Oeyama Mine (大江山鉱山)
The whole Mt. Oe area is composed of serpentinite which is made largely of ultrabasic rock. Due to weathering of serpentinite containing a small amount of nickel, the nickel component becomes concentrated and nickel-containing clay including nickel minerals such as garnierite which is secondarily generated from the weathering is distributed. From before the start of the Pacific War until the end of the war, the nickel mine was developed and dug to produce nickel as one of the important military materials in Japan domestically.
As the Pacific War loomed, the Japanese government and the military faced shortages of various mineral products and launched efforts to boost their domestic production. One of these mineral products was nickel, and one of the corporations most interested in its domestic production was then Nihon Kayaku Kogyo (Nihon Kako) which later became Nippon Yakin Kogyo Co., Ltd. The company was a gunpowder manufacturer for the navy and aiming to domestically produce light alloy metal, special steel, and so on.
In 1934, Nihon Kako conducted a survey on serpentine areas in Hyogo, Kyoto and Fukui Prefectures. As a result, they found that the most promising area was Oeyama mountain range centering on the former Yosano village (now the Yosano area, Yosano-cho), Yosa County, Kyoto Prefecture. Although its ore is poor, ore reserves are inexhaustible and in the same year, Nihon Kako established Oeyama Nickel Kogyo Co., Ltd., obtained a mining concession and continued the survey. Trial smelting was performed repeatedly using ore from Oeyama Mine etc., but because the ore was too poor in nickel, pure nickel remained unable to be refined as previously planned. In 1938, 'the Krupp-Renn process' was introduced from Krupp, a German company, as a suitable technology for the treatment of poor ore. With this technology, pure nickel could not be produced, but ferronickel could be recovered as grained iron (luppe).
Because ferronickel is adequate for the manufacture of special steel, stainless steel, high-speed steel and so on, Nihon Kako decided to employ the Krupp-Renn process with the aim of producing ferronickel. Nickel ore taken from Oeyama Mine was transported by truck or freight car to Nanao Cement in Nanao City, Ishikawa Prefecture where the industrial test for smelting was carried out repeatedly with the rotary kiln for manufacture of cement. In March 1940, Nihon Kako succeeded in smelting luppe and started full-scale manufacture. Furthermore, based on this result, they received assistance from the government and the army, and established Iwataki Smeltery, a smelting facility exclusively for nickel, which was only 11 kilometers away from Oeyama Mine in the former Yoshizu village, Yosa County (now Miyazu City, Kyoto Prefecture and Iwataki, Yosano-cho). Not only was this smeltery not far from the mine, but it was conveniently located for transportation of vital requirements for smelting such as anthracite from Chongjin, Korean Peninsula and limestone from Kyushu by ship.
Actual situations of forced labor
At that time, the extraction of nickel ore was conducted by open-air mining in Oeyama Mine using large scale mobilization of labor, but when many Japanese miners went on the warpath, thereby leading to a labor shortage, a large number of students and prisoners were poured in.
The details of the circumstances at the time are mentioned in "Oeyama Mine: the True Story of the Kidnapping of Chinese Nationals and the Forced Labor" written by Kaoru WAKUDA (published by Kamogawa Shuppan Publishers in 2006) and "Roll Call at Oeyama P.O.W. Remembers" written by Frank Evans (published in English only in England in 1985).
Due to the end of the Pacific War in 1945, Oeyama Mine was closed, and Iwataki Smeltery stopped producing luppe and decided to do nothing but maintain its facilities. Later, in 1952, the business of Oeyama Smeltery was planned to be resumed; subsequently, it has continued its business to this day since ore far better than one from Oeyama Mine started to be imported from New Caledonia of the French possessions in the South Pacific Ocean.