Studies on Rare-earth and Radioactive Minerals of Alkalline Complexes in Brazil.

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Research surveys of this project were performed for two years of 1989 and 1990, but have actually been continued since 1987. Main subjects of this project are the surveys of minerals which are closely related to alkaline rocks and carbonatite-alkaline complexes in Brazil and understanding their occurrences, mineral assemblages, textures, chemical compositions and so on. Concentration of rare-earth elements are characteristic in the complexes, and radioactive elements are often accompanied in minerals. Therefore, their minerals are also intersted as a natural analogue for the basic research of solidification and stabilities of radioactive wasted materials.In this project, survey and collection of rocks minerals were carried out in the carbonatitealkaline complexes which dot Brazilian shield along the lines from south to north. The main surveyed areas and collected rocks and minerals are summarized as follows : (1) fresh carbonatites and jacupirangite, and their thermal metamorphic rocks … More at the boundaries of carbonatites and jacupirangites at mines near Cajati in the state of Santa Catarina ; (2) Alkaline rocks such as caldasite which is extraordinarily enriched in Zr, phonolite, tinguite, rocks which include radioactive elements, ultrabasic rocks mainly composed of magnetite and so on, at Pocos de Caldas at the boundary of both states of Sao Paulo and Minas Gerais ; (3) Minerals of perovskite, anatase, pyrochlore and so on which are obtained from carbonatite-alkaline complexes at Araxa and Tapira in Minas Gerais ; (4) Weathered soil of carbonatie-alkaline complexes which are concentrated by such rare-earth elements as La and Ce at Catalao in the south of state of Goias ; (5) Ultrabasic rocks of which main components are crysotile, graphite and so on at Minacu of Minas Gerais ; (6) Zircon bearing alkaline rocks at Peixe in the State of Tocantins ; and (7) Nephelin-syenite and sodalite-nephelin syenite in south Bahia and in Para. The ages of intrusion of above alkaline rocks estimated in the range from 70-130Ma.All of collected samples are difficult to obtain in Japan and indispensable specimens in order to study the origin of carbon, minerallization processes of phosphate and rare-earth minerals, weathering processes, and description of varieties of minerals, and so on. The textures, constituent minerals, and their chemical compositions of some of above specimens have already been described by observations of optical microscope, X-ray diffraction apparatus, scanning electron microscope and so on, and further works will be continued in future.We wish to thank Brasilian scientists, many geologists in mines which we visited, for their colaborations and helps. We feel deep mortification at Professor Kenkichi FUJIMORI's sudden decease by cancer in July of 1990, who strongly promoted this project as one of investigators of this project. Less