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Michael J Rubenach - One of the best experts on this subject based on the ideXlab platform.
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the role of halogens during regional and contact metamorphism
2018Co-Authors: Johannes Hammerli, Michael J RubenachAbstract:Halogens are important elements for a range of geological processes during metamorphism from stabilizing mineral phases to being important ligands for mass transfer. Halogens are highly incompatible in most minerals, which makes it difficult to unravel their presence in the past. Minerals useful for understanding halogen behaviour during metamorphism include: scapolite, apatite, titanite, biotite, and amphibole. However, their ability to incorporate halogens depends on parameters such as bulk rock composition, fluid properties, and water-rock ratios. Comprehensive studies of halogens in regional metamorphic rocks and minerals, such as the Clearwater Region, Idaho, USA or the Mary Kathleen Fold Belt, Mt Isa Inlier, Australia, show that halogen contents are highly variable on a bulk rock- and rock layer-scale, reflecting protolith variations. Where low fluid-rock ratios occurred during regional metamorphism, pre-exisiting variations in halogen compositions and ratios across individual layers were not eliminated, resulting in large differences between halogen concentrations on a mineral- and rock-layer scale. Research on F and Cl in apatite in siliceous marbles from five classic aureoles highlights the use of this mineral regarding rock or fluid buffering, and in establishing fluid sources. Chlorine enrichment in biotite and amphibole, associated with regional Albitization observed in Cloncurry, Australia or the Bamble Sector Norway, demonstrate advection of saline fluids during Albitization and K-feldspar metasomatism that occur in association with regional mineralization. Chlorine-bearing fluids are capable of mobilizing large amounts of metals during large-scale metamorphism on a regional, whole rock, and mineral scale. Consequently, fluid flow could be an essential prerequisite to actively discharge metals from the metamorphic rocks. Recent analytical advancements allow for more routine analyses of halogen contents in minerals and fluid inclusions. For instance, in situ LA-ICP-MS analyses of Cl and Br allow for the reconstruction of the interaction of halogen-bearing fluids with crustal rocks in complex geological settings that have undergone multiple hydrothermal events. In such cases, scapolite can be used as an archive for fluid properties during metamorphism. For example, within the Mount Isa Inlier, it was found that the fluids, which interacted with calc-silicates in the Mary Kathleen Fold Belt, were of bittern brine derivation contrasting with the Cloncurry Region, where the fluids show evidence of dissolved halite. Magmatic fluid interaction with calc-silicate rocks was found to be localized.
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RELATIVE TIMING OF Albitization AND CHLORINE ENRICHMENT IN BIOTITE IN PROTEROZOIC SCHISTS, SNAKE CREEK ANTICLINE,
2015Co-Authors: Mount Isa Inlier, Northeastern Australia, Michael J RubenachAbstract:In the Snake Creek area, near Cloncurry, Mount Isa Inlier, in northeastern Australia, multiple episodes of deformation, low-pressure metamorphism, intrusion of abundant mafic and granitic bodies, and extensive metasomatism occurred throughout the Mesoproterozoic Isan Orogeny. Albitites and associated metasomatic biotite-rich schists are abundant in the core of the Snake Creek Anticline, and are concentrated in five areas. Albitization peaked during D1 and was commonly localized along shear zones. Muscovite schists adjacent to albitites were altered to albite-bearing biotite-rich schists. Porphyroblast growth in metasomatic rocks commenced with cordierite and andalusite from late syn-D1, but episodic growth continued to post-D5, with the peak of metamorphism occurring late syn-D3 to early syn-D4. The timing of Albitization was determined from the presence or absence of albite in various stages of andalusite growth, and similarly the Mg # [Mg/(Mg + Fe)] and Cl contents of biotite were examined over the span of porphyroblast-growth history. Differential mass-transport of Mg and Fe took place from the albitites to the adjacent schists predominantly during D1, and the Mg # for biotite in metasomatic rocks was largely fixed during D1. The Cl content of the matrix biotite varies considerably in the different areas of albitite development, from below detection to a maximum of 1.5 wt%. This could indicate that the Cl enrichment event was not related to Albitization, but there is nevertheless an overall spatial relationship between them. In any particular sample, the Cl content in biotite is generally higher in the matrix than for inclusions in late andalusite, with inclusions in early andalusite being the poorest in Cl. Enrichment of Cl in biotite is
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relative timing of Albitization and chlorine enrichment in biotite in proterozoic schists snake creek anticline mount isa inlier northeastern australia
