UNUSUAL URANIUM AND REE MINERALIZATION IN AN AREA BETWEEN THE HAYES AND OUTBACK PEGMATITES, NOYES MOUNTAIN, GREENWOOD, OXFORD CO., MAINE

During access road construction between the Hayes and Outback pegmatites on Noyes Mountain, Greenwood, Oxford Co., Maine, an unusual mineral assemblage of uranium-rich mineralization was discovered in a 3-6 cm thick garnet layer in pegmatite. Uraninite is the major component and forms black masses up to 1.5 cm across. Associated are black fibrous masses of coffinite up to 5 mm with patches and coatings of pale-yellow uranium silicate (possibly soddyite) and less common autunite/meta-autunite with intense yellow-green fluorescence. This fluorescent coating is wide-spread within and around the mineralized garnet-rich zone.

Accessory zircon, monazite and xenotime group species are intimately associated with the uranium assemblage. Inclusions in uraninite of U- and/or Pb-rich fluorcalciopyrochlore species (formerly known as uranpyrochlore and plumbopyrochlore), a light rare earth element enriched suite of minerals consisting of monazite group species, allanite group species, small amounts of a bastnäsite group species and a heavy-rare-earth-element enriched group of mineral species consisting of Yb-rich fergusonite-(Y) or euxenite-(Y) and xenotime group species have also been identified. This REE signature is more typical for anorogenic pegmatites formed in an extensional tectonic regime than those in a compressional regime like the pegmatites of the Oxford field. Uranium content of this pegmatite is consistent with either orogenic or anorogenic pegmatites but the HREE and LREE content is elevated, which is generally typical for anorogenic pegmatites.

The presence of elevated U is consistent with either orogenic or anorogenic pegmatites but elevated REE content is atypical for pegmatites in the Oxford pegmatite field. This pegmatite may represent a hybrid source or some unusual concentrations of both REE and U.