Abstract

Fission-track ages of selected minerals from intrusive rocks in and near the Ray porphyry copper deposit are in good agreement with published K-Ar ages of slightly chloritized igneous biotite (containing <10% chlorite) from the same rocks, and, except for one anomalously young fission-track age for an apatite, are consistent with the sequence of geologic events. The anomalous age is apparently the result of heating of the one sample after the deposition of ore at Ray.K-Ar ages of igneous and pegmatitic hornblende, partly chloritized igneous biotite (containing > 20% chlorite), and hydrothermal biotite at Ray are consistently older than the fission-track ages and K-Ar ages of slightly chloritized igneous biotite from the same or associated rocks. The discrepancies between the two sets of ages are explained by the incorporation of extraneous radiogenic argon into the hornblende, chlorite, and hydrothermal biotite as suggested in Part I of this paper. The fission-track ages indicate that the igneous activity associated with the Ray deposit began about 70 + or - 1 m.y. ago and ceased about 60 + or - 1 m.y. ago. A fission-track age of apatite from the Ray deposit suggests that the ore body cooled below 50 degrees C about 60 m.y. ago. The concordance of the fission-track ages of apatite in the several dated stocks with fission-track ages of coexisting sphene and zircon indicates that the stocks were emplaced at depths no greater, and probably less, than 5 km.

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