Potassium-argon analyses of vein adularia and of sericite from altered wall rocks yield a weighted mean age of 24.6 + or - 0.3 million years for the mineralization at Creede. The age of the youngest volcanic rocks exposed in the district, the Fisher Quartz Latite, has been determined by Steven and others (1967) as 26.4 + or - 0.6 m.y. The Fisher lavas were erupted through the ring-fracture zone of the Creede caldera after the caldera had been resurgently domed. The data permit interpretation of the mineralization as related either to a late intrusion related to the Fisher period of activity or to an early intrusion related to eruption of younger volcanic rocks of the Hinsdale Formation.
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