a class of hydrothermal mineral deposits originating in the earth’s interior by deposition of a mineral mass from hot mineralized aqueous solutions, circulating at depths of approximately 1,000 m; the solutions are under great pressure and have temperatures of 300°-200°C. Mesothermal deposits form veins, sheetlike bodies, and irregularly shaped deposits. They were first identified by the American geologist W. Lindgren in 1907.