Sir A. Geddes, Memorandum Prepared by Rhokana Corporation Limited on the Copper Mining Industry of Northern Rhodesia (London: Rhokana Corporation Ltd, 1932).

The estimated world production of copper in 1900 was 540,000 short tons, ² of which about one-half came from the United States, and less than 9 per cent. from the British Empire (Australia: 25,760 tons; Canada: 9,479 tons). Production and consumption rose steadily, and with remarkable regularity, until the outbreak of war, the production in 1914 being 1,018,395 tons. Practically the whole of the increase during this period came from the United States, being due to the development of the large, low-grade deposits in the State of Arizona, made possible by the discovery of the flotation method of treating ores of low metallic content.