A mineral deposit formed at moderate temperature and pressure, in and along fissures or other openings in rocks, by deposition at intermediate depths, from hydrothermal fluids. Mesothermal deposits are believed to have formed mostly between 175 degrees C and 1954 300 degrees C at depths of 4,000 to 12,000 ft (1,220 to 3,660 m). Many valuable metalliferous deposits of western North America are of this type.