Muscovite in pegmatitic ore from the Tamayama native gold deposit, southern Kitakami Mountains, is dated at 111.7 ± 3.0 Ma, which is consistent with those of Cretaceous granitoids in the Kitakami Mountains. Pegmatitic ore and its host Hikami granitic rocks have been thermally metamorphosed by the Kesengawa granodiorite of Cretaceous age. A pressure corrected homogenization temperature (ca. 400
oC ) of quartz in the pegmatitic ore is beyond the closing temperature (ca. 350
oC ) of muscovite with respect to radiogenic argon. Therefore, the obtained K-Ar age of muscovite is considered to be rejuvenated due to contact metamorphism. An oxygen isotopic ratio of quartz in the pegmatitic ore (
δ18OSMOW=10.0 ‰), resembles to that of quartz in an ilmenite-series pegmatite (ca. >10 ‰). The oxygen isotopic equibration temperature for a coexisting mineral pair of quartz-muscovite in the pegmatitic ore is calculated at 865
oC. The Hikami granitic rocks which host the pegmatitic ore, have also an ilmenite-series character. These data suggest that the pegmatitic ore from the Tamayama gold deposit is the final crystallization product of the Hikami granitic rocks which have been thermally metamorphosed intermittently after the formation of pegmatitic ore.
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