Hundreds of solution-collapse breccia pipes crop out in the canyons and on the plateaus of northern Arizona. Pipes originated in the Mississippian Redwall Limestone and stoped their way upward through the upper Paleozoic strata, locally extending into the Triassic Moenkopi and Chinle Formations. High-grade uranium ore associated with potentially economic concentrations of Ag, Pb, Zn, Cu, Co, and Ni in some of these pipes has stimulated mining activity in northern Arizona despite the depressed market for most of these elements.

More than 900 confirmed and suspected breccia pipes have been mapped during the past 6 years. Many exploration criteria for detecting mineralized breccia pipes were developed during this study. One pipe discovered on the west side of Mohawk Canyon during 1983, was selected for exploratory drilling in 1984 because it exhibited the following exploration criteria: (1) concentrically inward-dipping beds of Kaibab Limestone, (2) a circular erosion pattern, (3) anomalous radioactivity, which is highly significant for the oxidized surface exposure of breccia pipes, (4) goethite pseudomorphs and molds of pyrite, (5) colloform celadonite-stained chalcedony, (6) copper mineralization expressed on surface exposure as the supergene minerals malachite, azurite, brochantite, and chrysocolla, (7) br ccia, and (8) anomalous concentrations in surface exposure of such trace elements as Ag, As, Cd, Co, Cr, Cu, Mo, Ni, Pb, Se, V, and Zn.

Five rotary and core holes were drilled into this pipe. Numerous drilling problems caused by 30-ft (9-m) caverns within the breccia limited the drilling results. Core recovered from holes in the center of the pipe shows breccia to total depth of 1,010 ft (308 m), abundant pyrite, and minor galena. Gamma logs of a rotary hole penetrating to 1,335 ft (407 m) show a 1-ft (0.3-m) interval of 0.52 eU₃O₈ at a depth of 1,191 ft (363 m); this is at the same stratigraphic horizon as the top of ore bodies in mines located on similar plateaus capped with Kaibab Limestone. Sufficient mineralization was verified in the Mohawk Canyon pipe that further drilling is warranted to assess its economic potential.

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