History and Discovery of Yoshioka Copper Mine
The history of Yoshioka Copper Mine stretches back many centuries. According to tradition, the deposit was discovered in 807, during the Daido era. During the Edo period, it was counted among Japan’s six major copper mines and also prospered as a source of bengara, a traditional red pigment made from iron oxide.
In the early Edo period, the mine was briefly controlled by the Nariwa Domain before becoming a tenryo, or territory administered directly by the shogunate. Copper extraction continued under the supervision of shogunate-appointed officials.
From the Edo period through the Taisho period, the mine primarily produced chalcopyrite and pyrrhotite. Ore was transported on horseback to the main gate at Shimohara in present-day Nariwa, Takahashi City. From there, it was loaded onto takasebune riverboats and carried to Tamashima Port before being shipped to the Copper Office in Osaka. This transport network illustrates the important role the mine played in regional and long-distance trade.
Development and Opening of Sasaune Tunnel to the Public
Sasaune Tunnel was developed in the late Edo period and continued operating until the end of the Taisho period. In 1977, the nearby Fukiya district was designated a National Important Preservation District for Groups of Traditional Buildings. Following this designation, restoration and development work on the tunnel began the next year. It opened to the public in November 1979 and has since become a popular destination for visitors interested in mining history.
The section prepared for visitors extends approximately 320 meters. The route includes numerous rises and dips, giving the walk a varied and adventurous character. Visitors wear helmets and explore the tunnel on foot.
The temperature inside remains around 15°C throughout the year, providing a naturally cool environment even in the height of summer. Because of these stable conditions, parts of the underground mine have also been used for the long-term aging of alcoholic beverages.
The Mitsubishi Era and Technological Innovation
From the Meiji period (1868–1912) onward, Yoshioka Mine came under the management of Mitsubishi Metal Company, which expanded its operations by incorporating nearby smaller mines. Modernization included the construction of an in-house power station and the introduction of rock drills and mechanized processes. The mine also became the site of Japan’s first Western-style blast furnace.
These technological advances helped establish Yoshioka as one of Japan’s leading mining operations, earning it recognition both domestically and overseas.
Sasaune was originally operated as a subsidiary mine. It was later connected underground to the main Sakamoto workings, helping increase ore production. The tunnel yielded chalcopyrite and pyrrhotite, contributing to Japan’s industrial development.
An Adventurous Underground Exploration
Today, the publicly accessible Sasaune Tunnel offers visitors a chance to experience the mysterious atmosphere of a historic mine. Its cool, stable temperature makes it a refreshing place to explore during hot summer weather, while the winding passages provide a glimpse into the conditions under which miners once worked.
The Lasting Appeal of Sasaune Tunnel
Sasaune Tunnel is valued not only for its long history but also for the preservation of its distinctive underground environment. Visitors can learn about the development of copper mining from the Edo period onward and reflect on the lives of the workers who labored beneath the mountains.
A visit offers an opportunity to discover an important chapter in Japan’s industrial history and understand how mining shaped the surrounding community. Preserving this historic site will help ensure that its story continues to be shared with future generations.
Yoshioka Mine: A Copper Mine That Shaped Okayama’s History
Yoshioka Mine was a historic mining operation formerly located in Fukiya, Nariwa, Kawakami District, in what is now Takahashi City, Okayama Prefecture. Primarily a copper mine, it made a significant contribution to Japan’s industrial development. Although the mine finally closed in 1972, remnants of its operations survive as valuable industrial heritage.
The Mine’s Early History
According to one tradition, Yoshioka Mine was opened in 807. Another account dates its opening to around 1400, toward the end of the Nanboku-cho period. It is said to have initially operated as a silver mine before shifting to copper production during the Muromachi period (1336–1573).
During the Sengoku period (approximately 1467–1615), the mine became the focus of competition between the Amago and Mori clans. In the early Edo period, it came under the control of the Nariwa Domain before being placed under the direct administration of the shogunate for much of the Edo period.
Ore extracted at the mine was carried by horse to the main gate at Shimohara, now part of Nariwa, Takahashi City. It was then transported by riverboat along the Nariwa and Takahashi rivers to Tamashima Port in present-day Kurashiki. From there, the copper was shipped across the Seto Inland Sea to the Copper Office in Osaka.
Growth and Mitsubishi’s Involvement
Yoshioka Mine experienced significant growth after Kichiuemon Izumiya acquired the operating rights during the period when the mine was under direct shogunate control. Under Izumiya’s management, production expanded, and the population of the Fukiya district grew to more than 1,000 people.
When Izumiya shifted its attention to the newly discovered Besshi Copper Mine, it withdrew from Yoshioka. Local mining operators subsequently took over management.
In 1873, Mitsubishi Shokai acquired the operating rights and began modernizing the mine. Rock drills and dynamite were introduced to improve extraction efficiency. Mitsubishi also built its own power facilities and developed rail tracks and inclined transport systems to move ore and materials around the site.
Kasagami Power Station, completed in 1903, became Okayama Prefecture’s first hydroelectric power station. The introduction of Japan’s first Western-style blast furnace for smelting further strengthened Yoshioka’s position as one of the country’s leading copper mines.
Industrial Heritage and Historical Significance
Yoshioka was the first metal mine operated by Mitsubishi and later served as a model for mining development elsewhere in Japan. By the early 20th century, it was the largest copper mine in Okayama Prefecture and ranked among the five largest in Japan. At its peak, it employed approximately 1,300 workers and was regarded as one of Japan’s three major copper mines.
In 1931, Mitsubishi withdrew from the operation, and the mine temporarily closed. The downturn following World War I and the Great Depression contributed to its difficulties. Operations resumed for a time after World War II, but the mine finally closed in 1972.
Surviving Mining Remains
After the closure, many of the mine’s facilities were dismantled, and parts of the former site have gradually returned to nature. However, a number of industrial remains can still be found, including tunnels, ore-processing facilities, smelting works, settling tanks, and a partly underground flue leading to a large chimney.
Sasaune Tunnel, located in Naka-no, Nariwa, Takahashi City, was a subsidiary mine where extraction continued from the Edo period through the Taisho period. Part of the tunnel is now open to the public, allowing visitors to explore a surviving section of the former mining complex.
The remains of a mountain shrine bearing Mitsubishi’s distinctive three-diamond emblem also survive. These structures provide valuable evidence of the area’s industrial past. In 2007, Yoshioka Mine was recognized by Japan’s Ministry of Economy, Trade and Industry as a Heritage of Industrial Modernization, reaffirming its historical importance.
The Mine’s Economic and Cultural Influence
In addition to copper, Yoshioka Mine produced substantial quantities of green vitriol and bengara, a traditional red iron-oxide pigment. These products generated considerable wealth for merchants and helped support the growth of Fukiya’s historic townscape from the Edo period into the Meiji period.
The mine’s wealth and technological innovations had a lasting influence on the local economy and culture. Its history and surviving industrial remains offer valuable insight into the relationship between mining, community development, and Japan’s industrialization.
Visiting the former Yoshioka Mine allows travelers to experience this important part of Japan’s industrial heritage firsthand. Continued preservation will help pass the story of the mine and its contribution to the region on to future generations.