Uranium roll ore bodies form below the water table predominantly in arkosic sandstones. Exterior barren ground (EBG) outside of the crescentic roll may retain mafic detrital minerals or may be hematitic or pyritic. Pyritic EBG commonly contains coalified wood and calcite. Roll ore bodies generally grade into pyritic EBG, have sharper boundaries with interior barren ground (IBG), and are discontinuous along strike. IBG usually is devoid of pyrite, calcite, organic materials, and fresh feldspars. A disequilibrium mineralogic assemblage (or transitional zone) of variable width is present between roll ore and IBG in some deposits.

During the past decade, a bacterial origin for roll ore bodies has been more popular than other theories of origin. However, largely on the basis of laboratory experiments Granger and Warren suggested that the roll ore bodies may form inorganically. According to their model, incursion of groundwater may cause the oxidation of biogenic or other sulfides to sulfite; because sulfite disproportionates into SO₄^- and HS^-, inorganic HS^- rather than bacteriogenic H₂S may be responsible for the precipitation of pyrite and uranium minerals.

Isotopic data that seem to support the new hypothesis in the Gas Hills district of Wyoming include the following: (1) the lack of C¹²-enriched (i.e., methane-derived) calcite, (2) the variable and extreme enrichment of S³² in pyrite within transitional IBG and in pyrite associated with jordisite on the leading edge of some rolls, and (3) the greater enrichment of S³⁴ in the present groundwater sulfate than in the epigenetic sulfides that generate this sulfate. The unusual occurrence of roll ore bodies between EBG and IBG that contain almost no pyrite or calcite would be difficult to attribute to a bacterial origin.

The diagenetic formation of bacterial sulfides in sandstones can be viewed as ground preparation for the later and genetically unrelated formation of roll ore bodies. Accordingly, other factors being equal, wide ore zones should exist adjacent to pyritic EBG, and rolls should be absent or narrow next to nonpyritic EBG.