Unnamed (northeast side of Willoughby Island)

Prospect, Inactive

Commodities and mineralogy

Main commodities Cu
Other commodities As; Co
Ore minerals chalcopyrite; loellingite; pyrite
Gangue minerals calcite

Geographic location

Quadrangle map, 1:250,000-scale MF
Quadrangle map, 1:63,360-scale C-1
Latitude 58.6
Longitude -136.13
Nearby scientific data Find additional scientific data near this location
Location and accuracy The deposit is reported to be on the northeast side of Willoughby Island at an elevation of 450 feet. It is assumed to be about 0.5 mile southwest of Johnson Cove. Accuracy is uncertain. The site is about the same as locality 49 in Cobb (1972) and locality 95 in Kimball and others (1978). The deposit was not found by the U.S. Geological Survey in 1966 (MacKevett and others, 1971).

Geologic setting

Geologic description

The northeastern part of Willoughby Island is underlain by massive and bedded limestone of Devonian and Silurian age, part of a major reefoid mass (Brew and others, 1978). Locally the marble is cut by mafic dikes of Late Cretaceous or Tertiary age. At this prospect, pyrite, loellingite (?) and chalcopyrite form massive replacement layers or lenses in marble. One such massive sulfide deposit was described as 5-feet-thick and traceable on strike for 15 feet (Reed, 1938). At least three other similar occurrences were reported nearby by Reed.
Geologic map unit (-136.131843349936, 58.5996355160119)
Mineral deposit model Massive sulfide replacement in marble. Distal deposit related to subjacent intrusive; deposits formed after late emplacement of mafic dikes.
Age of mineralization Late Cretaceous or younger.

Production and reserves

Workings or exploration The deposit has not been found since Reed's visit in the 1930s (Reed, 1938). Workings are unknown, but there probably were shallow pits and trenches on the eight claims staked on the deposit before 1902.
Indication of production None

Additional comments

The deposit is in marble of Devonian and Silurian age; mineralization followed emplacement of mafic dikes of probable Late Cretaceous or Tertiary age.
The site is in Glacier Bay National Park and Preserve.

References