Snettisham Iron

Prospect, Undetermined

Commodities and mineralogy

Main commodities Fe; PGE; Ti; V
Ore minerals ilmenite; magnetite

Geographic location

Quadrangle map, 1:250,000-scale SD
Quadrangle map, 1:63,360-scale D-6
Latitude 57.98452
Longitude -133.774
Nearby scientific data Find additional scientific data near this location
Location and accuracy The large pyroxenite body that makes up much of the northern end of the Snettisham Peninsula was known to contain abundant magnetite locally as early as the 1890's. This site is the center of an area about 2000 feet by 1000 feet in size in which the U.S. Bureau of Mines diamond drilled more than 5,000 feet of hole in 1953 and was subsequently explored by private industry. The center of the area is about 0.5 mile east of the abandoned town of Snettisham and about 0.6 mile west-northwest of the center of section 9, T. 45 S., R. 72 E.

Geologic setting

Geologic description

The Snettisham iron deposit is one of the larger bodies in a belt of Alaska-type ultramafic-mafic intrusions that are spread along the length of southeastern Alaska (Taylor and Noble, 1960; Taylor, 1967; Himmelberg and Loney, 1995; Foley and others, 1997). The body in Port Snettisham is an elliptical intrusion about 2 miles in maximum outcrop that is mainly composed of hornblende-magnetite clinopyroxenite, biotite-magnetite pyroxenite, and hornblende-biotite-magnetite clinopyroxenite. The pyroxenite locally grades into diorite. As in several other such bodies in southeastern Alaska, the magnetite content is locally high enough to be considered as a source of iron, titanium, vanadium, and possibly platinum-group element (Buddington, 1925; Thorne and Wells, 1956; Page and others, 1973). The magnetite is titaniferous. The body is cut by numerous thrust and normal faults (Redman and others, 1989). Although there are several episodes of the intrusion of Alaska-type complexes in southeastern Alaska, the Snettisham body is probably 100-118 million years old (Brew and Morell, 1983; Himmelberg and Loney, 1995).
Although there was a small test shipment of magnetite ore to Juneau in about 1917 (Buddington, 1925), the first major effort to explore the iron potential of the deposit was in the 1950s by the U.S. Bureau of Mines who drilled at least 9 holes totaling 6,543 feet, did a geophysical survey over the body, and had beneficiation tests done on the ore (Thorne and Wells, 1956). The work outlined a magnetite-rich area of the pyroxenite about 2,400 feet by 9,600 feet in area with a vertical extent of 1,000 feet. The Bureau identified 450,000 tons of material that contained 19 percent iron, 2.6 percent titanium, and 0.05 percent vanadium, and these figures have been cited numerous times since in other publications (e.g. Carr and Dutton, 1959; Berg and Cobb, 1967; Fischer, 1975). In 1969, the Marcona Corporation optioned the Snettisham iron deposit and carried out extensive exploration, including diamond drilling and metallurgical tests. In addition, Page and others (1973) identified a resource of 4.55 million troy ounces of platinum-group metals in the orebody defined by Thorne and Wells that has an average grade of 0.0027 ounce of platinum-group-elements per ton. They also cite the potential for more platinum-group elements at a similar grade in extensions of the ore body.
Geologic map unit (-133.775737393929, 57.9841853047223)
Mineral deposit model Magnetite in clinopyroxenite.
Age of mineralization The magnetite-bearing clinopyroxenite is probably 110-118 Ma.
Alteration of deposit The magnetite is a primary constituent of the pyroxenite.

Production and reserves

Workings or exploration Although there was a small test shipment of magnetite ore to Juneau in about 1917 (Buddington, 1925), the first major effort to explore the iron potential of the deposit was in the 1950s by the U.S. Bureau of Mines who drilled at least 9 holes totaling 6,543 feet, did a geophysical survey over the body, and had beneficiation tests done on the ore (Thorne and Wells, 1956). The work outlined a magnetite-rich area of the pyroxenite about 2,400 feet by 9,600 feet in area with a vertical extent of 1,000 feet. In 1969, the Marcona Corporation optioned the Snettisham iron deposit and carried out extensive exploration, including diamond drilling and metallurgical tests.
Indication of production None
Reserve estimates The first major effort to explore the iron potential of the deposit was in the 1950's by the U.S. Bureau of Mines (Thorne and Wells,1956). The work outlined a magnetite-rich area of the pyroxenite about 2,400 feet by 9,600 feet in area with a vertical extent of 1,000 feet. The Bureau identified 450,000 tons of material that contained 19 percent iron, 2.6 percent titanium, and 0.05 percent vanadium, and these figures have been cited numerous times since in other publications (e.g. Carr and Dutton, 1959; Berg and Cobb, 1967; Fischer, 1975). In addition, Page and others (1973) identified a resource of 4.55 million troy ounces of platinum-group metals in the orebody defined by Thorne and Wells that has an average grade of 0.0027 ounce of platinum-group-elements per ton. They also cite the potential for more platinum-group elements at a similar grade in extensions of the ore body.

References

MRDS Number A013320; D000230

References

Brew, D.A., and Morell, R.P., 1983, Intrusive rocks and plutonic belts of southeastern Alaska: Geological Society of America Memoir 159, p. 171-193.
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, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 396-449.
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.
Taylor, H.P,. and Noble, J.A., 1960, Origin of the ultramafic complexes in southeastern Alaska: International Geological Congress, 21st, Copenhagen, Report, p. 175-187.
Reporters Donald Grybeck (U.S. Geological Survey)
Last report date 10/8/2004