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USGS CMG InfoBank: Hydrothermal Ore Deposits

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Comment: 21:48 - 22:58 (01:10)
Source: Annenberg/CPB Resources - Earth Revealed - 12. Minerals: The Materials of Earth
Keywords: "J. Lawford Anderson", magma, "igneous intrusion", "metallic mineral", "ore deposit", "hydrothermal ore deposit", metal, element, mineral, quartz, feldspar, mica, "lava flow", crystal, water, boiling, fracture, "magma chamber", precipitation

Our transcription: These waters are generally derived directly from crystallizing magma or from hot ground water circulating through the rock overlying an igneous intrusion.
Rocks containing economically viable concentrations of metallic minerals are called "ore deposits", and hydrothermal ore deposits are among the more important sources of metal known.
Most of the elements that make up ores don't have a home in everyday minerals, don't fit into the structures of quartz, or feldspar or mica, and as a lava or a magma begins to crystallize the common minerals, the elements are bunched up together and concentrated being dislodged away from the growing crystals.
Water is also building, and at some late stage in the crystallization of almost all magmas, water begins to boil off.
And as it boils and rises out of the magma system, it takes with it all those elements that didn't have a home, and these go off and fill up fractures up through the rocks above the magma chamber, and as they reach the cooler rocks, they begin to precipitate.

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Page Last Modified: Thu Oct 31 04:26:31 PDT 2013  (chd)