|Quadrangle map, 1:250,000-scale||PE|
|Quadrangle map, 1:63,360-scale||D-5|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The Raven Zone prospect is on northwest Duke Island about 1.5 mile south-southwest of Form Point and about 2.7 miles east-northeast of Point White. It is in the center of section 8, T. 80 S., R. 93 E. at an elevation of about 450 feet. The location is accurate.|
The Raven Zone prospect is on northwestern Duke Island, well known as the type locality of the Alaska-type, Cretaceous zoned ultramafic complex (Irvine, 1974). The ultramafic complex is concentrically zoned outward from a core of dunite and peridotite, succeeded by shells of olivine pyroxenite and hornblende pyroxenite. The complex is distinguished by locally conspicuous graded layering and other cumulate features, especially in the dunite, peridotite, and olivine pyroxenite. It has long been known (Berg and Cobb, 1967) that the dunite contains small lenses and disseminated chromite; the hornblende pyroxenite contains segregations of titaniferous magnetite that have been drilled; and rare specks of pyrrhotite, pyrite, pentlandite, and chalcopyrite occur widely (PR001). However, until recently no deposit of substantial size had been identified on Duke Island.
In 2001 and 2005, Quaterra Resources (2008a) drilled 11 holes totaling 5,971 feet in two area: 8 holes in the the Maquis Zone (PR New C110) and 3 in the Raven Zone, on mineralization they consider unlike anything that had previously been identified on Duke Island. They interpret the mineralization as possibly related to a layered mafic complex.
The Raven Zone is in a plug of gabbro and pyroxenite about a half mile in diameter surrounded by quartz diorite, granodiorite , and quartz monzonite (Quaterra Resources Inc., 2008b). The best intercept in the three holes drilled in 2005 was 387 feet that contained 2,035 parts per million ppm copper, 56 parts per billion (ppb) platinum, and 59 ppb palladium. The mineralization consists of disseminated and net-textured chalcopyrite and pyrrhotite in coarse-grained pyroxenite. The ore textures suggest sulfide-silicate immiscibility during sulfide deposition.No drilling was done in 2007. However, the data were reviewed and several other areas of interest were identified. In February, 2008, Quaterra had a 388-line-mile airborne geophysical survey flown over the area. Quaterra's work suggest that the mineralization extends for 14.5 kilometers along strike and is 3.8 kilometers wide.
|Geologic map unit||(-131.433775853939, 54.945963913538)|
|Mineral deposit model||Disseminated copper and platinum-group elements in a layered mafic complex.|
|Age of mineralization||The Duke Island complex is about 110 Ma; this mineralization is probably genetically related to it.|
|Workings or exploration||In 2005, Quaterra Resources Ltd., drilled 3 holes on the Raven Zone. No drilling was done in 2007. However, the data was reviewed and several others areas of interest were identified. In February, 2008, Quaterra had a 388-line-mile airborne geophysical survey flown over the area.|
|Indication of production||None|
Berg, H.C., and Cobb, E.H., 1967, Metalliferous lode deposits of Alaska: U.S. Geological Survey Bulletin 1246, 254 p.
Irvine, T.N., 1974, Petrology of the Duke Island ultramafic complex, southeastern Alaska: Geological Society of America Memoir 138, 240 p.
Quaterra Resources Inc., 2005, Drilling intersects new copper-PGE zone at Duke Island: http://www.quaterraresources.com/index.php?page=news&newsid=9 (News Release, December 10, 2005).
Quaterra Resources Inc., 2008, Duke Island Cu-NipOGE project Alaska: http://www.quaterraresources.com/index.php?page=projects&projectid=6 (as of May 5, 2008)
Quaterra Resources Inc., 2008, Duke Island NiS project: http://www.quaterraresources.com/uploads/projects/Duke%20Island%20NiS%20Prospect.pdf (as of May 5, 2008).
|Reporters||D.J. Grybeck (Port Ludlow, WA)|
|Last report date||6/5/2008|