The Hishikari Mine is located in the northern part of Kagoshima Prefecture. It has produced 248.2 tons (as of the end of March, 2020) of gold since production started.
The Hishikari Mine boasts high-grade gold containing an average of 30-40 grams of gold per 1 ton of ore (the average grade of the world's major gold mines is approximately 5 grams). And, to this day, it still produces about 6 tons of gold per year. Although there were many metal mines throughout Japan in the past, they closed down one after another. Today, the Hishikari Mine is the only domestic metal mine being operated on a commercial scale.
The ore deposits of the Hishikari Mine are known as "epithermal vein-type deposits". In the process of earth movements, known as "plate tectonics", in which the pacific plate slides under the Japanese archipelago, magma is generated. This magma comes up through cracks in the earth's crust, and erupts as volcanoes on the surface of the earth. When groundwater or water content of magma （hot water） is introduced into cracks of the surface of the earth during volcanic activity, substances that dissolved in hot water cool down and form ore veins. The gold deposits of the Hishikari Mine were formed in this way. They are believed to have formed approximately one million years ago. The gold deposits are very new from a geological standpoint and are characterized by their accompanying hot spring water with a temperature of 65 degrees C.
Hot water extraction room 50 m underground
The Yunoo hot spring resort, where hot spring water is supplied from the Hishikari Mine.
El : electrum
Nm : naumannite
Cp : chalcopyrite
The ore deposits of the Hishikari Mine are formed by several ore veins running vertically. Drifts are made for mining in a horizontal direction against these ore deposits.
Holes are drilled in the ore veins using a drilling machine （Jumbo）. 40 to 50 holes with a depth of 1.8 m to 3.5 m are drilled.
1kg to 2kg of water gel explosives are loaded into each hole to blast the holes.
Ore that was crushed through blasting is collected with a mucking machine known as an Load Haul Dump (LHD).
The collected ore is transferred from the LHD to a dump truck, and is carried to the above ground ore processing facilities.
Waste is removed out of the ore by handpicking and ore sorting facility.
The separated gold ore is loaded into a gold ore carrier at the Kajiki Port in Kinkowan, and is transported to the Toyo Smelter & Refinery, which is SMM's main smelter.
The gold ore carried to the Toyo Smelter & Refinery is put into a flash furnace and taken out as pure gold with 99.99% purity after being processed in the precious metals plant using a hydrometallurgical process.