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Abstract:To evaluate resource potential of rare earth elements (REE), umber (ferromanganese sediment), manganese ore and associated rocks such as basalt, chert and shale in the Itogo, Misoigawa, Usugaokayama, Komoridani and Ryujin areas in the Northern Shimanto Belt, SW Japan were examined. The umber in the Itogo area and manganese ore in the Ryujin area occur between a basaltic footwall and a hanging wall shale.The basalts from the five areas are altered, resulting in addition of water and alkaline elements. Chondrite-normalized REE patterns of the basalts have slightly LREE-depleted and flat-shaped patterns. The REE patterns and trace element compositions of the basalt indicate that they are MidOceanic Ridge Basalt in origin. Chemical compositions of umber are characterized by enrichments in REE and negative Ce anomalies relative to post-Archean average shale (PAAS). Manganese ores are depleted in REE and show positive Eu anomalies. Geochemical features and geological evidences suggest that both the umber and the manganese ores were formed by precipitation of iron and manganese from submarine hydrothermal solution near the Mid-Oceanic Ridge.The umber contains up to 1,441 ppm of total REE contents, while the manganese ores have less than 100 ppm in total REE. These umber are equivalent in HREE contents compared with those of the "ion-adsorption" deposits (weathered granite) in southern China, which is the present major HREE producer. Although the total amount of REE resources in the Itogo area is quite small, basalt-chert and basalt-shale successions are common in accretionary complexes of Japan, and REE potential of ferromanganese deposits deserve to be inverstigated.

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