Hydrothermal Deposits: Discovery and Preliminary Economic Evaluation

Deep-sea hydrothermal deposits are formed by precipitation from circulating hydrothermal solutions in association with submarine volcanic activity and can consist of sulphide (PMS), oxide and silicate minerals, of which the PMS are the most economically valuable. They were first discovered in the Red Sea, and later found to occur on mid-ocean ridges, on island arcs and in back-arc basins. Feasibility studies on mining them were carried out in the Red Sea in the 1970s but no mining took place. PMS were found on mid-ocean ridges in the late 1970s and early 1980s, some within the EEZs of coastal states including in the Escanaba Trough of the Gorda Ridge in the EEZ of the USA. Deposits commonly associated with PMS, like metalliferous sediments and hydrothermal ferromanganese oxide crusts, were thought to be of no economic value in their own right but could be used to help locate PMS deposits.