Skip to main content

Cleary Hill (Freegold)

Mine, Active

Commodities and mineralogy

Geographic location

Quadrangle map, 1:250,000-scale LG
Quadrangle map, 1:63,360-scale A-1
Latitude 65.065
Longitude -147.4387
Nearby scientific data Find additional scientific data near this location
Location and accuracy This record covers an area about 3,000 feet long and several thousand feet wide, centered about 0.2 mile south of the Cleary Hill Mine buildings near the mouth of Bedrock Creek. The site represents a major exploration program by Freegold Ventures Ltd. that began in 1996 and was ongoing in 2008 (Freeman, 2008). The area includes several old prospects and the Cleary Hill Mine (LG114-116 and LG118-121) that were previously described individually in ARDF. These individual records are retained in ARDF for their geologic detail and history. The work by Freegold, however, has revealed much new mineralization in the area and the company now interprets the deposits in the area as a single system of veins, what they call the 'Cleary Hill vein swarm'.

Geologic setting

Geologic description The ARDF record for the Cleary Hill Mine (LG119) gives many of the details of the mining and geology of the best known and most productive of the deposits within this site. To summarize from Freeman (2008), the Cleary Hill Mine produced about 281,000 ounces of gold from 1908 to 1942 at an average grade of about 1.3 ounces of gold per ton. The mineralization consists of quartz veins with varying amounts of arsenopyrite, pyrite, boulangerite, jamesonite, tetrahedrite, and stibnite. The veins cut interbedded Paleozoic volcanic rocks, quartzite, and quartz mica schists on the north flank of the Cleary antiform. Most of the production was from the Cleary Hill vein system that strikes about N70-80W and dips about 45-70 degrees south. The system consists of a set of subparallel veins that were exposed on 6 levels. Regionally, the deposit is part of a east-northeast-trending mineral belt at least six miles long that is related to a series of parallel, northeast-trending fault zones spaced about 8,000 feet apart. The mineralization is middle Cretaceous (McCoy and others, 1997).

Although it was examined intermittently by several generations of geologists, there was little exploration in the area from 1942 to 1996. In 1996, Freegold Ventures Ltd., drilled 7 reverse-circulation holes that totaled 2,080 feet. The drilling confirmed that the mineralization at the Cleary Hill Mine persisted below the lowest underground workings. In 1997 and 1998, they core drilled another 9 holes. Geochemical soil sampling indicated that the mineralization was much more extensive than just in the old mine workings. In 2000, one hole cut a previously unknown, mineralized shear zone, the Currey Zone. The Currey mineralization is marked by pervasive quartz veining and sericitic alteration and consists of coarse-grained pyrite and fine-grained sulfides and sulfosalts in the quartz. Several intercepts are characterized by a strong arsenic and antimony signature. In 2002, Freegold did 4.5 line miles of ground geophysical surveys. From 2002 to 2006, Freegold drilled at least 6 more core holes and dug several thousand feet of trenches over the Cleary Hill Mine workings and adjacent areas; this revealed many new veins and mineralized shear zones. In 2006, they collected 9,900 tons of bulk samples from surface exposures of 8 separate auriferous shear zones, to analyze and characterize the ore. They also collected 3,000 tons of material from the old mine dumps. Encouraging results from these samples led to a major drilling program beginning in December, 2006; it included 504 rotary-air-blast holes that totaled 28,602 feet along 14 fences of holes. The detailed results of this drilling and other Freegold exploration since 1996 is available in Freeman (2008).

As a result of this work, Freeman (2008) has outlined a system of pervasive mineralization and veins-many previously unrecognized -that extend for over 3,000 feet along strike to a depth of 1,000 feet. The mineralization is open at both ends and at depth. The mining before WWII was mainly on a few structurally continuous, high-grade quartz veins in a master shear zone. The newly revealed mineralization is much more extensive and structurally complex, featuring both pre- and post-mineralization faulting and several stages of deposition. Consequently, it is difficult to correlate the veins mined underground at the Cleary Hill Mine with those those newly discovered in the recent surface workings and drill holes.

Geologic map unit (-147.441147864062, 65.0645767963033)
Mineral deposit model Gold-arsenic-antimony quartz veins.
Age of mineralization Middle Cretaceous by analogy with other mineralization in the area.
Alteration of deposit Sericitic alteration adjacent to the quartz veins.

Production and reserves

Workings or exploration The ARDF record for the Cleary Hill Mine (LG119) that was in operation from 1908 to 1942 gives many of the details of the mining and the geology of the best known of the deposits within this site. Although it was examined intermittently by several generations of geologists, there was little exploration in the area from 1942 to 1996. In 1996, Freegold Ventures Ltd., drilled 7 reverse-circulation holes that totaled 2,080 feet. The drilling confirmed that the mineralization at the Cleary Hill Mine persisted below the lowest underground workings. In 1997 and 1998, they core drilled another 9 holes. Geochemical soil sampling indicated that the mineralization was much more extensive than just in the old mine workings. In 2000, one hole cut a previously unrecognized mineralized shear zone, the Currey Zone. In 2002, Freegold did 4.5 line miles of ground geophysical surveys done. From 2002 to 2006, Freegold drilled at least 6 more core holes and dug several thousand feet of trenches over the Cleary Hill Mine workings and adjacent areas; this revealed many new veins and mineralized shear zones. In 2006, they collected 9,900 tons of bulk samples of surface exposures from 8 separate auriferous shear zones to analyze and characterize the ore. They also collected 3,000 tons of material from the old mine dumps. Encouraging results from these samples led to a major drilling program beginning in December, 2006; it included 504 rotary-air blast holes that totaled 28,602 feet along 14 fences of holes. The detailed results of this drilling and other Freegold exploration since 1996 is available in Freeman (2008).
Indication of production Yes; medium
Production notes The Cleary Hill Mine (LG119) within this site produced about 281,000 ounces of gold from 1908 to 1942 at an average grade of about 1.3 ounces of gold per ton.

References

References
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).
McCoy, Dan, Newberry, R.J., Layer, Paul, and others, 2007, Pluton-related gold deposits of Interior Alaska, in Goldfarb, R.J., and Miller, L.D., (editors): Economic Geology Monograph 9, p. 191-241.
Reporters D.J. Grybeck (Port Ludlow, WA)
Last report date 6/5/2008