Unnamed (South Marble Island)

Prospect, Probably inactive

Commodities and mineralogy

Main commodities Cu; Fe; Ti
Ore minerals chalcopyrite; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale MF
Quadrangle map, 1:63,360-scale C-1
Latitude 58.643
Longitude -136.042
Nearby scientific data Find additional scientific data near this location
Location and accuracy The site is on South Marble Island in Glacier Bay. Its location is approximate, but probably correct within 0.1 mile. It is location number 51 of Cobb (1972) and number 25 of MacKevett and others (1978).

Geologic setting

Geologic description

The site is within the marble-rich province of Devonian and Silurian age that extends northwesterly from Willoughby Island to Queen Inlet (MacKevett and others, 1971; Brew and others, 1978). Bathymetric contours near South and North Marble Island indicate a barely submerged mass, inferred to be mostly marble, that is also aligned northwest. The exposures on the two small islands are the surface expressions of the inferred marble mass.
The island was investigated as a marble prospect Burchard (1914 and 1920).
The marble on South Marble island is locally cut by mafic dikes as much as 50 feet across that contain disseminated pyrite; pyrite also occurs in silicified marble near the dike rocks. Reed (1938) reported copper sulfide (chalcopyrite) occurrences.
Of four pyritic samples collected by the U.S. Geological Survey, three contained more than 10 percent iron and one contained about 7 percent iron; titanium content ranged from 0.5 to 1 percent in the same samples (MacKevett and others, 1971, table 9).
The sulfide deposits and silicification probably are related to the emplacement of the mafic dikes, possibly in Cretaceous or Tertiary time (Brew and others, 1978).
Geologic map unit (-136.043854195829, 58.6426342882651)
Age of mineralization Cretaceous or younger.
Alteration of deposit Marble is locally silicified.

Production and reserves

Workings or exploration No workings. MacKevett and others (1971) reported iron content as greater than 10 percent in three of four selected samples of marble and dike material. Maximum titanium content is 1 percent. All four samples contained 100 ppm nickel, and ranged from 150-200 ppm copper. It is doubtful if any of the samples reported by MacKevett and others represent the copper sulfide-bearing material seen by Reed (1938).
Indication of production None

Additional comments

The site is in Glacier Bay National Park and Preserve.

References