Uranium mineralization in the peralkaline Quanah Granite and related pegmatite-aplite dikes, wichita mountains, oklahoma

Abstract

The coarse-grained facies of the Cambrian peralkaline Quanah Granite and genetically related aegirine-riebeckite and zircon-bearing pegmatite and aplite dikes show significant enrichment in uranium. Quanah granite is ortho-magmatically enriched in uranium with concentrations ranging from 2.6 to 103.8 (ppm U 3O 8). Uranium mineralization of the pegmatite and aplite dikes occurred during the pegmatitic and autometasomatic stages. The mean U 3O 8 value of the dikes is 153 ppm with a range of 2.68 to 1814.7 ppm. Rim albite is commonly developed in the granite at the grain boundary between microperthite grains or between microperthite and quartz. Aegirine-riebeckite pegmatite dikes are located in the Hale Spring area. These dikes are essentially vertical and strike in both north-south and east-west directions. They are characterized by a coarsely crystalline border which grades inward to a fine-grained, aplitic core. The coarse border of the dikes consists predominantly of quartz, microperthite, and riebeckite. A xenomorphic granular aggregate of quartz, K-feldspar, albite, aegirine-riebeckite, and iron oxide constitutes the interior of the dike. Several of the dikes exhibit pronounced banding due to the abrupt variation in grain size and to alternating riebeckite-rich, aegirine-rich, and feldspar-rich layers. Primary minerals have been subjected to deuteric or hydrothermal alteration. Late albite occurs as replacement masses and small veinlets. Fission track analysis shown the uranium is associated with aegirine, riebeckite-arvedsonite, allanite and zircon. Zircon-bearing pegmatites are located mainly in Charon Garden area. These pegmatites occur both as pod-shaped bodies and as narrow dikes. A large mass of milky quartz containing a few large zircon and altered riebeckite crystals is present in the center of the pegmatite. It grades outward into the coarse feldspar-quartz-riebeckite-zircon pegmatite. Zircon is zoned as a result of differing degrees of metamicitization. The metamict zircon is rich in rare earths, Fe 2O 3, thorium and uranium compared to the fresh zircon. Dike systems show enrichment in Zr, Nb, La, Y and Li while relatively high concentrations of Zr and Nb were observed in granite. In general, uranium and other trace element geochemistry of Quanah granite is similar to that characteristic of peralkaline granite of Bokan Mountain, Alaska and the Liruei complex in Nigeria.