New Mexico Mineral Symposium — Abstracts

Solution-collapse breccia pipes in northwestern Arizona provided excellent conduits for fluid movement and sites for the precipitation of minerals containing Ag, Co, Cu, Mo, Ni, Pb, V, U, and Zn. Colorful minerals of the oxidized zones of breccia pipes have caught the attention of prospectors and mineral collectors for more than 100 years; recorded mining claims in breccia pipes of the Grand Canyon date back to the late 1860's (G. H. Billingsley, written communication 1989). In fact, the Grandview mine has long been known for its beautiful sprays of cyanotrichite. It was not until 1956, when uranium was first produced from the Orphan Lode breccia pipe, that interest peaked for minerals in the primary (unoxidized) ore zones; access to these minerals, however, is only available from underground workings, commonly from shafts as deep as 1200 ft below the Kaibab or Coconino plateau surfaces. Both the oxidized and primary minerals occur in the quartz-sand matrix of the breccia, with minor amounts occurring in clasts of Paleozoic or Triassic sandstone and little to none in the limestone or shale clasts. Unfortunately, most of the 104 minerals listed below that occur in these solution-collapse breccia pipes are so extremely fine grained (generally less than 1 mm) that they do not even lend themselves to photography, other than with the SEM, let alone to macro-specimen mineral collecting.

Most of the minerals listed below were precipitated from fluids that were cooler than 173½ C; fluid-inclusion studies suggest that sphalerite, dolomite, and calcite were formed from saline brines having more than 18 wt % NaCl equivalent at temperatures between 80½C and 173½C. The uranium mineralization occurred approximately 200 million years ago (Ludwig, 1988) and was preceded first by a stage of Co-Ni-As-Fe sulfide deposition and then by a Cu-Fe-Zn-Pb sulfide stage.

The breccia pipes in this region began to form at the close of the Mississippian after extensive karst development in the Redwall Limestone. Many of the pipes penetrate as much as 3,000 ft upward into overlying Pennsylvanian, Permian, and Triassic strata. No volcanic rock is associated with them. The pipes are less than 500 ft in diameter and contain strata that have been downdropped as much as 700 ft. The bottoms of small breccia pipes can be observed on the ceilings in Redwall Limestone caves. On the walls of one such pipe, in a Redwall Limestone cave, are speleothems and oncrustations formed from secondary minerals containing Mo, U, As, and Cu--all elements that are commonly enriched in primary breccia-pipe ore. These minerals include powellite, carnotite, conichalcite, talmessite, and hoernesite. Neither talmessite nor hoernesite have been reported previously from the United States.
Colorado Plateau-type breccia pipes also exist in the Basin and Range Province of southern Utah, Nevada, and California. The breccia-pipe host rocks extend into the Beaver Dam Mountains of southwestern Utah where a solution-collapse breccia pipe hosts the Ge and Ga ore of the Apex mine. The Apex minerals are almost totally oxidized, and the mine contains 24 of the minerals listed below that have been identified in the Colorado Plateau pipes.
In addition the Apex contains: adamite, allophane, cobaltoan adamite, duftite, plattnerite, plumbojarosite, rosasite, and svanbergite.

More than 1000 breccia pipes have been located in northwestern Arizona; all contain similar mineralogy and geochemistry. They are a species collector's paradise, but it is unlikely that many large showy crystals will ever surface from these pipes.