Unnamed (upper Dundas Bay)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Ag; Mo; Sn; W
Other commodities Au; Bi
Ore minerals cassiterite; molybdenite; powellite; scheelite; unknown bi-bearing mineral
Gangue minerals diopside; epidote; garnet

Geographic location

Quadrangle map, 1:250,000-scale MF
Quadrangle map, 1:63,360-scale B-2
Latitude 58.46
Longitude -136.54
Nearby scientific data Find additional scientific data near this location
Location and accuracy The site consists of an area near the head of Dundas Bay (sections 29-30, T. 39 S., R. 54 E., of the Copper River Meridian). The coordinates are the approximate location of a metallized skarn; they are at the approximate midpoint of sections 29 and 30.

Geologic setting

Geologic description

The country rocks in the area of this occurrence consist mainly of sedimentary rocks of Paleozoic age and sedimentary and granitic intrusive rocks of Paleozoic age. The area is east of the major fault that separates Mesozoic from Paleozoic terrane in southwest Glacier Bay National Park and Preserve (Brew and others, 1978). A granitic (granodiorite ) pluton of Tertiary age invades older sedimentary and granitic rock, including pendants of Paleozoic limestone, partly converting the limestone to skarn.
This occurrence encompasses an area characterized by anomalous amounts of molybdenum, tin, and tungsten in stream-sediment samples, rock samples, and in outcropping metaliferous skarn. The anomalous area is elongated east-west on the contact between Tertiary granodiorite to the south and Cretaceous and older sedimentary and igneous rocks to the north. The skarn, mainly developed in limestone of Paleozoic age, contains powellite and as much as 150 ppm tin , 200 ppm bismuth, 79 ppm tungsten and 8.5 ppm gold (Kimball and others, 1978, p. C257-C263). Scheelite and molybdenite also occur locally and scheelite is relatively abundant in panned concentrates. The sources of the anomalies are not fully known, but they probably include both the granitic rocks and the contact skarn zones.
Geologic map unit (-136.541840601689, 58.4596327163773)
Mineral deposit model Skarn and molybdenum-tungsten-tin porphyry similar to Sn skarn and porphyry Mo of Cox and Singer (1986; model 14b and 21b).
Mineral deposit model number 14b, 21b
Age of mineralization Tertiary.
Alteration of deposit Contact metasomatism, development of skarn.

Production and reserves

Workings or exploration There are no known workings. MacKevett and others (1971) reported anomalous concentrations of tungsten in stream sediments in 1966. I followed up these anomalies in 1972 for Union Carbide. We confirmed the results and found abundant scheelite in panned concentrates, but did not proceed because the location was then in the National Monument; the future of development was uncertain. More samples were collected by the Bureau of Mines (Kimball and others, 1978, p. C257-C263). Apparently the Bureau concentrated more on the skarn and Cretaceous rocks than on the Tertiary intrusive.
Indication of production None

Additional comments

The site is in Glacier Bay Park and Preserve.

References