Unnamed

Occurrence, Inactive

Commodities and mineralogy

Main commodities Cr; Ni
Ore minerals chromite

Geographic location

Quadrangle map, 1:250,000-scale TL
Quadrangle map, 1:63,360-scale C-4
Latitude 62.728
Longitude -151.909
Nearby scientific data Find additional scientific data near this location
Location and accuracy Reed and others (1978, locality 23) locate this occurrence in the southwest quarter of Section 33, T. 31 N., R. 14 W., of the Seward Meridian adjacent to the Dall Glacier on a ridge at about 5000 feet within Denali National Park and Preserve.

Geologic setting

Geologic description

Reed and others (1978) report massive and disseminated chromite within sheared ultramafic rock at this locality. This is one of several chromite occurrences in a 25-mile long belt of alpine-type ultramafic bodies that are discontinuously exposed from the Dall Glacier northeast to the Lacuna Glacier which is part of the Dall Trend, described by C.C. Hawley and Associates, Inc. (1978, Fig. 4.1-(C)3 and Fig. 4.0-B). These chromite- and magnetite-bearing dunite and peridotite sills are shown by Reed and Nelson (1980) in a narrow belt of middle to upper Paleozoic sedimentary rocks that are exposed between the middle Tertiary (38 m.y.) Foraker pluton and the northwest trending fault which places the Paleozoic rocks over Mesozoic marine sedimentary rocks (KJs). Foley and others (1997, p. 431) suggest that these ultramafic bodies may be genetically related to the composite plutons (Tcp) of Reed and Nelson (1980) in the upper Yentna River.
Reed and others (1978) describe the occurrences in this belt of ultramafic rocks as magmatic segregations of podiform and disseminated chromite hosted in dunite sills. Chromite occurs as: (1) disseminated rounded grains 1-3 mm in diameter, (2) streaks and lenses, (3) irregular pods up to 6 feet long and (4) lens-like bodies up to 6 feet thick and 60 feet long throughout the dunite. Chromium content of 0.7 to 1% from typical dunite is given in Reed and others (1978). The average of 3 microprobe analyses of one sample: 58.4% Cr2O3, 21.1% FeO, 8.9% MgO, and 9.7% Al2O3. Other chromite occurrences in this trend are described in TL002, TL003, TL008, TL010 - 012, and TL055.
Geologic map unit (-151.911238608789, 62.7274518401546)
Mineral deposit model Podiform chromite (Cox and Singer, 1986; model 8a).
Mineral deposit model number 8a
Age of mineralization Mesozoic and (or) Paleozoic (Reed and Nelson, 1980) or Late Cretaceous/early Tertiary (?) (Foley and others, 1997).

Production and reserves

Workings or exploration Reconnaissance mapping, stream silt and rock sampling are all that have been done here. Chromium content of 0.7 to 1% from typical dunite is given in Reed and others (1978). The average of 3 microprobe analyses of one sample: 58.4% Cr2O3, 21.1% FeO, 8.9% MgO, and 9.7% Al2O3.
Indication of production None

Additional comments

Mineral occurrences in the Dall Trend are all within Denali National Park and Preserve.

References