Abstract

Black Peak protrudes above a tableland of Navajo Sandstone on the Colorado Plateau just east of Echo Cliffs and 30 miles north of Cameron, Arizona. A breccia pipe on the west slope of the butte locally contains breccia fragments of sandstone, mudstone, shale, and altered dike rock believed to have been plucked from wall rocks and transported upward. Sources of uranium mineralization in the Cameron area may be inferred from the origin of the pipe.

A vesicular, silicified collar several feet thick encloses the pipe on three sides. Minute micro-acicular quartz overgrowths on quartz crystals in the wall rock suggest that explosive penetration of superheated steam formed the pipe. Irregularly distributed argillic alteration, silicification, and mineralization suggest subsequent hydrothermal activity.

Associated with the pipe are carbonates, alunite, gold, silver, iron, manganese, and possibly uranium and copper. Silica has been introduced in the largest quantities.

The butte was probably formed by vertical penetration by fluids of magmatic origin from below; this suggests a possible original source and one phase in the mechanism of introduction of mineralization in the Cameron area.

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