Facies variation of gabbro on the nickeliferous pyrrhotite deposits(I)

Abstract

The facies variation of the gabbro which is altered country rock of the nickeliferous pyrrhotite deposits, are reported in the present paper. The gabbro which is a member of the igneous rocks of the Hidaka metamorphic zone is distributed throughout the Hidaka Mountain range. The Satsunai-Dake area is situated in its northern part. The whole nickeliferous pyrrhotite deposits of the Hidaka metamorphic zone usually occur in the gabbro bodies. They are the coarsened gabbros owing to a kind of petroblastase. The olivine gabbro series has been distinguished as follows, (1) medium grained ophitic olivine gabbro, (2) coarse grained granoblastic olivine gabbro. Also in the norite series, (1) fine grained norite, (2) medium grained norite, (3) coarse grained granoblastic norite. The original rock of the olivine gabbro series is estimated the medium grained ophitic olivine gabbro (An70-75) and of the latter is the fine grained norite (An 33). These two series are used to be converged into coarse grained granoblastic olivine gabbro and norite with An60 plagioclase. In present investigation the plagioclase compositions are presented in the form of the An composition frequency diagrams. (Figures 4-10)