Donlin Creek

Prospect, Active

Commodities and mineralogy

Geographic location

Quadrangle map, 1:250,000-scale ID
Quadrangle map, 1:63,360-scale A-5
Latitude 62.0434
Longitude -158.209
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Donlin Creek prospect is a large mineralized area about 3.5 by 2 kilometers in size that has been extensively drilled and is being developed as an open-pit mine. The center of the area is about 1.4 miles east of the junction of American Creek and Crooked Creek and about 0.3 mile north of the center of section 35, T. 23 N., R. 49 W., of the Seward Meridian. The location is accurate within a few hundreds of feet.

Geologic setting

Geologic description

The Donlin Creek prospect is a large porphyry-gold deposit about 3.5 by 2 km in size that has been extensively drilled and studied since 2001 as a joint venture between NovaGold Resources Alaska Inc. and the Barrick Gold Corporation (NovaGold, 2010). In early 2010, the work had outlined a potential open pit mine that could ultimately cover a northeast-trending area about 2 by 3 kilometers in size. A second-generation feasibility plan was completed in 2009 (Hanson and others, 2009).
Placer gold was discovered in the area in 1909 and placer mining continues nearby (see ARDF sites ID162 to ID166 and ID168). The modern search for the lode source of the placer gold began in 1974 when Resource Associates of Alaska sampled a soil grid and dug three trenches on mineralization (McCoy and others, 1997; Szumigala and others, 2000; Hanson and others, 2009). The Calista Corporation, Cominco Alaska, Kennecott Exploration, and Lyman Resources then worked in the area from 1984 to 1987, mostly through limited surface sampling and auger drilling. From 1988 to 1989, Western Gold Exploration and Mining Company did an airborne geophysical survey and soil sampled a large area. They cut 13,525 meters of trench, drilled 3,106 meters of core hole, and 404 meters of auger drilling, and 10,423 meters of reverse circulation drilling. They identified seven areas of mineralization and prepared the first mineral-resource estimate. Teck Exploration Ltd. trenched and sampled soils in 1993. From 1995 to 2000, Placer Dome U.S. Inc. drilled 87,383 meters of core hole, drilled 11,909 meters of reverse-circulation holes, and did 8,493 meters of trenching. In 2001, NovaGold began working at the property and in early 2010 continued to develop the property under the joint agreement with Barrick Gold (NovaGold, 2010).
Approximately 1,676 exploration and development holes were drilled from 1988 to 2007; 88 percent are core holes and 12 percent are reverse-circulation holes (Hanson and others, 2009). About half were drilled in 2006 and 2007. In 2008, another 109 core holes were drilled to explore pit expansion and potential satellite deposits and for facility and geotechnical studies.
The rocks in the area are Cretaceous sedimentary rocks intruded by a swarm of 65 to 74 Ma dikes, sills, and small stocks. The sedimentary rocks are part of the Cretaceous Kuskokwim Group, mostly graywacke on the north side of the area and shaly rocks on the south side (Cady and others, 1955). The sedimentary rocks are generally monoclinal to the north and form a broad, open, east-trending fold to the south. There are two main types of igneous rocks (Szumigala and others, 2000; Hanson and others, 2009). The oldest are 74 to 72 Ma, mafic sills and dikes; they are not abundant. The more voluminous are 70 to 65 Ma granite porphyry or rhyodacite dikes and sills, a few feet to 60 meters wide, that form a northeast-trending belt 8 kilometers long and 3 kilometers wide. Five varieties of rhyodacite dikes are distinguished by their textures; they are the 'fine grained porphyry'; 'crowded porphyry'; 'lath rich porphyry'; aphanitic porphyry'; and 'blue porphyry'. There is little alteration of the sedimentary rocks adjacent to the dikes and sills.
The Donlin prospect is between two regional-scale northeast-trending faults; the immediate area has numerous north-northeast to east-northeast and northwest to west-northwest lineaments that probably represent steeply-dipping strike-slip faults (Szumigala and others, 2000; Hanson and others, 2009). These faults offset many of the dikes and sills. The mineralization is strongly controlled by the north-northeast-trending faults, especially in competent host rocks. The mineralization is best developed in the igneous rocks but also does occur in the sedimentary rocks.
