尾去沢鉱山

Osarizawa Mine - Osarizawa Kozan


Useful Information

Location: Shishizawa-13-5 Osarizawa, Kazuno, Akita 018-5202.
(40.185660, 140.746640)
Open: APR to OCT daily 9-17.
NOV to MAR daily 9-15:30.
[2022]
Fee: Sightseeing Tunnel Tour: Adults JPY 1,000, Children (12-17) JPY 800, Children (6-11) JPY 600, Children (0-5) free, Seniors (65+) JPY 900, Disabled JPY 500.
Groups (20+): Adults JPY 900, Children (12-17) JPY 720, Children (6-11) JPY 540, Seniors (65+) JPY 810.
Mine Guide JPY 2,000, max 20 persons.
Museum: free.
[2022]
Classification: MineCopper Mine MineGold Mine
Light: LightIncandescent Electric Light System
Dimension: L=800 km.
Guided tours: self guided, L=1.7 km, D=45 min.
Photography: allowed
Accessibility: no
Bibliography:
Address: Osarizawa Mine, Shishizawa-13-5 Osarizawa, Kazuno, Akita 018-5202, Tel: +81-186-22-0123.
As far as we know this information was accurate when it was published (see years in brackets), but may have changed since then.
Please check rates and details directly with the companies in question if you need more recent info.

History

708 discovery of the Osarizawa ore.
1481 copper was discovered in Shishizawa and Akazawa.
1598 mine opened by the Southern Clan as a gold mine.
1612 the Shogunate banns Christianity and believers become miners to be protected by the mine law which was extraterritorial over general law.
1666 many Christians are captured and executed at Shirane Gold Mine.
1695 copper ore in Tagun, Motoyama and Akazawa discovered.
1715 Nagasaka Copper Mine and Sakiyama Gold Mine discovered.
1865 blasting test with gunpowder conducted under the guidance of Americans.
1868 mine purchased by Locksmith Shigebei.
1872 Osarizawa Copper Mine Incident, mine confiscated by the Ministry of Finance.
1889 owned by the Iwasaki family, reverberatory furnace installed.
1893 managed by Mitsubishi Joint Stock Company, electricity power plant and underground pumps and hoisting machines introduced.
1896 hydroelectric power plant.
1916 fire destroys concentrator completely.
1936 Nakazawa Tailings Dam breaks with 374 dead.
1952 company name changed to Mitsubishi Metal Mining Co., Ltd.
1966 smelting department closed.
1968 copper prices fall, ore quality decline, operations reduced.
1978 mine closed due to low copper prices and depletion of ore.

Geology

Most of the copper ore mined at the Osarizawa Mine was a mineral called chalcopyrite. This mineral can be distinguished from pyrite by its strong yellow color and golden brilliance. There are many geodes in the veins of the Osarizawa Mine, and they are full of crystals of many beautiful minerals such as quartz.

Description

尾去沢鉱山 (Osarizawa Mine) was originally founded as a gold mine, but from the 17th century the copper ore was more valuable and so it became a copper mine. This is quite common for polymetallic ores, the most valuable ore in the mix is defining the profitability. Of course the other ores are also processed, but the mining follows the veins with the highest content of the main metal. The veins change their direction and become thicker and thinner, also the type of ore in the vein changes continually. As a result horizontal tunnels were built every 30 m to access the vein.

When the ore was reached the width and grade (copper content) of the vein in that section were checked. If it was profitable the ore was mined upward along the vein from the lower tunnel to the 30 m higher tunnel. A rock drill was used to dig a large number of holes with a diameter of 2 cm and a depth of 1.0 to 1.8 m. They were filled with explosives and blasted, then the loosened ore was collected from the floor of the tunnel. It was loaded into a mining cart and transported to the shaft, lifted by an elevator called a cage. Then the carts were pulled out of the mine by battery-powered electric locomotives.

The mining principle is always based on the situation, in this case the bedrock was solid, so a mining method called the shrinkage mining method was adopted. In other words, it was not necessary to fill the mined out veins with rocks to avoid collapses, because the surrounding rock was stable enough. The backfilling obviously would have cost money. The used explosives changed over the years. At first gunpowder was used, but the handling was quite difficult and dangerous. Much better was dynamite which did not bear the danger of exploding by accident. From 1965 it was replaced by the cheap ANFO. Also the ignition technology developed. First a fuse was used to ignite the gunpowder. From around 1955, electric blasting became the mainstream.

The ore was processed on the grounds of the mine, there was a mineral processing plant. The mined ores mixed with other minerals and rocks contained only about 1% copper. The concentrator separated the ores from the regular rocks which were called slack, the resulting ore had about 25%. The ore was first crushed by the crusher to become the same particle size, then it was sent into a rotating ball mill and crushed further. There was a ball of steel inside which crushed the ore. The result was sent to the flotation process where ore and rock were seperated by their specific weight. The mixture of dust and water was moved and the ore floated and was picked. This worked for sulfide minerals, and pyrite and copper ores were dehydrated to become copper concentrate. This was sent to a smelter and melted to make blister copper. Using electricity the copper was converted into electrolytic copper in the electrolytic process.

The 観光坑道見学コース (Sightseeing Tunnel Tour) is the underground tour of the show mine, which is located in the 石切沢通洞 (Ishikiri Sawa Tsūdō, Ishikirisawa Tunnel). This was the main shaft of the Osarizawa Mine. There are numerous remains of the mining on display like transportation equipment, underground offices, and the original elevator cages.

The 鹿角市鉱山歴史館 (Katsunoshi kōzan rekishi-kan, Kazuno Mining History Museum) has exhibitions of ores mined at the Osarizawa Mine, historical materials from the Edo period, and models of tunnels. The model shows the structure of the mine, the Ogasawa Mine has horizontal tunnels every 30 metres. Those levels were connected by shafts.