# Hypogene

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{{short description|Geologic processes which occur deep below the surface}}
In [ore](/source/ore) deposit [geology](/source/geology), '''hypogene''' processes occur deep below the Earth's surface, and tend to form deposits of [primary minerals](/source/primary_minerals), as opposed to [supergene](/source/supergene_(geology)) 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](/source/magma)s, deep sedimentary basins, or areas of elevated geothermal gradients can contain metals and other [ions](/source/ions) derived from the magma itself or from [leaching](/source/Leaching_(chemistry)) of [sedimentary](/source/sedimentary), [igneous](/source/igneous), or [metamorphic](/source/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](/source/chlorine), [sodium](/source/sodium), [calcium](/source/calcium), [magnesium](/source/magnesium) and [potassium](/source/potassium), and other important components include [iron](/source/iron), [manganese](/source/manganese), [copper](/source/copper), [zinc](/source/zinc), [lead](/source/lead), [sulfur](/source/sulfur) (as [{{chem|SO|4|2−}}](/source/sulfate) or [S<sup>2−</sup>](/source/sulfide) or both) [carbon](/source/carbon) (as [{{chem|HCO|3|−}}](/source/bicarbonate) and [CO<sub>2</sub>](/source/carbon_dioxide)) and [nitrogen](/source/nitrogen) (as [{{chem|NH|4|+}}](/source/ammonium)). Most ore fluids contain [chloride](/source/chloride) as the dominant [anion](/source/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](/source/Sulfur) is a common component of the fluids, and most of the common ore metals, [lead](/source/lead), [zinc](/source/zinc), [copper](/source/copper), [silver](/source/silver), [molybdenum](/source/molybdenum) and [mercury](/source/Mercury_(element)), occur chiefly as [sulfide](/source/sulfide) and [sulfosalt](/source/sulfosalt) minerals.<ref name=UMD/>  
Examples of primary minerals formed in this way include the sulfide minerals [pyrite](/source/pyrite) (FeS<sub>2</sub>), [galena](/source/galena) (PbS), [sphalerite](/source/sphalerite) (ZnS), and [chalcopyrite](/source/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)](/source/Supergene_(geology))

==References==
{{Reflist}}

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Category:Economic geology

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Adapted from the Wikipedia article [Hypogene](https://en.wikipedia.org/wiki/Hypogene) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Hypogene?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.