Shellhouse

Prospects, Undetermined

Alternative names

Miller

Commodities and mineralogy

Main commodities Ag; Au; Cu; Mo
Ore minerals chalcopyrite; pyrite; pyrrhotite
Gangue minerals actinolite; calcite; chlorite; diopside; garnet; quartz

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale A-4
Latitude 55.05157
Longitude -133.10471
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Shellhouse prospect is about 0.8 mile west-northwest of the northwest head of Coco Harbor, and about 0.4 mile northeast of the center of section 6, T. 79 S., R. 82 E. The location is accurate.

Geologic setting

Geologic description

The Shellhouse and Miller prospects have been known since before 1909, but the early descriptions say little more than that the deposits consist of bodies of chalcopyrite and pyrrhotite in quartz-calcite gangue in limestone and siliceous schist (Wright, 1909; Chapin, 1918). Maas and others (1991) located several open cuts and an adit in dense vegetation. They describe the deposit as a 4-foot-thick sulfide lens with pyrite, pyrrhotite, and chalcopyrite in a contact zone between altered [Cretaceous?] diorite porphyry and metamorphosed, calcareous sedimentary rocks. They collected two samples that averaged 0.3 percent copper and 1.6 parts per million (ppm) silver. One sample contained 1.6 parts per billion (ppb) gold. Samples of massive pyrrhotite and pyrite collected by Hedderly-Smith (1999 [Inventory]) contained up to 1.17 percent copper, 403 ppm molybdenum, 6.5 ppm silver, and 121 ppb gold. He describes the deposit as a garnet-chlorite-actinolite-diopside skarn near the contact of weakly propylitized granodiorite. The sedimentary rocks in the area are part of Descon Formation of Silurian and Ordovician age (Eberlein and others, 1983; Brew, 1996).
Geologic map unit (-133.10635401813, 55.051218022542)
Mineral deposit model Cu-Mo skarn (Cox and Singer, 1986; model 18b).
Mineral deposit model number 18b
Age of mineralization This skarn deposit is probably related to altered granodiorite. Its age is uncertain, but similar intrusions in the area have been variously dated as Mesozoic or Paleozoic, or Cretaceous (Eberlein and others, 1983; Brew, 1996).
Alteration of deposit The deposit is mineralized garnet-chlorite-actinolite-diopside skarn associated with altered [Cretaceous?] diorite porphyry (Maas and others, 1991) or propylitized granodiorite (Hedderly-Smith, 1999 [Inventory]).

Production and reserves

Workings or exploration The only workings on the property are several open cuts and an adit that probably date to before WW I.
Indication of production None

Additional comments

This prospect is on land that has been conveyed to the Sealaska Corporation, who hold the surface and subsurface rights, or the land is under application for transfer to them.

References

MRDS Number A010151; A010166

References

Glavinovich, P.S., 1987, Sealaska Corporation Minerals Breifing Book, December 1987: Sealaska Corporation, 40 p. and plates. (Unpublished report held by Sealaska Corporation, Juneau, Alaska).
Hedderly-Smith, D.A., 1991, Report of the 1990 field season-Sealaska Mineral Reconnaissance Project: Sealaska Corporation: Sealaska Corporation, 2 vols., 180 p., 13 plates. (Unpublished report held by the Sealaska Corporation, Juneau, Alaska.)
Hedderly-Smith, D.A., 1992, Report of the 1991 field season - Sealaska Mineral Reconnaissance Project: Sealaska Corporation, 2 vols., 225 p. 23 plates. (Unpublished report held by the Sealaska Corporation, Juneau, Alaska.)
Hedderly-Smith, D.A., 1999, Inventory of metallic mineral prospects, showings and anomalies on Sealaska lands, 1988 through 1998: Sealaska Corporation, Juneau, Alaska, 217 p. (internal report held by Sealaska Corporation, Juneau, Alaska).
Reporters D.J. Grybeck (Applied Geology)
Last report date 5/1/2004