Iron Mask

Prospect, Inactive

Commodities and mineralogy

Main commodities Cu; Zn
Ore minerals chalcopyrite; pyrite; sphalerite
Gangue minerals calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale BS
Quadrangle map, 1:63,360-scale D-7
Latitude 59.907
Longitude -149.289
Nearby scientific data Find additional scientific data near this location
Location and accuracy The prospect is on the east shore of Resurrection Bay, opposite Renard Island (Fox Island) in the NW1/4 of section 21, T. 3 S., R. 1 E., of the Seward Meridian. A small adit has been driven above the high tide level in a brecciated metamorphosed basalt. The breccia as exposed is 12 feet thick and has been traced 100 feet or more along the shore. This is prospect number 78 of Martin and others (1915, p. 235) and location 108 of Tysdal (1978). This location is accurate to within a quarter of a mile.

Geologic setting

Geologic description

The host rock is a Lower Cretaceous diabase (Tysdal and Case, 1979) that has been brecciated and recemented by quartz and sulfide mineralization. The breccia is composed of fine-grained, diabase fragments which range in size from less than a fourth of an inch to several inches in size. The matrix material is a greenish cement. The original breccia is probably a flow breccia mixed with tuffaceous material that has been slightly broken and rehealed with quartz, and pyrite with a little calcite and chalcopyrite (Martin and others, 1915). The breccia is about 12 feet wide at this location and an sample across this zone showed 1.1 percent copper (Grant and Higgins, 1909, p. 104-105).
Geologic map unit (-149.291128752574, 59.9064411354838)
Mineral deposit model Cyprus massive sulfide (Cox and Singer, 1986; model 24a).
Mineral deposit model number 24a
Age of mineralization Probably Upper Cretaceous; massive sulfide.
Alteration of deposit Silicification.

Production and reserves

Workings or exploration A small adit above the high tide line assayed 1.1 percent copper (Grant and Higgins, 1909, p. 104-105).
Indication of production None

Additional comments

On the 1:250,000-scale map the island is called Fox Island while on the 1:63,000-scale map is Renard Island.