Unnamed Occurrences (ARDF - CR140), Coco Harbor, Dall Island, Ketchikan Mining District, Prince of Wales-Hyder Census Area, Alaska, USAi

Regional Level Types
Unnamed Occurrences (ARDF - CR140)	- not defined -
Coco Harbor	- not defined -
Dall Island	Island
Ketchikan Mining District	Mining District
Prince of Wales-Hyder Census Area	Census Area
Alaska	State
USA	Country

NOTE:These occurrences are 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.

Location: These occurrences are along the shoreline at the northwest head of Coco Harbor; they are about 0.2 mile southeast of the center of section 5, T. 79 S., R. 82 E.

Geology: As described by Maas and others (1991), this deposit consists of a large area of hornfels and skarn with molybdenum and copper mineralization. The deposit is in marble interlayered with felsic and mafic metavolcanic rocks, metagraywacke, and chlorite schist, all of which are cut by diorite dikes. The hornfels contains disseminated pyrite, pyrrhotite, molybdenite, and minor chalcopyrite. Quartz veins with pyrite, pyrrhotite, minor molybdenite, and rare chalcopyrite, are locally abundant. In 28 samples, the highest molybdenum value was 0.24 percent across a foot-thick quartz vein. The maximum copper value was 601 parts per million (ppm); the highest gold value was 34 ppm, but most samples contained less than 5 parts per billion. Hedderly-Smith (1999 [Inventory]) sampled a piece of limestone float with an 8-inch-thick quartz vein containing chalcopyrite, pyrite, and an unidentified black mineral. The sample contained 2,375 ppm copper, 4.2 ppm silver, and 1.1 ppm gold. The rocks in the area are part of the Descon Formation of Silurian and Ordovician age (Eberlein and others, 1983; Brew, 1996). A Cretaceous(?) pluton is nearby (see CR139).

Workings: Only surface sampling by government and industry geologists.
Age: Silurian or Ordovician or younger.
Alteration: Mineralization associated with skarn and hornfels.

Commodities (Major) - Ag, Au, Cu, Mo
Development Status: None
Deposit Model: Ag-Cu-Mo skarn (Cox and Singer, 1986; model 18b).

Other Databases

Link to USGS - Alaska:	CR140

Other Regions, Features and Areas containing this locality

References