Unnamed (northwest of Mt. Marchainville)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Fe; Ti
Other commodities Cu
Ore minerals chalcopyrite; ilmenite; malachite

Geographic location

Quadrangle map, 1:250,000-scale MF
Quadrangle map, 1:63,360-scale B-4
Latitude 58.476
Longitude -137.084
Nearby scientific data Find additional scientific data near this location
Location and accuracy The occurrence is at an elevation of about 2000 feet about 3 miles northwest of Mt. Marchainville, and 1.5 miles southeast of Finger Glacier. It is near the approximate center of section 24, T. 39 S., R. 50 E., of the Copper River Meridian. The location is accurate to about 0.1 mile based on transposition of Rossman's (1963) sample no. 40 to the topography of the 1961 edition of the Mt. Fairweather B-4 quadrangle. The location is the same as number 15 of Kimball and others (1978), and location 7 of Cobb (1972). MacKevett and others (1971, p. 52) cite Rossman for authority on copper-staining close to this location. The approximate location of copper-staining reported by MacKevett and others (1971--location 82) is about 0.25 mile southeast of the coordinate position.

Geologic setting

Geologic description

The occurrence is within the Fairweather terrane of Brew and others (1978). It is in the southwest part of the Crillon-LaPerouse mafic-ultramafic body which is intruded into biotite and hornblende schist of the upper Chugach terrane of Berg and others (1972).
At the occurrence, an ilmenite-rich layer in gabbro is approximately 50-feet thick. Its strike length is uncertain because of the extremely rough topography. Rossman (1963) determined 1 - 10 percent titanium by spectroscopic analyses (sample 52A Rm g 40). The sample also contained up to 100 percent iron, but only 0.1 - 0.1 percent of copper, cobalt, or nickel. Ilmenite determined by weight in mineral separates ranged from 5 to 11.4 weight percent.
A nearby copper (malachite-stained) occurrence is near or at the contact of the intrusion; possibly the occurrence represents oxidized cupriferous amphibolite schist at the contact.
Geologic map unit (-137.085915734036, 58.4756357020104)
Mineral deposit model Possibly Bushveld Fe-Ti-V (Cox and Singer, 1986; model 3?). Magmatic segregation of ilmenite in layered mafic-ultramafic intrusion. The mafic intrusion is synorogenic (Foley and others, 1997).
Mineral deposit model number 3?
Age of mineralization Tertiary.
Alteration of deposit Local iron-and copper-(malachite) staining.

Production and reserves

Workings or exploration No workings, surface outcrop only.
Indication of production None
Reserve estimates Possibly extensive deposits are suggested by the thickness (50-feet) and by several nearby ilmenite-rich occurrences.

Additional comments

Chugach terrane. The ilmenite locality and the nearby copper-stained sites are in Glacier Bay National Park and Preserve.

References

MRDS Number A013132

References

Foley, J.Y., Light, T.D., Nelson, S.W., and Harris, R.A., 1997, Mineral occurrences associated with mafic-ultramafic and related alkaline complexes in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 396-449.
Reporters C.C. Hawley (Hawley Resource Group)
Last report date 4/4/1999