Platypus Mountain

Occurrence in Alaska, United States with commodities Silver, Gold, Copper

Geologic information

Identification information

Deposit ID 10307474
Record type Site
Current site name Platypus Mountain

Geographic coordinates

Geographic coordinates: -146.4067, 62.85364 (WGS84)
Relative position This occurrence is on a rounded mountain labeled '4666' on the USGS 1:63,360-scale, topographic map; it is in a range locally called the Alphabet Hills. The occurrence is about 2.5 miles north-northeast of the point where Keg Creek bends from southwest to south. The occurrence is on the southwest flank of the mountain at an elevation of about 4100 feet. It is in the NW1/4NW1/4, section 5, T. 12 N., R. 6 W., Copper River Meridian. The prospect is known accurately within 500 feet.
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Geographic areas

Country State
United States Alaska


Commodity Importance
Silver Primary
Gold Primary
Copper Primary

Materials information

Materials Type of material
Azurite Ore
Chalcocite Ore
Chalcopyrite Ore
Malachite Ore
Pyrite Ore
Chlorite Gangue


  • (Local) Chloritization of felsic tuff and exhalite.

Mineral occurrence model information

Model code 90
USGS model code 24a
Deposit model name Massive sulfide, Cyprus
Mark3 model number 11

Nearby scientific data

(1) -146.4067, 62.85364

Comments on the geologic information

  • Geologic Description = The Platypus Mountain occurrence is in a thin unit of felsic tuff and exhalite within a 5000-meter-thick section dominated by mafic volcanic flows, tuffs, and breccia. The section also contains subordinate, weakly metamorphosed siltstone, claystone, and marble. The rocks are probable late Paleozoic in age. They are possibly correlative with the Pennsylvanian to Permian, Tetelna Formation and probably are correlative with the country rocks at the KFC occurrence (GU001). Prospecting in the area is handicapped by extensive Quaternary gravel which mantles many of the hills. Chalcopyrite, partly oxidized to azurite and malachite, occurs in stringers within a chloritic, rhyolite(?) flow-breccia at this occurrence (Arehart, 1982). Samples of the breccia contain as much as 4,100 ppm copper, 1.5 ppm silver, and 620 ppb gold. Semi-massive pyrite occurs in a cherty exhalite unit adjacent to the flow-breccia. Lenses and stringers of chalcocite, partly oxidized to malachite and azurite, are associated with the predominant mafic rocks. The pyritic, cherty, exhalite unit which hosts the flow-breccia extends east-west for about two miles.
  • Age = Diagenetic or epigenetic remobilization of copper and associated metals in a volcanic pile of Pennsylvanian and Permian age. Remobilization of copper may have occurred during green-schist metamorphism in the Jurassic.

Economic information

Economic information about the deposit and operations

Development status Occurrence

Comments on exploration

  • Status = Inactive

Comments on the workings information

  • Workings / Exploration = The Platypus Mountain occurrence was discovered in 1981 by a Noranda Exploration company team (Arehart, 1982). A gridded, soil survey and a CEM geophysical survey were completed on the prospect. The lands are mainly covered by selections of Ahtna Inc., a regional Native corporation.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF GU003

Bibliographic references

  • Deposit

    Arehart, G.B., 1982, Reconnaissance geology/geochemistry of the Alphabet Hills, Gulkana Quadrangle, Alaska: Noranda Exploration, 4 p., maps and appendices. (Report held by Ahtna Minerals Co., Anchorage, Alaska).

Comments on the references

  • Primary Reference = Arehart, 1982

General comments

Subject category Comment text
Deposit Model Name = Cyprus massive sulfide (Cox and Singer, 1986, model 24a)
Deposit Other Comments = Arehart (1982) reported numerous copper occurrences in intermediate and mafic volcanics near the Platypus Mountain occurrence. Additional information can be obtained from Ahtna Minerals in Anchorage, Alaska.

Reporter information

Type Date Name Affiliation Comment
Reporter 20-DEC-00 W.T. Ellis Alaska Earth Sciences
Reporter 20-DEC-00 Hawley, C.C. Hawley Resource Group
Reporter 20-DEC-00 W.J. Nokleberg U.S. Geological Survey