Rare earth minerals in Shikoku, with special reference to the occurrences of rare earth minerals in pegmaties in the Ryoke and Hiroshima granites

摘要

31 REE mineral species, made up as follows, oxides 3,phosphates 7,carbonates 5,silicates 15,arsenate 1,occurs in pegmatites of the Ryoke and Hiroshima granitic rocks in the inner zone of Shikoku, and in outer zone, 14 REE mineral species, made up as follows, oxides 6,halide 1,carbonate 1,silicates 5,phosphate 1,have been found from pegmatites in Oshima metamorphic rocks and A type granite bodies which intrudes into Shimant formation. The occurrence of their minerals are divided into four types as follows : primary products, exolution lamellas, pseudomorphs and veinlets and crusts. The representative primary minerals are zircon, allanite, fergusonite-(Y) and gadolinite. Lamella minerals are uraninite, tHORIte and xenotime. Thorogummite and tengerite occur as pseudomorphs after yltrialite. Allanite frequently are replaced by synchysite-(Ce) and bastnaesite-(Ce). Secondary xenotime and thalenite-(Y) occur by decomposition of britholite-(Y). Churchite, rhabdophane-(Nd), cerite, monazite-(Nd) and liandratite-petscheckite like mineral occur as fissure filling minerals or crusts. Among them, syncysite-(Ce) and cerite was the first occurrence in Japan, and uraninite, britholite, masutomilite, grayite, manganocolumbite and brockite were the first occurrence in Shikoku. Allanite from the Ryoke pegmatites is characterized by high Yttrium content, and one from the Hiroshima pegmatite has high cerium content. In this paper, the occurrences and mineralogical properties of REE and U-Th minerals from granitic pegmatites in Shikoku are summarized.