Cleary Hill; Summit; Cleary; Freegold Mine, Fairbanks District, Fairbanks North Star Borough, Alaska, USA
|Latitude & Longitude (WGS84):||65° 4' 1'' North , 147° 25' 58'' West|
|Latitude & Longitude (decimal):||65.06694,-147.43278|
Location: The coordinates given are near the Cleary Hill Mine marked on the Livengood (A-1) quadrangle; SW1/4SW1/4 sec. 19, T. 3 N., R. 2 E., of the Fairbanks Meridian. The mine is east of Bedrock Creek, a tributary of Cleary Creek.
Geology: The Cleary Hill mine was the largest lode gold producer in the Fairbanks mining district, prior to the first production from the Fort Knox gold mine in 1996. The average grade of gold produced was approximately 1.3 ounces of gold per ton. Recent drilling in the 1990's has shown that the Cleary Hill mine still has an approximate resource of 100,000 ounces of gold with a grade of 0.81 ounces of gold per ton. In the early 1900's, gold was reported to be found in quartz veins within schist with quartz stringers (Prindle, 1910). Visible gold was found in quartz veins that were largely free of sulfides (Smith, 1913; B 525). The principle vein averages about 1 foot in thickness with a maximum thickness of about 3 feet. There are smaller, similar, parallel veins in both the hanging and footwalls; the veins are crushed, cross the foliation of schist country rock, and are complexly faulted (Smith, 1913; B 525). The Cleary Hill Mine is hosted in mafic volcanics, quartzites and quartz muscovite schists on the north flank of the Cleary antiform (Freeman and others, 1998). The Cleary Hill vein strikes N 70-80 W and dips 45 to 70 S. The dip of the vein varies according to the host rock, with steeper dips in more competent rock units and shallow dips in less competent rock units (Freeman and others, 1998). The mine consisted of over six levels that produced ore from quartz veins that contained coarse free gold, and trace arsenopyrite, pyrite, boulangerite, and tetrahedrite. Higher grade intervals have gold values from the hundreds to the thousands of ounces of gold per ton. These intervals are commonly associated with acicular needles and felted masses of boulangerite and jamesonite, in white to gray quartz veins that are 1 to 5 feet thick (Freeman and others, 1998). During the 1986 field season, the mine waste dumps of the Cleary Hill mine were examined and grab samples were collected by Fairbanks Exploration Inc. (Fairbanks Exploration Inc., unpublished report, 1986). Quartz vein samples on the Penrose and Upper adit dumps are associated with chlorite-actinolite schists of mafic volcanic origin, typical of the the lower third of the Cleary Sequence. Dump samples contained arsenopyrite, pyrite, stibnite, jamesonite, native gold, and minor scheelite hosted by quartz-bearing shear zones and stockworks with thin argillized selvages. Significant ankerite occurs in some shear zones and weathers to a bright ocherous, red color. Visible gold is usually associated with jamesonite needles and rosettes similar to mineralization in the Christina adit (ARDF no. LG146) and Nordale adit of the Homestake mine (ARDF no. LG157). Up to one-half percent scheelite is finely disseminated in chlorite-actinolite schist and less commonly forms coarser grained crystal aggregates in sulfide-free quartz shear zones. Gold values vary up to 0.558 ounces of gold per ton and appear to be higher in samples of siliceous exhalite, metarhyolite tuff and carbonaceous quartzite from the lower production dumps at the mine. Reserve estimates of the waste dump made by Fairbanks Exploration Inc. in 1988 indicated the Cleary Hill mine dumps contained 71,176 tons of rock grading 0.159 ounces of gold per ton and 0.099 ounces of silver per ton (Fairbanks Exploration Inc., unpublished report, 1987; Fairbanks Exploration Inc., unpublished report, 1988). Reverse circulation drilling at the Cleary Hill Mine in late 1996 encountered at least two vein systems with values of more than 0.5 ounces of gold per ton over narrow widths below the old underground workings (Freeman and others, 1997). Complete production records are not available for the Cleary Hill mine, however, existing published and private records indicate the Cleary Hill mine produced more than 100,000 fine ounces of gold from approximately 77,000 tons of material with an average grade of 1.3 ounces of gold per ton (Porterfield and Croff, 1986; Metz and others, 1987). This ranks the Cleary Hill mine as the largest lode gold producer in the Fairbanks Mining District, prior to the development of the Fort Knox mine. Recent drilling shows that Cleary Hill Mine, in addition to a 100,000-ounce resource grading 0.81 ounces of gold per ton, has potential for bulk tonnage, lower-grade material in the footwall of the high-grade veins (Swainbank and others, 1998).
