Rubble

Occurrences, Undetermined

Alternative names

East Duncan Pyrite

Commodities and mineralogy

Main commodities Ba; Cu; Pb; Zn
Ore minerals barite; chalcopyrite; galena; pyrite; pyrrhotite

Geographic location

Quadrangle map, 1:250,000-scale PE
Quadrangle map, 1:63,360-scale C-4
Latitude 56.655
Longitude -133.0863
Nearby scientific data Find additional scientific data near this location
Location and accuracy
These occurrences are on large block of claims on the east side of Duncan Canal, east of the Castle Islands. The claim block extends for about 2 miles along the shoreline and inland for about 1.2 miles to the crest of the ridge that parallels Duncan Canal. The coordinates are on the shoreline at about the middle of the west side of the claim block along Duncan Canal. The occurrences are spread along the shoreline in section 23, T. 59 S., R. 78 E., and probably extend some distance into the sections to the northwest and southeast.
This record also includes the 'East Duncan Pyrite' occurrence listed in Still and others (2002) as a separate site. It appears similar to other occurrences described in this record and they note that it is within the claim block that defines this record. It is on a logging road just above the east shoreline of Duncan Canal opposite Big Castle Island.

Geologic setting

Geologic description

After Amoco Minerals Co looked at this area and defined several geophysical and geochemical anomalies, in 1985, Atna Resources Ltd. staked 70 claims here and termed the property the 'Rubble'. They abandoned the claims in 1988. Much of the area is covered by heavy vegetation but Still and others (2002) examined the outcrops along the shoreline for several miles and collected numerous rock and stream sediment samples.
Most of the shoreline exposures are part of the Triassic Hyd Group that is the host rock for many volcanogenic massive sulfides deposits in Duncan Canal and beyond (Karl and others, 1999). The claim block is underlain by alternating bands of Hyd Group rocks and the Permian and Mississippian Cannery Formation; the Hyd and Cannery rocks are separated by east-dipping thrust faults. The rocks along the shoreline that Still and others (2002) examined are mainly slate with interbeds of quartz-sericite schist, calcite-chlorite schist, and chert. The schist commonly contains bands and disseminations of pyrite and analyses commonly show 1 to 2 percent barite. Usually the pyrite bands are thin but locally they may be up to a foot thick and consist of to 80 percent pyrite. Samples from most of the pyrite bands are devoid of other metals in notable quantity. However, in one area marked by a conductive geophysical anomaly defined in a 1997 airborne geophysical survey (Alaska Division of Geological and Geophysical Surveys, 1997). Still and others (2002) examined the ground under the anomaly and found a 0.5-inch-thick quartz vein with sphalerite, galena, and chalcopyrite; boulders with 30-50 percent barite; and sulfide bands that include pyrrhotite in addition to pyrite. The geophysical anomaly was also marked by geochemical anomalies in copper, zinc, barium, and molybdenum (Bittenbender and others, 2001).
This record also includes the 'East Duncan Pyrite' occurrence listed by Still and others (2002). It is within the claim block that defines this site. At the occurrence, a pyrite-rich band occurs in a medium to dark gray slate. Karl and others (1999) map the rocks in this area as part of the Triassic Hyd Group. Still and others (2002) collected three samples; the highest values in them were 9 parts per billion gold, 998 parts per million (ppm) copper, 244 ppm zinc, and all of the samples had about 0.5 percent barium.
Geologic map unit (-133.088025182143, 56.6546559057635)
Mineral deposit model Barite facies of a Kuroko massive-sulfide model (Cox and Singer, 1986; model 28a); alternatively a barite facies of a Sierran Kuroko model (Bliss, 1992; model 28a.1).
Mineral deposit model number 28a or 28a.1
Age of mineralization Triassic based on the age of the host rocks.

Production and reserves

Workings or exploration No workings are described but a large claim block was staked over the occurrences in 1985 and there probably was at least some ground exploration. Sampled by government geologists in the late 1990s.
Indication of production None

References

References

Bittenbender, P.E., Bean, K.W., and Still, J.C., 2001, Stikine airborne geophysical survey followup, central southeastern Alaska: Bureau of Land Management, Alaska Technical Report 37, 116 p.
Still, J.C., Bittenbender, P.E., Bean, K.W., and Gensler, E.G., 2002, Mineral assessment of the Stikine area, central Southeast Alaska: U.S. Bureau of Land Management Technical Report 51, 560 p.
Reporters D.J. Grybeck (Port Ludlow, WA)
Last report date 4/8/2007