Abstract

Lead isotope ratios measured for the black ore ("kuroko") deposits from Miocene mineralization in Japan show only small variation over an extensive area. They are similar to the available isotopic data for some Cenozoic and Mesozoic igneous rocks in the Japaneses Islands and for pelagic sediments near Japan, namely, they are less radiogenic than the crustal leads from other regions. It seems probable that the isotopic composition of the black ore leads represents the average value for Japanese Miocene crustal leads. The possibility of the derivation of ore leads from the pelagic sediments is also discussed.

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