Uranium is the fuel of nuclear power, and it concentrates in a few special settings. Two models dominate. The key to both: uranium travels easily in water and drops out where the chemistry changes.

Unconformity-related — the richest of all

An unconformity is a buried ancient land surface — a gap in the rock record where old basement rock meets much younger sedimentary rock above. Uranium-bearing fluids concentrate right at this boundary, forming small but staggeringly high-grade deposits. Canada's Athabasca Basin is the showcase, with grades many times richer than ordinary ore.

Sandstone "roll-front" — easy to mine

Here uranium dissolved in groundwater moves through a porous sandstone and precipitates in a crescent-shaped front where the water turns from oxygen-rich to oxygen-poor. It's lower grade, but mined by in-situ recovery (ISR) — pumping a solution down wells to dissolve the uranium and pumping it back up, a kind of solution mining.