Abstract

The age of precious and base metal mineralization in the Central City district has been determined as 59 + or - 1 m.y. directly by potassium-argon dating of associated sericites, and indirectly by dating of pre- and postore intrusions. The results show the intrusives are of Paleocene age and they also suggest some minor revision of the accepted intrusive sequence in the central Front Range. Some small granodiorite stocks are reinterpreted as being associated with rhyodacite dikes as the youngest rocks in the sequence and are temporally, although not obviously spatially, associated with the mineralization.All four stages of mineralization in the district, i.e., uranium --> pyrite (Au) --> base metal (Au, Ag) -->, telluride, may have resulted from the operation of a single, short-lived ( approximately 1 m.y.) complex hydrothermal system developed at the end of a period of igneous activity. Intrusion and mineralization in the central Front Range form part of a regional late Laramide magmato-hydrothermal event that occurred in the northeast Colorado mineral belt around 60 m.y. ago.

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