 But copper prices fell drastically after the war, and in 1921 copper production fell to 15 million pounds (6,800 metric tons) as the company shut the Osceola (amygdaloid) mine in 1920, and shut down mining on the Calumet conglomerate in April 1921.Copper production rebounded in 1922, and rose steadily through the 1920s.Calumet and Hecla grew in the 1920s by buying and merging with neighboring copper mines.