Editing Syenite (section)

==Episyenite==
'''Episyenite''' (or ''epi-syenite'') is a term used in [[petrology]] to describe veins, pods, or lenses of rock originally rich in [[silicon dioxide]] (SiO<sub>2</sub>) from which quartz has been severely depleted.<ref name=RecioEtal>{{cite journal |last1=Recio |first1=C. |last2=Fallick |first2=A.E. |last3=Ugidos |first3=J.M. |last4=Stephens |first4=W.E. |title=Characterization of multiple fluid-granite interaction processes in the episyenites of Avila-Béjar, Central Iberian Massif, Spain |journal=Chemical Geology |date=December 1997 |volume=143 |issue=3–4 |pages=127–144 |doi=10.1016/S0009-2541(97)00106-X|bibcode=1997ChGeo.143..127R }}</ref> This is often accompanied by strong enrichment in potassium and [[rare earth elements]], leaving the altered rock a distinctive brick red color,<ref name="McLemore-2016">{{cite journal |last1=McLemore |first1=Virginia T. |title=Episyenites in the Sevilleta National Wildlife Refuge, Socorro County, New Mexico: preliminary results |journal=New Mexico Geological Society Field Conference Series |date=2016 |volume=67 |pages=255–262 |url=https://nmgs.nmt.edu/publications/guidebooks/downloads/67/67_p0255_p0262.pdf |archive-url=https://web.archive.org/web/20200611140309/https://nmgs.nmt.edu/publications/guidebooks/downloads/67/67_p0255_p0262.pdf |archive-date=2020-06-11 |url-status=live |access-date=11 June 2020}}</ref> or by albitization (enrichment in sodium), leaving the altered rock a conspicuous white color.<ref name=SuikkanenRamo2019>{{cite journal |last1=Suikkanen |first1=E. |last2=Rämö |first2=O. T. |title=Episyenites—Characteristics, Genetic Constraints, and Mineral Potential |journal=Mining, Metallurgy & Exploration |date=October 2019 |volume=36 |issue=5 |pages=861–878 |doi=10.1007/s42461-019-00120-9|hdl=10138/306792 |s2cid=201313988 |hdl-access=free }}</ref>

Episyenites are heterogenous in their properties, but all have experienced nearly complete disappearance of quartz at sub-[[Solidus (chemistry)|solidus]] temperatures; that is, at temperatures below the melting point of the host rock. The formation of episyenites (''episyenitization'') typically takes place through leaching of quartz by mildly saline hydrothermal fluids, typically near a cooling [[intrusion]]. Because episyenitization usually takes place in [[granitoid]] rock and usually involves alkaline [[metasomatism]] (addition of alkali metal oxides to the rock) the result is a rock that has the mineral composition of an igneous syenite.<ref name=SuikkanenRamo2019/>

In addition to rare earth elements,<ref name="McLemore-2016"/> episyenites may be important sources of [[uranium]]<ref>{{cite journal |last1=Leroy |first1=J. |title=The Margnac and Fanay uranium deposits of the La Crouzille District (western Massif Central, France); geologic and fluid inclusion studies |journal=Economic Geology |date=1 December 1978 |volume=73 |issue=8 |pages=1611–1634 |doi=10.2113/gsecongeo.73.8.1611|bibcode=1978EcGeo..73.1611L }}</ref> and other valuable metals.<ref name=SuikkanenRamo2019/>

Notable occurrences of episyenite are found in the [[Hesperian Massif|Central Iberian Massif]] of Spain,<ref name=RecioEtal/> in [[Cambrian]] to [[Ordovician]] beds of New Mexico and Colorado,<ref name="McLemore-2016"/> Scandinavia, Brazil, and Ukraine.<ref name=SuikkanenRamo2019/>