Hiroko Tabuchi It has become important, especially after a diplomatic spat with China. Two decades after global competition drove the mines in this corner of Japan to extinction, Kosaka is again abuzz with talk of new riches. The treasures are not copper or coal. They are rare-earth elements and other minerals that are crucial to many Japanese technologies and have so far come almost exclusively from China, the global leader in rare earth mining. Recent problems with Chinese supplies of rare earths have sent Japanese traders and companies in search of alternative sources, creating opportunities for Kosaka.