Yttrium and rare-earth element pegmatite dikes are associated with a peralkaline granitic and nephelene syenite complex near Dora Bay on Southern Prince of Wales Island. Mineralized dikes were mapped and sampled during U.S. Bureau of Mines investigations in 1987 and 1988. Coarse-grained pegmatite dikes emanating as late-stage magmatic fluids from the intrusive complex further evolve into vein-dikes and ultimately silica-rich veins. The dikes can be traced up to 2 miles along a north-south zone. Lithophile elements exhibit a pronounced zonation in vein-dikes and veins that are distal to the Dora Bay complex, with increasing values correlating with increasing distance. The pattern of mineralization suggest very late stage magmatic fluids containing the incompatible lithophile elements were injected into a preexisting north-south fracture zone. Rare-earth- element mineralogy exhibits fine-grained intergrowths of principally thalenite and bastnaesite with less monazite and eudialyte. Euxenite contains most of the columbium values, and zircon is commonly associated with the dikes. Estimates of inferred and hypothetical resource tonnage range from 1.7 to 8.5 Mm/st for two deposits. Contained rare-earth oxides (including yttrium) average 0.5 pct and range up to 2.0 pct. Deposits are of polymineralic composition, and about half of this resource comprises the heavy yytrium subgroup.
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