DD North

Prospect, Active

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-1
Latitude 63.2686
Longitude -144.265
Nearby scientific data Find additional scientific data near this location
Location and accuracy The DD North prospect is located at an elevation of about 6,300 feet in the headwall basin of a small remnant glacier one-half mile northeast of peak 7440. The prospect in the east-central part of section 9, T. 17 N., R. 6 E., Copper River Meridian. The location is accurate.

Geologic setting

Geologic description

The DD North prospect is a lens-shaped massive sulfide body in the uppermost part of the Drum metarhyolite unit of Devonian to Mississippian age. Mineralization subcrops beneath ice and moraine and is expressed at the surface by a train of massive sulfide boulders in glacial moraine leading up to the prospect site on the remnant glacier. The massive sulfide is pyrrhotite-rich with lesser pyrite and scattered sphalerite, galena, arsenopyrite, and chalcopyrite. Native gold was observed in core from quartz veins at the hanging-wall contact of the massive sulfide. Numerous lithic fragments of metasedimentary and metavolcanic protolith occur in the sulfide body (Dashevsky and others, 2003).
Twelve core holes totaling 7,055 feet have been drilled in the DD North deposit. The deposit appears to have an elongated lensoidal shape and is open down-dip to the southwest. Drilling has identified a 35-foot-thick central zone that contains 1.2 million tons averaging 1.6 percent copper, 2.4 percent lead, 3.2 percent zinc, 102 parts per million (ppm) silver, and 3.1 ppm gold.
The Drum unit that hosts the DD North prospect consists of white to pale gray-green, rusty weathering, quartz-sericite(-chlorite-pyrite) schist with minor gray to black carbonaceous phyllite and rare interbeds of chloritic phyllite. The schist commonly contains 1 to 5 percent quartz eyes but may contain more. The protoliths of the schist are about two-thirds of volcanic origin and one-third of sedimentary origin. The schist has a phyllitic parting. in many places. Metasedimentary rocks of the Tok River unit immediately overlie the DD North massive sulfide layer or unit (Dashevsky and others, 2003).
Geologic map unit (-144.267248500121, 63.2682223531574)
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 Development of sericite, quartz, pyrite, and carbonate in the hanging wall; extensive chlorite and magnesium enrichment and sodium depletion in the footwall.

Production and reserves

Workings or exploration The massive sulfide float boulders were discovered in 1976 at the DD North prospect during stream-sediment reconnaissance (Rodney A. Blakestad and others, unpublished Resource Associates of Alaska, Inc. report, 1976). Extensive geological, geochemical, and geophysical surveys were conducted in 1976 through 1981 by Resource Associates of Alaska, in 1990 by Phelps Dodge, and from 1994 to 1997 by American Copper and Nickel Company (S.S. Dashevsky, oral communication, 2002). Twelve core holes totaling 7,055 feet have been drilled in the DD North prospect.
Indication of production None
Reserve estimates The DD North deposit has an inferred resource of 1.2 million tons with 1.6 percent copper, 2.4 percent lead, 3.2 percent zinc, 102 parts per million (ppm) silver, and 3.1 ppm gold. The resource calculation includes only those contiguous bodies with a true thickness greater than 8 feet and a gross metal value of greater than $80.00 per ton at 1998 prices (Dashevsky and others, 2003).

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.

References

References

Lange, I. M., Nokleberg, W.J., Newkirk, S. R., Aleinikoff, J.N., Church, S.E., and Krouse, R.H., 1993, Devonian volcanogenic massive sulfide deposits and occurrences, southern Yukon-Tanana terrane, eastern Alaska Range, Alaska: Economic Geology, v. 88, p. 344-376.
Reporters W.T. Ellis (Alaska Earth Sciences) and A.W. Wyatt and S.S. Dashevsky (Northern Associates Inc.)
Last report date 3/20/2003