On the Geology and Prospecting of the Akaiwa and Doshinkubo Deposits, Chichibu Mine

Abstract

As a result of active exploitation of the Daikoku deposits in the Chichibu Mine, much information was obtained on the structural features controlling the localization of the ore deposits.On the basis of this information, new ore deposits were researched both in the Akaiwa and the Doshinkubo sections. Geophysical prospecting and drilling were carried out effectively.
In consequence, in the lower horizon of the Akaiwa pit, a large massive ore deposit of replacement type was discovered in the Paleozoicc limestone. The ore consists mainly of sphalerite and pyrrhotite, with subordinate amounts of galena, chalcopyrite and magnetite.
In the Doshinkubo section, major iron ore deposit of contactmetasomatic origin occurs along the contact between limestone and quartz-diorite. The deposit is composed chiefly of magnetite, accompanied by some pyrite and locally concentrated chalcopyrite. Garnet skarn occurs in abundance in the footwall side of the deposit. Many large crystals of vesuvianite are contained in some parts of the skarn.