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Hydrothermal Environment

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A hot, fluid residue, usually of magmatic origin, that is chiefly water contains a rich supply of metallic elements. It becomes further enriched through chemical reactions with the surrounding crustal rock. As it cools, this solution many form massive concentrations of minerals bearing gold, copper, and zinc and other metallic elements that may have great commercial value. Some of the world’s richest deposits of these metals were formed under such hydrothermal conditions.

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Magmatic fluids are chemically quite complex and, during the cooling process, may develop into a pegmatitic fluid. It is possible, too, that the magma may differentiate into what is often called a hydrothermal fluid, a very hot and exceptionally watery fluid. In a manner of speaking, the pegmatitic fluid is a hydrothermal fluid, too. 

But pegmatitic fluid does not usually contain concentrations of the metallic elements, such as zinc, iron, copper, and lead, or such precious metallic elements as gold and silver. These metallic elements, present in the hydrothermal fluid, and carried in it's movement through the Earth's crust, may also interact chemically with already-form minerals as they pass through the rock. 

Geoscientists classify hydrothermal fluids essentially in terms of the temperature and pressure conditions under which they begin to crystallize and form minerals. Those hydrothermal fluids that form under fairly high temperature and pressure conditions are referred to as hypothermal mineral deposits. Those forming under more moderate temperature conditions, the mesothermal mineral deposits. And the epithermal mineral assemblage is developed under the relatively coolest, and, therefore, shallowest, p