Unnamed (west of Lynn Canal)

Occurrence, Inactive

Commodities and mineralogy

Main commodities Au; Co; Cu; Ni
Other commodities Cr
Ore minerals chalcopyrite; pyrite; pyrrhotite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale D-5
Latitude 58.9308
Longitude -135.5194
Nearby scientific data Find additional scientific data near this location
Location and accuracy This occurrence is at an elevation of about 1,500 feet, at the northwest margin of the moraine at the foot of the glacier about 5 miles west of Lynn Canal, in the SE1/4 section 11, T. 34 S., R. 59 E. of the Copper River Meridian.

Geologic setting

Geologic description

This occurrence, referred to as the West Dream occurrence by the U.S. Bureau of Mines, was discovered in 1988 by following the stratigraphy south of the Dream prospect (JU009) (Clough and Redman, 1989). The country rocks are siliceous argillite that strikes northerly and dips moderately to the west. Discontinuous quartz veins and stratiform and stratabound sulfide pods and stringers occur in the siliceous argillite. The dominant sulfide minerals are pyrite and pyrrhotite, with minor chalcopyrite. Samples collected by U.S. Bureau of Mines contained up to 12,000 ppm copper, 7,100 ppm nickel, 910 ppm cobalt, and 900 ppm chromium. A sample of a quartz vein in volcaniclastic rocks contained 0.58 ppm gold (Clough and Redman, 1989).
This deposit is one of many in the Dream prospect area that includes numerous veins, stockworks, stratabound and stratiform sulfide deposits (also see JU002, JU006, JU009, JU011, JU013, JU014, JU016, JU019), most of which occur near a volcaniclastic-marble contact. The U.S. Bureau of Mines (Clough and Redman, 1989), International Curator Resources, Ltd. (Huber and Barnett, 1988), and Placer Dome U.S. (Bull and others, 1989) explored the area in the late 1980s and developed a general lithology of the area. They divide the rocks into four major rock units. From the base up, they are: 1) a volcaniclastic unit approximately 2000 feet thick that consists of albite-chlorite schist, chlorite schist, and chlorite-quartz-sericite schist that may in part be metaplutonic as well as metavolcanic; 2) a unit 800 feet thick of micaceous marble, pelitic schist, graphite schist, gray to white, cliff-forming marble, chlorite-amphibole schist, greenstone, and phyllitic graphite schist; and 3) a unit of very fine-grained chlorite-sericite-biotite schist over 1000 feet thick that includes metatuff and pelitic, mafic and graphitic schist. The upper contact of this unit is a thrust fault that trends N-S for several miles; quartz veining is common along the thrust contact. The rocks overlying the thrust are middle- to upper-greenschist-facies graphitic schist, argillite, phyllite, and marble. The metamorphic grade of the rocks varies from mid- to upper-greenschist facies in the south, to amphibolite facies in the north. There have been at least two stages of folding.
The Dream prospect area was the site of extensive exploration and mapping from 1987 through 1990 by International Curator Resources Ltd. and Placer Dome U.S. The area was covered by 600 federal mining claims in 1989 and more than 5000 feet of drilling was completed by the end of 1990 (Swainbank and others, 1991).
The general area consists predominantly of metamorphosed Silurian and Devonian clastic rocks, limestone, and volcanic units; Permian limestone and siltstone; and small plutons of Tertiary and Cretaceous granodiorite (Brew and Ford, 1985).
Geologic map unit (-135.521250531213, 58.9304666365656)
Mineral deposit model Possibly a metamorphosed Kuroko massive sulfide deposit (Cox and Singer, 1986; model 28a) or a metamorphosed polymetallic replacement deposit (Cox and Singer, 1986; model 19a)
Mineral deposit model number 28a or 19a

Production and reserves

Workings or exploration Surface sampling only . The Dream prospect area, was the site of extensive exploration and mapping from 1987 through 1990 by International Curator Resources Ltd. and Placer Dome U.S. The area was covered by 600 federal mining claims in 1989 and more than 5000 feet of drilling was completed by the end of 1990 (Swainbank and others, 1991).
Indication of production None

References