Thursday, February 10, 2022

North to Alaska - Gold!

Abandoned gold dredge, Flat, Alaska
On a cool, humid and windless day, my connecting flight from Anchorage likely wouldn't offer many amenities. After wandering around the airport, I found my gate and flight, a little Bearhawk with some 100 mph tape stuck to the wing and more scattered on the tail rudder. Inside, first class seating was held together by more duct tape with rolls of the life line sitting in the back seat. My pilot - Rob - welcomed all passengers aboard Flight-7 to Donlin Creek by announcing the flight was not full, so we were welcome to spread out. Where? I wondered. This old plane only had four seats and one occupied by the bush pilot. 

After the pilot announced our flight time would be about 1 hour and 45 minutes, I asked about the rest room? "If it comes to that, just hang it out the door. But remember, the cockpit forms a low pressure zone that will suck much of the waste back inside". So, no toilet, no movie, no peanuts, no coffee and no first class, but this is what I expected and I was greatly excited - this was my first trip to Alaska. It was 1988.

Back when Alaska was still part of the Russian Empire, explorers reported finding gold within stream gravels of Kenai River of southern Alaska in 1848. 
But by 1869, the first commercial gold cache was found in gravel at Windham and Sumdum Bays near the future site of Juneau, and within a year, the first attempt to mine lode gold occurred (1870) near the present site of Sitka (75-miles west of Juneau) near Sitka Sound. Nine years later (1879), n
uggets were found near the head of Gold Creek, southeast of  Juneau. 

Extensive copper mineralization was identified on the Prince of Wales Island (150-miles southeast of Sitka). These were noted, but because of extreme remoteness, they sat unexplored for years. Then in 1898, rich gold placers were discovered in the Seward Peninsula in western Alaska at Nome. This led to a gold rush, and thousands of prospectors headed to Nome. Four years later (1902), the next gold rush sent prospectors  to the Fairbanks region inland. 

Placers in Alaska are widespread, found in nearly every major river system and beach sands at Nome, Kodiak Island, Yakataga, Lituya Bay and the Cook Inlet. Since 1988, two major lode-gold discoveries were made at Donlin Creek and Pebble. These could result in world-class lode mines

Lode mineralization is associated with Mesozoic felsic plutons (granite, granodiorite) and volcanic rocks intruded in Precambrian and Phanerozoic age rocks in Alaska. The precious metal  has also been found throughout much of Alaska except vast uninhabitable swamps of the Yukon Flats and on the North Slope of the Arctic between the Brooks Range and the Beaufort Sea. In the vast central uplands and plains and in the Pacific Mountains to the south, numerous gold, silver and massive sulfide deposits are found. The central uplands and plains between the Brooks Range to the north and the Pacific Mountains to the south is a vast region of alluvial lowlands and eroded plateaus known for placer gold such as Seward, Koyukuk, Yukon and Kuskokwim uplands and peninsulas that overlook the broad flat plains of the Yukon River. 

The Kennecott mine, Nizina district, Alaska
In the Copper River region of the Pacific Range to the south, the bedrock is formed of Late Paleozoic to Quaternary graywacke, slate, and greenstone with lesser carbonates. Felsic (granite, granodiorite) and mafic (dunite, quartz diorite) intrusives invaded the basement terrain during late Mesozoic to early Tertiary. Mineralization includes copper, gold, silver, molybdenum, antimony, nickel, chromite, lead and zinc. Mines, such as the Kennecott copper operation near McCarthy in the Nizina district and in the southwestern and northeastern parts of Prince William Sound accounted for much of the copper produced in Alaska.

From 1869 to 2018, Alaska produced more than 48-million troy ounces of gold. Future exploration should focus on areas containing gold placers and examine the morphology of the gold grains, and then search for nearby source lode(s). For instance, rough gold having texture of corn flakes with rough edges, along with fragile nuggets and/or large nuggets, suggest a nearby lode source. Other types of gold deposits of interest will be polymetallic massive sulfide deposits, porphyry copper deposits, and replacement deposits. Being that Alaska is covered with large regions of marsh  and swamps, there will be many new discoveries in the future.

Southeastern Alaska

Admiralty Island district
Admiralty Island encloses the mining district identified by the same namesake, located adjacent to the Juneau district. The principal deposit on the island is the volcanogenic massive sulfides known as Greens Creek 16 miles south of Juneau. The Greens Creek mine is located in a complex silver-rich polymetallic massive sulfides in Late Triassic, Hyd Group metamorphic rocks. The mine is one of the largest silver operations in the world, and discovered in 1975. Production began in 1989. Much of the ore is found as silver-zinc-lead-gold-barium massive sulfides hosted by hydrothermally altered, complexly folded and faulted metamorphosed phyllite, argillite and lesser mafic volcanics. Mineralization is distinctly laminated and exhibits replacement textures. Sulfides include pyrite, sphalerite, galena, tetrahedrite and tennantite. In 2020, the operation yielded 10.5 million ounces of silver, 48,491 ounces of gold, 21,400 tons of lead, and 56,814 tons of zinc. Mine reserves (2020) plus resources include: 249.5 million ounces of silver, 1,853,000 ounces of gold, 652,170 tons of zinc and 254,840 tons of lead.

Gold mined in the Admiralty mining district is a by-product of silver and base-metal mining. At the Alaska Empire mine, gold and silver were recovered along with lead, zinc and copper in quartz veins hosted by metamorphic rocks. The deposit was discovered in 1919, and production averaged about 20,000 tonnes containing 0.25 ounce-per-ton gold (opt) in the mid-1930s. Several other properties are described in the district. The Funter Bay underground mine produced about 500 thousand tonnes of copper-nickel-cobalt ore, from a Mesozoic gabbro-norite pipe. In total, about 500,000 ounces of gold, almost all from the Greens Creek mine, was recovered from the Admiralty district.

Berners Bay district 
Forty to 45-miles north-northwest of Juneau, the Kensington underground mine in the Berners Bay district, produced 124,867 ounces of gold in 2020. The mine was dug on gold-quartz-veins with an average grade of 0.23 opt. The Kensington mine has multiple mesothermal quartz-carbonate-pyrite veins with discrete quartz-pyrite veins in Cretaceous diorite over a vertical extent of >2,500 feet. Gold occurs as gold-telluride (calaverite), and as inclusions in pyrite. Resources identified at the Kensington mine in 2020 amounted to 1,555,000 troy ounces of gold and 1, 853,00 ounces of silver, 

Chichagof mining district
Approximately 800,000 ounces of gold was mined in this district found on Chichagof, Yakobi, Baranof and smaller islands west of Juneau. In this region, numerous lode and placer prospects occur with major production from underground lode mines developed on gold-in-quartz veins.

