DD South

Prospect, Active

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-1
Latitude 63.2645
Longitude -144.2323
Nearby scientific data Find additional scientific data near this location
Location and accuracy The DD South prospect is located at an elevation of about 5,900 feet 1.4 miles east of peak 7440. It is about in the middle of the SE1/4 section 10, T. 17 N., R. 6 E., Copper River Meridian. This location is accurate.

Geologic setting

Geologic description

Boulders of massive sulfide in talus at DD South Float occurrence are derived from erosion of rocks at the southeastern edge of the DD South prospect. The DD South deposit is trough shaped and can be traced along strike 1,400 feet, and the main deposit is 400 to 500 feet wide (www.grayd.com). The central axis is 20 to 50 feet thick and tapers to a thickness of less than 10 feet (Dashevsky and others, 2003).
The deposit has a drill-inferred resource of 2.3 million tons with an average grade of 1.1 percent copper, 2.6 percent lead, 6.5 percent zinc, 102 parts per million (ppm) silver, and 2.4 ppm gold. Beyond this resource the deposit tapers to 1 foot and less over the next 150 feet. The deposit is pyrrhotite-rich with lesser pyrite and scattered sphalerite, galena, arsenopyrite, and chalcopyrite. Lithic fragments of metasedimentary and metavolcanic protolith are common in portions of the sulfide body (Dashevsky and others, 2003). Twenty-four core holes totaling 14,828 feet have been drilled in the DD South deposit (S.S. Dashevsky, unpublished data, 2002).
The DD South massive sulfide body is in the basal 120 feet of the Drum felsic metavolcanic unit, the age of which is that of the Mississippian-Devonian boundary. The Drum unit that hosts this 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. The DD South mineralized horizon is underlain by the barren Tiger metavolcanic unit (Dashevsky and others, 2003).
Geologic map unit (-144.234548913524, 63.2641226876119)
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 this prospect.
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 DD South prospect was discovered in 1976 after finding massive sulfide blocks in talus at the DD South Float prospect. Extensive geological, geochemical, geophysical surveys and drilling were conducted by Resource Associates of Alaska from 1976 to 1981, by Phelps Dodge in 1990, and by American Copper and Nickel Company from 1994 to 1997. Twenty-four core holes totaling 14,828 feet have been drilled in the DD South deposit (S.S. Dashevsky, unpublished data, 2002).
Indication of production None
Reserve estimates The DD South deposit has an inferred resource of 2.3 million tons that averages 1.1 percent copper, 2.6 percent lead, 6.5 percent zinc, 102 parts per million (ppm) silver, and 2.4 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 3/26/2003