Natural Occurrence and Stability of Pyrochlore in Carbonatites, Related Hydrothermal Systems, and Weathering Environments

1995 ◽  
Vol 412 ◽  
Author(s):  
Gregory R. Lumpkin ◽  
Anthony N. Mariano
Keyword(s):  
Exchange Rate ◽  
Ion Exchange ◽  
Cation Exchange ◽  
Low Temperatures ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Natural Environments ◽  
Natural Occurrence ◽  
The Stability ◽  
A Site

AbstractStoichiometric and non-stoichiometric (defect) pyrochlores crystallize during the magmatic and late magmatic-hydrothermal phases of carbonatite emplacement (T > 450–550 °C, P < 2 kb). Defect pyrochlores can also form at low temperatures in laterite horizons during weathering. After crystallization, pyrochlore is subject to alteration by hydrothermal fluids (T ∼ 550-200°C) and ground water. Alteration occurs primarily by ion exchange of low valence A-site cations together with O, F, and OH ions. The high valence cations Th and U are generally immobile; however, we have documented one example of hydrothermal alteration involving loss of U together with cation exchange at the B-site in samples from Mountain Pass, California. During laterite accumulation, the cation exchange rate of pyrochlore greatly exceeds the rate of matrix dissolution. The exceptional durability of pyrochlore in natural environments is related to the stability of the B-site framework cations. In carbonatites, defect pyrochlores may contain significant amounts of Si (up to 7.6 wt% SiO2) which is negatively correlated with Nb.

scholarly journals Isotope geochemistry of gallium in hydrothermal systems

2021 ◽  
Author(s):  
◽  
Constance E. Payne
Keyword(s):  
New Zealand ◽  
Ion Exchange ◽  
Column Chromatography ◽  
Hot Spring ◽  
Isotope Geochemistry ◽  
Isotopic Ratio ◽  
Hydrothermal Systems ◽  
Phase Changes ◽  
Hydrothermal Fluids ◽  
Taupo Volcanic Zone

<p>Little is known about the isotope geochemistry of gallium in natural systems (Groot, 2009), with most information being limited to very early studies of gallium isotopes in extra-terrestrial samples (Aston, 1935; De Laeter, 1972; Inghram et al., 1948; Machlan et al., 1986). This study is designed as a reconnaissance for gallium isotope geochemistry in hydrothermal systems of New Zealand. Gallium has two stable isotopes, ⁶⁹Ga and ⁷¹Ga, and only one oxidation state, Ga³⁺, in aqueous media (Kloo et al., 2002). This means that fractionation of gallium isotopes should not be effected by redox reactions. Therefore the physical processes that occur during phase changes of hydrothermal fluids (i.e. flashing of fluids to vapour phase and residual liquid phase) and mineralisation of hydrothermal precipitates (i.e. precipitation and ligand exchange) can be followed by studying the isotopes of gallium. A gallium anomaly is known to be associated with some hydrothermal processes as shown by the unusual, elevated concentrations (e.g. 290 ppm in sulfide samples of Waiotapu; this study) in several of the active geothermal systems in New Zealand.  The gallium isotope system has not yet been investigated since the revolution of high precision isotopic ratio measurements by Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) and so a new analytical methodology needed to be established. Any isotopic analysis of multi-isotope elements must satisfy a number of requirements in order for results to be both reliable and meaningful. Most importantly, the analysis must represent the true isotopic composition of the sample. Ion-exchange chromatography is generally utilised to purify samples for analysis by MC-ICPMS and exclude potential mass interfering elements but care must also be taken to recover as close to 100% of the element of interest as possible, as column chromatography can often result in fractionation of isotopes (Albarède and Beard, 2004).  An ion exchange column chromatography methodology for the separation of gallium based on earlier work by Strelow and associates (Strelow, 1980a, b; Strelow and van der Walt, 1987; Strelow et al., 1974; van der Walt and Strelow, 1983) has been developed to ensure a quantitative and clean separation from the majority of elements commonly associated with hydrothermal precipitates and waters (i.e. As, Sb, Mo, Hg, W, Tl, Fe and other transition metals). A protocol to measure the isotopes of Ga was developed by the adaptation of methods used for other stable isotope systems using the Nu Plasma MC-ICPMS at the School of Geography, Environment and Earth Sciences, Victoria University of Wellington, NZ.  Gallium isotopic ratios have been collected for a suite of samples representing the migration of hydrothermal fluids from deep fluids in geothermal reservoirs to the surface expression of hot spring waters and associated precipitates in hydrothermal systems. A range in δ⁷¹GaSRM994 values is observed in samples from Taupo Volcanic Zone geothermal fields from -5.49‰ to +2.65‰ in silica sinter, sulfide, mud and brine samples. Mineral samples from Tsumeb and Kipushi mines range from -11.92‰ to +2.58‰ δ⁷¹GaSRM994. Two rock standards, BHVO-2 and JR-2 were also analysed for gallium isotopes with δ⁷¹GaSRM994 values of -0.92‰ ±0.12‰ and -1.91‰ ±0.23‰ respectively.</p>