Cinnabar (red) from Decourcy, Alaska, photo
by the author.
At the Apex-El Nido mines, 50,000 ounces of gold was recovered underground from polymetallic quartz veins. From 1922 to 1933 the Hirst-Chichagof produced 133,000 ounces of gold and 33,000 ounces of silver from the high-grade veins. Significant reserves remain, which attracted exploration in the 1980s and 1990s.

The Chichagof mine opened in 1905 and by 1942 the property yielded 660,000 ounces of gold and 195,000 ounces of silver from high-grade quartz veins. Several miles of workings were dug on 5-levels  accessed by 6 shafts dug to a maximum depth of 2,750 feet below sea level. Between 1981 and 1988 several thousand feet of new workings were dug.

Copper River Basin
Copper Basin is located about 15o miles east of Anchorage. To the north and west of the basin, the Kenai Peninsula-Cook Inlet region encloses the Susitna and Matanuska Rivers near Turnagain Arm, and is bordered to the north by the Alaska Range and south and east by the Chugach and Talkeetna Mountains. The region includes the Moose Pass, Hope, Homer, Seward, Girdwood, Turnagain Arm, Valdez Creek, Willow Creek and Yentna-Cache Creek districts. 

The Kenai Mountains to the south consist of limestone, chert and tuff (Triassic) resting on older metamorphic volcanic and clastic rocks. These Triassic rocks are overlain by Jurassic volcanics and deformed and metamorphosed Late Cretaceous slate and greywacke, that are locally intruded by felsic intrusives. The Tertiary age Kenai Formation contains coal inter-layered with sandstone and claystone that is an important source of oil and gas. Gold was initially discovered in the Kenai River, but it wasn’t until the 1890s that minable placers were found in the Turnagain Arm area to the north.

The first lode discovery in this region occurred in 1896 in the Moose Pass-Hope district to the southeast of Turnagain Arm; however, these fissure veins were small, even though rich. At the old Hirshey mine 8 miles southeast of Hope, mineralization included gold with arsenopyrite (arsenic-sulfide), galena (lead-sulfide), sphalerite (zinc-sulfide), pyrite (iron-sulfide) and chalcopyrite (copper-iron-sulfide) in quartz, calcite, ankerite gangue. Placers were found in the adjacent Palmer Creek and Canyon drainages from the Hershey mine, as well as in Crow, Resurrection, Bear, Mills, Falls, Copper and Valdez creeks. At Valdez Creek, the Tammany paleo-channel was discovered and mined by hydraulic and underground methods in the early part of the 20th century. Placers were also discovered in the Yentna-Cache Creek district in 1905. One of the more productive districts was found north of Palmer and Wasilla, where quartz diorite intruded schist. These rocks contain quartz veins in shear zones along the margin of the quartz diorite. Gold is found with pyrite, arsenopyrite, sphalerite and chalcopyrite. More than a million ounces of gold were recovered from the region.

Resurrection Creek was the site of Alaska's first gold rush in the late 1890s, and placer mining continues today. The Resurrection Creek watershed drains 161-mi2 on the north side of the Kenai Peninsula, and the community of Hope, Alaska is located at the mouth of Resurrection Creek. 

Gold was first reported at Willow Creek (also known as the Independence Mine/Hatcher Pass District) by Robert Hatcher. Hatcher discovered and staked the first lode gold claim in the Willow Creek Valley in September 1906. Through 2006, the district produced 609,000 ounces of lode gold and 58,841 ounces of placer gold

Gold was discovered near Valdez Creek in 1903. Valdez Creek, a tributary of the Susitna River in central Alaska. A 52-troy ounce nugget (Alaska's 18th-largest) came from Lucky Gulch, a tributary of Valdez Creek. Cambior's Valdez Creek Mine recovered over 75,000 ounces of gold annually, making it the largest placer operation in North America in 1992. Produced 459,162 ounces of gold from 1984 to 1995. Substantial reserves remain upstream of the active mine. The mine has been shut down and the site reclaimed, but other small-scale placer and lode deposits remain nearby.

Juneau District
In 1880 a local inhabitant, Chief Kowee, lead prospectors Joe Juneau and Richard Harris to gold in Gold Creek in Silver Bow Basin. The strike sparked the Juneau gold rush, which resulted in the development of many placer and lode mines including the Treadwell complex on Douglas Island. The town of Juneau was established at the discovery site. Over 7 million ounces of lode gold and 80,000 troy ounces of placer gold were recovered from the Juneau district.

Ketchikan mining district
Approximately 58,000 ounces of lode gold and 4,000 ounces of placer gold were produced in the  Ketchikan district. This district encloses DallPrince of WalesRevillagigedo, and smaller islands, as well parts of the mainland in southernmost Alaska. Historical lode mines and prospects were dug for base metals, uranium, rare earth metals, iron, platinum group metals, and gold within the district. Significant amounts of gold were recovered from underground lode mines (Gold Standard, Sea Level, Dawson, Golden Fleece, and Goldstream mines) dug on gold-bearing quartz veins hosted by metamorphic rocks; skarns (Jumbo and Kassan Peninsula copper-gold mines); zoned mafic-ultramafic plutons (Salt Chuck silver-gold-copper-platinum-group mine); and volcanic massive sulfides (Niblack). The Niblack mine is south of Myrtle Lake: 2011 resources were reported as 10 million tons of copper, gold, silver, zinc ore.

Petersburg-Sumdum district
15,000 ounces of gold were recovered from placers in the Petersburg-Sumdum district which consists of; ZaremboEtolin, and Wrangell Islands, and the mainland between the Juneau and Ketchikan districts. Many small lode deposits were identified from the late 1890s and early 1900s. The most significant lode was the Sumdum Chief, discovered in 1889 and operated until 1903. Approximately 24,000 ounces of gold were extracted from two quartz veins averaging ore of about 0.39 opt gold and silver. The mine reached a depth of 1,200 feet. 

Porcupine district
The town of Haines lies in-between the Chilkoot Inlet to the east, and the Chilkat Inlet to the west. Juneau is 75 miles south. The town of Haines is located within the Porcupine mining district. Skagway lies 15 miles north of Haines, while the Chichagof district lies to the south.

