Unilateral isotopic variation of Miocene ore leads from Japan

Lead isotope ratios of Miocene ore deposits in Japan are examined in reference to their positions relative to the geological structure of the island arcs. A detailed inspection of the data indicates that in northeast Japan the ore lead becomes slightly less radiogenic from the Pacific Ocean side to the Japan Sea side, suggesting some coherence between ore and volcanic rock leads along zones parallel to the magmatic front. Also, in southwest Japan a slight but systematic difference in isotopic composition appears to exist in the Miocene ore leads which might be correlated with the positions of individual deposits relative to assumed magmatic front lines.