Some mineralogical equilibria in the system K 2 O-Al 2 O 3 -SiO 2 -H 2 O

Hemley, J. J.

doi:10.2475/ajs.257.4.241

Cited by 191 publications

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“…Dickite and nacrite commonly occur in deposits of hydrothermal origin (Murray, 1984). Numerous authors have synthesized pyrophyllite at temperatures above 260ºC (Grim, 1969;Roy & Osborn, 1954;Hemley, 1959;Reed & Hemley, 1967;and Tzuzuki & Mizutani, 1971). The coexistence of pyrophyllite and kaolinite allows us to estimate a maximum temperature of 350ºC.…”

Section: Discussionmentioning

confidence: 99%

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Geochemistry of Hydrothermal Alteration in Volcanic Rocks

Marfil¹,

Maiza²

2012

Geochemistry - Earth's System Processes

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Section: Discussionmentioning

confidence: 99%

“…Higher temperatures would not be reasonable as kaolinite coexists with pyropyillite and lower values would not be compatible with the presence of pyrophillite. Numerous authors have synthesized pyrophyllite at temperatures above 260ºC (Grim, 1969;Roy & Osborn, 1954;Hemley, 1959;Reed & Hemley, 1967;Tzuzuki & Mizutani, 1971). …”

Section: Discussionmentioning

confidence: 99%

Geochemistry of Hydrothermal Alteration in Volcanic Rocks

Marfil¹,

Maiza²

2012

Geochemistry - Earth's System Processes

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“…Experimental work by others indicates that the activity ratio of alkali ions to hydrogen ions and the activity of silica are the major chemical parameters of the water that control whether clay minerals, zeolites, or feldspars will form at conditions that approximate surface temperatures and pressures (Hemley, 1959(Hemley, , 1962Garrels and Christ, 1965, p. 359-370;Hess, 1966). Zeolites and feldspars are favored over clay minerals by relatively high alkali ion to hydrogen ion activity ratios and by relatively high silica activities.…”

Section: Clinoftilolite-analcime-fotassium Feldspar Relationships In mentioning

confidence: 99%

Diagenesis of tuffs in the Barstow Formation, Mud Hills, San Bernardino County, California

Sheppard¹,

Gude²

1969

Professional Paper

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“…The concentrations of H , K , and aqueous SiO_ control the pH of the sericite-adularia phase boundary at a particular temperature. Silica minerals were neither formed in nor removed from the host rocks during early alteration, and thus the activity of aqueous silica was likely near unity (Hemley, 1959). The altering fluids had a relatively high aK , as indicated by the influx of K«0 into the rocks.…”

Section: Analyses Listed Inmentioning

confidence: 99%

“…Because the stabilities of both hematite and sericite may be pH-dependent, an increase in the pH could remove seri cite and precipitate hematite. Adularia would form with an increase in pH (Hemley, 1959), and the codeposition of hematite and adularia would be expected under such conditions. Continued deposition of hematite with adularia in the altered wall rocks indicates that the pH continued to increase within the stability field of adularia.…”

Section: Analyses Listed Inmentioning

confidence: 99%

Alteration and vein mineralization, Schwartzwalder uranium deposit, Front Range, Colorado

Wallace¹

1983

Open-File Report

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The Schwartzwalder uranium deposit, in the Front Range west of Denver, Colorado, is the largest vein-type uranium deposit in the United States. The deposit is situated in a steeply dipping fault system that cuts Proterozoic metamorphic rocks. The host rocks represent a submarine volcanic system with associated chert and iron-and sulfide-rich pelitic rocks. Where faulted, the more competent garnetiferous and quartzitic units behaved brittlely and created a deep, narrow conduit.The ores formed 70-72 m.y. ago beneath 3 km of Phanerozoic sedimentary rocks. Mineralization included two episodes of alteration and three stages of vein mineralization. Early carbonatesericite alteration pseudomorphically replaced mafic minerals, whereas the ensuing hematite-adularia episode replaced only the earlier alteration assemblage. Early vein mineralization produced a minor sulfide-adularia-carbonate assemblage. Later vein mineralization generated the uranium ores in two successive stages. Carbonates, sulfides, and adularia filled the remaining voids. Clastic dikes composed of fault gouge and, locally, ore were injected into new and existing fractures.Geologic and chemical evidence suggest that virtually all components of the deposit were derived from major hornblende gneiss units and related rocks. The initial fluids were evolved connate/metamorphic water that infiltrated and resided along the extensive fault zones. Complex fault movements in the frontal zone of the eastern Front Range caused the fluids to migrate to the most permeable segments of the fault zones. Heat was supplied by increased crustal heat flow related to igneous activity in the nearby Colorado mineral belt. Temperatures decreased from 225°C to 125°C during later mineralization, and the pressure episodically dropped from 1000 bars. The CO^ fugacity was initially near 100 bars, and uranium was carried as a dicarbonate complex. Sudden decreases in confining pressure during fault movement caused evolution of 009 and a consequent increase in pH. Uranium was released with destruction of the uranyl complexes; it was subsequently reduced by aqueous sulfur species, thereby leading to the precipitation of pitchblende. ACKNOWLEDGMENTS

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Some mineralogical equilibria in the system K 2 O-Al 2 O 3 -SiO 2 -H 2 O

Cited by 191 publications

References 0 publications

Geochemistry of Hydrothermal Alteration in Volcanic Rocks

Geochemistry of Hydrothermal Alteration in Volcanic Rocks

Diagenesis of tuffs in the Barstow Formation, Mud Hills, San Bernardino County, California

Alteration and vein mineralization, Schwartzwalder uranium deposit, Front Range, Colorado

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