In 1898, placer gold was discovered on Porcupine Creek, 30 miles northwest of Haines. The placer became popular to America because of the second season of the 'Gold Rush' TV program, in which the  series featured the Big Nugget placer mine and John Schnabel. In 2020, the Constantine exploration company described potential sources for placer gold at the Big Nugget that include Golden Eagle and falls of McKinley Creek (a tributary of Porcupine Creek), where the former US Bureau of Mines, identified anomalous rock samples at the Golden Eagle assaying nil to 531 g/t gold! At McKinley Creek falls, the USBM collected grab samples of rock that assayed 1.37 to 8.69 g/t gold in quartz-sphalerite veins. One 2.5 chip sample assayed 24.83 g/t Au and 280 ppm Zn.

A total of more than 81,000 troy ounces of placer gold was mined in the district, from Porcupine, Glacier, Nugget and Cottonwood Creeks. The area around the Reid Inlet in Glacier Bay National Park and Preserve, includes some lode prospects, such as the LeRoy mine, which was dug on quartz veins and yielded 10,000 ounces of gold. 

South-Central Alaska
Chulitna-Yentna Belt
The Chulitna-Yentna mineral belt extends northeastward 100-miles along the southern flank of the west-central Alaska Range. The belt lies nearly parallel to the trend of sedimentary and volcanic strata, major faults, lineaments and the elongation of of intrusive masses. Epigenitic mineral deposits aline with the trend of the belt. According to the USGS, arsenic and gold are characteristic of mineral deposits throughout this belt that shares tectonic features comparable with some well-known mineral belts of the western Cordillera, including the Juneau gold belt. 

The Golden Zone Mine within this belt, forms a pipe-like breccia in the Bryn Mawr creek basin that produced 1,581 ounces of gold, 8,617 ounces of silver, 21 tons of copper and minor arsenic and zinc. Measured and indicated resources of the mine are reported to include 1.68 million tonnes with an average grade of 4.33 g/t Au, 20.94 g/t Ag, and 0.11% Cu. An inferred resource of 186,181 tonnes at an average grade of 1.52 g/t Au, 6.49 g/t Ag and 0.4% Cu. Ore minerals include arsenopyrite, chalcopyrite, pyrite, sphalerite, and tetrahedrite in a gangue of calcite, quartz and sericite.

Recent work indicates mineral reserves of the Pipe, Bunkhouse and Copper King deposits as 13.3 million tons grading 0.095 ounces per ton of gold.

Yentna Cache-Creek district
Gold was discovered in the Yentna District (aka Cache Creek District) of the upper Susitna Valley in 1898Placer mining was reported in the Cache Creek drainage of the Dutch Hills by 1906. Quaternary glaciofluvial deposits, alluvial deposits, and Tertiary conglomeratic white quartz-breccia units were mined in the Dutch Hills. About 200,000 ounces of gold has been produced from the placer deposits.
Willow Creek Mining District

Southwestern Alaska
A giant, 9 billion tonne ore deposit, known as the Pebble copper-gold porphyry was discovered in the mid-1980s west of Cook Inlet and northwest of Iliamna, Alaska. This is one of the largest Cu-Au porphyry deposits in the world hosting a minimum of 72 billion pounds of Cu, 94 million ounces of Au, and 4.8 billion pounds of Mo. The deposit lies within a environmentally sensitive area, and is hosted by porphyritic granodiorite and tonalite (Upper Cretaceous) intruded into deformed sedimentary rock (Jurassic to Cretaceous).

Nuggets nuggets recovered from Julian
Creek, 1988, photo by the author.
The ore body (86 to 89.5 Ma) is exposed at the surface and continues >5,500 feet deep. In the western part of the deposit, mineralization is in complex granodiorite cupolas, diorite sills, older intrusions, breccias and sediments. This part of the deposit is exposed at the surface and expressed as gossan (rusty rock). The ore body extends eastward across a fault contact at depth. East of the fault, mineralization is found in abundant sills and in intruded sediments. Farther east, and deeper, the sills coalesce into a deeply-buried mineralized granodiorite pluton. The eastern extent of the deposit is overlain by Tertiary sedimentary and volcano-sedimentary rocks. Sulfide and oxide ore minerals include pyrite, chalcopyrite, molybdenite (molybdenum sulfide), bornite (copper iron sulfide), minor covellite (copper sulfide), chalcocite (copper sulfide), digenite (copper sulfide) and magnetite (iron oxide).

Kuskokwim Gold Belt
Further west and north of Pebble, is the Kuskokwim Gold Belt: a broad belt of country that forms an 300 mile across southwestern Alaska. It lies northwest of the Alaska Range and is centered on the Kuskokwim River basin. Geologically it is dominated by flysch of Cretaceous-age Kuskokwim Group sediments and a variety of igneous rocks. 

In 1913, Alfred H. Brooks described the terrain as, "a more or less broken belt of gold-bearing rocks which stretches northeastward from Goodnews Bay parallel to the lower course of the Kuskokwim, toward the Iditarod District, and a number of streams traversing this belt carry auriferous gravels." The belt lies mostly within the southwestern part of the Tintina Gold Province which lies roughly between the Denali-Farewell and Kaltag-Tintina fault systems that arc north from southwest Alaska, through central Alaska, and down across the Yukon Territory to British Columbia.

The Kuskokwim Belt includes all or parts of several historic mining districts including: Aniak/TuluksakAnvikBethelGoodnews BayIditarod-FlatInnokoMarshallMcGrathRuby, and Tolstoi. More than 3.2 million ounces of gold have been recovered from the belt. The first mineral discovery by the Russians in Alaska (a cinnabar-stibnite deposit) occurred in the Aniak district in 1838. Commercial amounts of gold were found in 1901 in tributaries of the Kuskokwim River in the Aniak district.

Aniak mining District
About 220,000 ounces of gold produced from the Tuluksuk River at the village of Nyac ( 61°0'19"N; 159°56'13"W). Gold was also recovered from the Crooked Creek basin with lesser amounts at Wattamuse. Mining continues at present, but reserves are unknown. Cinnabar (mercury-sulfide) and native mercury occurs in many placer mines in this district.

Anvik-Marshall District
The Marshall and Anvik districts produced 124,000 troy ounces of gold and minor amounts of platinum, mainly from Wilson Creek. The Bering Sea lies west, the Yukon River to the south, and the Iditarod and Kaiyuh districts to the east.

Donlin Creek District
Placer mining began on benches and tributaries on the east side of Crooked Creek and its tributary Donlin Creek in 1910. Granitic dike swarms cutting the shales and sandstones of the Kuskokwim Group rocks in the hills east of upper Crooked Creek were identified by USGS geologists in 1915 as the probable source of the placer gold.

In the 1970s Calista Corporation (an Alaska Native Corporation), as part of its land grant under ANSCA selected land east of Crooked Creek based on mineral potential. In 1986 modern hardrock exploration of the Donlin area began with WestGold (a subsidiary of DeBeers and Anglo American), which was abandoned after a few years due to company politics. Even so, a world-class discovery was made by WestGold geologists. 

