|Quadrangle map, 1:250,000-scale||CR|
|Quadrangle map, 1:63,360-scale||B-4|
|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.|
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sphalerite.There was considerable diamond drilling at an elevation of about 950 feet near a steep gully (D.J. Grybeck, unpublished field notes, 1984).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.|
|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was considerable diamond drilling at an elevation of about 950 feet near a steep gully (D.J. Grybeck, unpublished field notes, 1984).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 commentsThe subsurface rights to the land in the vicinity of this prospect are held by the Sealaska Corporation.
Brew, D.A., 1996, Geologic map of the Craig, Dixon Entrance, and parts of the Ketchikan and Prince Rupert quadrangles, southeastern Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2319, 53 p., 1 sheet, scale 1:250,000.
Clark, A.L., Berg, H.C., Grybeck, D.J., Ovenshine, A.T., and Wehr, Raymond, 1970, Analyses of rock and stream-sediment samples from the Craig B-4 quadrangle, Alaska: U.S. Geological Survey Open-File Report 418, 89 p.
Cobb, E. H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Craig quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-869, 262 p.
Eberlein, G.D., Churkin, Michael, Jr., Carter, Claire, Berg, H.C., and Ovenshine, A. T., 1983, Geology of the Craig quadrangle, Alaska: U.S. Geological Survey Open-File Report 83-91, 52 p.
Maas, K.M., Bittenbender, P E., and Still, J.C., 1995, Mineral investigations in the Ketchikan mining district, southeastern Alaska: U.S. Bureau of Mines Open-File Report 11-95, 606 p.
|Reporters||D.J. Grybeck (Applied Geology)|
|Last report date||5/1/2004|