system. The latest resource released by joint venture partners Anglo American plc and Northern Dynasty Minerals Ltd. estimates the Pebble deposit contains more than 107 million ounces of gold, along with its 80 billion pounds of copper and 5.6 billion pounds of molybdenum.

Knowing that porphyry deposits like Pebble are seldom an isolated occurrence, explorers are wondering if another enormous copper-gold deposit of this type lies hidden under the glacial gravels that cover much of Southwest Alaska.

“The discovery potential is very high for porphyry deposits generally in this arc environment, but I would also say that Pebble-look-alikes are probably not likely. However, this does not preclude the potential to find other large porphyry deposits with their own unique sets of characteristics. So, we should not over-focus on the Pebble model, but we should focus more on the favorable environment that Pebble represents,” Pebble Chief Geologist James Lang expounded.

The copper-gold-molybdenum was being deposited at Pebble during the same time period as much of the gold of Alaska’s Eastern Interior.

“At about the time Pebble was being formed (around 90 million years ago) there was an oceanic plate being subducted under Alaska called the Kula Plate, and that seems to have been a fairly productive time period where Pebble, Fort Knox, Livengood and Pogo were created from the oceanic plate and the current Pacific Plate that is subducting Alaska,” St. George explained. “The Kula Plate was still being subducted during the Donlin age.”

A belt of porphyry deposits that stretches from Southwest Alaska along the Alaska Range and into the Yukon Territory dates to the time Donlin age, or 65 million to 70 million years ago.

A belt of much younger porphyries can be found further southwest on the Alaska Peninsula and Aleutian Islands.

This island arc, formed as the Pacific Ocean plate dives under the North American plate, has received limited modern exploration and is prospective for both epithermal gold, and porphyry copper-gold mineralizing systems.

Several prospects have been identified along the nearly 1,000-mile- or 1,600-kilometer-long peninsula and island chain.

Full Metal has an agreement to explore around 1.4 million acres of prospective Native-owned land on the Alaska Peninsula. The Pyramid copper-molybdenum porphyry and Unga-Popov epithermal gold project highlight the potential of the region.

The Pyramid copper-molybdenum porphyry deposit hosts 125 million tons of copper mineralization grading 0.403 percent copper and 0.025 percent molybdenum near-surface. More recent exploration by Battle Mountain Gold in the late 1980s identified associated gold values that have greatly improved the potential at Pyramid.

Unga-Popov — which lies on an island about 20 miles, or 32 kilometers, south of Pyramid — hosts two historical resources; Apollo with 280,000 metric tons averaging 27.7 g/t gold and 92.6 g/t silver and Centennial, which has about 6 million metric tons at 1.5 g/t, or 290,000 ounces of gold.

Tomes to be written

Precious metals-enriched volcanogenic massive sulfide deposits, such as the Arctic deposit in Northwest Alaska and the Niblack deposit in Southeast Alaska, are another target for gold seekers looking to the Far North state.

An estimate completed in 2008 for NovaGold’s Arctic deposit outlined an indicated resource of 16.8 million metric tons containing 4.1 percent copper, 6 percent zinc, 0.83 grams per metric ton gold, 59.6 grams per metric ton silver and 0.94 percent lead. The estimate includes an additional inferred resource of 11.9 million metric tons with an average of 3.6 percent copper, 5.0 percent zinc, 0.67 g/t gold, 48.4 g/t silver, and 0.80 percent lead.

Even richer in gold, the Lookout deposit at Heatherdale Resources Inc.’s Niblack project contains an indicated resource of 4.14 million metric tons averaging 1.13 percent copper, 2.32 grams per metric ton gold, 2.27 percent zinc and 38.7 g/t silver. Lookout has an additional inferred resource of 1.74 million metric tons grading 1.09 percent copper, 1.77 g/t gold, 2.02 percent zinc and 25.52 g/t silver. The Trio deposit has an inferred resource of 756,000 metric tons averaging 1.5 percent copper, 1.75 g/t gold 2.91 percent zinc and 26.65 g/t silver.

Located in the eastern Alaska Range, Heatherdale’s Delta property represents an emerging VMS region in Interior Alaska. An inferred resource of 15.4 million metric tons grading 0.6 percent copper, 1.7 percent lead, 3.8 percent zinc, 62 g/t silver, and 1.7 g/t gold has been calculated for this property.

Explorers are also finding high-grade orogenic gold in Southcentral and Southeast Alaska, two regions notable for historical high-grade gold mines. Coeur d’Alene Mines Corp.’s Kensington gold mine in Southeast, the historical Independence and Lucky Shot gold mines in Southcentral are just a few examples of historical high-grade gold regions that hold promise for the contemporary fortune hunter.

Tomes can be, and have been, written about Alaska’s gold potential, and more chapters are sure to be added as fortune hunters continue to make new discoveries in this vast aurum producing state.

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