Placer Dome later signed a lease with Calista and began exploration at Donlin in 1995. That effort continues today, having evolved to a 50:50 partnership between Barrick Gold and NovaGold Resources, in cooperation with Calista, the landowner. 

If eventually exploited, the mine will be an open pit several miles wide. Estimates report that Donlin contains 46 million ounces of gold. The gold occurs within the crystal lattice of arsenopyrite and stibnite in veins, veinlets, and disseminations mainly in the felsic dikes, but also in less common altered mafic dikes and in the sediments.

Placer gold is found in nearby Omega, Lewis, Quartz, Ruby, Snow and Queen Gulches. The gold includes pristine gold flakes and fragile nuggets suggestive of a nearby lode source, which attracted the attention of WestGold's geologists in the 1980s. As a result, geologists of WestGold discovered a large disseminated gold deposit with >5-mile strike length. Donlin Creek is similar in size to the legendary Homestake mine (which produced a total of 41 million ounces during its lifetime) and hosts as much gold as has been mined in all of Alaska from the 1869 to 2007! 

Pristine gold nugget attached to rounded pebble, Snow Gulch,
Alaska. Such nuggets provide evidence of regeneration of gold
possibly related to organic deposition (Paul Graff, personal 
communication, 1988 (photo by the author).
Donlin Creek mine is one of the largest undeveloped gold deposits in the world with an estimated 46 million ounces of gold. If developed based on 2009 plans, the property will become one of the largest gold mines in the world. Mine permit applications were submitted in 2009. The deposit consists of a group of felsic sills and dikes that host gold in association with quartz veinlets and breccias. The higher gold values are associated with arsenopyrite and stibnite (antimony iron sulfide) and associated with sills that intrude a thick sequence (>5000 feet) of folded graywacke, sandstone, and shale. Mining is anticipated at 1.5 million oz/yr from ore with average grade of 0.07 to 0.08 opt Au.

In the region, gold at Julian Creek, about 25 miles northeast of Donlin Creek, was described by WestGold geologists as being in a similar geologic setting as Donlin Creek. 

Mercury-gold anomalies occur at DeCourcy, 8 miles to the west of Donlin Creek. Placer gold was also mined at Flat Creek, 25 miles northeast of Donlin Ceek. 

Ganes Creek
Ganes Creek placers are 80 miles northeast of Donlin Creek and 30 miles west of McGrath. Ganes is famous for spectacular gold nuggets including the 5th (122-troy-ounce) and 13th-largest (62.5-troy-ounce) in Alaska. The presence of cobble-size quartz with sulfide boxwork along with coarse gold suggest that gold in the placer originated from nearby bedrock sources. Historical production figures from Ganes Creek are in excess of 250,000 oounces; an additional estimated resource of 736,000 ounces of placer gold exists on patented claims. The area has considerable dredge tailings.

Goodnews Bay District
The Goodnews Bay district along the edge of the Bering Sea produced about 600,000 ounces of platinum (plus some iridium, osmium, ruthenium, palladium, and rhenium) and 27,000 ounces of gold from placer deposits in the Salmon River from 1934 to 1976. Extensive dredge tailings (58°55'8"N; 161°42'24"W) are visible in the area. The source of platinum-group metals may be from nearby Red Mountain and Susie Mountain ultramafic rocks to the north of the placers. Extensive geochemical and geophysical surveys identified areas with as much as 0.1 ounce per ton platinum in the soils, but no reserve has been demonstrated.

Iditarod District
The Iditarod district lies between the lower Yukon and Kuskokwim Rivers: the Aniak district abuts it to the south. A gold rush followed discovery of gold on Otter Creek in 1909, where over 1.5 million ounces of placer gold and a few thousand ounces of lode gold have been recovered from the Iditarod area, making it one of the more important gold districts in Alaska.

Innoko District
The Aniak district lies to the south, the Tolstoi district to the west. About 750,000 ounces of placer gold was mined from Innoko River and tributaries in the district. Cripple, Colorado, Yankee, Games, Ophir, and Little Creeks had prominent placer mines, but a third of the district's production was from Ganes Creek. Gold-bearing porphyritic intrusive rocks adjacent to the Ganes Creek and Colorado Creek placers are similar in composition and age to the dike swarms at Donlin Creek.

McGrath-McKinley district
About 200,000 ounces of lode gold and more than 130,000 ounces of placer gold were mined in the district located on the northeast flank of the Aniak district. The Nixon Fork mine was an underground lode gold-copper mine located 32 miles northeast of McGrath, Alaska

Placer gold was discovered nearby in 1917, by 1918 hardrock mining began and continued intermittently until 1964. Ore consists of shoots of massive sulfides and native gold found with skarns along the contact of sedimentary rocks and the Mystery Creek quartz monzonite stock. The mine was reopened in 1995 and operated until 1999. In 2005, resource and exploration development resumed. Gold production occurred in 2006 and 2007, and again from 2011 to 2013. Production has totaled 187,000 ounces of gold, 2,190,000 pounds of copper, and at least 11,000 ounces of silver.

The Nixon Fork mine was developed on high-grade gold-copper skarn (Bluemink, 2009). Eighty miles north of the Nixon Mine, placers in the Ruby district Alaska, include several sizable nuggets including the largest in Alaska – a 294-ounce nugget found on Swift Creek in 1998. Nuggets have also been found at nearby Long Creek, Poorman Creek and Moose Creek. The presence of several sizable nuggets indicates that a nearby hidden rich lode (or lodes) likely remains to be found: 75 to 100 miles southwest of McGrath, placers in the Georgetown district were mined at Snow Gulch and Julian Creek. South of McGrath, 1.7 million ounces of gold is reported at the Vinasale gold project art Vinasale.

Tolovana River District
The Tolovana River district lies 60 miles northwest of the Fairbanks district along the Tolvana River. Lode mineralization at the Livengood Mine occurs in a thrust sequence of Proterozoic to Paleozoic sedimentary and volcanic rock with the gold mineralization (90 Ma) associated with a dike swarm. The gold is associated with arsenopyrite and pyrite in quartz veins. The project hosts 8.97 million ounces of gold. Just 2 to 3 miles southeast of Livengood, are extensive gold placers along Olive creek. Other placers include Amy, Lillian, and Griffin creeks. In 1968, the USGS investigated potential for lodes in the area and described gold mineralization in veins in Amy, Lillian, Ruth, and Griffin creek drainages.

