Hoover was a doctor and investor
Following his departure from Bewick Moreing, Hoover worked as an independent mining consultant and investor in London. Hoover spent a lot of time raising money, reorganizing company structures, and funding new initiatives despite having achieved fame as a geologist and mine operator. He specialized in turning around struggling mining businesses in return for a cut of the earnings for his technical and financial know-how. Hoover had a reputation as a "doctor of sick mines" and saw himself and his colleagues as "engineering doctors to sick concerns." He maintained offices in San Francisco, London, New York City, Paris, Petrograd, and Mandalay, British Burma, and he made investments across all continents. Hoover had an estimated personal fortune of $4 million by 1914, which is comparable to $108.21 million in 2021.
To harvest zinc close to the Australian city of Broken Hill, New South Wales, he co-founded the Zinc Corporation. The Zinc Corporation ran the first selective ore differential flotation facility in the world and created the froth flotation method to recover zinc from lead-silver ore. Hoover collaborated with the British company Burma Corporation, which operated the Namtu Bawdwin Mine and generated significant amounts of silver, lead, and zinc. He also promoted the use of pyritic smelting to boost copper output in Kyshtym, Russia. A second mine in the Altai Mountains that, in Hoover's words, "produced possibly the biggest and richest single deposit of ore known in the world" was another commitment he made.
