Fremming

Prospect, Active

Commodities and mineralogy

Main commodities Ag; Au; Cu; Pb; Zn
Ore minerals chalcopyrite; galena; gold; pyrite; sphalerite
Gangue minerals calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale D-4
Latitude 58.8317
Longitude -135.0355
Nearby scientific data Find additional scientific data near this location
Location and accuracy This prospect is at an elevation of about 350 feet on Johnson Creek. It is 2 miles northwest of Berners Bay and 3/4 mile southeast of the Jualin Mine (JU044), in the SW1/4 section 14, T. 35 S., R. 62 E. of the Copper River Meridian. The location is accurate.

Geologic setting

Geologic description

Note: Beginning in the 1990s, this and other old mines and prospects in the vicinity were consolidated by Coeur-Alaska into a single property (Birak, 2006). They have carried out major new drilling and underground exploration that better defines the mineralization, largely blurs the geologic distinction among the old deposits, and extends the ore bodies greatly. They have developed a coherent modern interpretation of the mineralization as a single deposit which Coeur-Alaska intends to mine as a unit. This deposit is described separately in ARDF as the Jualin (Coeur-Alaska) deposit (JU262). For geologic reference purposes and for their historic value, the pre-Coeur-Alaska data for this and the other old mines and prospects that Coeur-Alaska consolidated are retained in ARDF.
The Fremming prospect was discovered by Frank Fremming in about 1897. Fremming drove a 360-foot adit and sank a 85-foot inclined shaft by 1905. The deposit consists of a 6-foot thick phyllite layer that contains 1 to 3 percent disseminated pyrite and thin, stratiform lenses of pyrite. The stratiform pyrite has been traced on the surface for 800 feet by trenching (Redman and others, 1989). Underground, at the end of the adit, there is a 6-foot-wide zone of sulfide-bearing schist and quartz-calcite stringers that contains pyrite, chalcopyrite, galena, sphalerite, and free gold (Knopf, 1911). A shear zone near the Fremming shaft contains a quartz vein with sphalerite, galena, pyrite, and chalcopyrite (Redman and others, 1989). Redman and others (1989), interpret the Fremming prospect as a volcanogenic massive sulfide deposit. However, exploration of the Fremming prospect area by International Curator Resources Ltd., combined with observations of drill core from both the Jualin mine (JU044) and the Fremming prospect, indicate that the predominant host rock is Jualin Diorite (Barnett and others, 1988). This interpretation is supported by Kaplar (1988) who showed that the diorite loses its textural and mineralogical identity as shearing becomes more intense. Rocks at or near the Fremming workings thus can be classified as greenstone and phyllite but their protolith probably was Jualin Diorite (Kapler, 1988). Exploratory drilling by International Curator Resources Ltd. encountering minor zones of anomalous metal values (Barnett and others, 1988).
Geologic map unit (-135.037310835883, 58.8313731201954)
Mineral deposit model Volcanogenic massive sulfide deposit or a remobilized epigenetic copper-lead-zinc-gold deposit?
Age of mineralization Hydrothermal muscovite from veins in the Jualin mine are 53.2 Ma to 55.5 Ma (Miller and others, 1994). This coincides with the 55 Ma age of the other mesothermal gold veins in the Juneau Gold Belt (Goldfarb and others, 1997).
Alteration of deposit Chloritic.

Production and reserves

Workings or exploration Workings consist of a 360-foot adit and an 85-foot inclined shaft.
Indication of production None

References

MRDS Number A012022

References

Barnett, J.C., Hayden, T.J., Bair, D.K., and Croff, T.C., 1988, 1987 summary report, Jualin gold project, Berners Bay District: Unpublished report for International Curator Resources, Ltd., 75 p.
Birak, D.J., 2006, Kensington gold project: Unpublished Technical Report for Cour d'Alene Mines, 116 p. (posted on www/.sedar.com, April 20, 2006).
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.
Kaplar, J., 1988, Jualin prospect analysis--Petrographic microprobe, SEM, and XES geochemical analysis of core: Unpublished report for International Curator Resources, Ltd., Denver, Colo., 18p.
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
Miller, L.D., Goldfarb, R.J., Snee, L.W., Gent, C.A., and Kirkham, R.A., 1995, Structural geology, age, and mechanisms of gold vein formation at the Kensington and Jualin deposits, Berners Bay district, southeast Alaska: Economic Geology, v. 90, p. 343-368.
Reporters J.C. Barnett and L.D. Miller (Juneau, Alaska ); D.J. Grybeck (Port Ludlow, WA)
Last report date 6/5/2008