Prospect, Active

Commodities and mineralogy

Main commodities Ag; Au; Cu
Ore minerals pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale D-4
Latitude 58.8267
Longitude -135.0201
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Mystery prospect is at an elevation of 350 feet, on the north wall of lower Johnson Creek. It is 1.5 miles northwest of Berners Bay and 1.5 mile southeast of the Jualin mine (JU044), in the NE1/4 section 23, 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 rocks at the Mystery prospect are similar to those at the Fremming prospect (JU049). They consist of light green, chloritic phyllite and greenstone. Redman and others (1989), interpret the Mystery prospect as a stratabound, volcanogenic massive sulfide deposit. However, exploration by International Curator Resources Ltd., combined with observations of drill core from both the Jualin Mine (JU044) and the nearby Fremming prospect (JU049), indicate that the predominant host rock is probably 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 Mystery workings thus can be classified as greenstone and phyllite, but their protolith probably was Jualin Diorite (Kapler, 1988). Workings at the Mystery prospect include a water-filled shaft and several sloughed-in pits. The shaft is sunk on a 3-foot-thick layer of light green phyllite that contains 5-15 percent disseminated pyrite, and massive pyrite layers parallel to the foliation. The pyrite layers are up to 2 inches thick. Samples contain up to 1.4 part per million (ppm) gold, 1.5 ppm silver, and 5,500 ppm copper (Redman and others, 1989).
Geologic map unit (-135.021908862643, 58.8263739654053)
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 at the Mystery prospect include a water-filled shaft and several sloughed-in pits.
Indication of production None



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/, 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., 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