Uraninite with Uranophane

specimen number:
2262288

location:
Pumpkin Buttes, Campbell Co., Wyoming, USA

description:
Rich black masses of uraninite throughout matrix with yellow powdery uranophane. The specimen comes with a previous collection data card dating this to the late 1950s.

The Pumpkin Buttes mining district, located within the Powder River Basin across Campbell and Johnson counties in northeastern Wyoming, was a historically significant roll-front uranium district characterized by numerous open-pit and surface quarrying operations. Geologically, the sandstone-hosted uranium deposits are situated within the Eocene-age Wasantic and Fort Union formations, where porous, fluvial arkosic sandstones acted as conduits for oxygenated, uranium-bearing groundwater. When these oxidizing solutions encountered reducing geochemical environments created by carbonaceous organic matter and pyrite within the host strata, the uranium precipitated out along a dynamic oxidation-reduction front, forming classic roll-front mineralizations dominated by carnotite, uraninite, and coffinite. Historically, the district gained national attention in 1951 when anomalous radioactivity was detected during airborne radiometric surveys conducted by the United States Geological Survey, triggering a major uranium rush in 1952. Private prospectors and mining companies established dozens of small, shallow open pits to extract the near-surface carnotite ores throughout the 1950s and 1960s, delivering the raw material to regional processing mills. Commercial surface extraction systematically declined as high-grade shallow reserves were exhausted and the domestic uranium market shifted, leading to the winding down of traditional open-pit operations in the late twentieth century before modern operations in the wider basin transitioned toward solution-based in-situ recovery methods.

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