Antimony Deposits of the Shizunai Mine in Hidaka, Hokkaido

Abstract

Along the Hidaka mountain range, which constitutes the geological back-bone of the island of Hokkaido, several ore deposits are found closely associated with basic igneous rocks. Shizunai mine described in this paper is an antimony deposit.
Around the mining district extensive schalstein and slate formations trend N 20-30°W; their structure was determineded by tectonic effects similar to those which formed the back-bone region.
The ore deposits are imbedded in a "mineralized sheared zone" which trends N 70°W through a normal diabase mass. The mineralized sheared zone is characterized by altered rocks such as 1) albite-chloritized diabase, 2) chlorite rock, and 3) carbonitized rock. These rock types are-arranged in zones around a stibnite-quartz vein, the core of the deposit. The stibnite-quartz vein is contained only in the carbonitized rock, which constitutes such a characteristic feature for developement of the deposits that the veins and carbonitized rock have long been treated inclusively as "Hinouchi" by Japanese miners.
Carboriitized rock, the main constituent of "Hinouchi" is subdivided as follows:
1) chlorite-carbonate part.
2) carbonate-sericite part.
3) quartz-sericite part.
The quartz-sericite part represents the thin sheath of the ore body; it is surrounded by the carbonate-sericite part which is thicker.
The vein consists chiefly of stibnite and quartz, and diverges into many units about 3m long which are arranged in a "scale-like structure."
Ore minerals are stibnite and a small amount of sphalerite, chalcopyrite, and native gold. Stibnite is in the form of small acicular crystals in low grade ores, but is in columnar aggregates with deformational textures in high grade ores.