Donlin Gold project (Donlin Creek prospect), Iditarod Mining District, Bethel Census Area, Alaska, USAi

Regional Level Types
Donlin Gold project (Donlin Creek prospect)	Project
Iditarod Mining District	Mining District
Bethel Census Area	Census Area
Alaska	State
USA	Country

If one restores the 54 miles of right lateral offset along the Iditarod-Nixon Fork fault, the Donlin Creek dike and sill swarm correlates with the Ganes-Yankee dike and sill swarm and nearby deposits (ID024, ID028, ID035, and ID039) in the Ganes Creek-Yankee Creek areas in the Innoko district in the northern Iditarod Quadrangle (Miller and Bundtzen, 1988).

The Donlin Creek lode is a northeast-trending area about 1.2 miles wide and 5 miles long on the ridge east of Crooked Creek. The coordinates are at an area that is being considered as an open pit. That location is at an elevation of about 1,100 feet, about 1.4 mile east-southeast of the mouth of Queen Gulch and about 0.2 mile west of the center of section 25, T. 23 N., R. 49 W., of the Seward Meridian. Note: This deposit is distinct from the several placers in the vicinity of Crooked Creek and Donlin Creek and over the years, 'Donlin Creek' has been used to refer to both one or more of these placers and this lode.

Geology: The Donlin Creek lode is Alaska's largest gold deposit, with more than 22.9 million ounces of gold in measured, indicated, and inferred resources (Novagold press release, January 28, 2002; Placer Dome Exploration press release, May 4, 2003).

The deposit is in an elongate, northeast-trending mineralized area about 1.2 mile wide and 3 miles long that runs along the ridge east of Crooked Creek at the heads of Lewis, Queen, Ruby, and Snow Gulches. As currently developed, the main area of mineralization is about 6,500 feet long, trends east-west, and is about 3,200 feet wide. Individual centers of mineralization have been designated 'South Lewis', 'North Lewis', 'Vortex', '400', 'Richelieu', and 'Acma'.

The rocks in the area are calcareous shale and graywacke of the Upper Cretaceous, Kuskokwim Group. These detrital rocks strike west-northwest and dip 10-50 SW; they are cut by dikes and sills of several ages. Mafic sills that are extensively altered to quartz-carbonate rock are cut by at least four subtypes of younger rhyodacite to granite-porphyry sills and dikes. A major northeast-striking dike swarm cuts west-northwest-striking sills and dikes on the ridge crest between Lewis and American Creeks. Late northeast and northwest-striking, high-angle faults appear to offset the mineralized zones (Miller and Bundtzen, 1994; Vaillancourt, 2002; St. George, 2004).

The deposit is best developed in the felsic dikes and sills, and lesser so in the graywacke, particularly where north-northeast striking fault zones intersect the favorable felsic intrusion and graywacke host rocks. The ore minerals are primarily gold-bearing arsenopyrite and arsenian pyrite which are disseminated in the felsic igneous rocks and in veins and networks of veinlets in the igneous and and sedimentary rocks.

The veins and veinlets consist of quartz and carbonate gangue, with gold and several ore minerals. The gold occurs mainly in the lattice of the arsenopyrite (St. George, 2003). In addition to the arsenopyrite, pyrite, and stibnite which are the dominant ore minerals, minor chalcopyrite, cinnabar, cassiterite, covellite, galena, marcasite, molybdenite, native arsenic, pyrrhotite, sphalerite, scheelite, and the alteration products of sulfides also occur. The gangue and alteration minerals include crystalline and chalcedonic quartz, carbonate minerals, and dickite. The garnet and high tin values in some of the granite porphyry dikes indicate that at least part of the intrusive suite is peraluminous.

Based on crosscutting relationships, the altered mafic dikes were intruded first, followed by the intermediate and felsic dikes. Despite the intensity of intrusive activity, there is little thermal alteration of host rocks, i.e., the development of hornfels, as compared to similar-sized intrusive centers in other areas of the Kuskokwim mineral belt (Bundtzen and Miller, 1997). Miller and Bundtzen (1994) report that the felsic dikes vary in age from 65.1 to 70.9 Ma. More recent age dating summarized in Szumigala, Dodd, and Arribas (2000) and Ebert and others (2000) give similar radiometric ages. According to Szumigala, Dodd, and Arribas (2000), the gold mineralization is in disseminated sulfides, sulfide veins, and in quartz-carbonate-sulfide veining in sericitically-altered igneous rocks. There is a positive correlation between high fracture density, alteration, and the amount of gold. Ore shoots at Donlin Creek are developed in dilatant zones along normal faults where the faults steepened in felsic intrusions and graywacke. Fluid inclusion, and ore and alteration mineral assemblage data indicate that pervasive sericitization developed under a lower mesothermal regime, but some of the ore probably was epithermal (Bundtzen and Miller, 1997; Szumigala, Dodd, and Arribas, 2000).

