Unnamed (DeLangle Mountain)

Prospect, Inactive

Commodities and mineralogy

Main commodities Fe; Ti
Other commodities Cu; Ni
Ore minerals chalcopyrite; ilmenite; magnetite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale MF
Quadrangle map, 1:63,360-scale B-3
Latitude 58.409
Longitude -136.931
Nearby scientific data Find additional scientific data near this location
Location and accuracy
Magnetite deposits occur on the southern peaks of DeLangle Mountain. Deposits are found in the SE 1/4 section 11 and the NE 1/4 section 14 (T. 40 S., R. 51 E., of the Copper River Meridian). They probably extend into adjacent parts of sections 12 and 13 of the same township and range. The coordinates are the approximate center of a group of samples collected by the U.S. Bureau of Mines (Kimball and others, 1978, samples 046-050, fig. C-35) near elevation 2700-ft on DeLangle Mountain. The occurrences are about 1.5 miles southwest of the summit of DeLangle Mountain.
Leo Mark-Anthony (1977) reported another magnetite occurrence at the head of Boussole Bay approximately in the SW 1/4 NW 1/4, section 13 and the NW 1/4 SW 1/4 of the same section (T. 40 S., R. 51 E.).

Geologic setting

Geologic description

The mineralized sites are in the Astrolobe-DeLangle mafic stock, the southernmost layered mafic pluton exposed in the rugged Fairweather Range of Glacier Bay National Park and Preserve (Brew and others, 1978). The magmatic oxide minerals occur in a sub-horizontal hornblende-plagioclase pegmatite body that is approximately 100 feet wide and 20 feet thick. The body crops out discontinuously for 1,000 feet in gabbro near the northern contact of the Astrolobe-DeLangle layered mafic stock. Hornblende forms crystals to 1 foot in length in the pegmatitic phase. Segregations of magnetite less than 0.2 inch (5 mm) long are concentrated near larger hornblende and plagioclase crystals (Kimball and others, 1978, p. C120). The magnetite-rich body produces an extreme magnetic deviation.
Four chip samples, ranging from 18 to 40 feet in length, across the pegmatite body contained more than 10 percent iron and more than 1 percent titanium. Maximum copper content was 500 ppm.
At Boussole Bay, about one mile south of the pegmatite occurrence, a two-foot-wide band exposed over 225 feet contained 64 percent iron, 20 percent titanium, and 0.28 percent nickel (Kimball and others, 1978, p. C122-123). At this location, Mark-Anthony (1977) reported that an intrusive exposed over an area of approximately 1500 x 4000 feet contains about 10 percent iron.
Geologic map unit (-136.932899932337, 58.4086370114001)
Mineral deposit model Cumulus layered mafic intrusion with iron-titanium enriched hornblende-plagioclase pegmatites (segregations), possibly localized near the contact of the Astolobe-DeLangle synorogenic intrusion with schistose rocks of the Chugach terrane (Foley and others, 1997; Berg and others, 1972).
Age of mineralization Tertiary.

Production and reserves

Workings or exploration
A few claims are reported to have been staked on the south part of DeLangle Mountain, but there are no workings or evidence of mine activity. An occurrence chip-sampled by Kimball and others (1978, p. C120) contained greater than 10 percent iron, greater than 1 percent titanium and 150-500 ppm copper. The samples ranged from 18 to 40 feet in length.
Mark-Anthony (1977) reported samples from the head of Boussole Bay to contain as much as 64 percent iron and 0.28 percent nickel.
Indication of production None

Additional comments

Chugach terrane. The sites are in Glacier Bay National Park and Preserve.

References