Brady Glacier nickel-copper deposit

Site Name

Primary: Brady Glacier nickel-copper deposit

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Commodity

Primary: Nickel
Primary: Copper
Secondary: Iron
Secondary: Chromium
Secondary: Rhodium
Secondary: Platinum
Secondary: Lead
Secondary: Palladium
Secondary: Titanium
Secondary: Tellurium

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Location

State: Alaska
District: Glacier Bay

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Land Status

Not available

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

Record Type: Site
Operation Category: Prospect
Operation Type: Unknown
Years of Production:
Organization:
Significant:

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Physiography

Not available

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Mineral Deposit Model

Model Name: Stillwater Ni-Cu

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Orebody

Not available

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Structure

Not available

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Alterations

Not available

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Rocks

Not available

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Analytical Data

Not available

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Materials

Ore: Altaite
Ore: Mackinawite
Ore: Pyrite
Ore: Pentlandite
Ore: Niccolite
Ore: Magnetite
Ore: Ilmenite
Ore: Cubanite
Ore: Chromite
Ore: Chalcopyrite
Ore: Bornite
Ore: Violarite

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Comments

Comment (Commodity): Ore Material = hexagonal

Comment (Reference): Primary Reference = Himmelberg and Loney, 1981

Comment (Deposit): Other Comments = and scale of operation.. Patented claims at the site are now owned by the University of Alaska; they are in Glacier Bay National Park and Preserve.

Comment (Exploration): Status = Inactive

Comment (Reserve-Resource): Reserves = Drill-indicated reserves are about 100 million tons of rock containing 0.5 percent nickel and 0.3 percent copper. PGEs average about 0.18 ppm and exceed 1 ppm in massive sulfide units and in flotation concentrates. About 250,000 ounces of PGEs exist in the drilled Ni-Cu resource area (Czamanske and others, 1981).

Comment (Deposit): Model Name = Disseminated to massive sulfide deposit formed from immiscible sulfide fluid injected into cumulus layers of silicate minerals. Similar to Stillwater Ni-Cu and Duluth Cu-Ni-PGE (Cox and Singer, 1986; models 1 and 5a). The deposits are synorogenic to mid-Tertiary tectonic activity (Foley and others, 1997, p. 441-443).

Comment (Deposit): Model Number = 1, 5a

Comment (Geology): Age = Probably mid-Tertiary (Goldfarb, 1997; Himmelberg and Loney ,1981).

Comment (Geology): Geologic Description = The Brady Glacier nickel-copper deposit is near the local floor of the Crillon-LaPerouse layered intrusion near an east-pointing embayment of the contact of the intrusive (Himmelberg and Loney, 1981, figs. 2 and 3, p. 4-5; Cornwall, 1971, p. 79-82). The mafic complex was intruded into hornblende schist interfingered with biotite schist. The schistose host rocks were interpreted as Alexander complex by Brew and others (1978, p. B12-13). Berg and others (1972) and Jones and others (1978) have placed the rocks in Wrangellia or Chugach terranes. The Tertiary age of the mafic intrusions (see below) is more consistent with the Chugach-Wrangellia interpretation. The Crillon-LaPerouse host intrusion is the largest of four layered mafic-ultramafic plutons in the Fairweather Range in Glacier Bay National Park and Preserve (Brew and others, 1978). The intrusion has an exposed thickness of about 6000 feet, and consists mainly of interlayered olivine gabbro and norite. Thin layers of ultramafic rock occur throughout the section, but are most abundant near the base. Layering and other sedimentary-like features suggest the body formed mostly by cumulus processes. The Crillon-LaPerouse pluton, and the other layered plutons of the National Park, are probably underlain by a dike-like feature of north-northwest trend. The structure is indicated by the +30 mGal contour (Barnes, in Brew and others, 1978, p. B51-69, esp. p. 67 and figure B4; Barnes and Watts, 1977). An underlying dike-like feature is also suggested by magnetics (Griscom, in Brew and others, 1978, p. B22-37, figure B1). It appears to be thickest underneath the Crillon-LaPerouse pluton. Its probable existence is consistent with the trend of significant cumulate-type ore deposits along the Fairweather Range. The proposed underlying dike is a megadike like the Great Dyke of Rhodesia (Zimbabwe); the overlying layered intrusions are like the major chromite-bearing mafic-ultramafic funnels that form the upper part of the Great Dyke (Worst, 1960; Bichan, 1969). In the Crillon-LaPerouse body itself, the predominantly mafic host rocks of the deposit consist of magnesian augite and bronzite, plagioclase (An81-63) and olivine (Fo71-86), also accessory chromite, ilmenite, magnetite, and graphite. Local phases are ultramafic in composition. The Brady Glacier nickel-copper deposit consists mainly of stratigraphically continuous disseminated-sulfide zones locally more than 400 feet thick that contain as much as 10 percent sulfide minerals. Massive sulfide zones of up to 10 feet in thickness occur locally, especially near the contacts of gabbroic and ultramafic cumulates. The dominant ore sulfides are hexagonal and monoclinic pyrrhotite, pentlandite and chalcopyrite. Altaite, cubanite and niccolite occur as minor components of the primary ore. Bornite, mackinawite, and violarite appear to have formed by secondary reactions between the primary sulfide phases (Czamanske and