The occurrence of gold in the intrusive rocks at the Donlin Creek deposit was recognized as early as 1912 (Maddren, 1915). There was increasing more thorough work in the 1980's when a joint effort by Alaska Earth Sciences and the Calista Corporation suggested that the Donlin Creek deposit could be an important bulk-mineable gold deposit. Trenching and drilling done by Westgold from 1988 to 1990 identified seven ore bodies that contained about 392,090 ounces of gold (Retherford and McAtee, 1994). Placer Dome US conducted exploration from 1995 to 2000 and announced that the Donlin Creek deposit contained about 11 million ounces of gold (Swainbank and others, 2002). Placer Dome's first exploration phase at the Donlin Creek deposit ended in 2000. Later in 2000, Novagold Resources Inc. signed agreements with Placer Dome Exploration and Calista Corporation, who owns the deposit, to acquire a 70 percent interest in the Donlin Creek deposit by spending $10 million to explore the deposit over a ten year period (Swainbank and others, 2002). Novagold fulfilled the exploration commitment during 2001 and 2002. In the spring of 2003, after reviewing the results of the two-year Novagold exploration program, Placer Dome Exploration reacquired a majority interest in the project by agreeing to spend $30 million on further exploration and to complete a feasibility study of the project (February, 2003 Press release, Novagold Resources, Inc.). Exploration at the Donlin Creek gold deposit is in progress as of March 2004.

By the end of 2001, the deposit had been explored by about 287,000 feet of diamond core drilling in 361 holes, about 43,700 feet of reverse-circulation drilling in 117 hole, and 7,000 feet of trenches (Novagold Press release, January 28, 2002). The total measured and indicated reserves are 115 million tons of material with 0.1 ounces of gold per ton, or about 10.0 million ounces of gold. The total inferred reserves and resources are 142 tons of material with 0.1 ounce of gold per ton, or about 12.9 million ounces of gold.

Workings: The occurrence of gold in the intrusive rocks at the Donlin Creek deposit were recognized as early as 1912 (Maddren, 1915).

Cady and others (1955) reported that lode gold occurrences exposed between Queen and Snow Gulches contained stibnite and up to a half ounce of gold per ton During the 1950s, Robert F. Lyman trenched the Snow Gulch stibnite-gold prospect.

In 1974, Resource Associates of Alaska, Inc. on behalf of the Calista Corporation, carried out surface investigations including some trenching in the Donlin Creek dike swarm. This firm detected high gold values in a soil survey and recommended that an induced polarization survey and a drill program be conducted on the property (Muntzert and others, 1975). In 1984, Bundtzen and Miller mapped and sampled trenches at Snow Gulch; the samples yielded up to 0.35 ounce of gold per ton, 7,000 ppm arsenic, 70 ppm tin, and several percent antimony (Bundtzen and Miller, 1997).

In the mid-1980s, Rob Retherford, Bruce Hickok, Tom Turner, and Toni Hinderman of Alaska Earth Sciences, Inc. and Calista Corporation investigated the pervasive presence of gold-rich arsenopyrite at Snow Gulch and other areas, and suggested that the Donlin Creek dike swarm could be an important bulk-mineable gold deposit.

Trenching and drilling done by Westgold from 1988 to 1990 indicated that seven ore bodies in the Donlin intrusive swarm contained 4.26 million tons of material with a grade of 0.09 ounces of gold per ton, or about 392,090 ounces of gold (Retherford and McAtee, 1994). Placer Dome US conducted exploration from 1995 to 2000 and announced that the Donlin Creek deposit contained about 11 million ounces of gold (Swainbank and others, 2002). Placer Dome's first phase of exploration phase at the Donlin Creek deposit ended in 2000.

Later in 2000, Novagold Resources Inc. signed agreements with Placer Dome Exploration and Calista Corporation, who owns the deposit, to acquire a 70 percent interest in the Donlin Creek deposit by spending $10 million in exploration over a ten year period (Swainbank and others, 2002).

Novagold fulfilled the exploration commitment during 2001 and 2002. In the spring of 2003, after reviewing the results of the two-year Novagold exploration program, Placer Dome Exploration reacquired a majority interest in the project by agreeing to spend $30 million on further exploration and complete a feasibility study of the project (February, 2003 Press release, Novagold Resources, Inc.). Exploration at the Donlin Creek gold deposit is in progress as of March 2004.

Age: The felsic intrusions at Donlin Creek have 40K/40Ar ages of from 65.1 to 70.9 Ma (Miller and Bundtzen, 1994).

Alteration: The alteration is marked by sericite, illite, kaolinite. dickite, carbonate minerals, and pyrite (Szumigala, Dodd, and Arribas, 2000).

Reserves: By the end of 2001, the total measured and indicated reserves were 115 million tons of material with 0.1 ounces of gold per ton, or about 10.0 million ounces of gold. The total inferred reserves and resources are 142 tons of material with 0.1 ounce of gold per ton, or about 12.9 million ounces of gold. The total of 22.9 million ounces of gold rank this in the top 30 gold deposits known in the world (Novagold Press release, January 28, 2002). The bulk of the reserve is in the Lewis, 400, Acma, and Richelieu ore bodies. This total does not include reserve estimates for the Snow and Far Side deposits.

Based on earlier work by Westgold, the Snow deposit contains 44,000 ounces of gold with an average grade of 0.10 ounce of gold per ton (Retherford and others, 1989). The Far Side deposit contains 38,400 ounces of gold of unstated grade.

Commodities (Major) - Au; (Minor) - Ag, As, Be, Cd, Cu, Hg, Mo, Pb, Sb, Sn, W, Z

Deposit Model: Porphyry gold-copper deposit; (Cox and Singer, 1986; model 20c)

Other Databases

Link to USGS - Alaska:	ID167

Other Regions, Features and Areas containing this locality

References