Episyenites—Characteristics, Genetic Constraints, and Mineral Potential

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Suikkanen , E & Rämö , T 2019 , ' Episyenites—Characteristics, Genetic Constraints, and Mineral Potential ' , Mining, metallurgy & exploration , vol. 36 , no. 5 , pp. 861-878 . https://doi.org/10.1007/s42461-019-00120-9

Title: Episyenites—Characteristics, Genetic Constraints, and Mineral Potential
Author: Suikkanen, E.; Rämö, Tapani
Contributor: University of Helsinki, Department of Geosciences and Geography
Date: 2019-10
Language: eng
Number of pages: 18
Belongs to series: Mining, metallurgy & exploration
ISSN: 2524-3462
URI: http://hdl.handle.net/10138/306792
Abstract: Episyenites are sub-solidus, quartz-depleted alkali-feldspar-rich rocks. They form veins and lenticular bodies in granitoid rocks and migmatites in a late- to post-orogenic or anorogenic setting. Leaching of quartz is usually a response to a flux of weakly saline hydrothermal solution in circulation cells above cooling intrusions, where sufficient fluid-rock ratios and thermal gradients are achieved. Fluid Si-undersaturation is achieved by rapid cooling within the field of retrograde Si solubility or by temperature and pressure increase outside retrograde conditions. Some quartz may also be consumed in metasomatic reactions and in response to pressure fluctuation in sealed episyenite bodies. The small size and overall rarity of episyenites imply that conditions for episyenite formation are not commonly encountered in the crust. In addition to quartz depletion, episyenites record complex histories of metasomatic alteration and hydrothermal mineral growth. Nearly all episyenites have undergone Na-metasomatism, which may have led to the formation of nearly monomineralic albitite, and which is occasionally followed by late K-metasomatism, phyllic alteration, and argillization. Depending on the effectiveness of later compaction, recrystallization and vug-filling episyenites may preserve the macroscopic porosity formed by quartz dissolution and brittle deformation. Vuggy episyenites can act as significant sinks for metals carried by crustal fluids and host many significant U, Sn, and Au deposits worldwide. Rare earth-critical syenitic fenites around alkaline intrusions share mineralogical and genetic traits with episyenites.
Subject: 1171 Geosciences
Episyenite
Metasomatism
Na-metasomatism
Uranium
Tin
Gold
Hydrothermal processes
Critical metals
SLIP SHEAR ZONES
URANIUM MOBILIZATION
NA-METASOMATISM
CRETACEOUS ALBITIZATION
ALKALI METASOMATISM
QUARTZ DISSOLUTION
ELEMENT MOBILITY
AMAZONIAN CRATON
BOHEMIAN MASSIF
WESTERN MARCHE
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