From abstract: Pitchblende, associated with base-metal sulfides, has been found at eight localities in the northern part of Jefferson County, Colo., in shear zones that cut pre-Cambrian metamorphic and igneous rocks, chiefly hornblende gneiss, biotite schist, and granite pegmatite. The pitchblende deposits, with one exception, are in major shear zones that contain vein-like bodies of carbonate-rich breccia. The breccia bodies range from 1 to 5 feet in thickness and are related probably to the Laramide faults, or "breccia reefs" of similar trend, mapped by Lovering and Goddard (1950).