Prospect in Alaska, United States with commodities Gold, Copper, Arsenic, Antimony

Geologic information

Identification information

Deposit ID 10307777
Record type Site
Current site name Tarn

Geographic coordinates

Geographic coordinates: -154.54197, 63.53449 (WGS84)
Relative position 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).
(click for info)

Geographic areas

Country State
United States Alaska


Commodity Importance
Gold Primary
Copper Primary
Arsenic Secondary
Antimony Secondary

Materials information

Materials Type of material
Arsenopyrite Ore
Chalcopyrite Ore
Quartz Gangue
Tourmaline Gangue


  • (Local) Biotite in hornfels; ankerite in intrusions.

Mineral occurrence model information

Model code 78
USGS model code 20c
Deposit model name Porphyry Cu-Au
Mark3 model number 34

Nearby scientific data

(1) -154.54197, 63.53449

Comments on the geologic information

  • 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. Malichite 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.
  • Age = the Tarn prospect is inferred to be Late Cretaceous, based on isotopic ages of plutonic rocks in Mystery Mountains (Moll and others, 1981).

Economic information

Economic information about the deposit and operations

Development status Prospect

Comments on exploration

  • Status = Inactive

Mining district

District name McGrath

Comments on the workings information

  • Workings / 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.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF MD027

Bibliographic references

  • Deposit

    Andrews, Tom, 1978, Summary of Progress, Doyon Project, Mystery Mountains, (Block 10): Anchorage, Alaska, WGM Inc., 24 pages (Held by Doyon Ltd., as proprietary report 78-42).

  • Deposit

    Moll, E.J., Silberman, M.L., and Patton, W.W. Jr., 1981, Chemistry, mineralogy, and K-Ar ages of igneous and metamorphic rocks of the Medfra quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-811C, 15 p., 2 sheets, scale 1:250,000.

  • Deposit

    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.)

Comments on the references

  • Primary Reference = DiMarchi and others, 1997

General comments

Subject category Comment text
Deposit Model Name = Porphyry Cu-Au (Cox and Singer, 1986; model no. 20c)
Deposit Other Comments = See Copenhagen Hill (MD030), Frozen Creek (MD032), Pork Chop (MD031), and Mystery Mountains West (MD029) prospects.

Reporter information

Type Date Name Affiliation Comment
Reporter 06-JUN-98 Bundtzen, T.K. Pacific Rim Geological Consulting