Abstract

Uraninite from the ore deposits at Bisbee, Arizona has an age of 104 + or - 6 million years, corresponding to the expectable age for the end of the Lower Cretaceous period. An obscure orogeny and volcanic series in the Southwest have this relative geologic age and are believed to be a part of the important metallogenic disturbance for the Bisbee region. The Sacramento porphyry appears to have been intruded before deposition of the Lower Cretaceous strata, and sericitization of it seems to have occurred after the series was deposited and during the mineralization episode about 104 million years ago. The uraninite is an early mineral in the paragenetic sequence and the hypogene bornite is relatively late. The early uraninite is excluded mechanically during the growth of such later minerals, as pyrite, with high "crystallizing power."

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