Tolstoi District
The Tolstoi Creek drainage is a north-flowing tributary of the Dishna River, and roughly defines the location of this district. The district is east of the Iditarod and Innoko districts. Placer gold and platinum were discovered by drifts dug in frozen gravels 35-feet deep on Boob Creek in the winter of 1915–1916. A gold rush to the district in the following winter resulted in production of 11,000 ounces of gold, as well by-product platinum.

Interior of Alaska (north of Yukon River)

Two drainages that empty into the Kotzebue Sound of the Bering Sea, include Noatak River and Kobuk River. These rivers define the locations of the Kiana, Shungnak, Noatak, and Selawick districts. The Noatak district is now within the Noatak National Preserve

Brooks Range district
The Red Dog mine ( 68° 4'34"N; 162°51'5"W) in northwestern Alaska, lies at the western extent of the Brooks Range, to the east of Kavilina. This world-class zinc-lead open pit mine (world's largest producer of zinc) mines considerable sphalerite (zinc-sulfide) with significant amounts of galena (lead-sulfide) and millions of ounces of silver. The deposit is classified as a stratiform Zn-Pb-Ag, sediment hosted, massive-sulfide deposit hosted by Carbonfierous black shale and altered carbonates.

Chandalar mining district
The Chandalar district is the area around the upper drainage of the Chandalar River, includes some southern foothills of the Brooks Range, and extends to the crest of the Brooks Range. Discovery of placer gold in 1906 was quickly followed by lode discoveries. Most of the placer-producing creeks drain the area of lode mineralization. The district produced about 48,000 ounces of placer gold and 17,000 ounces of lode gold.

Little Squaw Creek drains an area cut by many auriferous veins. Some of the placers in the basin are exceptionally rich. By 1916 most of the shallow placers were playing out so miners shifted their interest to the placer drift mines. The most notable of these is the Little Squaw Bench, including the Mellow Bench. Approximately 29,000 ounces of gold were recovered averaging 1.0 oz/cubic yard of gold in the gravels with spikes of up to 4.6 oz/cubic yard. Some individual nuggets were over 10 ounces. In 2010, gold production resumed with mining of the placer deposits.

In 1909 to 1915 development and underground gold mining occurred at the Little Squaw, with a few hundred feet of workings built and a few dozen ounces of gold recovered. The nearby Mikado mine enjoyed similar efforts around 1913. In the 1960s, 1970s and 1980s additional work was done. These later efforts probably recovered more than 10,000 ounces of gold. Significant efforts resumed in 2006, and are ongoing, to explore the Little Squaw placer and lode deposits.

Few roads exist in Alaska, and access to many communities is by bush plane.

Hughes District
The Hughes district extends into the lower Koyukuk River basin, where much of the area is swampy, lake-studded lowland and into the adjacent hills. Placer mines in the Zane Hills on Bear Creek, a tributary of the Hogatza River, are a source of gold from the district. Placer deposits clustered near the village of Hughes and Indian Mountain are the other significant source of placer gold from the district. The district has produced about 245,000 ounces, with traces of copper, lead, zinc, tin, silver and platinum.

Kiana district
Placer gold was discovered on Klery Creek in 1909 within the Kiana district. More than 40,000 ounces, for gold was mined from this area from placers in tributaries of Squirrel River. Mining has been nearly continuous in this area since discovery. Nephrite jade also occurs in this area.

Kobuk River
In 1898, placer and lode gold were discovered on several of the Kobuk River's tributaries. The gold strike (by some accounts was a fraud) attracted nearly 2,000 people to Alaska, though only 800 actually stayed to find gold. Although mining has continued to take place in this area, little gold has been discovered.

Koyukuk-Nolan district
The district encompasses the upper Koyukuk River basin including the Alatna and Kanuti rivers and the village of Bettles. The district extends from the southern flank of the Brooks Range to the northern Ray Mountains, and is directly west of the Chandalar district. Much of the district is now in Gates of the Arctic National Park. Gold was discovered in placer deposits in the district in 1901. About 350,000 ounces of placer gold have been won from the area, perhaps 85% of it from near Wiseman. Mining continues today in the district. Much of the district is underlain by bedded Paleozoic rocks, a schist belt extends along the southern foothills of the Brooks Range. Cretaceous plutons intrude metamorphic rocks in the southern part of the district. Pleistocene ice sheets from the Brooks Range and cirque glaciers in the Ray Mountains covered much of the higher elevations. Glaciers are now restricted to the highest cirques of the Brooks Range.

Miners produced 235,000 ounces of gold from Nolan Creek between 1904 and 1999. Some of the placer gold is mined by underground methods in frozen gravels. A 42-troy ounce nugget, Alaska's twentieth-largest, came from Marys Bench on Nolan Creek. Placer mining activity continues, with a reserve of 214,760 ounces of gold reported in 2000.

Mining occurred on the Hammond River, a tributary of the Koyukuk River, from about 1900 to at least 2000. Exact production is unknown, but is estimated at about 80,000 ounces.

A rich, deep channel was struck beneath the Hammond River in 1912, and during the following 4 years, over 48,000 oz gold were produced. This area has also been very productive for large gold nuggets. These include a 138.8-oz nugget. Other nuggets include: the 3rd (146-troy ounces), 4th (139-troy ounces), 14th (61-troy ounces), and 17th (55-troy ounces) largest nuggets in Alaska found on the Hammond River between Discovery claim and Vermont Creek a distance of 4 miles. Only the richest ground was possible to mine as the Hammond River was one of the most remote placer districts in North America until 1975, when the Dalton Highway for the Alaskan Pipeline project was completed. 

Historically the Hammond River is one of the largest gold producers in the Koyukuk district. Gold was discovered on the Hammond River, just above the lower canyon mouth, about 2 miles upstream from the Koyukuk River. In the early years, attempts were made to mine the modern stream gravels. At the mouth of Swift Creek a wing dam was built to divert the river for mining, but numerous cobbles and small boulders made the venture unprofitable. Approximately 500 ounces was recovered with pick and shovels in Summer of 1902. Later, shafts sunk 66 feet to bedrock at the discovery site were reported to show the presence of gold in paying quantities. The majority of the gold production on the Hammond came out of the deep channel as early miners were unable to deal with the water and cobbles in the present river channel.

The Hammond River contains deep channel, bench, and modern stream placers. Much of the Hammond River gold is of the coarse nugget variety. Several nuggets weighing from 45 to 59 oz were found in the early days. In 1914, a 138.8 ounce nugget (4th largest in Alaska) was found in a mud-filled crack on bedrock near Gold Bottom Gulch (Engineering and Mining Journal, 1915, p. 1021).

