Unnamed (Northwest part of Yakobi Island)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Cu; Ni; PGE

Geographic location

Quadrangle map, 1:250,000-scale MF
Quadrangle map, 1:63,360-scale A-2
Latitude 58.05
Longitude -136.55
Nearby scientific data Find additional scientific data near this location
Location and accuracy The location is at sea level on the west coast of Yakobi Island about 1.5 miles west of Hoktaheen Lake (Rossman, 1959, plate 12). Location is accurate within about 0.1 mile.

Geologic setting

Geologic description

A gabbro body on northern Yakobi Island is geologically permissive for nickel-copper deposits similar to those that occur at Takanis and Bohemia Basin in the Sitka D-8 quadrangle, about two miles south of the southern boundary of the Mt. Fairweather A-2 quadrangle. (The gabbro body on Mt. Fairweather A-2 quadrangle is about 6 miles northwest of the Takanis nickel-copper deposit.) The structural setting on the northwest part of Yakobi Island is the same as at Bohemia Basin where barren and ore- bearing gabbro occur within the same large dike-like intrusion of non-foliated light colored sodic quartz diorite of Tertiary age that hosts the gabbro body on Fairweather A-2. The dike-like quartz diorite mass crops out for about seven miles on the Mt. Fairweather quadrangle; to the south, it thickens, becomes more complex, and extends into the Sitka quadrangle for about ten more miles (Rossman, 1959, plate 12; Loney and others, 1975, plates 1 and 2).
The eastern part of the gabbro body on northern Yakobi Island is on the mainland of the island; much of the body is on an offshore island complex.
Nickel-bearing norite gabbro is unknown at the occurrence, but the intrusion is large enough to host nickel-copper deposits in the body, especially the part exposed on small islands and largely covered by sea water.
Geologic map unit (-136.55185499486, 58.0496165283755)
Mineral deposit model Igneous-affiliated deposit, mafic to ultramafic.
Age of mineralization Tertiary.

Production and reserves

Workings or exploration None.
Indication of production None

Additional comments

The gabbro body is in the West Chichagof-Yakobi Island Wilderness Area of the Tongass National Forest.

References