Potassium-argon ages of intrusion, extrusion, and associated oredeposits, Park City mining district, Utah

Abstract

Potassium-argon age determinations on 19 samples of igneous rocks fromthe Park City mining district, Utah, and on 7 samples of hydrothermalalteration minerals associated with ore deposits in the district,indicate that a varied sequence of intrusion, volcanism, andmineralization took place within a period of a few million years inearliest Oligocene, and perhaps latest Eocene, time. Ages determinedon biotite from igneous rocks suggest that igneous activity occurred36 to 31 m.y. ago, whereas ages determined on hornblende suggest asomewhat longer period between 41 and 31 m.y. ago. Ages ofhydrothermal minerals are 36 to 33 m.y. and thus are indistinguishablefrom rock ages.

36 samples from this reference