In 1914, on No. 4 Above, Hammond River (Goldbottom Gulch), J. C. Kinney and partners picked up nuggets from bedrock valued at about $20,000; one nugget, the second largest ever found in Alaska, was worth $2600. The rest of the dump when sluiced yielded a little less than the value of the "pickings." (Engineering and Mining Journal, 1914, 62 v. 98 no. 24. (Gold at $20.00 per ounce.)

Placers on Slisco bench, an ancient buried channel of Hammond River near Vermont Creek on the west side of the present Hammond River contain a measured resource of 31,099 ounces gold at grades of up to 0.3 oz/yd3. Inferred resources on the same bench range from 50,000 to 150,000 ounces. Other benches of Hammond River between Discovery Claim and Slisco Bench have similar potential but have not been systematically prospected with modern technology.

Melozitna District
On the northern side of the Yukon River, between the Melotizna and Ray rivers, most of the district is rolling ridges with highest elevations over 5,000 feet (1,500 m), where now-gone Pleistocene cirque glaciers developed. Placer gold was discovered in 1907, but activity was sporadic and poorly recorded. About 10,000 ounces of gold, with significant by-product tin, was won from placer deposits by the 1960s.

Shungnak district
All of the 15,000 ounces of gold recovered came from streams draining the Cosmos Hills, a low range along the Kobuk Valley. Gold was discovered on Dahl Creek in 1898, which was the major producer. Copper, chromium, cadmium, and silver, were also recovered with the gold.

Interior of Alaska (south of Yukon River)
Circle district
More than a million ounces of gold were recovered from placers in the Circle district along the Yukon River, west of Canada. Uplands with thousands of feet of generally mild relief are underlain by a complex metamorphic terrain intruded by a broad range of igneous rocks. Many gold occurrences are known, but no lodes are identified. Placer mining has been reported for every year since 1894.

Council-Solomon District
The district, located about 40 miles east of Nome, produced over a million ounces of gold.

Eagle district
This small district includes the village of Eagle on the Yukon River bordering Canada. About 50,000 ounces of gold, all from placer deposits, has been recovered from the district since gold was discovered in 1895 on American Creek and the Seventy-mile River.

Fairbanks district
Placer gold was discovered near Fairbanks in 1902, after Felix Pedro and Tom Gilmore discovered gold in the hills north of the Tanana and Chena rivers in 1901. These two rivers converge at Fairbanks. The district is a major producer of gold from both placer and lodes: placers yielded more than 8 million troy ounces, and lodes yielded more than 4 million ounces of gold.

Significant lode gold production at the Fort Knox open pit mine in the Tanana River region northeast of Fairbanks resulted in 237,925 ounces produced in 2020. The Fort Knox mine, located 15 miles northeast of Fairbanks, is a low-grade (0.024 opt Au) ore body consisting of finely disseminated gold in Cretaceous porphyritic granodiorite, and along margins of quartz veinlets and vein swarms controlled by NW-structural trends. Satellite deposits of Fort Knox include the inactive True North pit about 7 miles west, and the Gil-Sourdough deposit about 8 miles east.

The Gil property has gold localized in quartz-sulfide and quartz-carbonate veins, clay-filled shear zones, and limonite-stained fractures that crosscut lithologies. At Main Gil and South Sourdough, gold is stratabound within calc-silicates, within veins and joints in the highly fractured rock. At North Gil and North Sourdough, gold is associated with quartz veins. These lie in quartz-mica schist, feldspathic schist, and calcareous biotite-chlorite-quartz schist. The veins are small, milky quartz-arsenopyrite, quartz-calcite, and quartz-feldspar veins.

Nearby creeks draining the Fort Knox granodiorite include some of the more productive placers in the district. These placers led to exploration and subsequent discovery of the lode, and production commenced at Fort Knox in 1997: 2020 total drilled reserves and resources are estimated at 4.96 million ounces. 

Nearby gold properties include the True North open pit mine, the Amanita prospect, and many placers in Fairbanks, Cleary, Nugget, Smallwood, Last Chance, Johnson, Victoria, Ester, Chatham, Dome, Wolf, Moose, Too Much Gold and Kokomo creeks, as well as the Chatanika river placers. 

Fairhaven Inmachuk District
The Fairhaven-Inmachuk district lies north of the Solomon District and extends north to Kotzebue Sound of the Chukchi Sea. The district (including Candle) produced about 600,000 ounces of gold with minor amounts of chromium, copper, lead, platinum, bismuth, tungsten, mercury, molybdenum, silver, and rare-earth elements.

Kougarok district
The district is the central part of the Seward Peninsula, draining into the Imruck Basin. Gold was discovered in 1900 and production from placer mines continues to this day. 177,000 ounces of gold have been recovered from the Kougarok district.

Koyuk district
84,000 ounces of placer gold came from the district, the southeastern part of the Seward Peninsula. Major producers were; the Ungalik River and its tributary, Bonanza Creek, which produced significant by-product tin, and Dime Creek, which also produced significant platinum. The district encompasses the basins of the Koyuk, Inglutalik, Ungalik, and Shaktoolik Rivers, all draining into northeastern Norton Sound.

Dr. Paul Graff looks at abandoned monitor in Alaska, 1988
Nome District
In the Seward Peninsula, within the Nome Mining District along the west coast of Alaska, is the site of a historical gold rush that involved some 20,000 prospectors who constructed a lawless, wild-west tent city on the beachfront tundra following placer gold discoveries in 1898. Only limited amounts of gold were initially found in the region leaving most prospectors penniless until someone panned beach sands resulting in a major discovery. Gold was found in the beach and traced over tens of miles up and down the beach from Nome. Gold was also found along Anvil Creek to the north, which was a source of several large nuggets including the second-largest found in Alaska (182 troy ounces) suggesting possibilities for hidden lode deposits.

Hardrock mines near Nome include Rock Creek and Big Hurrah. Rock Creek was originally a placer exploited in the 20th century. Early prospectors explored underlying rocks and found gold in a cluster of low-grade sheeted gold-sulfide-quartz veins in deformed metapelite (mica schist) that were uneconomic. However, at higher gold prices in the 21st century, the property was considered for mining. Construction began in 2006, a few miles north of Nome. The mine produced ore in 2008 until design flaws in the mill resulting in termination of operations two months later. 

The Big Hurrah, the largest underground mine in the Seward Peninsula (40 miles east of Nome) initially operated in 1908 with only sporadically production. The mine is underlain by the Nome Group (metapelites containing mixed mafic schists, metapelite, calc schists and marble). The main ore body is known as the Abion vein, a sheared quartz vein breccia with fine-grained sulfides. Combined resources for the Big Hurrah and Rock Creek mines are 510,000 ounces of gold with another 32,000 ounces of indicated and inferred resources. Ore grades average 0.05 opt Au.

