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大泉鉱山跡

県中西部の山間を流れる西大鳥川の上流域に位置し、かつては大鳥鉱山として銅鉱を産出しました。 1717 年（享保 2 年）の外平金山の発見が起源とされ、明治初期には金鉱や銅鉱が小規模に採掘されました。 東京の実業家 浅野総一郎は 1887 年（明治 20 年）以降、複数の借区を取得して開発を試み、次いで、鉱区の一部を譲り受けた富山の岩脇時四郎が、1893 年（明治 26 年）に採掘特許を取得しました。 2 年後に権利を買収した古河鉱業創業者 古河市兵衛は、大床の旧坑に富鉱帯を発見し、外平に製錬所を設けて粗銅の生産を開始します。 1905 年（明治 38 年）に事業を継承した古河鉱業は、坑外施設を新設し、大戦景気を背景に生産を拡大しました。 しかし、記録的な雪崩災害や戦後恐慌の影響により、1922 年（大正 11 年）に事業は撤退を余儀なくされました。 昭和期に移ると、愛知の資本家 德倉充治らが 1936 年（昭和 11 年）に大滝に試掘鉱区を取得し、翌年に大泉鉱山として採掘権に転願します。 同年に権利を譲り受けた大日本鉱業は、3 年後に選鉱場を設けて操業に入り、大鳥鉱山を買収して大泉に統合しました。 1943 年（昭和 18 年）の生産量は粗鉱 31,606 t、銅精鉱 4,525 t、鉛精鉱 254 t、亜鉛精鉱 1,090 t、硫化鉄精鉱 3,410 t に及び、銅精鉱は最大量を記録しました。 終戦後、選鉱場は 1946 年（昭和 21 年）の火災によって焼失しますが、大床での新鉱体の発見を受けて 4 年後に再建され、朝鮮戦争の特需を背景に生産は徐々に回復しました。 昭和後期に入ると、鉛鉱、亜鉛鉱の増加を受けて選鉱場の拡張が重ねられ、大泉は出鉱の最盛期へと向かいました。 しかし、大日本鉱業は石油危機による金属市況の低迷から 1977 年（昭和 52 年）に解散に至り、新たに発足した出羽鉱業に事業が譲渡されることとなります。 寿岡の外れには往時の選鉱場跡が今も残ります。

1979 年閉山

Oizumi Mine

The mine was situated in the upper Nishi-Otori River basin in the western part of the prefecture and was formerly known as Otori Mine, producing copper ore. According to local lore, a gold vein was discovered at Tohira in 1717, and various ores, including gold and copper, were mined on a small scale in Otori in the second half of the 19th century. From 1887 onward, Soichiro Asano, a businessman in Tokyo, acquired several leasehold areas and attempted to develop the mine on a small scale. Later, Tokishiro Iwawaki in Toyama purchased part of the leasehold area and acquired the mining rights in 1893. Two years later the mining rights were transferred to Ichibei Furukawa, the founder of Furukawa Mining Co., Ltd. Furukawa discovered a rich copper ore shoot in old workings at Odoko and then constructed a smelter at Tohira, commencing crude copper production. Afterwards, Furukawa & Co. took over management of the mine in 1905 and later constructed new surface facilities, increasing production in response to demand during the First World War. However, the mine faced challenges due to large-scale avalanche damage and the postwar recession, which led to its withdrawal from mining operations in 1922. In 1936, Mitsuharu Tokukura, a businessman from Aichi, and others acquired exploration rights for Otaki, and in the following year, some of those rights were converted into mining rights under the name Oizumi Mine. The same year, Dai-Nippon Mining Co., Ltd. purchased the rights and three years later commenced operations following the completion of a beneficiation plant, expanding its mining areas through the acquisition of Otori Mine. In 1943, the mine produced 31,606 tonnes of crude ore, 4,525 tonnes of copper concentrate, 254 tonnes of lead concentrate, 1,090 tonnes of zinc concentrate, and 3,410 tonnes of pyrite concentrate, and copper concentrate production reached its peak. Although the beneficiation plant was destroyed by a fire in 1946, a new ore body was discovered at Odoko, which led to the reconstruction of the plant four years later. Thereupon, production gradually recovered due to special procurement during the Korean War. From the 1960s onward, beneficiation capacity was repeatedly expanded as lead and zinc ore production increased, and the mine approached its peak in crude ore production. However, the company was dissolved in 1977 due to a downturn in metal prices following the oil crisis, and the mining rights were transferred to newly established Dewa Mining Co., Ltd. The remains of the beneficiation plant can still be seen today in a corner of Toshioka.

closure in 1979