Unnamed (on Blashke Islands)

The Unnamed (on Blashke Islands) is a nickel, copper, chromium, and pge mine located in Alaska.

About the MRDS Data:

All mine locations were obtained from the USGS Mineral Resources Data System. The locations and other information in this database have not been verified for accuracy. It should be assumed that all mines are on private property.

Mine Info

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Site Name

Primary: Unnamed (on Blashke Islands)

Commodity

Primary: Nickel
Primary: Copper
Primary: Chromium
Primary: PGE

Location

State: Alaska
District: Petersburg

Land Status

Not available

Holdings

Not available

Workings

Not available

Ownership

Not available

Production

Not available

Deposit

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

Physiography

Not available

Mineral Deposit Model

Model Name: Alaskan Cr-Pt (PGE)

Orebody

Not available

Structure

Not available

Alterations

Alteration Type: L
Alteration Text: None other than hornfelsing of the country rock adjacent to the complex.

Rocks

Not available

Analytical Data

Not available

Materials

Ore: Rhodium
Ore: Osmium
Ore: Ruthenium
Ore: Iridium
Ore: Palladium
Ore: Platinum
Ore: Chromite
Ore: Chalcopyrite

Comments

Comment (Reserve-Resource): Reserves = There are no economic reserves; however, there are many occurrences of ore minerals and metals of economic interest (Kennedy and and Walton, 1946). Chromite is a sparse, but ubiquitous accessory mineral in the dunite core. Disseminated sulfides, mainly pyrrhotite and chalcopyrite, occur near the boundary between pyroxenite and gabbro. There is a large aggregate tonnage of material containing 1%-2% sulfides. Analyses of the more sulfide-rich gabbro indicate as much as 0.016% Cu, 0.05% Ni, and less than 0.1 ounce per ton Pt-group elements. Other rock analyses show 0.004 ounces per ton Au, 0.04 ounces per ton Pd, and a trace of Pt. Rock samples collected by Clark and Greenwood (1972) contained an average of 0.011 ppm of both Pt and Pd with maxima of 0.020 ppm of each.

Comment (Workings): Workings / Exploration = Apparently no claims have ever been staked on this occurrence. This is not surprising considering that the highest elevation is about 120 feet and that most of the complex is barely above sea level and within a few hundred yards of the ocean. The complex has been visited by generations of geologists as a classic, easily accessible example of an Alaska-type mafic-ultramafic complex; inevitably it has been sampled for the metal suite that is often associated with such rocks, e.g. Cu, Ni, Co, Cr, and PGE. However, the metal content of samples from the body have so far proved consistently low, reflecting the geochemical background in these types of rocks rather than anything close to an economic concentration. The Bureau of Land Management (Mass, Bittenbender, and Still, 1995) recently indicated that the complex has low economic potential.

Comment (Reference): Primary Reference = Kennedy and Walton, 1946; Himmelberg and Loney, 1995

Comment (Exploration): Status = Probably inactive

Comment (Production): Production Notes = None

Comment (Geology): Age = the complex is Late Cretaceous; K-Ar ages from 93.4 to 102.0 Ma (Himmelberg and Loney, 1995).

Comment (Deposit): Model Name = Alaskan or Zoned type mafic-ultramafic complex; portions may have PGE potential (Cox and Singer, 1986; model 9)

Comment (Geology): Geologic Description = The site is a classic Early Cretaceous, zoned or Alaska-type mafic-ultramafic intrusive complex about 2 miles in diameter whose circular form is reflected in the arcuate pattern of the islands themselves. The body has long been known and has best been described in detail by Kennedy and Walton (1946), Walton (1951), Himmelberg and others (1946), and Himmelberg and Loney (1995) as follows. The complex consists of a large central core of dunite surrounded by successive shells of wehrlite, olivine clinopyroxenite, and gabbro. The concentric geometry of the body suggests that it is a steeply dipping to subvertical cylinder; it is essentially undeformed. The complex intrudes Early Silurian-Devonian Descon Formation that consists mainly of of graywacke, with conglomerate, limestone, shale, and volcanic rocks. The contact of the intrusive complex is marked by a hornfelsed zone about 300-700 feet wide. . As described by Kennedy and Walton, (1946), chromite is a sparse, but ubiquitous accessory mineral in the dunite core. Disseminated sulfides, mainly pyrrhotite and chalcopyrite, occur near the boundary between pyroxenite and gabbro. There is a large aggregate tonnage of material containing 1%-2% sulfides. Analyses of the more sulfide-rich gabbro indicate as much as 0.016% Cu, 0.05% Ni, and less than 0.1 ounce per ton Pt-group elements. Other rock analyses show 0.004 ounces per ton Au, 0.04 ounces per ton Pd, and a trace of Pt. Rock samples collected by Clark and Greenwood (1972) contained an average of 0.011 ppm of both Pt and Pd with maxima of 0.020 ppm of each.

References

Reference (Deposit): Cobb, E. H., 1972, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Petersburg Quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-870, 53 p.

Reference (Deposit): Kennedy, G.C. and Walton, M.S., Jr., 1946, Geology and associated mineral deposits of some ultrabasic rocks in southeastern Alaska: U.S. Geological Survey Bulletin 947-D, p. 65-84.

Reference (Deposit): Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Petersburg quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-870, 53 p.

Reference (Deposit): Taylor, H.P., 1967, The zoned ultramafic complexes of southeastern Alaska, in Wyllie, P.J., ed., UIltramafic and related rocks: New York, J. Wiley and Sons, p. 97-121.

Reference (Deposit): Walton, M.S., 1951, The Blashke Island ultrabasic complex with notes on related areas in southeastern Alaska: U.S. Geological Survey Open-File Report 126, 266 p.

Reference (Deposit): Himmelberg, G.R., and Loney, R.A., 1995, Characteristics and petrogenesis of Alaskan-type ultramafic-mafic intrustions, southeastern Alaska: U.S. Geological Survey Professional Paper 1564, 47 p.

Reference (Deposit): Clark, A.L., and Greenwood, W.R., 1972, Geochemistry and distribution of platinum-group metals in mafic to ultramafic complexes of southern and southeastern Alaska: U.S. Geological Survey Professional Paper 800-C, p. C157-C160.

Reference (Deposit): Cobb, E.H., 1972, Metallic mineral resources map of the Petersburg quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-415, 1 sheet, scale 1:250,000.

Reference (Deposit): Maas, K.M., Bittenbender, P E., and Still, J.C., 1995, Mineral investigations in the Ketchikan mining district, southeastern Alaska: U.S. Bureau of Mines Open-File Report 11-95, 606 p.

Reference (Deposit): Himmelberg, G.R., Loney, R.A., and Craig, J.T., 1986, Petrogenesis of the ultramafic complex at the Blashke Islands, southeastern Alaska: U.S. Geological Survey Bulletin 1662, 14 p.

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