Unnamed (on San Juan Bautista Island)

Prospect, Undetermined

Commodities and mineralogy

Main commodities Cu; Mo
Other commodities Ag; Au; Zn
Ore minerals chalcopyrite; pyrite; pyrrhotite; sphalerite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale B-4
Latitude 55.40979
Longitude -133.29892
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site is at an elevation of about 950 feet where several holes were diamond drilled in the early 1970's. The location is near the middle of the west boundary of section 32, T. 74 S., R. 80 E. There are several other occurrences in the vicinity; all are probably less than 0.3 mile from the drill site.

Geologic setting

Geologic description

This prospect is associated with a small Cretaceous granitic pluton at the center of San Juan Bautista Island (Eberlein and others, 1983; Brew, 1996). The pluton intrudes Devonian graywacke, mudstone, and siltstone of the Port Refugio Formation, which crops out along the entire coastline of the island.
Clark and others (1970 [OF 418]) describe several types of deposits, most of which are probably at or near the contact between the pluton and the sedimentary rocks. The deposits include tactite with pyrite, pyrrhotite, and chalcopyrite; diorite with disseminated pyrite and chalcopyrite; and hornfels (?) cut by a quartz veinlet with pyrite and sphalerite.
There was considerable diamond drilling at an elevation of about 950 feet near a steep gully (D.J. Grybeck, unpublished field notes, 1984). There are 3 or more sites where AlVenCo Inc. drilled in the early 1970s. The rock near the drill sites consists of hornblende-biotite monzonite or granodiorite. The granitic rock contains considerable disseminated pyrite and pyrite along fractures; it is also silicified and argillized. Six grab samples of outcrop and float of the richest mineralized rock contained 300 parts per million (ppm) to 2 percent copper; one contained 100 ppm silver and 150 ppm molybdenum; and one contained 0.75 ppm gold. The deposit was probably drilled as a copper or molybdenum porphyry deposit.
Geologic map unit (-133.300610516044, 55.4094528688753)
Mineral deposit model Porphyry copper or molybdenum deposit?
Age of mineralization Probably related to the emplacement of a Cretaceous granitic stock.
Alteration of deposit Silicification and argillization of granitic rock.

Production and reserves

Workings or exploration There was considerable diamond drilling at an elevation of about 950 feet near a steep gully (D.J. Grybeck, unpublished field notes, 1984). There are 3 or more sites where Alvenco Exploration, Inc. drilled in the early 1970s.
Indication of production None

Additional comments

The subsurface rights to the land in the vicinity of this prospect are held by the Sealaska Corporation.

References