TA

Occurrence, Inactive

Commodities and mineralogy

Main commodities Zn
Other commodities Ag; Cu; Pb
Ore minerals chalcopyrite; galena; pyrite; sphalerite
Gangue minerals calcite; chlorite; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale MH
Quadrangle map, 1:63,360-scale B-1
Latitude 63.2793
Longitude -144.1969
Nearby scientific data Find additional scientific data near this location
Location and accuracy The TA occurrence is at an elevation of about 5,400 feet on the east flank of peak 7835, locally called Tiger Tooth Mountain. It is southwest of the confluence of the Robertson River and Rumble Creek and in the SE1/4 section 2, T. 17 N., R. 6 E., Copper River Meridian. The location is accurate.

Geologic setting

Geologic description

The TA occurrence has disseminated to semimassive pyrite, sphalerite, chalcopyrite, and galena in a sequence of fine- to coarse-grained quartz arenite, quartzite, quartz siltstone, lesser chloritic and sericitic metavolcanic schist, and limestone. The sulfides occur in poorly developed bands and concentrations along foliation and fracture planes; the mineralized rocks can be traced for at least 1,500 feet along strike. At least two mineralized horizons as much as 5 feet thick have been recognized. They contain both discontinuous cherty layers (exhalite?) and coarse-grained quartz arenite (R.A. Blakestad and others, unpublished Resource Associates of Alaska, Inc. report, 1978).
Early workers considered the sulfide horizon at this prospect to possibly be a time-stratigraphic equivalent of the mineralized horizon at the DD North prospect (MH319) (R.A. Blakestad and others, unpublished Resource Associates of Alaska, Inc. report, 1978). Subsequent examination by American Copper and Nickel Company in 1995 failed to find any massive mineralization, and the geologists concluded that the disseminated sulfides that were seen were probably a secondary remobilization into the porous metasedimentary rocks.
The TA occurrence is in the Lagoon unit, which is considerably older than the Drum unit that hosts the DD North deposit. Average grades of the TA sulfide occurrence are 0.2 percent copper, 2.2 percent zinc, and 20 parts per million silver (S.S. Dashevsky, unpublished data, 2002).
Geologic map unit (-144.199150464855, 63.2789237975041)
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) (Dashevsky and others, 2003).

Production and reserves

Workings or exploration The TA occurrence was discovered during the course of geologic mapping in 1978. Only surface sampling and mapping have been done.
Indication of production None

Additional comments

Unpublished data cited is available for viewing by contacting Grayd Resources Inc. in Vancouver, B. C., Canada (www.grayd.com), or Northern Associates Inc. in Fairbanks, Alaska.

References