There are two distinct styles of mineralization: the ACMA-Lewis style and the Dome-Duqum style (McCoy and others, 1997, Szumigala and others, 2000; Hanson and others, 2009). (The names are based on specific centers of mineralization within the the prospect.) The ACMA-Lewis style, which is the main type, consists mainly of sheeted quartz, quartz-carbonate and sulfide (only) veins characterized by abundant arsenopyrite and pyrite. Disseminated arsenopyrite occurs widely. Most of the gold is in the lattice structure of the arsenopyrite. Stibnite, realgar, and native arsenic are common, but are associated with relatively little gold compared to the arsenopyrite veins. The ACMA-Lewis-style mineralization was deposited by a late, low-temperature, low-sulfidation epithermal system. The Dome-Duqum mineralization is an earlier higher-temperature, porphyry-style of mineralization characterized by quartz veins that contain various proportions of copper, zinc, bismuth, silver, tellurium, selenium and native gold. The Dome-Duqum mineralization is not included in the 2008 resource/reserve estimates by Hanson and others (2009).
The main ore minerals in the deposit are pyrite, stibnite, and gold-bearing arsenopyrite. Native gold is rare, minor hydrothermal pyrrhotite and marcasite are present. Copper, lead, and zinc minerals are rare, but chalcopyrite, chalcocite, covellite, tennantite, tetrahedrite, bornite, native copper, galena, sphalerite, boulangerite, molybdenite, and millerite have been identified. Microscopic cinnabar is generally absent or exceedingly rare.
There have been several generations of resource estimates as the drilling has proceeded. The latest in early 2010 was by Hanson and other (2009). They estimate that on December 31, 2008, the Donlin Creek deposits contained: 1) 1.2 million tonnes of measured resources with an average grade of 2.19 grams of gold per tonne; 2) 93.4 million tonnes of indicated resources with an average grade of 1.98 grams of gold per tonne; 3) 8.4 million tonnes of proven reserves with a grade of 2.59 grams of gold per tonne; and 4) 375.4 million tonnes of probable reserves with a grade of 2.37 grams of gold per tonne.
The Donlin project is being proposed as a large open-pit gold mine by Donlin Gold, LLC, a 50/50 partnership between Barrick Gold Corp. and NovaGold Resources Inc. Their preferred design for the Donlin project anticipates a throughput of approximately 59,000 tons (53,524 tonnes) per day. Donlin Gold's proposal to power the mine includes a 14-inch-diameter, 315-mile-long natural gas pipeline starting in Beluga, Alaska, passing north through the Alaska Range, and continuing to the mine site. Donlin Gold estimates the project would take 3 to 4 years to construct, with a projected mine life of approximately 27.5 years, and is estimated to produce (on average) approximately one million ounces of gold per year (Lipiec and others, 2012).
In 2016, Donlin Gold’s major milestones included advancement of the permitting and technical work at the Donlin project, including completion of a six-month public comment period on the draft Environmental Impact Statement (EIS) completed by the U.S. Army Corps of Engineers, and completion of public working sessions attended by all cooperating agencies to address comments on key topics and how to address them in the final EIS, which is expected to be completed in early 2018 (Athey and Werdon, 2017).
Geologic map unit (-158.211409387978, 62.0427062413339)
Mineral deposit model Mostly epithermal gold-arsenopyrite-quartz veins and disseminated auriferous arsenopyrite; earlier, higher temperature polymetallic porphyry-style mineralization (Cox and Singer, 1986; model 22c, 25).
Mineral deposit model number 22c, 25
Age of mineralization The felsic intrusions which predate the mineralization have 40K/40Ar ages of from 65.1 to 70.9 Ma (Miller and Bundtzen, 1994).
Alteration of deposit The alteration is marked by sericite, illite, kaolinite. dickite, carbonate minerals, and pyrite (Szumigala, Dodd, and Arribas, 2000); there is little alteration of the sedimentary rocks adjacent to the igneous rocks.

