|Quadrangle map, 1:250,000-scale||FB|
|Quadrangle map, 1:63,360-scale||D-3|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The Clipper mine is located in the SE1/4SW1/4 sec. 32, T. 1 N., R. 2 W., Fairbanks Meridian, near the head of Eva Creek. It is approximately 1.4 miles north-northeast of the town of Ester at an elevation of about 1,100 feet. It is included in locality 14 of Cobb (1972 [MF 410]).|
The Clipper mine consists of gold-bearing quartz-sulfide zones along a north-northwest-trending, nearly vertical fracture that cuts foliation and compositional banding in polymetamorphic schist and quartzite (Bundtzen and others, 1982 [OFR 157]). The 1- to 2-inch wide vein is laterally displaced 2 to 11 feet by seven cross-cutting faults that strike N. 50-85 E. and dip 35-65 N.
In 1982, Bundtzen and others (1982 [OFR 157]) spent seven days mapping approximately 800 feet of underground workings at the Clipper gold mine, and the following is a summary of their findings. Bedrock in the area is Fairbanks Schist that consists of four lithologic units: chlorite-muscovite schist, quartz-mica schist with quartzite bands, a porphyroblastic feldspathic schist, and a bleached, garnetiferous biotite-muscovite schist. The more quartzose rocks form blocky, resistant walls in mine workings, whereas the more micaceous rocks form irregular walls, cavities, and open spaces. In thin section, the schist is composed of as much as 50 percent white mica, 30 to 65 percent interlocking quartz grains, minor albitized plagioclase, chlorite and very minor garnet. tourmaline, sphene and zoisite inclusions. The mineral assemblages suggest that a prograde, upper greenschist facies metamorphic event (garnet plus plagioclase plus biotite plus white mica) has been overprinted by a lower grade metamorphic event (chlorite plus albite plus zoisite).
Structurally, an early crenulation-kink-band deformation (F1) consistently records a northwest-southeast stress field that plunges to the northeast. During a later F2 event, the rocks were gently folded into synclines and anticlines with amplitudes ranging from 6 to 50 feet. A major, north-northwest-trending, steeply dipping, joint set cuts the layered rocks underground. These structural features apparently served as primary channels for ore fluids; the majority of veins in the drift and stopes are parallel to these joint sets. A few prominent, but unmineralized, steeply dipping joints and fractures strike N 25-35 W.
The fault above the Clipper vein varies from N5E to N25W and generally trends N 5-10 W, almost normal to regional structure. The mineralized shears dip from 65 SW. to vertical, and only rarely does the fault system associated with the veins dip steeply to the northeast. The vein system south of an old seismograph station consists of thin, gold-bearing veinlets, 1 to 3 inches wide in 2- to 4-foot-wide, horse-like stockwork zones. Within these zones, hand sorting produced very high grade ore; one 3-inch channel sampled from the Bonanza winze assayed 26.09 ounces of gold per ton. North of the seismograph station, the vein occupies a significantly wider (4 to 24 inches) zone in single or multiple splays. Assays from eight channel samples along two major sections of ore averaged 0.87 ounce of gold per ton over an average width of 12 inches. The last structural event in the Clipper mine is represented by a series of faults that trend N 50-85 E and dip 35-55 N; they offset the Clipper vein system laterally from 2 to 11 feet.
This deposit is a hydrothermal vein; massive, fractured to euhedral, crystalline quartz constitutes greater than 95 percent of the vein material. Wall-rock silicification was followed by at least two stages of silica vein injection; the last was accompanied by free gold and disseminated to rare massive arsenopyrite, stibnite, and boulangerite. In one specimen, free gold is intimately associated with fine needles of boulangerite that apparently intrude arsenopyrite. Free gold observed in hand specimens occurs as small angular segregations or thin plates averaging about 0.5 mm in length. Select samples showed masses of free gold as much as a quarter of an inch in diameter. One sample of gold was 768 fine and had silver as the major impurity. Other samples analyzed ranged from 682.9 to 790.4 fine (Glover, 1950).According to G.P. Lounsbury, the mine owner at the time of Bundtzen's visit in 1982, the most productive years were 1937-42 when approximately 1,400 ounces of gold worth about $50,000 were recovered from an unknown amount of high-grade, hand-sorted ore (Bundtzen and others, 1982 [OFR 157, p. 3]). Investigations by Hill (1933) and Pilgrim (1931, 1932, 1933) indicated that by 1932, a 235- to 250-foot drift had been driven to explore a 1- to 8-inch-thick, steeply dipping vein trending N 10-15 E. Most of these workings were mined by hand by the owner, Lloyd Lounsbury (D. Wietchy, oral communication, 2000). By 1982, there was at least 800 feet of underground workings but there is no record of recent production (Bundtzen and others, 1982 [OFR 157]).
