Moreover, in 1884, he purchased the Kosaka Mine (Akita Prefecture) from the government and, by focusing on technical innovation, had turned it into Japan's most productive copper and silver mine by the early 1900s.
さらに17年、小坂鉱山（秋田県）の払い下げを受けると、技術革新に力をいれ、明治30年代後半には、銀と銅の生産で日本有数の鉱山に成長させた。