Production and reserves

Workings or exploration
The Donlin Creek prospect is a large porphyry-gold deposit that has been extensively drilled and studied since 2001 as a joint venture between NovaGold Resources Alaska Inc. and the Barrick Gold Corporation (NovaGold, 2010). In early 2010, the work had outlined a potential open pit mine that could ultimately cover a northeast-trending area about 2 by 3 kilometers in size. A second-generation feasibility plan was completed in 2009 (Hanson and others, 2009).
Placer gold was discovered in the area in 1909 and placer mining continues nearby (see ARDF sites ID162 through ID166 and ID168. The modern search for the lode source of the placer gold began in 1974 when Resource Associates of Alaska sampled a soil grid and dug three trenches on mineralization (McCoy and others, 1997; Szumigala and others, 2000; Hanson and others, 2009). The Calista Corporation, Cominco Alaska, Kennecott Exploration, and Lyman Resources then worked in the area from 1984 to 1987, mostly through limited surface sampling and auger drilling. From 1988 to 1989, Western Gold Exploration and Mining Company did an airborne geophysical survey and soil sampled a large area. They cut 13,525 meters of trench, drilled 3,106 meters of core hole, and 404 meters of auger drilling, and 10,423 meters of reverse circulation drilling. They identified 7 areas of mineralization and prepared the first mineral-resource estimate. Teck Exploration Ltd. trenched and sampled soils in 1993. From 1995 to 2000, Placer Dome U.S. Inc. drilled 87,383 meters of core hole, drilled 11,909 meters of reverse-circulation holes, and did 8,493 meters of trenching. In 2001, NovaGold began working at the property and in early 2010 continued to develop the property under the joint agreement with Barrick Gold (NovaGold, 2010).
Approximately 1,676 exploration and development holes were drilled from 1988 to 2007; 88 percent are core holes and 12 percent are reverse-circulation holes (Hanson and others, 2009). About half were drilled in 2006 and 2007. In 2008, another 109 core holes were drilled to explore pit expansion and potential satellite deposits and for facility and geotechnical studies.
Indication of production None
Reserve estimates
There have been several generations of resource estimates as the drilling has proceeded. The early 2010 update was by Hanson and other (2009). They estimate that on December 31, 2008, the Donlin Creek deposits contained: 1) 1.2 million tonnes of measured resources with an average grade of 2.19 grams of gold per tonne; 2) 93.4 million tonnes of indicated resources with an average grade of 1.98 grams of gold per tonne; 3) 8.4 million tonnes of proven reserves with a grade of 2.59 grams of gold per tonne; and 4) 375.4 million tonnes of probable reserves with a grade of 2.37 grams of gold per tonne.
In early 2012, an updated 43-101 report by Lipiec (2011) estimated that as of July 11, 2011, the Donlin Creek deposits contained 1) 7.7 million tonnes of measured resources with an average grade of 2.52 grams of gold per tonne; 2) 533.6 million tonnes of indicated resources with an average grade of 2.24 grams of gold per tonne; 3) 92.2 million tonnes of inferred resources with an average grade of 2.02 grams of gold per tonne.

References

References

Francis, K., 2008: Donlin Creek Project, NI 43-101 Technical Report,
Gray, J.E., Gent, C.A., Snee, L.W., and Wilson, F.H., 1997, Epithermal mercury-antimony and gold-bearing vein lodes of southwest Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 287-305.
Hodgson, Stephen, 2002, Preliminary assessment Donlin Creek project, Alaska: Technical Report, 109 p. (posted on www.sedar.com, March 15, 2002).
Juras, S., 2002: Technical Report, Donlin Creek Project, Alaska;
Muntzert, J., Haverslew, R.E., Hirst, P.E., Knaebel, J., and Heiner, L.E., 1975, Land and mineral resource evaluation for Calista Corporation-final report of exploration activities during 1974: Fairbanks, Alaska, Resource Associates of Alaska, Inc. unpublished report, p. 20-22.
NI43-101F1 Technical Report for NovaGold Resources Inc., 179 p. (posted on www.sedar.com, February 22, 2002).
NovaGold Resources Inc., 243 p, (posted on www.sedar.com, September 20, 2006).
Retherford, R.M., Graff, P., and Hinderman, Toni, 1989, Donlin Creek project (Alaska) 1989 exploration program final report: Anchorage, Alaska, unpublished Western Gold Exploration and Mining Company Ltd. report, 186 p.
Southwest Alaska, U.S.: NI43-101F1 Technical Report for
St. George, P., 2003, Donlin Creek--Alaska's development of one of the world's largest gold deposits (abs.): 2003 Cordilleran Exploration Round-up, Yukon and British Columbia Chamber of Mines, Vancouver, British Columbia, Canada, p 50.
Reporters T.K. Bundtzen (Pacific Rim Geological Consulting, Inc.), M.L. Miller (U.S. Geological Survey); and C.C. Hawley (Hawley Resource Group); D.J. Grybeck (Contractor, U.S. Geological Survey); V.C. Zinno (Alaska Earth Sciences, Inc.); M.B. Werdon (DGGS)
Last report date 8/26/2017