Placer gold deposits on Anvil Creek and on the Snake River, a few miles from Nome, were discovered in 1898 by "Three Lucky Swedes". Word of the strike caused a major gold rush to Nome in the spring of 1899. Over 3.6 million ounces of gold have been recovered from the Nome district, almost all of it from placer deposits. The Rock Creek mine, owned by Bering Straits Native Corporation, was constructed in 2007 by NovaGold Resources. The mine began producing gold in September 2008, but ceased two months later due to difficulties with the ore crushing and grinding circuit. 

Port Clarence district
Mainly a tin district, the westernmost Seward Peninsula, 42,000 ounces of placer gold have been recovered, much of it as a by-product of tin mining.

Hot Springs District
This district, which produced about 576,000 ounces, includes placer mines at Manley and Eureka.

Kaiyuh-Ruby Districts
The Illinois Creek mine is located in the remote Kaiyuh Mountains of west-central Alaska about 40 miles (64 km) south of the Yukon River village of Galena. The Illinois Creek lode gold-silver mine exploited a shear-hosted gold deposit which was partly expressed as color anomalies visible from aircraft. Located on State of Alaska land, it was discovered in the 1980s. In February 1996 a feasibility study was completed, with the deposit estimated to contain about 350,000 ounces of gold and 2,500,000 ounces of silver. Construction began the next month, but was halted by winter conditions in November. By then, with the development uncompleted and six-million more than the total mine construction-and-operating budget of 26-million dollars already spent, USMX, the mining company that owned Illinois Creek, was millions of dollars in arrears on invoices and short on cash. New financing allowed construction to resume in 1997; the mine poured its first gold in June 1997. In 1998 the company entered bankruptcy. In 1999 the State of Alaska assumed control of the mine. A mine-to-reclaim arrangement between the state and a newly involved mining contractor resulted in the reclamation and closure of the mine by 2005. A bond is in place to provide environmental monitoring for 30 years. 

Rampart district
Nearly 200,000 ounces of gold was recovered from placer mines in the district.

Ruby-Poorman mining district
Ruby-Poorman District lies south of the Yukon River and is attributed with nearly a half million ounces of gold, all from placer mines. The largest gold nugget found in Alaska (294.1-troy ounces) was recovered from Swift Creek in 1998. The placers are mostly deeply buried, and most were originally worked with shafts and drifts. Dozens of creeks in the district were mined, many more bear gold prospects. Cassiterite, platinum, scheelite, allanite, and native bismuth have been recovered along with gold from placer mines in the district.

Tok district
The Peak Gold (Manh Choh) deposit is located on top of a group of low hills in the northern part of the Tetlin Lease. It is accessible from the Alaska Highway via a 15-kilometer exploration road. Drilling to date, has identified a 1.3 million ounces of measured and indicated gold resources averaging 4g/t Au and 14g/t Ag in skarn.

Tolovana-Livengood district
Livengood is about 50 miles (80 km) northwest of Fairbanks on the Dalton Highway. In July, 1914 Jay Livengood and N.R. Hudson discovered gold on Livengood Creek. Hundreds of people arrived in the district the following winter. A post office existed at Livengood from 1915 to 1957. Only a few dozen people live at Livengood today, some only seasonally. A variety of creeks in the district were mined. Many gold lode occurrences are known and exploration continues for open pittable lode deposits. Over 500,000 ounces of gold have been recovered from placers in the district.

Early development and production was from relatively shallow pay in tributaries of Livengood Creek. By 1939, large, deeply buried (80 to 110 feet), thawed, bench placer deposits on the northwest limit of Livengood Creek valley were defined. The pay streak varied from 100 to 1,000 feet (300 m) wide and was at least 6 miles (9.7 km) long. Gold reserves of over 1 million ounces were defined by drilling prior to 1940. A dredge operated near the town of Livengood in 1940, 1946 and probably other years. Alaska's 12th-largest (73 troy ounces) and 16th-largest (56 troy ounces) nuggets were found in the district, on Dome Creek.

Goodpaster District (Pogo Mine)
Only a few thousand ounces of gold from placer mines, and a few hundred ounces from lode gold mines were produced from the Goodpaster district before the discovery of the Pogo deposit within the Tintina gold province. The district lies east of the Fairbanks and south of Circle.

The Pogo mine lies on a hillside above the Goodpaster River, 85 miles southeast of Fairbanks, and was  discovered in 1995 by Sumitomo Metal Mining and Sumitomo Corporation on land owned by Alaska. A private 49-mile gravel access road and power line connects the mine to the Richardson Highway near Delta Junction. The gold is found as inclusions in arsenopyrite and quartz.

The underground operation focuses on numerous, massive, high-grade gold-sulfide quartz veins in Proterozoic- to mid-Paleozoic-age amphibolite-grade para- and ortho-gneiss. Mid-Cretaceous granite plutons and dikes intrude gneiss, which are in turn cut by veins. The rock package is cut by low-angle shear zone and high angle faults. Gold mineralization is Cretaceous (104 Ma).

The mine was developed by Teck Cominco. Sumitomo Metal Mining (a non-operating partner and part-owner of the Pogo deposit since discovery) bought Teck's share of the mine in 2009. Sumitomo sold the mine to Northern Star Resources in 2018.  The Pogo produced 260,000 ounces in 2007. 

The first gold ore bar was poured on February 12, 2006. The mine has estimated and inferred resources of 4.15 million ounces of gold at a grade of 14.7 g/t.

Gold-stibnite ore, Alaska (photo by the
Fortymile mining district
The 1886 discovery of gold on Franklin's Bar on the Fortymile River touched off Interior Alaska's first gold rush. The mining boom ushered in a wave of settlement that forever changed the place, not only for its new residents but for the Athabascan Indians who occupied this region long before them. The miners who prospected nearly every creek in the region eventually extracted more than a half-million ounces of gold from the Fortymile, including a 56.8 troy ounce nugget, Alaska's 15th-largest. Reports of starvation and lawlessness among the miners resulted in the Army sending troops to the Eagle area to provide law enforcement in 1899. Soldiers soon began work on a trail from Valdez to Eagle.

Gold was first discovered in the Chicken Creek drainage in 1896, 10 years after the gold discovery on the Fortymile River. The F.E. Company, a subsidiary of the U.S. Smelting Refining & Mining Co., acquired most of the claims during the 1940s and dredged 2 miles (3.2 km) of the creek from 1959 to 1967. Since then, several family operations have mined on the creek. It is estimated that over 100,000 ounces of gold has been produced from the Chicken Creek drainage.

