URANIUM MINERALS AT MAW BRIDGE PEGMATITE NEAR CENTRAL, SOUTH CAROLINA

Uranium-bearing minerals up to 5 cm long have been discovered at Maw Bridge pegmatite about 2.8 km northwest of Central, South Carolina. The uranium minerals are black with brownish black to black streak, have glassy luster and conchoidal fracture, and are metamict. Microprobe analysis reveals that they are complex intergrowths of niobium-tantalum oxides belonging to the samarskite, fergusonite and pyrochlore mineral groups. Subsequent heating experiments on pulverized material successfully induced crystallinity and allowed x-ray diffraction confirmation of the microprobe identifications. The samarskite is the yttrium-rich variety, samarskite-(Y); it contains a moderate quantity of iron as well as appreciable amounts of rare earth elements. Fergusonite is marked by even higher concentrations of yttrium and rare earth elements, and is further distinctive in that it is devoid of detectable iron. The pyrochlore mineral is the Ti-rich variety, betafite. The betafite is tantalum-rich, which is unusual for this mineral. Betafite is the most uranium-rich (24-28 wt % UO2) of the niobium-tantalum oxides and was in general the first to crystallize. Fergusonite contains the least uranium (5-8 wt % UO2) of the three niobium-tantalum minerals, and is always late in the paragenesis. Secondary alteration of betafite has taken place along cracks and is marked chiefly by loss of calcium and sodium, but the alteration apparently has not resulted in mobilization of uranium into the environment.