Hydrogen-ion metasomatism is the process that causes phyllic alteration. While the mineralogy of the rock is altered throughout, texture is preserved and primary porphyry structure (including position of original veins) may still be visible.[2] If a rock undergoes phyllic alteration, then orthoclase feldspar, biotite and various silicates are altered in addition to plagioclase. Plagioclase will be altered to sericite (a fine-grained white mica) by sericitic alteration, and mafic minerals are replaced by quartz.[2]Tourmaline may appear as radiating aggregate or prismatic crystals between the quartz-sericite assemblage.[2] Phyllic alteration is often closely associated with argillic alteration, which occurs at lower temperatures and dominantly affects plagioclase.[3]
Variation with depthEdit
Phyllic alteration typically forms in the base-metal zone of a porphyry system.[2] Alteration assemblages vary with depth and with degree of fluid interaction. In deep environments, the most highly altered areas are veins and thin selvages, or halos, that surround them. The selvages are generally <10 cm in diameter and composed of major sericite and minor quartz. Vein orientation is preserved from original rock, but minerals within are mostly replaced by pyrite.[3] With decreasing depth, selvages widen (10 cm - 1m) and contain more quartz and pyrite.
Outside of selvages, most alteration occurs in replacement of mafic minerals by chlorite and of plagioclase by sericite.[3]
^ abcdDamian, Floarea (2003). "The Mineralogical Characteristics and the Zoning of the Hydrothermal Types of Alteration from the Nistru Ore Deposit, Baia Mare Metallogenic District". scholarcommons.usf.edu. Studia Universitatis Babes-Bolyai. Retrieved 18 April 2014.
^ abcParry, W. T.; Jasumback, M.; Wilson, P. N. (2002). "Clay Mineralogy of Phyllic and Intermediate Argillic Alteration at Bingham, Utah". Economic Geology. 97: 221–239. doi:10.2113/gsecongeo.97.2.221.
September 01, 2023
phyllic, alteration, hydrothermal, alteration, zone, permeable, rock, that, been, affected, circulation, hydrothermal, fluids, commonly, seen, copper, porphyry, deposits, calc, alkaline, rocks, characterised, assemblage, quartz, sericite, pyrite, occurs, high,. Phyllic alteration is a hydrothermal alteration zone in a permeable rock that has been affected by circulation of hydrothermal fluids It is commonly seen in copper porphyry ore deposits in calc alkaline rocks Phyllic alteration is characterised by the assemblage of quartz sericite pyrite and occurs at high temperatures and moderately acidic low pH conditions 1 Hydrogen ion metasomatism is the process that causes phyllic alteration While the mineralogy of the rock is altered throughout texture is preserved and primary porphyry structure including position of original veins may still be visible 2 If a rock undergoes phyllic alteration then orthoclase feldspar biotite and various silicates are altered in addition to plagioclase Plagioclase will be altered to sericite a fine grained white mica by sericitic alteration and mafic minerals are replaced by quartz 2 Tourmaline may appear as radiating aggregate or prismatic crystals between the quartz sericite assemblage 2 Phyllic alteration is often closely associated with argillic alteration which occurs at lower temperatures and dominantly affects plagioclase 3 Variation with depth EditPhyllic alteration typically forms in the base metal zone of a porphyry system 2 Alteration assemblages vary with depth and with degree of fluid interaction In deep environments the most highly altered areas are veins and thin selvages or halos that surround them The selvages are generally lt 10 cm in diameter and composed of major sericite and minor quartz Vein orientation is preserved from original rock but minerals within are mostly replaced by pyrite 3 With decreasing depth selvages widen 10 cm 1m and contain more quartz and pyrite Outside of selvages most alteration occurs in replacement of mafic minerals by chlorite and of plagioclase by sericite 3 References EditSericite at Mindat Yant Marcella 2009 Hydrothermal Alteration www indiana edu Indiana University a b c d Damian Floarea 2003 The Mineralogical Characteristics and the Zoning of the Hydrothermal Types of Alteration from the Nistru Ore Deposit Baia Mare Metallogenic District scholarcommons usf edu Studia Universitatis Babes Bolyai Retrieved 18 April 2014 a b c Parry W T Jasumback M Wilson P N 2002 Clay Mineralogy of Phyllic and Intermediate Argillic Alteration at Bingham Utah Economic Geology 97 221 239 doi 10 2113 gsecongeo 97 2 221 Retrieved from https en wikipedia org w index php title Phyllic alteration amp oldid 1109108649, wikipedia, wiki, book, books, library,
