Prospect, Inactive

Commodities and mineralogy

Main commodities Au; Cu
Other commodities As; Sb
Ore minerals arsenopyrite; chalcopyrite
Gangue minerals quartz; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale MD
Quadrangle map, 1:63,360-scale C-4
Latitude 63.535
Longitude -154.539
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Tarn prospect is situated on a steep cirque headwall in the north-central Mystery Mountains at an elevation of 3,200 feet (975 m) in Section 1, T. 23 S., R. 22 E., of the Kateel River Meridian. Location is accurate to within about 500 feet (152 m).

Geologic setting

Geologic description

The Tarn prospect is within the eastern part of a northeast trending belt of porphyry-like copper-gold prospects that strike for 7 miles (11 km) in the central Mystery Mountains. The Tarn prospect consists of hydrothermal breccias in monzonitic dikes and small stocks that contain chalcopyrite, pyrite, tourmaline, and minor to trace arsenopyrite. Malachite occurs in hairline fractures in intrusive rocks; alteration and mineralization is not well developed in country-rock hornfels. The Tarn prospect is inferred to be Late Cretaceous, based on isotopic ages of plutonic rocks in Mystery Mountains (Moll and others, 1981). No assay data was found for this summary.
Geologic map unit (-154.541343872981, 63.5344035565292)
Mineral deposit model Porphyry Cu-Au (Cox and Singer, 1986; model 20c).
Mineral deposit model number 20c
Age of mineralization The Tarn prospect is inferred to be Late Cretaceous, based on isotopic ages of plutonic rocks in Mystery Mountains (Moll and others, 1981).
Alteration of deposit Biotite in hornfels; ankerite in intrusions.

Production and reserves

Workings or exploration Regional exploration work conducted by WGM Inc. in the late 1970s discovered the Tarn and related prospects in the Mystery Mountains (Andrews, 1978). From 1988 to 1990, American Copper and Nickel Company conducted regional exploration, which included a detailed airborne geophysical survey. ASA Inc. continued detailed exploration work from 1991 to 1997 (DiMarchi and others, 1997). No drilling has taken place on the property, and no assay data was found for this summary.
Indication of production None
Reserve estimates None.

Additional comments

See Copenhagen Hill (MD030), Frozen Creek (MD032), Pork Chop (MD031), and Mystery Mountains West (MD029) prospects.


MRDS Number 10307777


Andrews, Tom, 1978, Summary of Progress, Doyon Project, Mystery Mountains (Block 10): Anchorage, Alaska, WGM Inc., 24 p. (Held by Doyon, Limited, Fairbanks, Alaska, as proprietary report 78-42).
DiMarchi, J.J., and Frantz, P.S., 1997, Annual Report for 1997-Doyon Option Lands, Block 10: ASA Inc.-Montague Gold Joint Venture Report, Volume II: Unpublished report, 189 p. (Report held by Doyon, Limited, Fairbanks, Alaska.)
Reporters Bundtzen, T.K. (Pacific Rim Geological Consulting)
Last report date 6/6/1998