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{{short description|Geologic processes which occur deep below the surface}}
In [[ore]] deposit [[geology]], '''hypogene''' processes occur deep below the Earth's surface, and tend to form deposits of [[primary minerals]], as opposed to [[supergene (geology)|supergene]] processes that occur at or near the surface, and tend to form secondary minerals.<ref>{{Cite journal |last=Rakovan |first=John |title=A Word to the Wise: Hypogene & Supergene |journal=Rocks & Minerals |volume=78 |issue=6 |pages=419 |date=November–December 2003 |publisher=Taylor & Francis |url=http://www.cas.muohio.edu/~rakovajf/WTTW%20Hypogene%20Supergene.pdf |doi=10.1080/00357529.2003.9926759 |bibcode=2003RoMin..78..419R |s2cid=128609800 |accessdate=August 18, 2012}}</ref>
At great depth the pressure is high, and water can remain liquid at temperatures well above 100&nbsp;°C.  Hot aqueous solutions originating from [[magma]]s, deep sedimentary basins, or areas of elevated geothermal gradients can contain metals and other [[ions]] derived from the magma itself or from [[Leaching (chemistry)|leaching]] of [[sedimentary]], [[igneous]], or [[metamorphic]] rocks.  Hypogene deposition processes include crystallization from the hot aqueous solutions flowing through the Earth's crust, driven by temperature and pressure gradients, as well as topographic, orogenic, and structural changes and/or controls.<ref name=EGM>The Encyclopedia of Gemstones and Minerals (1991).  Martin Holden.  Publisher: Facts on File</ref>
Major dissolved components are [[chlorine]], [[sodium]], [[calcium]], [[magnesium]] and [[potassium]], and other important components include [[iron]], [[manganese]], [[copper]], [[zinc]], [[lead]], [[sulfur]] (as [[sulfate|{{chem|SO|4|2−}}]] or [[sulfide|S<sup>2−</sup>]] or both) [[carbon]] (as [[bicarbonate|{{chem|HCO|3|−}}]] and [[carbon dioxide|CO<sub>2</sub>]]) and [[nitrogen]] (as [[ammonium|{{chem|NH|4|+}}]]). Most ore fluids contain [[chloride]] as the dominant [[anion]].<ref name=UMD>Understanding Mineral Deposits (2000).  Kula C Misra.  Kluwer Academic Publishers</ref>
As the solutions rise the temperature and pressure fall.  Eventually a point is reached where the minerals start to crystallise out.<ref name=EGM/> Minerals formed in this way are called primary, or hypogene, minerals.  [[Sulfur]] is a common component of the fluids, and most of the common ore metals, [[lead]], [[zinc]], [[copper]], [[silver]], [[molybdenum]] and [[Mercury (element)|mercury]], occur chiefly as [[sulfide]] and [[sulfosalt]] minerals.<ref name=UMD/>
Examples of primary minerals formed in this way include the sulfide minerals [[pyrite]] (FeS<sub>2</sub>), [[galena]] (PbS), [[sphalerite]] (ZnS), and [[chalcopyrite]] (CuFeS<sub>2</sub>).
==Etymology==
The word ''hypogene'' is derived from the Greek roots ''hypo-'' ({{wikt-lang|grc|ὑπο-}}) meaning 'under' and ''-gene'' ({{wikt-lang|grc|-γενής}}) meaning 'born' or 'produced'. The terms ''hypogene'' and ''supergene'' refer to the depth at which they occur.
==See also==
*[[Supergene (geology)]]
==References==
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[[Category:Economic geology]]
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