A concentration of ore bodies occurs in a belt across the Lukachukai Mountains. The ore belt conforms to a facies of lenticular sandstone and mudstone that apparently provided sufficient permeable sandstone for the passage of ore solutions, and sufficient impermeable mudstone to restrict movement of solutions to particular sandstone beds. An unusual concentration of carbon appears to have served as a precipitation agent. Lateral changes in permeability of the sandstone beds, related to the old stream systems, influenced the movement of mineralizing solutions. The solutions apparently bleached red sandstones to gray or to limonitic brown.Mapping of drill-core data shows that ore bodies (1) are elongate parallel to sedimentation, (2) tend to occur along the flanks of sandstone channels that are bounded laterally by zones of "flood-plain" lithology, (3) commonly occur in groups, (4) tend to "build up" against permeability barriers.The degree of mineralization in an area is related to the initial quantity and quality of: (1) ore solutions, (2) carbon, and (3) permeability variations. Permeability changes probably do not directly cause precipitation, but are effective in the formation of large deposits.