Cleary Hill

Mine, Active

Alternative names

Summit
Cleary
Freegold

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Cu; Pb; Sb; W; Zn
Ore minerals arsenopyrite; boulangerite; chalcopyrite; covellite; galena; gold; jamesonite; pyrite; scheelite; silver; sphalerite; stibnite; tetrahedrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale LG
Quadrangle map, 1:63,360-scale A-1
Latitude 65.0666
Longitude -147.4386
Nearby scientific data Find additional scientific data near this location
Location and accuracy The coordinates are near the main portal of the Cleary Hill Mine, which is labeled on the Livengood (A-1) quadrangle. The mine is north of Bedrock Creek, a tributary of Cleary Creek, in section 19, T. 3 N., R. 2 E., of the Fairbanks Meridian. The underground workings extend east-southeast from the portal for at least 2,000 feet. It is located with within the Golden Summit Project area. The location is accurate within 100 feet.

Geologic setting

Geologic description

As of 2008, this site and several others in the vicinity are being explored as a single entity by Freegold Ventures Inc. (Freeman, 2008). Considerable new mineralization has been discovered that indicates this is part of a larger mineralized system that is described as a separate ARDF site (LG205).
In the early 1900s, visible gold was reported in quartz veins within schist at what would become the Cleary Hill Mine (Prindle, 1910). The Cleary Hill Mine operated intermittently from 1911 to 1950. The Cleary Hill mine was the largest lode-gold producer in the Fairbanks Mining District, prior to the development of the Fort Knox mine.
The Cleary Hill Mine is in mafic volcanics, quartzites and quartz muscovite schists on the north flank of the Cleary antiform (Freeman and others, 1998). Mineralization style is characterized as schist-hosted shear zones with discrete and/or crushed gold-arsenic-antimony- quartz vein. The Cleary Hill vein strikes N70-80W and dips 45 to 70S. The dip of the vein varies according to the host rock, with steeper dips in more competent rocks and shallow dips in less competent rocks (Freeman and others, 1998). The mine consisted of over six levels that produced ore from quartz veins that contained coarse free gold, and minor 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 that occur in white to gray quartz veins that are 1 to 5 feet thick (Freeman and others, 1998).
During the 1986 field season, the 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 schist of mafic volcanic origin, that are typical of the the lower third of the Cleary Sequence. Dump samples contained arsenopyrite, pyrite, stibnite, jamesonite, native gold, and minor scheelite from 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 (LG146) and the Nordale adit of the Homestake mine (LG157). Along the shear zones, up to one-half percent scheelite is finely disseminated in chlorite-actinolite schist and less commonly forms coarse-grained aggregates in sulfide-free quartz. Gold values vary up to 0.558 ounce of gold per ton and appear to be higher in samples of siliceous exhalite, metarhyolite tuff and carbonaceous quartzite from the lower dumps at the mine. Reserve estimates of the waste dump made by Fairbanks Exploration Inc. in 1988 indicated the Cleary Hill mine dumps contain 71,176 tons of rock with an average grade of 0.159 ounce of gold per ton and 0.099 ounce of silver per ton (Fairbanks Exploration Inc., unpublished report, 1987; Fairbanks Exploration Inc., unpublished report, 1988).
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.
Geologic map unit (-147.441048043317, 65.066176820391)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c)
Mineral deposit model number 22c
Age of mineralization Probably about 90 Ma based on analogy with similar gold deposits nearby (Freeman, 2008).
Alteration of deposit Deposition of quartz, sericite and ankerite in alteration zones (Freeman and others, 1998).