Comment (Deposit): Other Comments = Brady Glacier is the largest or among the largest of nickel-copper deposits in the United States (Ellett, 1975). It also has a substantial resource of PGEs. . Extensive metallurgical work done by Newmont and followed up by Czamanski and others (1981) show that resouces are only partly recoverable. Only about 1/2 of the estimated PGE resource is recoverable using the techniques tested. Distinct phases of PGEs have not been identified, but some are liberated after regrinding of the bulk flotation concentrates, and are potentially recoverable by ultrafine gravity or electrodynamic separators. Nickel recovery is about 80 percent. At low nickel concentrations, a considerable amount of the nickel is in the silicate phase and is not recoverable. . The work done suggests that recoveries in an industrial-scale operation could be maximized. Inasmuch as the deposit is not yet limited to the west, any increase in reserves could contribute towards process development

Comment (Geology): Geologic Description = others, 1977, p. 14; Czamanske and others, 1981, p. 2001-2010; Himmelberg and Loney , 1981). Thicknesses where Ni + Cu equal or are greater than 0.5 percent exceed 100 feet are common. In drill hole NUC-3, in an apparent keel-like zone, apparent ore thickness exceeds 400 feet (Himmelberg and Loney, 1981, fig. 5). The deposit contains relatively low concentrations of PGEs (Pd, Pt, and Rh). The total PGE content of disseminated or average ore is about 0.18 ppm. Massive sulfide zones contain about 1 ppm total PGEs. Abundant carbon (now graphite), possibly derived from the intruded sedimentary rocks, kept low-valent sulfur stable and allowed the formation of a stable immiscible ore-sulfide phase that separated from the magma (Czamanske and others, 1977). The deposit is Tertiary in age. A mid-Tertiary age of about 30 Ma is consistent with new data reported by Goldfarb (1997) and with Ar-Ar dates reported by Himmelberg and Loney in 1981 (p. 5) The deposit appears to thicken and become richer to the west, suggesting that resources identified to date by drilling are probably minimal.

