DW East

Occurrence, Inactive

Commodities and mineralogy

Main commodities Pb; Zn
Other commodities Ag; Au; Cu
Ore minerals arsenopyrite; chalcopyrite; galena; gold; magnetite; pyrite; pyrrhotite; sphalerite
Gangue minerals quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-1
Latitude 63.2584
Longitude -144.089
Nearby scientific data Find additional scientific data near this location
Location and accuracy The DW East prospect is approximately 3.4 miles south-southeast of the confluence of the Robertson River and Rumble Creek in the NW1/4 section 16, T. 17 N., R. 7 E., Copper River Meridian. The prospect is at an elevation of about 5,800 feet one-half mile south-southeast of peak 6220. The location is accurate.

Geologic setting

Geologic description

The DW East prospect is a massive sulfide outcrop less than 2 feet thick at the northern fringe of the DW-LP mineralized system (Dashevsky and others, 2003). The prospect is one block of what was once part of a single continuous massive sulfide sheet that extends more than 2 miles along strike and is more than 40 feet thick. The sheet is now offset by high-angle faults into six deposits (Dashevsky and others, 2003).
The average grade of samples from the DW East occurrence is 0.3 percent copper, 2.5 percent lead, 1.6 percent zinc, 90 parts per million (ppm) silver, and 2.2 ppm gold (S.S. Dashevsky, unpublished data, 2002).
The DW East massive sulfide is in metavolcanic rocks of the upper Lagoon unit of Devonian age. The unit consists of a succession of dark gray, rusty, phyllitic metamudstones with interbedded light gray to white to pale green siliceous, quartz sericite (-chlorite) schists. Locally the unit has coarse-grained blue quartz eyes and rare fragmental volcanic textures preserved as chloritized lithic fragments. The uppermost part of the unit is dominated by white to pale green, massive to laminated, quartz-eye-bearing, quartz-sericite(-chlorite-pyrite) schist and finely laminated quartz-sericite paper schist with lesser black phyllitic metamudstones and thin intercalations of quartzite and fine metagrit. The volcanic protoliths of the upper Lagoon are rhyodacite and dacite, but it contains rare rhyolite and minor andesite and basalt (Dashevsky and others, 2003).
Geologic map unit (-144.0912510276, 63.2580247431056)
Mineral deposit model Kuroko massive sulfide (Cox and Singer, 1986; model 28a).
Mineral deposit model number 28a
Age of mineralization The Drum unit, which is part of the metamorphic sequence that includes the rocks at this deposit, has been dated at the Devonian-Mississippian boundary on the basis of one SHRIMP U-Pb zircon age of 359 +/- 6 Ma at the nearby DD South prospect (MH325).
Alteration of deposit Extensive chlorite (-chalcopyrite) footwall alteration.

Production and reserves

Workings or exploration Extensive geological, geochemical, and geophysical surveys were conducted at the DW East prospect from 1976 to 1981 by Resource Associates of Alaska and 1994 through 1998 by American Copper and Nickel Company (S.S. Dashevsky, oral communication, 2002).
Indication of production None

Additional comments

The unpublished data that is cited can be seen by contacting Grayd Resources Inc. in Vancouver, B.C., Canada (www.grayd.com), or Northern Associates Inc. in Fairbanks, Alaska.