Unnamed (on Idaho Ridge)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Mo; W
Other commodities Ag; Cu
Ore minerals chalcopyrite; molybdenite; scheelite; sulfides
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale MF
Quadrangle map, 1:63,360-scale D-1
Latitude 58.901
Longitude -136.258
Nearby scientific data Find additional scientific data near this location
Location and accuracy Occurrence is at an elevation of about 2900 feet on Idaho Ridge about 0.1 mile east of hill 2994 (section 21, T. 34 S., R 55 E., of the Copper River Meridian). It is located within 0.05 mile accuracy. The location of the site is shown on figure C65 of Kimball and others (1978).

Geologic setting

Geologic description

The Idaho Ridge area is underlain mostly by foliated granitic rock of Cretaceous age, covered locally by deep glacial moraine (MacKevett and others, 1971; Brew and others, 1978). At the site investigated by the U.S. Bureau of Mines widely distributed fractures in granitic rock had propylitic alteration (epidote); the intrusive was also cut by unmineralized breccia zones (Kimball and others, 1978; p. C310-312). A float rock sample (75CN108A) collected near this area by the U.S. Geological Survey in 1975 contained 700 ppm molybdenum, 300 ppm tungsten, 100 ppm bismuth, and 10 ppm silver (Brew and others, 1978, table B-8). In follow-up activity conducted by the U.S. Bureau of Mines in 1976, significant mineralization was found in narrow (to 0.15 foot) quartz-sulfide veins, but not in chip samples collected over a 5 to 13 foot width (Kimball and others, 1978, table C56). Selected samples of thin quartz-sulfide veinlets contained as much as 240 ppm copper, 500 ppm tungsten, 300 ppm molybdenum, and 15 ppm silver.
Geologic map unit (-136.259870817933, 58.900607008323)
Mineral deposit model Low-grade porphyry molybdenum-tungsten deposit.
Age of mineralization Cretaceous or younger. Veins postdate foliated granitic intrusion of Cretaceous age.
Alteration of deposit Epidote along quartz veins.

Production and reserves

Workings or exploration No workings. A sample of mineralized float (USGS No. 75CN108A of Brew and others, 1978, table B-8) contained 700 ppm molybdenum, 300 ppm tungsten, 100 ppm Bi, and 10 ppm silver. In 1976, the U.S. Bureau of Mines found thin quartz-sulfide veinlets at two locations on Idaho Ridge that contained as much as 500 ppm tungsten, 300 ppm molybdenum, 15 ppm silver, and 240 ppm copper (Kimball and others, 1978, p. C310-312). The Bureau suggested that prospecting around the margins of the host intrusive could reveal better mineralized zones.
Indication of production None

Additional comments

Veins found to date are too thin to be of economic interest, but anomalous geochemical samples suggest more prospecting of the area would be justified (Kimball and others, 1978, p. C310-312, including fig. C65). The site is in Glacier Bay National Park and Preserve.

References