Unnamed On Blashke Islands

Occurrence in Alaska, United States with commodities Chromium, Copper, Nickel, PGE

Sections on this page

Identification information
Geographic coordinates
Site location context
Geographic areas
Commodities
Mineral occurrence model information
Nearby scientific data
Ore body information
Economic information about the deposit and operations
Mining district
Links to other databases
Bibliographic references
General comments
Reporter information

Geologic information

Identification information

Deposit ID	10003646
MRDS ID	A106412
Record type	Site
Current site name	Unnamed On Blashke Islands

Geographic coordinates

Geographic coordinates:	-132.88962, 56.12167 (WGS84)
Relative position	SEE LOCATION COMMENTS

Site location context

Political divisions (FIPS codes)

Prince of Wales-Hyder(Census area)

Alaska(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Petersburg A-3(quadrangle 1:63,360 scale)

Petersburg S(quadrangle 1:100,000 scale)

Petersburg(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Prince of Wales(hydrologic unit)

Southern Southeast Alaska(hydrologic accounting unit)

Southeast Alaska(hydrologic subregion)

Alaska(hydrologic region)

Federal lands

Tongass National Forest(National Forest)

National Forest FS(Type of land area)

FS(Federal land areas administered by FS)

Geographic areas

Country	State
United States	Alaska

Comments on the location information

OCCURRENCE IS A MAFIC-ULTRAMAFIC INTRUSIVE COMPLEX ABOUT 2 MILES IN DIAMETER THAT FORMS THE SOUTHERN HALF OF THE BLASHKE ISLANDS. COORDINATES ARE FOR THE APPROXIMATE CENTER OF THE INTRUSION. LOCALITY IS EASILY ACCESSIBLE BY WATER AND THE ROCKS OF THE COMPLEX ARE WELL EXPOSED ALONG THE COAST AND IN THE INTERNAL WATERWAYS BETWEEN THE ISLANDS.

Commodities

Commodity	Importance
Chromium Critical	Primary
Copper	Primary
Nickel Critical	Primary
PGE Critical	Primary

Mineral occurrence model information

Model code	23
USGS model code	9
Deposit model name	Alaskan Cr-Pt (PGE)
Mark3 model number	120

Nearby scientific data

(1)	-132.88962, 56.12167	ListMap

Economic information

Ore body information

General form SEE DEPOSIT DESCRIPTION COMMENTS

General form	SEE DEPOSIT DESCRIPTION COMMENTS

Economic information about the deposit and operations

Development status	Occurrence
Commodity type	Metallic
Significant	No

Comments on exploration

Status = Probably inactive

Mining district

District name	Petersburg

Comments on the production information

NONE

Comments on the reserve resource information

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.

Comments on the workings information

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.

Reference information

Links to other databases

Agency	Database name	Acronym	Record ID	Notes
USGS	Mineral Resources Data System	MRDS	A106412
USGS	Alaska Resource Data File	ARDF	PE057

Bibliographic references

Deposit

Kennedy, G. C., and Walton, M. S., Jr., 1946, Geology and associated mineral deposits of some ultra basic rock bodies in southeastern Alaska: U. S. Geological Survey Bulletin 947-D, p. 65-84.
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.
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.
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, in Geological Survey Research: U.S. Geological Survey Professional Paper 800-C p. C157-C160.
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.
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.
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.
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.
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

General comments

Subject category	Comment text
Deposit	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
Deposit	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.

Subject category

Comment text

Deposit

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

Deposit

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.

Reporter information

Type	Date	Name	Affiliation	Comment
Reporter	01-NOV-1998	Berg, H. C. (Grybeck, D. J.)	U.S. Geological Survey

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