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As we have already seen in this series, copper was Japan’s leading export under the administrative trading controls of the time, and Sumitomo took a leading role in its refining and export. Under the leadership of the third Sumitomo patriarch, Tomonobu (1647–1706), Sumitomo began developing copper mines throughout the country, accumulating experience and know-how, and became Japan’s largest player in the field. It was also during the Genroku era that Japan’s copper production grew to lead the world at about 6,000 tons. A major contributor to this global leadership was the Besshi mine, which was discovered by Sumitomo under the leadership of its fourth patriarch Tomoyoshi (1670–1719), in the third year of Genroku (1690).
The new copper vein was just below the surface. It was between 50cm and 8 meters thick, 1,500 meters wide, and 2,300 meters long—a mother lode on a scale rarely seen anywhere in the world. Over the next 283 years, the Besshi mine would produce about 650,000 tons of blister copper, making the mine a rich source of revenue that would take on a principal role in driving the development of the entire the Sumitomo group. |
