How does it form?

Burro_Mine_Lead_Vanadium_Ore
Uranium deposit in the Burro Mine – Image Courtesy of the Colorado Geological Survey

Uranium is a widespread and ubiquitous element. It has a crustal abundance of 2.8 parts per million, slightly more than tin. Primary deposits of uranium tend to concentrate in granitic or alkalic volcanic rocks, hydrothermal veins, marine black shales, and Precambrian age placers.Secondary (or epigenetic) deposits of uranium are formed later than the surrounding rocks that host the mineral deposit. Uranium is soluble in oxidizing aqueous solutions, especially the U+6 valence state, and can be redistributed from primary source rocks into porous sedimentary rocks and structures by groundwater and form secondary(epigenetic) uranium mineral deposits.

Uranium_Injection_MiningOrganic material in the pore spaces of rocks create a reducing environment in the water. The oxidizing, uranium-bearing waters passing through the rock precipitate uranium in the rock where the reducing environment exists. Sometimes whole logs (organic matter) buried in the rocks become rich in uranium deposited through this process. This process is what allows in-situ mining of the uranium. Humans pump oxidizing water into the uranium ore, dissolve it, the bringthe solution to the surface and precipitate out the uranium.

Epigeneticdeposits of uranium in sedimentary rocks form the bulk of uranium deposits in Colorado. Epigenetic deposits in Colorado include the many mines of the Uravan, Cochetopa, Maybell, and Rifle districts, and other scattered places including the Front Range and Denver Basin. Primary uranium deposits in Colorado occur in hydrothermal veins, especially in the Front Range.