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Abstract
Tuffites of the core taken from the underwater Krishtofovich Rise in the southeastern Sea of Japan contain phosphate inclusions that were studied by scanning electron microscopy and chemical methods. The tuffites relatively enriched in phosphorus represent products of Miocene alkaline volcanism and are overlain by a thin layer of sediments partly transformed into smectites and containing microfossils presumably of the Late Miocene age. The phosphate inclusions variable in shapes and consistency are largely confined to the lower sedimentary layer, although occurring as single fragments of compact rock and nonlithified small inclusions in voids of altered tuffs as well. By their structure, microtextures, and main chemical composition, the phosphate inclusions are similar to the phosphorites from other areas of the ocean, which indicates their similar biogenic-diagenetic origin. Judging from the REE composition in the most phosphatized matter, they originate largely from seawater and, to a lesser extent, from tuffites. The redistribution of mobile phosphorus enclosed in the tuffites results in a small-scale phosphatization insufficient for ore formation.[PUBLICATION ABSTRACT]