Duke Island Project, Alaska (copper-nickel-PGE)
A new dimension has been added to Quaterra´s 100%-owned copper-nickel-PGE project at Duke Island. Although the project has been the site of intermittent activity since the Company first identified occurrences of sulfide mineralization in 2001, subsequent drilling has not yet found the high nickel and copper grades identified in the surface samples. Quaterra´s 2008 program of air and ground geophysical exploration may have explained the lack of success to date and defined an anomaly that could significantly upgrade the project´s future potential for discovery.
The Duke Island project consists of 129 unpatented federal claims and 11 state claims in south east Alaska, 30 miles south of Ketchikan. The claims were acquired following the discovery of nine occurrences of Cu-Ni-PGE mineralization in mafic/ultramafic rocks on the island that were similar to intrusive rocks that host the world´s largest magmatic sulfide deposits. Samples of the mineralization contained up to 1.95% Cu, 0.25% Ni and 1.0 gpt combined platinum and palladium. Limited drilling programs in 2002 and 2005 encountered up to 387 feet of disseminated and semi massive sulfide mineralization but with low copper and nickel grades.
The Duke Island complex appears to have the principal ingredients necessary to host a large Cu-Ni-PGE deposit. The complex shows compositional layering due to changes in magma chemistry and subsequent fractionation and precipitation of mineral crystals settling through the lighter melt. Flow textures, graded bedding and dislodged xenolith fragments observable in outcrop and drill core indicate the presence of sill-like intrusions that form magma conduits for large volumes of mafic magmas. Net textured sulfides visible in core and outcrops are thought to have accumulated by gravity separation from the magma. A detailed review of the Duke Island data in 2007 suggested that it is not a typical Ural Alaska ultramafic intrusive and that mineralization may be related to an elongate sill or dike complex north of the Marquis target area.
An examination of the core and assay data from the Marquis drilling identified one hole, DK-05-01 located on the northern edge of the Marquis target, that contained the most consistent section of magmatic sulfide mineralization. The section exhibited an excellent correlation among Cu, Ni, Co, Fe, S and PGE concentrations and contained 100 feet averaging 0.23% Cu, 68 ppb Pt, 72 ppb Pd. More importantly, the mineralization correlated to higher magnetic susceptibilities and conductivities and suggested that the strong EM conductors to the north also may represent net-textured to massive sulfides.
Surface gravity and natural source AMT surveys were conducted along two lines between Marquis and Far North across an area of low resistivity identified in the airborne EM surveys. The resulting profiles defined a spectacular ‘wine glass´ conductive anomaly extending more than 3,000 feet with the Marquis and Far North anomalies forming the rims of the glass. More significantly, the ‘stem´ of the wine glass shows up as a strongly conductive keel at a depth of 1,500 to 2,000 feet. The gravity survey showed an anomalous high over the keel area that modeling suggests could be a large sulfide body at depth. The coincident gravity and conductive anomalies adjacent to known sulfide mineralization are compelling targets that require one to two core holes drilled to a depth of approximately 3,000 feet. The geometry of the mineralization and the size of the related anomalies present an opportunity for Quaterra to discover a premier copper-nickel sulfide deposit in southeastern Alaska.
Drilling commenced at Duke Island in June 2010 including a 1,500-meter core drilling program that will target high grade massive to semi-massive Cu-Ni-PGE sulphide mineralization within the Marquis Zone of this ultramafic intrusive complex.
- Duke Island NiS prospect (62.17 KB)