Unnamed (near the north end of Forrester Island)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Mo
Ore minerals molybdenite; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale DE
Quadrangle map, 1:63,360-scale D-5
Latitude 54.8361
Longitude -133.5356
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence consists of two sample sites on the shoreline near the north tip of Forrester Island. One is about 0.2 mile southwest of Point Forrester; the other is about 0.7 mile southwest of Point Forrester. The coordinates are for the first site. Both are in section 24, T. 81 S., R. 79 E., and the locations are accurate.

Geologic setting

Geologic description

During reconnaissance surveys in 1969, Clark and others (1971) identified a porphyry molybdenum deposit on the north end of Forrester Island. A similar occurrence is near Wood Cove (DE002) about 1.3 miles to the southeast. Forrester Island consists mainly of Cretaceous(?) diorite and quartz monzonite (Clark, Berg, and others, 1971; Gehrels and Berg, 1992). At the northeast corner of the island, the pluton intrudes Silurian or Ordovician conglomerate that is contact metamorphosed near the pluton. Several samples of quartz-veined metaconglomerate and pyritized quartz monzonite contained up to 200 parts per million molybdenum.
Geologic map unit (-133.537246581056, 54.835740097061)
Mineral deposit model Porphyry molybdenum (Cox and Singer, 1986; model 21b).
Mineral deposit model number 21b
Age of mineralization Probably related to the Cretaceous(?) diorite and quartz monzonite pluton that makes up most of Forrester Island.
Alteration of deposit The quartz monzonite and diorite associated with the deposit is strongly propylitized; the metaconglomerate adjacent to the pluton is hornfelsed and is cut by numerous quartz veins.

Production and reserves

Indication of production None
Reserve estimates Clark and others (1971) suggest that the resource potential of these occurrences is extremely limited.

Additional comments

The occurrence is in the Forrester Island National Wildlife Refuge and the area is closed to exploration.