The Japanese government developed tunnels at the mine to extract tungsten, a high-density mineral essential to defense, electronics, manufacturing and other industries. After conducting drilling for sampling and feasibility tests, the company found that the mine contains some of the world's highest grade tungsten ore with enough volume to remain productive for 100 years. It expanded tunnels in multiple directions to create a network encircling a layered reserve of potential tungsten ore.On Sept. 15, tungsten ore and rock waste were piled outside the mine’s entrance. For now, the company keeps extending one of the galleries left by Korea Tungsten Company, a state-run firm that ran the mine from 1952 to 1994. “One of the reasons Korea Tungsten Company had closed the mine was because of the monopoly by Chinese tungsten.