|Geologic map unit||(-148.006429428239, 64.8665636911173)|
|Mineral deposit model||Schist-hosted gold-quartz vein|
|Age of mineralization||Auriferous quartz veins cut Fairbanks Schist; these are considered to be pre-Devonian and probably Proterozoic in age (Newberry and others, 1996).|
|Alteration of deposit||Wall-rock silicification extends at least 10 inches into both the footwall and hanging wall of the vein (Bundtzen and others, 1982 [OFR 157]). Later hydrothermal silica vein injection was accompanied by the emplacement of free gold with arsenopyrite, stibnite, and boulangerite.|
|Workings or exploration||Investigations by Hill (1933) and Pilgrim (1930, 1931, 1932 indicate that by 1932, a 235- to 250-foot drift had been driven to explore a 1- to 8-inch thick, steeply dipping vein trending N. 10-15 E. Most of these workings were mined by hand by the owner at that time, Lloyd Lounsbury (D. Wietchy, oral communication, 2000). In 1982, Bundtzen and others (1982 [OFR 157]) spent seven days mapping approximately 800 feet of underground workings at the mine. It was unclear to Bundtzen and his colleagues if the early work reported by Hill and Pilgrim were part of the workings accessible to them or were part of older, caved workings on the hillside about 60 vertical feet above the portal open to them.|
|Indication of production||Yes; small|
|Production notes||There is no record of production prior to 1932. In 1937, nineteen tons of ore averaging 0.8 ounce of gold per ton was milled, and in 1938, twenty-five tons of ore of the same grade was milled (Reed, 1938). According to G.P. Lounsbury, the mine owner at the time of Bundtzen's visit in 1982, the most productive years were 1937-42, when approximately 1,400 ounces of gold worth $50,000 were recovered from an unknown amount of high-grade, hand-sorted ore (Bundtzen and others, 1982 [OFR 157, p. 3]).|
Bundtzen, T.K., Robinson, M.S., Kline, J.T., and Albanese, M.D., 1982, Geology of the Clipper gold mine, Fairbanks mining district, Alaska: Alaska Division of Geological and Geophysical Surveys Open-File Report 157, 13 p., 1 sheet, scale 1:120.
Chapman, R.M., and Foster, R.L., 1969, Lode mines and prospects in the Fairbanks district, Alaska: U.S. Geological Survey Professional Paper 625-D, 25 p., 1 plate.
Cobb, E.H., 1972, Metallic mineral resources map of the Fairbanks quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-410, 1 sheet, scale 1:250,000.
Cobb, E.H., 1976, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Fairbanks quadrangle, Alaska: U.S. Geological Survey Open-File Report 76-662, 174 p.
Glover, A.E., 1950, Placer gold fineness: Alaska Territorial Department of Mines Miscellaneous Report 195-1, 38 p.
Hill, J.M., 1933, Lode deposits of the Fairbanks district, Alaska: U.S. Geological Survey Bulletin 849-B, p. 29-163.
Killeen, P.L., and Mertie, J.B., 1951, Antimony ore in the Fairbanks District, Alaska: U.S. Geological Survey Open-File Report 51-46, 43 p.
Newberry, R.J., Bundtzen, T.K., Clautice, K.C., Combellick, R.A., Douglas, T., Laird, G.M., Liss, S.A., Pinney, D.S., Reifenstuhl, R.R., and Solie, D.N., 1996, Preliminary geologic map of the Fairbanks mining district, Alaska: Alaska Division of Geological and Geophysical Surveys Public Data File 96-16, 17 p., 2 sheets, scale 1:63,360.
Pilgrim, E.R., 1930, Various properties in the Fairbanks district: Alaska Territorial Department of Mines Miscellaneous Report 58-2, 38 p.
Pilgrim, E.R., 1931, Gold lodes of the Nenana district: Alaska Territorial Department of Mines Miscellaneous Report 58-3, 11 p.
Pilgrim, E.R., 1932, Progress of lode mining in interior Alaska, 1930: Alaska Territorial Department of Mines Miscellaneous Report 194-4, 28 p.
|Reporters||J.R. Guidetti Schaefer and C.J. Freeman (Avalon Development Corporation)|
|Last report date||7/31/2001|