Workings: Mineralization was first discovered on the Freegold claim prior to 1910, near the juncture of Cleary and Bedrock Creeks. Shortly after discovering the rich surface outcrops of the Cleary Hill lode (selected samples assayed up to 5,950 ounces of gold per ton), the main production adit was collared about 50 feet above Bedrock Creek (Freeman, 1991). By the summer of 1910 the Main adit had been driven 630 feet on the Free Gold claim and a 50 foot shaft with 90 feet of drift was also driven on the main shear zone approximately 800 feet uphill from the Main adit portal (Brooks, 1911). On August 27, 1911, a five stamp Joshua Hendy mill, the first private mill in the Fairbanks Mining District, was put into production on the Free Gold claim. By the end of 1911 there were about 1,200 feet of underground workings at the Cleary Hill mine (Brooks, 1911). By 1912 the Main adit had been driven over 1,050 feet and a second adit, the 215 foot deep Penrose adit, had been driven at an elevation 140 feet higher than the Main adit (Cunningham, 1912). The two adits were connected by a 170 foot raise driven 900 feet from the Main adit portal. Over 500 feet of drifting from the Main adit level had developed over 20 stopes. A 30 foot winze was sunk 650 feet from the main adit portal but water hampered its sinking. By the end of 1912, the winze exposed ore 300 feet below the surface outcrops of the lode (Cunningham, 1912). By the end of 1913, Brooks and others (1913) stated that the Main adit of the Cleary Hill mine was 1,280 feet long, the Penrose adit was 280 feet long and the Upper adit was 200 feet long at an elevation 50 feet above the Penrose adit. A total of 1,000 feet of workings were accessed by the main winze with working drifts at the 70- and 112-foot levels. Operating cost allowed only 200 feet of new drifting to be completed in 1915 and the mine closed on September 10, 1915 (Brooks, 1915; Stewart, 1915). The Cleary Hill mine remained closed until 1924 when it was amalgamated with the neighboring Wyoming mine (Stewart, 1923). Efforts to reopen the Cleary Hill mine began in the fall of 1923 and continued through 1929 (Smith, 1924; Moffit and others, 1927; Smith, 1930, B 813). This work included driving a 400 foot adit to access the mine at the 70-foot level of the Main winze. This Lower adit was collared at the level of Bedrock Creek near the mill site (Moffit and others, 1927). In addition, the Upper adit was extended to a total length of 900 feet and 538 feet of crosscuts and a 40 foot raise were extended from this adit (Stewart, 1931). The Penrose adit was extended 45 feet (total length 325 feet) and three crosscuts were driven a total of 595 feet from this adit. An 89 foot raise was driven to connect the Penrose and Upper adits. The Main adit was extended 192 feet (total length of 1,472 feet) and 51 feet of drift was driven on the Powder House shear zone while 154 feet of drift was driven on the Doget shear zone. At a point near the mill a shaft was driven 185 feet and a crosscut extended from the shaft bottom for 280 feet. A shaft was also sunk on the ridge an unknown distance above the Upper adit. This shaft, known as the Deep shaft, was 50 feet deep with an 80 foot crosscut at the bottom (Stewart, 1931). The mine was back in production again in 1929 and rapidly became one of the largest operations in the district (Smith, 1930, B 810; Smith, 1931). In 1930, mining was concentrated in the Penrose adit (Stewart, 1931) and the Cleary Hill mine was again the largest producer in the Fairbanks Mining District (Pilgrim, 1931). The mill operated for a total of 7 months during 1932 and development was concentrated below the Main adit level (Pilgrim, 1933). In 1938 the Cleary Hill mine conducted 250 feet of new drifts and cross-cuts, sank 100 feet of winze and drilled 4,200 feet of AX diamond core. No other work was conducted at the Cleary Hill mine until 1969 when International Minerals and Chemicals excavated two bull dozer trenches on the expected trace of the Cleary Hill shear zone (Pilkington, 1970). This work produced only weakly anomalous gold and silver. The mine waste dumps of the Cleary Hill mine were examined and grab samples were collected by Fairbanks Exploration Inc. during the 1986 field season (Fairbanks Exploration Inc., unpublished report, 1986). In 1988, Tri-Con Mining conducted bulk sampling of the upper and lower Cleary Hill mine dumps to determine if this material could be profitably trucked to the Grant mill for processing.
Alteration: Quartz, sericite and ankerite.