Production and reserves

Workings or exploration
Mineralization was first discovered on the Freegold claim prior to 1910, near the junction of Cleary and Bedrock Creeks. Shortly after, rich surface outcrops were discovered at the surface at what would become the Cleary Hill Mine; selected samples assayed up to 5,950 ounces of gold per ton.
By the summer of 1910, the Main adit had been driven 630 feet on the Freegold 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 portal of the main adit (Brooks, 1911). In 1911, a five stamp Joshua Hendy mill, the first private mill in the Fairbanks Mining District, was put into operation on the Freegold claim. By the end of 1911, there were about 1,200 feet of underground workings (Brooks, 1912). By 1912, the Main adit had been driven over 1,050 feet and a second adit, the 215-foot-long Penrose adit, had been driven from a portal 140 feet higher than the Main adit (Cunningham, 1912). The two adits were connected by a 170-foot raise driven 900 feet from the portal of the Main adit. Twenty stopes were developed on the Main-adit level. A 30-foot winze was sunk 650 feet from the portal of the Main adit but water hampered sinking it. By the end of 1912, the winze exposed ore 300 feet below the surface (Cunningham, 1912). By the end of 1913, Brooks and others (1914) stated that the Main adit was 1,280 feet long, the Penrose adit was 280 feet long, and the Upper adit was 200 feet long. A total of 1,000 feet of workings were accessible from the main winze with working drifts at the 70- and 112-foot levels.
Funding allowed only 200 feet of new drifting in 1915 and the mine closed in September, 1915 (Brooks, 1916; Smith, 1917). 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, 1926; Moffit and others, 1927; Smith, 1930, B 813). This work included a 400-foot adit to reach the ore bodies at the 70-foot level of the Main winze. This Lower adit was collared at the elevation of Bedrock Creek near the mill site (Moffit and others, 1927). In addition, the Upper adit was extended to a length of 900 feet; 538 feet of crosscuts and a 40-foot raise extended from this adit (Stewart, 1931). The Penrose adit was extended 45 feet to a total length of 325 feet, and three crosscuts totaling 595 feet were driven from it. A 89-foot raise was driven to connect the Penrose and Upper adits. The Main adit was extended 192 feet to a total length of 1,472 feet , 51 feet of drift was driven on the Powder House shear zone, and 154 feet of drift was driven on the Doget shear zone. Near the mill a shaft was sunk 185 feet and a crosscut was driven from the bottom of the shaft for 280 feet. A shaft was also sunk on the ridge above the Upper adit. This shaft, known as the Deep shaft, was 50 feet deep; it had a 80-foot crosscut at the bottom (Stewart, 1931).
The mine resumed production in 1929 and rapidly became one of the largest operations in the district (Smith, 1930, B 810; Smith, 1932). 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 7 months during 1932 and development was concentrated below the Main adit level (Pilgrim, 1933). In 1938 the Cleary Hill mine drove 250 feet of new drifts and crosscuts, 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 surface projection of the Cleary Hill shear zone (Pilkington, 1970). Samples were only weakly anomalous in gold and silver.
The dumps of the mine were sampled by Fairbanks Exploration Inc. in 1986 (Fairbanks Exploration Inc., unpublished report, 1986). In 1988, Tri-Con Mining bulk sampled the upper and lower dumps to determine if this material could be processing economically.
Freegold Ventures Ltd. conducted drilling at Clear Hill mine area from 2011 to 2013. Cleary Hill area was included in with Dolphin zone for revised NI 43-101 compliant resource estimates created each year following drilling (Abrams and Giroux, 2013).
Indication of production Yes; medium
Reserve estimates As estimated by Abrams and Giroux (2013), based on drilling through 2013 and a cut-off grade of 0.3 gram of gold per ton, the Dolphin stock has an indicated resource of 79.800 million tonnes with an average grade of 0.66 gram of gold per tonne (or 1.683 million ounces of gold) and an inferred resource of 248.060 million tonnes with an average grade of 0.61 gram of gold per tonne (or 4.841 million ounces of gold). Included within this new resource is an oxide component.
Production notes
Waste dump reserve estimates made by Fairbanks Exploration Inc. in 1988 indicated the Cleary Hill mine dumps contained 71,176 tons of rock that averaged 0.159 ounce of gold per ton and 0.099 ounce of silver per ton (Freeman and others, 1987; Freeman and others, 1988).
Prior to World War II, 280,000 ounces of gold were mined from Cleary Hill (Abrams and Giroux, 2013).

References

MRDS Number A010678; A015431; A015519; D002655

References

Cunningham, A., 1912, Engineer describes the Rhoad-Hall mine: Tanana Magazine, Quartz Edition, p. 39-46.
Freeman, C.J., 2008, Executive summary report for the Golden Summit project, Fairbanks Mining District, Alaska: Unpublished Technical Report for Freegold Ventures Ltd., 112 p. (posted on www.sedar.com, March 31, 2008) http://www.sedar.com/GetFile.do?lang=EN&docClass=24&issuerNo=00004004&fileName=/csfsprod/data88/filings/01242796/00000001/k%3A%5CSedar%5Cfilings%5Clivework%5Cwkout%5C19016%5CCS_tech.pdf (as of December 23, 2014).
Freeman, C.J., Flanigan, B., Currey, J., Wolf, K., and Wietchy D.W., 1998, 1997 and 1998 Final report, Golden Summit project, Fairbanks mining district, Alaska: Avalon Development Corp. Geologic Report GS98-1, 37 p. (Report held by Freegold Recovery Inc. USA, Vancouver, British Columbia.)
Metz, P.A., Freeman, C.J., and Calvin, J.S., 1987, Bulk mineable vein-type and disseminated gold mineralization of the Fairbanks mining district, Alaska: Australasian Institute of Mining and Metallurgy, Pacific Rim Congress 87, Proceedings, p. 333-342.
Pilgrim, E.R., 1933, Progress of lode mining in interior Alaska, 1932: Alaska Territorial Department of Mines Miscellaneous Report 194-4, 11 p.
Porterfield, J. and Croff, C., 1986, Summary report for the Cleary Project, Fairbanks district, Alaska - 1985: Placid Oil Company report, 36 p.
Smith, S.S., 1917, The mining industry in the territory of Alaska during the calendar year 1915: U.S. Bureau of Mines Bulletin 142, 66 p.
Stewart, B.D., 1931, Report on cooperation between Territory of Alaska and the United States in making mining investigations: Alaska Territorial Department of Mines, Annual Report 1931.
Reporters C.J. Freeman, J.R. Guidetti Schaefer (Avalon Development Corporation); D.J. Grybeck (Port Ludlow, WA); V.C. Zinno (Alaska Earth Sciences, Inc.)
Last report date 12/23/2014