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Energetics of Hydrothermal Ore Deposition

The process of hydrothermally concentrating trace metals into ores is endothermic. The necessary energy is supplied as heat either directly from the mantle or by igneous bodies. For epithermal ores, heat from intrusives causes advective circulation of hydrothermal fluids, which leach ore components from various source rocks. If minerals that precipitate from the circulating fluid are to reach ore concentrations, then the plutonic heat source must provide energy at a rate sufficient for adequate mass transport, roughly 1014 kJ/a, and must continue for about 106 a. To power a continuing hydrothermal circulation cell to form an ore deposit, such plutons should be intruded within an area less than about 50 km in diameter and with a frequency at least as often as every 25 ka. The rarity of mineral districts results principally from the enormous heat requirements of the processes that generate major mineralization. Consequently, in mineral exploration, an initial objective ideally is to find evidence of extraordinarily persistent heat and fluid flow.