Canadian Mineralogist, 2005Co-Authors: Michael J RubenachAbstract:In the Snake Creek area, near Cloncurry, Mount Isa Inlier, in northeastern Australia, multiple episodes of deformation, lowpressure metamorphism, intrusion of abundant mafic and granitic bodies, and extensive metasomatism occurred throughout the Mesoproterozoic Isan Orogeny. Albitites and associated metasomatic biotite-rich schists are abundant in the core of the Snake Creek Anticline, and are concentrated in five areas. Albitization peaked during D1 and was commonly localized along shear zones. Muscovite schists adjacent to albitites were altered to albite-bearing biotite-rich schists. Porphyroblast growth in metasomatic rocks commenced with cordierite and andalusite from late syn-D1, but episodic growth continued to post-D5, with the peak of metamorphism occurring late syn-D3 to early syn-D4. The timing of Albitization was determined from the presence or absence of albite in various stages of andalusite growth, and similarly the Mg# [Mg/(Mg + Fe)] and Cl contents of biotite were examined over the span of porphyroblast-growth history. Differential mass-transport of Mg and Fe took place from the albitites to the adjacent schists predominantly during D1, and the Mg# for biotite in metasomatic rocks was largely fixed during D1. The Cl content of the matrix biotite varies considerably in the different areas of albitite development, from below detection to a maximum of 1.5 wt%. This could indicate that the Cl enrichment event was not related to Albitization, but there is nevertheless an overall spatial relationship between them. In any particular sample, the Cl content in biotite is generally higher in the matrix than for inclusions in late andalusite, with inclusions in early andalusite being the poorest in Cl. Enrichment of Cl in biotite is a function of f(HCl)/f(H2O) rather than salinity, and so could be related to the replacement of muscovite by albite, as this involves release of H + . The ratio f(HCl)/f(H2O) would have been low during periods of high flux of fluid that produced the albitites, but increased during low flux, in the waning stages of Albitization, resulting in maximum enrichment in Cl relatively late in the metasomatic history.
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modeling the role of sodic alteration in the genesis of iron oxide copper gold deposits eastern mount isa block australia
Economic Geology, 2004Co-Authors: Nicholas H S Oliver, Michael J Rubenach, James S Cleverley, Geordie Mark, Peter J Pollard, Bin Fu, Lucas J Marshall, Patrick J Williams, Timothy R BakerAbstract:Liberation of iron and potassium by widespread postmetamorphic Albitization of country rocks was one of the likely contributing processes in the formation of both barren and mineralized magnetite ± chalcopyrite + biotite + gold + hematite + clinopyroxene + actinolite + apatite ironstones in the Cloncurry district of the Proterozoic Mount Isa block. Whole-rock geochemical data indicate nearly immobile Al, Ga, ±Ti, Zr during transformation of a variety of least altered rocks toward albitite. The data indicate that the addition of Na from a brine to the rock accompanied the loss of Fe, K, Ba, Rb ± Ca, Sr, Co, V, Mn, Pb, and Zn from those altered rocks and enrichment in the brine, but that Cu was not systematically stripped from a variety of wall rocks during Albitization. Conversely, the formation of metasomatic ironstones, the immediate hosts to some Cu-Au ores, involves addition of most of the same elements that were lost during Albitization. The correlation between intensity of alteration, its distribution and timing (e.g., in breccias cored by ca. 1530–1500 Ma granitoids), and convergence of all rock types toward magmatic stable isotope values provides strong evidence for a substantial component of igneous-derived fluid. Simulations of the Albitization process were carried out isothermally at 550°C and 350 MPa and polythermally from these conditions down to 400°C and 200 MPa, using the Gibbs minimization method with HCh software and the UNITHERM database. Both simple fluid-rock mixing models and more complicated reactor-style algorithms used a range of input fluids (from fluids equilibrated fluid with two-feldspar granite through to Na/K ratios consistent with fluid inclusion results) and geochemical data for initially unaltered wall rocks. The apparent paradox of widespread Albitization resulting from fluid released by two-feldspar granites can be explained by relatively small shifts away from the K-feldspar-albite equilibrium curve, and even isothermal model fluids derived from two-feldspar granites produce albitites in calc-silicate rocks outboard of granite-proximal K-feldspar-clinopyroxene skarns, matching field patterns. Those models with fluid Na/K ratios similar to those of fluid inclusions produced the most realistic alteration assemblages, dominated by albite, for both isothermal conditions and decreasing temperature, which approximate those observed in the field. PIXE and microthermometric data on fluid inclusions from quartz in two-feldspar quartz monzonite and pegmatite at the top of the Mount Angelay pluton indicate bulk Na/K molar ratios in the fluid of between 10 and 20, considerably higher than our thermodynamically calculated values for fluid in equilibrium with two-feldspar granite of around 3 (at 550°C, 350 MPa). Such shifts may have been attained by admixture of magmatic-hydrothermal fluid with small amounts of NaCl brines trapped along grain boundaries in scapolite-bearing calc-silicate wall rocks, by fluid immiscibility due to high initial CO2 contents in the felsic intrusions, by contributions from mafic magmas, or from dissolution of salt-rich layers into the intrusions prior to crystallization and fluid release. With increasing amounts of fluid-rock interaction in the models, the fluids were enriched in K, Fe, and Ca, approaching compositions observed in fluid inclusions in the ore deposits. These fluids, reacted with pelitic rocks (which are common ore hosts), would produce magnetite-clinopyroxene ± biotite-actinolite alteration at high temperature, similar to the proximal alteration around ore deposits. We infer that precipitation of sulfides in the Cu-Au deposits was the result of mixing of Cu-bearing brine, of ultimately magmatic origin, but modified extensively via Albitization, with sulfur-bearing fluids or reaction of the brine with sulfur-bearing rocks. When Cu was absent from the initial magmatic fluid, barren ironstones may have been the result.