The beginning of the end of the Fortymile Gold Rush came in August 1896 when George Carmack reported the first gold strike along the Klondike River in Canada. Within a few years the once-booming towns in the Fortymile region were abandoned and forgotten. Some of the original Fortymile miners returned to the area after the Klondike Gold Rush passed. From 1887 to 1890 the Upper Yukon region was the richest and most productive mining area in the region. During those three years the area produced 1,200,000 ounces of gold, accounting for 5 percent of Alaska's total gold production.

Chisana-White River district
Gold production from this area is balanced between 78,000 ounces of placer and 66,000 ounces of lode gold. Directly south of the Fortymile district, the Chisana district includes headwaters of the Nabesna and White rivers, and tributaries of the Tanana River; it includes parts of the Wrangell Mountains and the Alaska Range. Difficulties of location, lack of water, and small deposit size limited placer activity. The Nabesna underground lode mine produced gold-copper-silver ore between 1930 and WWII.

Kantishna district
The Kantishna Gold Rush began soon after The Nome Nugget printed the headline “FOUND HIGH GRADE GOLD” on September 9, 1903. Located on the north flanks of Denali (Mount McKinley), the District was a hard place to operate a mine. Nevertheless, some of the largest gold nuggets found in Alaska have been found in the area, including the 9th largest (92 troy ounces). 92,000 ounces of placer gold and 8000 ounces of gold from lode mines has come from the district. Today, the district is located within Denali National Park and Preserve.

Do the World a Favor: Dump Social Media Sites that censor Americans. These people are corrupt beyond comprehension and are looking to remove you from the surface of the earth and hoard as much money as they can - they are a disgrace to the human race.

Tuesday, February 26, 2013

A Monster Gold Deposit

Discovery of a 'monster gold deposit' at Donlin Creek near Flat

The Northern Miner (Feb 11-17, 2013) reported two monster gold deposits were discovered in Alaska, both in 1988. One, the Pebble deposit, has gold along with base metals; the second, Donlin Creek in the Kuskokwim Mountains of Alaska is classified as the largest undeveloped gold deposit in the world!

Comparing Donlin Creek to the Homestake gold mine in South Dakota. The Homestake was discovered in 1876 and mining began in 1878 ending 123 years later in 2001, only after the Homestake had produced 39.8 million ounces of gold. The Homestake was one of the longest listed stocks on the NYSE in history!

The Northern Miner (2013) now reports that the Donlin Creek property is a Monster Gold deposit discovered in Alaska in 1988. The property was reported as the largest undeveloped gold deposit in the world - with 45 million ounces identified to date, by the Northern Miner. This one deposit has drilled resources indicating that in hosts more than twice the amount of gold mined during the entire history of the Klondike and 125 times more gold than mined during the entire history of Wyoming.

Saturday, September 24, 2011

NovaGold reports capitalization costs for Donlin Creek

Exploring Donlin Creek in 1988. Photo of the author taken while mapping on a
ridge overlooking Snow Gulch (background)
The Donlin Creek gold deposit in the central Kuskokwim Basin in southwestern Alaska, is one of the largest, undeveloped, gold deposits on earth and contains as much gold as the Homestake mine. And it is likely to be larger with continued exploration of the deposit and future mining. The gold resource is more than 40 million ounces. To develop this property, it is estimated that capitalization will be as much as $7 billion in that the property is in the middle of nowhere in the Kuskokwim Mountains in southwestern Alaska. 

NovaGold reported proven and probable mineral reserves of 33.6 million ounces, measured and indicated mineral resources of 4.3 million ounces and inferred resources of 4.4 million ounces.

Rocks in the basin include Upper Cretaceous Kuskokwim Group, the most extensive rock unit in southwestern Alaska that consists of graywacke, siltstone, and shale. Additional rock types  include Proterozoic metamorphic rocks, Paleozoic clastic and carbonate rocks, and Mesozoic marine volcanic rock.

Late Cretaceous and Early Tertiary volcano-plutonic complexes in placers, intrude and overlie Kuskokwim Group sediments. The volcanic rocks are intermediate tuffs and flows that are  dominantly andesite, but also include dacite, rhyolite, and basalt. Plutons consist of calc-alkaline monzonite and granodiorite. Felsic to intermediate subvolcanic granite to granodiorite porphyry dikes, sills, and plugs are widely distributed and host gold mineralization at Donlin Gold.

NovaGold goes on to report, the Kuskokwim basin was formed by two continental-scale right-lateral strike-slip fault zones. The Denali−Farewell Fault bounds the southern flank of the basin, and the Iditarod−Nixon Fork Fault system limits the north.

Folding and thrusting followed deposition of Kuskokwim sediments. Eastward-trending folds and thrust faults are common in the central Kuskokwim basin, including Donlin Creek area.

Map from NovaGold.

Younger north–northeast-trending folds formed throughout the region in response to the basin-scale movement. Most of the folds predate emplacement of the volcano-plutonic complexes. Northeast-striking normal and oblique slip faults formed during the late compressional and extensional events that resulted in mineralizing hydrothermal systems across the basin.

The Donlin Gold deposits comprise a northeast elongated cluster, roughly 5,000 feet wide x 10,000 feet long, that extends vertically over 3,100 feet. The deposits are hosted primarily in igneous rocks associated with a late Cretaceous hydrothermal system. Gold occurs in broad disseminated sulfide zones in rhyodacite and in vein networks.

Two primary deposits are recognized at Donlin: (1) ACMA and (2) Lewis. These have different geological settings. The ACMA deposit is comprised of dikes and sills intruded into folded shale and siltstone rocks.  The Lewis deposit consists of dikes intruded into massive greywacke. Mineralized material in the ACMA deposit tends to be higher grade and more continuous compared to Lewis and other dike dominant areas of the deposit.  The most extensive and highest-grade mineralized zones in ACMA are located where “feeder” dikes intersect the sill sequence.  Mineralized zones follow steeply dipping dikes and sills beyond the depth limits of current drilling, or over a vertical range of at least 3,100 feet

North-northeast mineralized corridors are made up of similar striking, high-angle fracture zones that are the primary control of gold-bearing veins.  These mineralized corridors of veins range up to 98 feet wide and hundreds of meters long.  Intrusive rocks and competent massive greywacke are the favored host rocks.  Gold distribution in the deposit closely mimics the intrusive rocks, which contain about 75% of the resource.  Structural zones in competent sedimentary units account for the remaining 25%.