Geological Studies on the Dolomite Deposits of Chichibu Terrain

Abstract

Dolomite deposits of western Shikoku are distributed in some definite stratigraphic and geotectonic zone. They are classified into the following group.
1) Siliceous dolomite deposits of the northern zone of upper Carboniferous in age. These deposits are associated with red tuff, red chert, and other clastic sediments of volcanic materials.
2) Some workable dolomite deposits of the southern zone of lower Triassic Uonashi formation, independent of volcanic activities.
Chief factors of the formation of dolomite are temperature, pH, Eh and concentration of Mg-ion in the sea-water of geosynclinal basin. These factors are related to some paleogeographical environments, such as submarine volcanism (Northern zone) and development of shallow sedimentary basin of nearshore line (Southern zone).
Chemical compositions of mineral dolomites, mechanism of dolomitization, deformation and recrystallization of ores, and relation of dolomite bed to other submarine sedimentary ore deposits are also discussed in this paper.