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metasomatic albitites and related biotite rich schists from a low pressure polymetamorphic terrane snake creek anticline mount isa inlier north eastern australia microstructures and p t d paths
Journal of Metamorphic Geology, 2002Co-Authors: Michael J Rubenach, K A LewthwaiteAbstract:Rocks of the Snake Creek Anticline are mainly pelitic schists, psammitic schists and quartzites that were metamorphosed during multiple high-T/low-P events extending from D1 to D5, with the metamorphic peak occurring late to post-D3. Albitites are widespread, but are concentrated in five areas. They are typically fine- to medium-grained, and consist of albite, with or without combinations of quartz, biotite, staurolite, cordierite, garnet, andalusite, sillimanite, kyanite, gedrite and tourmaline. From the presence or absence of albite inclusions in porphyroblasts, the albitites are interpreted as forming early in the D3 event as a result of infiltration of external fluids. Psammitic schists and quartzites were preferentially altered, but pelitic schists were also albitized in localities where the alteration was more extreme, with the replacement of muscovite total and the replacement of quartz and biotite variable. Structural controls on Albitization include fracturing and syn-D3 shear zones in fold hinges. Biotite schists with abundant porphyroblasts (combinations of staurolite, garnet, andalusite and cordierite) occur adjacent to albitites, and it is argued that they formed by the addition of Fe and Mg sourced from the albitites. In several albitite-rich areas, cordierite grew early in D3 and was partly or entirely replaced during or after D3 by combinations of biotite, andalusite, tourmaline, staurolite and sillimanite. A postulated P–T–d path involved an increase in pressure (with or without a decrease in temperature) subsequent to early D3 Albitization, followed by an increase in temperature up to the metamorphic peak (late D3 to early D4. The metamorphism was contemporary in part with the emplacement of the Williams Batholith (c. 1550–1500 Ma), which probably supplied the Na-rich fluids.
K A Lewthwaite - One of the best experts on this subject based on the ideXlab platform.
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metasomatic albitites and related biotite rich schists from a low pressure polymetamorphic terrane snake creek anticline mount isa inlier north eastern australia microstructures and p t d paths
Journal of Metamorphic Geology, 2002Co-Authors: Michael J Rubenach, K A LewthwaiteAbstract:Rocks of the Snake Creek Anticline are mainly pelitic schists, psammitic schists and quartzites that were metamorphosed during multiple high-T/low-P events extending from D1 to D5, with the metamorphic peak occurring late to post-D3. Albitites are widespread, but are concentrated in five areas. They are typically fine- to medium-grained, and consist of albite, with or without combinations of quartz, biotite, staurolite, cordierite, garnet, andalusite, sillimanite, kyanite, gedrite and tourmaline. From the presence or absence of albite inclusions in porphyroblasts, the albitites are interpreted as forming early in the D3 event as a result of infiltration of external fluids. Psammitic schists and quartzites were preferentially altered, but pelitic schists were also albitized in localities where the alteration was more extreme, with the replacement of muscovite total and the replacement of quartz and biotite variable. Structural controls on Albitization include fracturing and syn-D3 shear zones in fold hinges. Biotite schists with abundant porphyroblasts (combinations of staurolite, garnet, andalusite and cordierite) occur adjacent to albitites, and it is argued that they formed by the addition of Fe and Mg sourced from the albitites. In several albitite-rich areas, cordierite grew early in D3 and was partly or entirely replaced during or after D3 by combinations of biotite, andalusite, tourmaline, staurolite and sillimanite. A postulated P–T–d path involved an increase in pressure (with or without a decrease in temperature) subsequent to early D3 Albitization, followed by an increase in temperature up to the metamorphic peak (late D3 to early D4. The metamorphism was contemporary in part with the emplacement of the Williams Batholith (c. 1550–1500 Ma), which probably supplied the Na-rich fluids.
