Emery Deposits Recently Found at the Shin-Kiura Mine, Oita Prefecture

Abstract

Emery deposits have recently been found at the Shin-Kiura mine, Oita Prefecture, the first occurrence in Japan. The emery ore, being composed predominantly of corundum, spinel and iron oxides, is closely associated with Paleozoic limestone. The writers present here the mineralogical and chemical compositions of the ore.
Corundum is often contained as much as 60% in the Kiura emery, which shows tints of blue due to the presence of sapphire. Spinel constituent of the emery belongs to hercynite, which is always existent, in a large quantity. The emery often contains also considerable quantities of magnetite, ilmenite and andalusite. Anorthite and alkali-amphiboles are seen frequently as accessory minerals along with some garnet, tourmaline, cordierite, biotite, titanite, quartz and calcite. It is noteworthy that hematite and sulphide minerals are scanty in the emery ore.
The main chemical constituents of the emery ore are AL₂O₃ (35-65%) and Fe₂O₃+FeO(30-55%), with a subordinate content of SiO₂, which ranges from 5% to 20%. The Kiura emery is characterized by low MgO content and high CaO content, as compared with emery ores of other localities.
The Kiura emery deposits are thought to have been formed mainly by contact metasomatism, as a reaction between basic igneous emanations and the Paleozoic limestone: The origin can be ascribed to a process of desilication of the igneous media by limy or peridotitic rocks.