Prospect, Active

Commodities and mineralogy

Main commodities Ag; Pb; Zn
Other commodities As; barite; Cu
Ore minerals galena; pyrite; sphalerite

Geographic location

Quadrangle map, 1:250,000-scale PE
Quadrangle map, 1:63,360-scale C-4
Latitude 56.672
Longitude -133.2608
Nearby scientific data Find additional scientific data near this location
Location and accuracy The prospect is in the intertidal zone at the mouth of a small creek that enters the northern side of the large shallow bay at the mouth of the Castle River; the site is in the NE1/4 section 15, T. 60 S., R. 77E. The locality as seen in 1996 was about 250 feet downstream from a log jam at the high tide mark on the creek. Massive sulfide lenses occur in the center of the creek bed but they are not conspicuous. The location is accurate.

Geologic setting

Geologic description

Thin lenses of massive sulfides occur in siliceous phyllite that is intercalated with fossiliferous, Upper Triassic black carbonaceous phyllite; garnet-bearing limestone; siltstone; and silvery dark gray muscovite- and quartz-rich phyllite (Berg and Grybeck, 1980; Berg, 1981). The carbonaceous phyllite contains abundant pyrite. The massive sulfide lenses are in several zones 10-12 feet wide and 80-100 feet long in the creek bed in the intertidal zone. Individual lenses within these zones are up to 1 foot wide and 3 feet long; they contain abundant pyrite and up to 5 percent galena and sphalerite. Analyses of grab samples show up to 100 parts per million (ppm) copper, 100 ppm silver, and 1000 ppm arsenic. Several examples of the fossil Halobia collected in rocks interbedded with the sulfide lenses at the deposit unambiguously date the deposit as Late Triassic. Recent mapping by Karl and others (1999) include the rocks at this prospect in the Triassic Hyd Group, which is extensive in the area and hosts several volcanogenic massive sulfide deposits. The deposit is part of the Triassic Duncan Canal-Zarembo Island belt of dismembered, volcanogenic massive-sulfide deposits described by Berg and Grybeck (1980) and Berg (1981). Also see PE024 which is similar in origin and probably a continuation of this deposit.
Pacific Alaska Resources explored in the area in the 1980s and 1990s. They planned to drill several geochemical anomalies in copper, lead, and zinc, about one to one and one-half miles to the west of this occurrence at an elevation of 300 to 700 feet. They apparently did not follow through. Still and others (2002) who mention this work, say that the area to be drilled was east of the Halobia occurrence but that is unlikely as it would be near the shoreline or under Duncan Canal. Bittenbender and others (2000) describe several geochemical anomalies in this area. Still and others (2002) sampled the Halobia occurrence; their samples contained up to 30.8 ppm silver, 5,400 ppm lead, and 5.4 percent zinc.
Geologic map unit (-133.262534803547, 56.6716593538143)
Mineral deposit model Kuroko massive-sulfide deposit model (Cox and Singer, 1986, model 28a); alternately a Sierran Kuroko deposit (Bliss, 1992; 28a.1).
Mineral deposit model number 28a or 28a.1
Age of mineralization Unambiguously Late Triassic based on the age of fossils at the site.

Production and reserves

Workings or exploration Discovered by the U.S. Geological Survey in 1979 (Berg and Grybeck, 1980). Nine lode claims were staked on the deposit in 1979; by 1995, a considerable block of ground several square miles in area was staked on and northwest of the original discovery (Department of Natural Resources unpublished Kardex mining claim information system). Informal discussions with industry geologists who worked in the area indicate that they have identified several to numerous additional occurrences of similar deposits on these claims (D.J. Grybeck, oral communications, 1996). Sampled by Still and others (2002).
Indication of production None


MRDS Number A010319


Bittenbender, P.E., Still, J.C., McDonald, M.E. Jr., and Gensler, E.C., 2000, Mineral investigations in the Stikine area, central southeast Alaska, 1997-1998: U.S. Bureau of Land Management Open-File Report 83, 265 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