Jesper Petersson - One of the best experts on this subject based on the ideXlab platform.
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Albitization and quartz dissolution in paleoproterozoic metagranite central sweden implications for the disposal of spent nuclear fuel in a deep geological repository
Lithos, 2012Co-Authors: Jesper Petersson, Michael B Stephens, Hakan Mattsson, Charlotte MollerAbstract:Abstract Hydrothermal alteration resulting in Albitization and quartz dissolution has been identified in Paleoproterozoic metagranites down to − 1000 m elevation at Forsmark, Sweden. The alteration features were discovered during investigations to locate a site for the disposal of spent nuclear fuel in a deep geological repository. In general, Albitization occurs extensively, but it is also observed locally adjacent to minor intrusive bodies of amphibolite. The altered rocks show a marked decrease in K-feldspar and an increase in quartz relative to the unaltered equivalents, resulting in an epitonalitic composition. Plagioclase is metamorphic in character and generally richer in albite than in the unaltered rocks. It is inferred that Albitization was triggered by the input of basic or intermediate melts into the crust during igneous activity close to the peak of regional metamorphism at 1.87–1.86 Ga. The mineralogy of the epitonalites gives rise to an increased thermal conductivity and, thereby, a positive influence for the design and safety of a deep geological repository for spent nuclear fuel. However, the increased frequency of low conductive amphibolite in the albitized volumes, consistent with the proposed mechanism for alteration, gives a negative influence. In sharp contrast to the Albitization, a majority of the occurrences of quartz dissolution, which resulted in the formation of episyenite, are located along fracture zones. Quartz dissolution took place between or after 1.8–1.7 Ga, when the bedrock was able to respond to deformation in a brittle manner. Most of the vugs left after the removal of quartz are, to a variable extent, refilled by hydrothermal assemblages, including quartz, albite, K-feldspar, hematite, chlorite and calcite. The geometry and spatial distribution of episyenite argue against an extreme fluid/rock ratio and it is inferred that the fluids had at least a moderate salinity with a temperature in excess of 300 °C. The dissolution process was promoted by the generation of secondary permeability localized in columnar or pipe-like volumes. The close spatial connection to fracture zones provides a basis to avoid bedrock affected by this type of alteration and, thereby, reduce the negative mechanical and hydrogeological aspects for a deep geological repository.
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mineral evolution and element mobility during episyenitization dequartzification and Albitization in the postkinematic bohus granite southwest sweden
Lithos, 1997Co-Authors: Jesper Petersson, Thomas EliassonAbstract:Abstract The petrography and geochemistry of two subsurface occurrences of pervasively albitized and episyenitized (i.e. dequartzified) granite in the central part of the postkinematic Sveconorwegian Bohus granite, in southwestern Sweden, were studied. The altered granite is whitened and consists of an albite-microcline framework with a very fine-grained interstitial assemblage of illite + hematite + ankerite ± anatase. Textural relations indicate that the initial dissolution of magmatic quartz, accompanied by Albitization of plagioclase, left a vuggy reservoir rock, which facilitated fluid penetration and thereby further alteration. The subsequent stage is characterized by infilling of vugs by the very fine-grained authigenic assemblage and by concomitant alteration of igneous minerals such as magnetite, ilmenite and biotite. Deuteric alteration products of magmatic minerals are affected by these two alteration stages, implying that episyenitization occurred widely after emplacement and cooling of the host granite. Mass balance calculations, with reference to adjacent unaffected granite, evince mainly Si loss and Na gain, reflecting the observed mineralogical changes. The volume decrease is estimated to be ~ 9%, owing to compaction accompanying the dequartzification and a slight porosity increase. The calculations revealed a slight enrichment in HREEs ± Y, essentially hosted by xenotime and a thorite-xenotime solid solution, both exsolved during recrystallization of monazite. Oxidation of ferrous iron and partial loss of chalcophile elements reflect oxidizing conditions. The alteration episode is Permo-Carboniferous and is possibly associated with circulation of oxidizing fluids through the Bohus granite.
Charlotte Moller - One of the best experts on this subject based on the ideXlab platform.
