Sills in the Coal Seams and the Thermal Metamorphism of Coal at Takashima Colliery, Nagasaki Prefecture

Abstract

Mode of intrusion of an igneous rock into coal seams and some noticeable aspects of thermal metamorphism of the coal at Takashima colliery are summarized in this paper. The igneous rock mentioned above consists only of one rock type, which has been difined as a tholeiitic basalt on account of itschemical and mineralogical compositions. This rock has changed generally to a saponitecarbonate rock due to autoalteration.
The igneous rock intrudes the coal seams as a sill. The intrusions took place evidently after the main tectonic movements which formed the major fault system. The feeder of the basaltic magma should be a system, which is supposed to occupy a tension crack system formed in the Takashima dome. The movement of the sill intrusion has been controled by the pre-existing fault system, by the load of the roof sediments, and also by the dip of the seam.
Zones of differentially metamorphosed coal are distinguished from the contact between the coal and the basaltic sill. A few examples of such zonal arrangement are interpreted in this paper, thoughthe chemical and physical details of the metamorphosed coals will be published in other papers.