Chronological study on the cretaceous igneous rocks and related ore deposits by Rhenium-Osmium method

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(1)Much time has been spent for improving the analytical methods, and thus, the analyzed samples were limited to the Kuroko ores and other some ore minerals. However, important aspects were obtained concerning the analytical methods, and those will much contribute to further studies in this field.(2)The photon-counting unit was purchased, and the computer programs were refined to attain speedy and precise measurements. Noise-cut transformer and electro-magnetic shield were introduced and worked effectively.(3)In order to diminish the chemical blanks, much effort has been made by repeated trials. Os blanks were successfully reduced to below 0.2pg, but Re blanks are still high (ca.17ph). In addition to such blank problem, Re in the filament and source contamination remained serious problem, and further development should be needed.(4)The mineral isochron method was applied to the Kuroko ores. The age of 18.6 Ma obtained is somewhat older than the previously recommended value of 15 Ma. However, this data is not so reliable and further study is necessary.(5)Other ore sulfide minerals and Fe-Ti minerals in granitic rocks were attempted. The low concentrations of Re and Os prohibit accurate analyses, but further efforts for lowering the blank would reserve promising results.