鉱床の年代測定の最近の進展(1991年度日本地球化学会奨励賞受賞記念)

概要

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Recent developments in dating two types of deposits, Mississippi Valley-type (MVT) deposits which are related to crustal fluid flow and rare-earth deposits, are reviewed here. The MVT deposits are epigenetic carbonate-hosted Pb-Zn deposits. They have concealed their precise ages in spite of many attempts using variety of techniques. The Rb-Sr method has been sucessfully applied to sphalerites from MVT deposis. The result indicated that mineralization in East Tennessee took place at 350-380Ma, which denies genetic linkage of the deposits to the late Paleozoic crustal fluid flow during the Alleghanian orogeny (320-250Ma). The application of this dating method will put reliable geochronological constraints on the formation of the MVT deposits and shed light on the genesis of the deposits. A new geochronometer using electron capture decay of ^<138>La has been applied to rare-earth rich minerals such as monazite, allanite and bastnaesite. The method allowed to determine an age of otherwise undatable bastnaesite in Gakara, Burundi.
日本地球化学会の論文
1992-09-24