Comment (Workings): Workings / Exploration = The deposit was discovered in a helicopter exploration conducted by Fremont Exploration Co. in 1958. Fremont covered the anticipated area of the deposit with 224 claims. Fremont drilled a total of 32 core holes in the nunataks or through the ice before turning the project over to Newmont Exploration, Ltd. Newmont drilled 14 additional holes and conducted extensive metallurgical tests on the core from the property. An additional 36 holes were drilled after 1961; drill hole total is 82 holes (Kimball and others, 1978, p. C99-101). Twenty claims covering the core of the deposit and, supported by drill discovery data, were patented in 1965. Later Newmont joint ventured the deposit with Cities Service and Union Pacific Resources. Although Richard Ellett of Newmont (1975) considered the deposit the largest nickel-copper deposit in the United States, its location within Glacier Bay National Park and Monument precludes its development. The deposit is now owned by the University of Alaska. Newmont and partners also did considerable project planning. The project could be developed from a ten-mile-long tunnel driven from the Boussole Bay area. An ice-depth survey suggests a deep canyon exists about a mile or two north of the deposit (Watts and England, 1976). This canyon may limit potential of the deposit, but it does not affect currently estimated resources.

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References

Reference (Deposit): Ellett, R.D., 1975, Statement and discussion: Adverse effects of proposed legislation upon Alaska nickel mining, in The regulation of mining activities within areas of the National Park System: U.S. Congressional Senate Committee hearing before the Committee on Internal and Insular Affairs, Oct. 7, 1975, 94th Congress, 1st Session, p. 311-316

Reference (Deposit): Watts, R.D., and England, A.W., 1976, Radio-echo soundings of temperate glaciers: Journal of Glaciology, v. 17, no. 75, p. 39-48.

Reference (Deposit): Worst, B.G., 1960, The great dyke of Southern Rhodesia: Southern Rhodesia Geological Survey Bulletin 47.

Reference (Deposit): Bichan, R., 1969, Chromite seams in the Hartley complex of the Great Dyke of Rhodesia: Economic Geology Monograph 4, p. 95-113.

Reference (Deposit): Cornwall, H.R., 1971, Brady Glacier Prospect, in MacKevett, E.M., and others, Mineral resources of Glacier Bay National Monument: U.S. Geological Survey Professional Paper 632, p. 79-82.

Reference (Deposit): Czamanske, G.K., and others, 1977, The Brady Glacier Ni-Cu deposit, southeastern Alaska [abs.]: Program with abstracts, v. 2, 1977, Annual Meeting of the Geological Association of Canada, Vancouver, p. 14.

Reference (Deposit): Barnes, D.F. and Watts, R. D., 1977, Geophysical surveys in Glacier Bay National Monument: U S. Geological Survey Circular 751-B, p. B93-B95.

Reference (Deposit): Brew, D.A., Johnson, B.R., Grybeck, D., Griscom, A., Barnes, D.F., Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources of the Glacier Bay National Monument Wilderness Study Area, Alaska: U.S. Geological Survey Open-File Report 78-494, 670 p.

Reference (Deposit): Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources, in Brew, D. A., and others, Mineral resources of the Glacier Bay National Monument wilderness study area, Alaska: U.S. Geological Survey Open-File Report 78-494, p. C1-C375.

Reference (Deposit): Jones, D.L., Silberling, N.L., and Newhouse, John, 1978, Wrangellia, a displaced terrane in northwestern North America: Canadian Journal of Earth Science, v. 14, p. 2365-2477.

Reference (Deposit): Czamanske, G.K., Haffty, Joseph, and Nabbs, S.W., 1981, Pt, Pd, and Rh analyses and beneficiation of mineralized mafic rocks from the LaPerouse layered gabbro, Alaska: Economic Geology, v. 76, p. 2001-2011.

Reference (Deposit): Himmelberg, G.R. and Loney, R.A., 1981, Petrology of the ultramafic and gabbroic of the Brady Glacier nickel-copper deposit, Fairweather Range, Southeastern Alaska: U.S. Geological Survey Professional Paper 1195, 26 p.

Reference (Deposit): 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: Economic Geology, Monograph 9, p. 396-449.

Reference (Deposit): Berg, H.C., Jones, D. L., and Richter, D. H., 1972, Gravina-Nutzotin Belt-tectonic significance of an Upper Mesozoic sedimentary and volcanic sequence in southern and southeastern Alaska: U.S. Geological Survey Professional Paper 800-D, p. D1-D24.

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