Gold Fork

Prospect, Active

Alternative names

Silver Falls
Kathleen

Commodities and mineralogy

Main commodities Ag; Au
Other commodities Pb; Sb; Zn
Ore minerals arsenopyrite; galena; pyrite; sphalerite; stibnite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale B-1
Latitude 58.3343
Longitude -134.2566
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is on the northwest valley wall of Gold Fork at an elevation of 1,400 feet. It is about 1 mile upstream from the mouth of Carlson Creek in the NW1/4NW1/4 section 11, T. 41 S., R. 68 E. of the Copper River Meridian. The location is accurate.

Geologic setting

Geologic description

The Gold Fork deposit was discovered in 1911 and developed by a 10-foot adit and a 150-foot adit. The deposit was explored by Curator American in 1988 and drilled by Kennecott Exploration and Echo Bay Mines in the early 1990s. The prospect is currently (2001) being explored (Dale Henkins, oral communication, 2001). The Gold Fork deposit consists of at least four, fault-controlled quartz veins and quartz-breccia zones in biotite-hornblende gneiss and banded calc-schist. The veins can be traced along the north side of Gold Fork on the surface for nearly 1,000 feet and vertically for nearly 600 feet. Reconnaissance drilling by Kennecott suggests a total strike length of over 8,000 feet. The veins are slightly banded, with alternating layers of quartz and graphitic schist, and are locally brecciated. The banded veins dip north to northeast, and contain pyrite, stibnite, arsenopyrite, and galena. Four major veins up to 20 feet thick have been identified. Noteworthy intercepts from Kennecott core drilling in 1992 included 17 feet with 0.35 ounce of gold per ton and 39 feet with 0.22 ounce of gold per ton (Huber and Barnett, 1989; Dale Henkins, oral communication, 2001). Quartz vein stockworks and stringers also occur as well as intense silicification in the adjacent wallrock. The veins appear to have undergone brecciation and subsequent healing by quartz and minor pyrite. These veins are crosscut by multiple generations of quartz-pyrite veinlets with associated clay-ankerite wall rock alteration (Redman and others, 1989).
This prospect is in the Juneau Gold Belt, which consists of more than 200 gold-quartz vein deposits that have produced nearly 7 million ounces of gold. These gold-bearing mesothermal quartz vein systems form a 160-km-long by 5- to 8-km-wide zone along the western margin of the Coast Mountains. The vein systems are in or near shear zones adjacent to west-verging, mid-Cretaceous thrust faults. The veins are hosted by diverse, variably metamorphosed, sedimentary, volcanic, and intrusive rocks. From the Coast Mountains batholith westward, the host rocks include mixed metasedimentary and metavolcanic sequences of Carboniferous and older, Permian and Triassic, and Jurassic-Cretaceous age. The sequences are juxtaposed along mid-Cretaceous thrust faults (Miller and others, 1994). The sequences are intruded by mid-Cretaceous to middle Eocene plutons, mainly diorite, tonalite, granodiorite, quartz monzonite, and granite. Sheetlike tonalite plutons emplaced just east of the Juneau Gold Belt and undeformed granite and granodiorite bodies that are emplaced farther to the east are between 55 and 48 Ma (Gehrels and others, 1991). The structural grain of the belt is defined by northwest-striking, moderately to steeply northeast-dipping, penetrative foliation that developed between Cretaceous and Eocene time (Miller and others, 1994). The majority of the veins in the Juneau Gold Belt strike northwest. Isotopic dates indicate that the auriferous veins in the Juneau Gold Belt formed between 56 and 55 Ma (Miller and others, 1994; Goldfarb and others, 1997).
Geologic map unit (-134.258365396956, 58.3339752386931)
Mineral deposit model Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization Isotopic dates indicate that the auriferous veins in the Juneau Gold Belt formed between 56 and 55 Ma (Miller and others, 1994; Goldfarb and others, 1997).
Alteration of deposit Silicification and clay-ankerite wall rock alteration.

Production and reserves

Workings or exploration The Gold Fork deposit was discovered in 1911 and developed by a 10-foot adit and a 150-foot adit. The prospect was explored by Curator American in 1988 and drilled by Kennecott Exploration and Echo Bay Mines in the early 1990s. The prospect is currently (2001) being explored.
Indication of production None

References

MRDS Number A012021

References

Gehrels, G.E., McClelland, W.C., Samson, S.D., and Patchett, P.J., 1991, U-Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska: Canadian Journal of Earth Sciences, v. 28, no. 8, p.1285-1300.
Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 151-190.
Huber, J.A., and Barnett, J.C., 1989, 1988 Progress Report, Gold Fork Project: Unpublished report for International Curator Resources, Ltd., Denver, Colo., 35 p.
Miller, L.D., Goldfarb, R.J., Gehrels, G,E., and Snee, L.W., 1994, Genetic links among fluid cycling, vein formation, regional deformation, and plutonism in the Juneau gold belt, southeastern Alaska: Geology, v. 22, p. 203-206.
Reporters J.C. Barnett and L.D. Miller (Juneau, Alaska )
Last report date 12/15/2001