Unnamed (south of Monte Cristo Creek)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Mo
Ore minerals molybdenite; pyrite
Gangue minerals gypsum; quartz

Geographic location

Quadrangle map, 1:250,000-scale NB
Quadrangle map, 1:63,360-scale A-5
Latitude 62.1988
Longitude -143.0179
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is at an elevation of about 4,500 feet on the south valley wall of Monte Cristo Creek, about 1.1 miles southeast of elevation 6210, and 1.4 miles east-northeast of elevation 5535. The site is in the NW1/4 of section 21, T. 5 N., R. 13 E. of the Copper River Meridian. This is National Park Service locality WRST-21 (unpublished data) and the coordinates for this occurrence were provided by the National Park Service.

Geologic setting

Geologic description

An unpublished National Park Service map and accompanying database identify this locality as a porphyry molybdenum prospect. Bedrock in this part of Monte Cristo Creek is marine and subaerial volcanic and volcaniclastic rocks of the Lower Cretaceous, Chisana Formation (Richter, 1976). Nearly horizontal volcanic rocks of the upper Tertiary and Quaternary, Wrangell Lava unconformably overly the Chisana Formation. The Chisana Formation is extensively hydrothermally altered and characteristically replaced by gypsum-quartz-sulfide assemblages (Richter, 1976). Tertiary hornblende-plagioclase porphyry crops out downstream in Monte Cristo Creek in the Nabesna A-4 quadrangle. A K/Ar age for this porphyry is 17 Ma (Richter, 1973). A porphyry molybdenite prospect (NB037) located downstream just inside the Nabesna A-4 quadrangle is at the contact of a granodiorite pluton inferred to be mid-Cretaceous in age (Richter, 1976).
Geologic map unit (-143.020024845583, 62.1984084255318)
Mineral deposit model Porphyry Mo, low-F (Cox and Singer, 1986; model 21b).
Mineral deposit model number 21b
Age of mineralization Cretaceous or Tertiary? Hydrothermal alteration may be related to emplacement of hornblende-plagioclase porphyry downstream in the Nabesna A-4 quadrangle that has a 17 Ma K/Ar age (Richter, 1973). A porphyry molybdenite prospect (NB037) downstream just inside the Nabesna A-4 quadrangle is at the contact of a granodiorite pluton inferred to be mid-Cretaceous (Richter and others, 1975).
Alteration of deposit Gypsum-quartz-sulfide (pyrite?) replacement of Chisana Formation volcanic rocks. Oxidation is evidenced by abundant iron-oxide staining.

Production and reserves

Indication of production None

Additional comments

The prospect is in the Wrangell-St. Elias National Preserve.

References