Production: The first recorded production from the Cleary Hill mine was on February 9, 1910, when a five-ton lot was sent to the Tacoma, Washington, smelter and returned an average grade of 22.25 ounces of gold per ton (Times Publishing Company, 1912). On September 7, 1910, a 17-ton lot of ore from the Free Gold claim averaged 8.61 ounces of gold per ton. An additional 75 tons of ore was shipped to the Chena mill in Fairbanks in November, 1910, followed by a 100 ton lot sent to the Chena mill in early 1911. The grade of this material is unknown but reportedly paid for all past development work and a new stamp mill (Cunningham, 1912). On June 3, 1912, the Alaska Citizen, a Fairbanks newspaper, reported that 147 tons of ore from the Cleary Hill mine were milled at the Chena mill in 1911. The Cleary Hill mine operated 365 days and the mill operated for 350 days in 1914 and produced an estimated 5,950 tons of ore from 1,800 feet of productive lode (Brooks and others, 1914). Up through 1915, the Cleary Hill mine had produced approximately 29,000 fine ounces of gold from an estimated 17,000 tons of ore averaging 1.69 ounces of gold per ton (Stewart, 1922). Production from 1929 to the end of 1931 was 19,000 ounces from 9,800 tons grading 1.94 ounces of gold per ton (Hill, 1933). The high grades were derived from the Bankers stope between the Penrose and Upper adits. Total production from the mine was estimated at $1,000,000 in gold, or 48,379 ounces, through 1930 (Pilgrim, 1931). Pilgrim (1932) stated that in 1931 the Cleary Hill mine was the largest producer in the district and fourth largest lode producer in Alaska. The Cleary Hill mine remained the largest producer in the district in 1934 and 1935 due to additional production from the Main shaft and addition of a flotation circuit in the mill which increased recovery (Smith, 1936; Smith, 1937). Production from the Cleary Hill mine was interrupted in 1936 when a fire destroyed the mill and power plant (Smith, 1938). Production levels increased in 1937 due to the more efficient nature of the new mill installed after the fire (Smith and Mertie, 1941). A total of 2,085 tons of ore with an average grade of $80 per ton in gold (2.3 ounces of gold per ton) was milled in 1938 (Reed, 1939). In 1942, the War Powers Act Limitation Order L208 banned all non-essential mining in the United States, thereby forcing the closure of the Cleary Hill mine. Shortly after the Cleary Hill mine was closed, a 5 ton lot of high grade stibnite ore was shipped to Fairbanks for sale to the federal government (Joesting, 1943). This material was taken from a fault intersection just above the Main adit (Killeen and Mertie, 1951). A small amount of ore was mined by Doug Jackson and Earl Beistline during 1949 and 1950 from previously worked areas above the Main adit (Saarela, 1950; Wedow and others, 1954). The Cleary Hill mill was rehabilitated and used for custom milling by Adolph, Rudy and Grace Vetter in 1956. Complete production records are not available for the Cleary Hill mine, however, existing published and private records indicate the Cleary Hill mine produced in excess of 100,000 fine ounces of gold from approximately 77,000 tons of material at an average grade of 1.3 ounces of gold per ton (Porterfield and Croff, 1986; Metz and others, 1987). This ranks the Cleary Hill mine as the largest lode gold producer in the Fairbanks Mining District, prior to the development of the Fort Knox mine.
Reserves: Waste dump reserve estimates made by Fairbanks Exploration Inc. in 1988 indicated the Cleary Hill mine dumps contained 71,176 tons of rock grading 0.159 ounces of gold per ton and 0.099 ounces of silver per ton (Freeman and others, 1987; Freeman and others, 1988). Recent drilling shows that Cleary Hill Mine, in addition to a 100,000-ounce resource grading 0.81 ounces of gold per ton, has potential for bulk tonnage, lower-grade material in the footwall of the high-grade veins (Swainbank and others, 1998).
Commodities (Major) - Au; (Minor) - Ag, Cu, Pb, Sb, W, Zn
Development Status: Yes
Deposit Model: Schist-hosted auriferous shear systems with discrete and/or crushed veins and sk
14 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
358.9 - 443.8 Ma
|Quartzite and pelitic schist|
Age: Paleozoic (358.9 - 443.8 Ma)
Description: Fairbanks-White Mountains area: White felsic schist, micaceous quartzite, chloritic or actinolitic greenschist, greenstone, and marble. Lithologically, the protolith of combined Fairbanks schist and Wickersham units is continental shelf or slope facies which strongly resemble Windermere Supergroup in Canada. Alaska units offset right laterally along the Tintina fault system from Canada and are of same borderline Cambrian-Precambrian age, probably Hadrynian to Early Cambrian
Reference: Wilson, F.H., Hults, C.P., Mull, C.G, and Karl, S.M. (compilers). Geologic map of Alaska. doi: 10.3133/sim3340. U.S. Geological Survey Scientific Investigations Map 3340, pamphlet 196. 
|Devonian - Cambrian|
358.9 - 541 Ma
|Sedimentary; Clastic: shallow marine|
Age: Paleozoic (358.9 - 541 Ma)
Description: Eastern Alaska, Yukon, Mackenzie region, Yukon-Tanana upland
Comments: Orogen, magmatic arc/suite; Wilson & Hults, unpublished compilation, 2007-08
Reference: J.C. Harrison, M.R. St-Onge, O.V. Petrov, S.I. Strelnikov, B.G. Lopatin, F.H. Wilson, S. Tella, D. Paul, T. Lynds, S.P. Shokalsky, C.K. Hults, S. Bergman, H.F. Jepsen, and A. Solli. Geological map of the Arctic. doi:10.4095/287868. Geological Survey of Canada Map 2159A.