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Albitization and quartz dissolution in paleoproterozoic metagranite central sweden implications for the disposal of spent nuclear fuel in a deep geological repository
Lithos, 2012Co-Authors: Jesper Petersson, Michael B Stephens, Hakan Mattsson, Charlotte MollerAbstract:Abstract Hydrothermal alteration resulting in Albitization and quartz dissolution has been identified in Paleoproterozoic metagranites down to − 1000 m elevation at Forsmark, Sweden. The alteration features were discovered during investigations to locate a site for the disposal of spent nuclear fuel in a deep geological repository. In general, Albitization occurs extensively, but it is also observed locally adjacent to minor intrusive bodies of amphibolite. The altered rocks show a marked decrease in K-feldspar and an increase in quartz relative to the unaltered equivalents, resulting in an epitonalitic composition. Plagioclase is metamorphic in character and generally richer in albite than in the unaltered rocks. It is inferred that Albitization was triggered by the input of basic or intermediate melts into the crust during igneous activity close to the peak of regional metamorphism at 1.87–1.86 Ga. The mineralogy of the epitonalites gives rise to an increased thermal conductivity and, thereby, a positive influence for the design and safety of a deep geological repository for spent nuclear fuel. However, the increased frequency of low conductive amphibolite in the albitized volumes, consistent with the proposed mechanism for alteration, gives a negative influence. In sharp contrast to the Albitization, a majority of the occurrences of quartz dissolution, which resulted in the formation of episyenite, are located along fracture zones. Quartz dissolution took place between or after 1.8–1.7 Ga, when the bedrock was able to respond to deformation in a brittle manner. Most of the vugs left after the removal of quartz are, to a variable extent, refilled by hydrothermal assemblages, including quartz, albite, K-feldspar, hematite, chlorite and calcite. The geometry and spatial distribution of episyenite argue against an extreme fluid/rock ratio and it is inferred that the fluids had at least a moderate salinity with a temperature in excess of 300 °C. The dissolution process was promoted by the generation of secondary permeability localized in columnar or pipe-like volumes. The close spatial connection to fracture zones provides a basis to avoid bedrock affected by this type of alteration and, thereby, reduce the negative mechanical and hydrogeological aspects for a deep geological repository.
Charlotte Molle - One of the best experts on this subject based on the ideXlab platform.
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Albitization and quartz dissolution in paleoproterozoic metagranite central sweden implications for the disposal of spent nuclear fuel in a deep geological repository
Lithos, 2012Co-Authors: Jespe Petersso, Michael Stephens, Haka Mattsso, Charlotte MolleAbstract:Hydrothermal alteration resulting in Albitization and quartz dissolution has been identified in Paleoproterozoic metagranites down to - 1000 m elevation at Forsmark, Sweden. The alteration features were discovered during investigations to locate a site for the disposal of spent nuclear fuel in a deep geological repository. In general, Albitization occurs extensively, but it is also observed locally adjacent to minor intrusive bodies of amphibolite. The altered rocks show a marked decrease in K-feldspar and an increase in quartz relative to the unaltered equivalents, resulting in an epitonalitic composition. Plagioclase is metamorphic in character and generally richer in albite than in the unaltered rocks. It is inferred that Albitization was triggered by the input of basic or intermediate melts into the crust during igneous activity close to the peak of regional metamorphism at 1.87-1.86 Ga. The mineralogy of the epitonalites gives rise to an increased thermal conductivity and, thereby, a positive influence for the design and safety of a deep geological repository for spent nuclear fuel. However, the increased frequency of low conductive amphibolite in the albitized volumes, consistent with the proposed mechanism for alteration, gives a negative influence. In sharp contrast to the Albitization, a majority of the occurrences of quartz dissolution, which resulted in the formation of episyenite, are located along fracture zones. Quartz dissolution took place between or after 1.8-1.7 Ga, when the bedrock was able to respond to deformation in a brittle manner. Most of the vugs left after the removal of quartz are, to a variable extent, refilled by hydrothermal assemblages, including quartz, albite, K-feldspar, hematite, chlorite and calcite. The geometry and spatial distribution of episyenite argue against an extreme fluid/rock ratio and it is inferred that the fluids had at least a moderate salinity with a temperature in excess of 300 degrees C. The dissolution process was promoted by the generation of secondary permeability localized in columnar or pipe-like volumes. The close spatial connection to fracture zones provides a basis to avoid bedrock affected by this type of alteration and, thereby, reduce the negative mechanical and hydrogeological aspects for a deep geological repository. (C) 2012 Elsevier B.V. All rights reserved.