Prospect, Undetermined

Alternative names

Black Swan
Jim's cut

Commodities and mineralogy

Main commodities Au; Mo
Other commodities Cu
Ore minerals chalcopyrite; malachite; molybdenite; pyrite

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale B-5
Latitude 55.33
Longitude -131.62
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site represents four prospects or occurrences distributed along a northwest-trending line about a mile long on southwest Revillagigedo Island. They are at elevations ranging from near sea level to about 300 feet, and from about 0.4 to 1.5 miles southeast of Ketchikan Creek (sections 30 and 32, T. 75 S., R. 91 E., of the Copper River Meridian). The coordinates of the site are for the approximate midpoint of the line of prospects. The site includes loc. 66 in Elliott and others (1978), and locs. 281-283 in Maas and others (1995). The location is accurate within about 0.5 mile.

Geologic setting

Geologic description

This part of Revillagigedo Island is underlain mainly by marine, andesitic or basaltic volcanic rocks and interbedded pelitic sedimentary rocks that are intruded by Cretaceous stocks, sills, and dikes of feldspar-porphyritic granodiorite, and by a stock and probably related plugs of Tertiary gabbro (Berg and others, 1988). The strata were regionally metamorphosed to greenschist-grade phyllite and semischist in Late Cretaceous time. They subsequently were contact metamorphosed to hornblende hornfels: locally, near some of the Cretaceous granodiorite contacts, and, more widely, peripheral to the Tertiary gabbro. The premetamorphic age range of the strata is uncertain. Berg and others (1988) note that they closely resemble Upper Jurassic to mid-Cretaceous flysch and volcanic rocks nearby on Gravina Island. The country rocks are cut by a high-angle fault along Tongass Narrows that displays about 4 miles of right-lateral offset.
According to U.S. Bureau of Mines claim records (1977), the Venitia prospect, which appears to be in hornfelsed strata near the contact of a Tertiary gabbro stock, reportedly was staked for gold. No other information about this prospect has been made public.
The following three occurrences were examined by Maas and others (1995, loc. 281-283), who named them either from U.S. Bureau of Mines claim records, or, informally, for local landmarks.
Loc. 281 (Maas and others, p. 201): Black Swan. Samples of unidentified rock contained up to 555 ppm Cu.
Loc. 282. Laundromat. A sample of unidentified rock contained 11 ppb Au. There is a 15-foot adit on this property.
Loc. 283: Jim's cut. This occurrence, discovered during Maas and others' investigation, was exposed by residential and commercial development along the highway southeast of Ketchikan. It consists of diorite containing disseminated pyrite, chalcopyrite, molybdenite, and malachite that is exposed for 180 feet in a 12-foot deep cut in the back yards of several new houses. A 68-foot-long sample across disseminated sulfide mineralization in the diorite contained 163 ppb Au, 2632 ppm Cu, and 115 ppm Mo, Maas and others (1995, p. 201) interpret this occurrence as a porphyry molybdenum-type deposit.
Geologic map unit (-131.621685449389, 55.3296540193192)
Mineral deposit model Porphyry Mo, low-F (Jim's cut) (Cox and Singer, 1986; model 21b)
Mineral deposit model number 21b
Age of mineralization Probably Cretaceous (Jim's cut).
Alteration of deposit Local oxidation of copper minerals (Jim's cut).

Production and reserves

Workings or exploration
Workings dating from the early 1900s have largely been covered by housing or commercial development, or plugged.
At Jim's cut, a 68-foot-long sample across disseminated sulfide mineralization in the diorite contained 163 ppb Au, 2632 ppm Cu, and 115 ppm Mo (Maas and others, 1995, p. 201).
Indication of production None