scholarly journals Isotope geochemistry of gallium in hydrothermal systems

2021 ◽  
Author(s):  
◽  
Constance E. Payne
Keyword(s):  
New Zealand ◽  
Ion Exchange ◽  
Column Chromatography ◽  
Hot Spring ◽  
Isotope Geochemistry ◽  
Isotopic Ratio ◽  
Hydrothermal Systems ◽  
Phase Changes ◽  
Hydrothermal Fluids ◽  
Taupo Volcanic Zone

<p>Little is known about the isotope geochemistry of gallium in natural systems (Groot, 2009), with most information being limited to very early studies of gallium isotopes in extra-terrestrial samples (Aston, 1935; De Laeter, 1972; Inghram et al., 1948; Machlan et al., 1986). This study is designed as a reconnaissance for gallium isotope geochemistry in hydrothermal systems of New Zealand. Gallium has two stable isotopes, ⁶⁹Ga and ⁷¹Ga, and only one oxidation state, Ga³⁺, in aqueous media (Kloo et al., 2002). This means that fractionation of gallium isotopes should not be effected by redox reactions. Therefore the physical processes that occur during phase changes of hydrothermal fluids (i.e. flashing of fluids to vapour phase and residual liquid phase) and mineralisation of hydrothermal precipitates (i.e. precipitation and ligand exchange) can be followed by studying the isotopes of gallium. A gallium anomaly is known to be associated with some hydrothermal processes as shown by the unusual, elevated concentrations (e.g. 290 ppm in sulfide samples of Waiotapu; this study) in several of the active geothermal systems in New Zealand.  The gallium isotope system has not yet been investigated since the revolution of high precision isotopic ratio measurements by Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) and so a new analytical methodology needed to be established. Any isotopic analysis of multi-isotope elements must satisfy a number of requirements in order for results to be both reliable and meaningful. Most importantly, the analysis must represent the true isotopic composition of the sample. Ion-exchange chromatography is generally utilised to purify samples for analysis by MC-ICPMS and exclude potential mass interfering elements but care must also be taken to recover as close to 100% of the element of interest as possible, as column chromatography can often result in fractionation of isotopes (Albarède and Beard, 2004).  An ion exchange column chromatography methodology for the separation of gallium based on earlier work by Strelow and associates (Strelow, 1980a, b; Strelow and van der Walt, 1987; Strelow et al., 1974; van der Walt and Strelow, 1983) has been developed to ensure a quantitative and clean separation from the majority of elements commonly associated with hydrothermal precipitates and waters (i.e. As, Sb, Mo, Hg, W, Tl, Fe and other transition metals). A protocol to measure the isotopes of Ga was developed by the adaptation of methods used for other stable isotope systems using the Nu Plasma MC-ICPMS at the School of Geography, Environment and Earth Sciences, Victoria University of Wellington, NZ.  Gallium isotopic ratios have been collected for a suite of samples representing the migration of hydrothermal fluids from deep fluids in geothermal reservoirs to the surface expression of hot spring waters and associated precipitates in hydrothermal systems. A range in δ⁷¹GaSRM994 values is observed in samples from Taupo Volcanic Zone geothermal fields from -5.49‰ to +2.65‰ in silica sinter, sulfide, mud and brine samples. Mineral samples from Tsumeb and Kipushi mines range from -11.92‰ to +2.58‰ δ⁷¹GaSRM994. Two rock standards, BHVO-2 and JR-2 were also analysed for gallium isotopes with δ⁷¹GaSRM994 values of -0.92‰ ±0.12‰ and -1.91‰ ±0.23‰ respectively.</p>

scholarly journals Evaluation of Electrodialysis Desalination Performance of Novel Bioinspired and Conventional Ion Exchange Membranes with Sodium Chloride Feed Solutions

Membranes ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 217
Author(s):  
AHM Golam Hyder ◽  
Brian A. Morales ◽  
Malynda A. Cappelle ◽  
Stephen J. Percival ◽  
Leo J. Small ◽  
...  
Keyword(s):  
Ion Exchange ◽  
Cation Exchange ◽  
Current Density ◽  
Feed Solution ◽  
Laboratory Scale ◽  
Cation Exchange Membrane ◽  
Limiting Current ◽  
Ion Exchange Membranes ◽  
Experimental Apparatus ◽  
Exchange Membrane

Electrodialysis (ED) desalination performance of different conventional and laboratory-scale ion exchange membranes (IEMs) has been evaluated by many researchers, but most of these studies used their own sets of experimental parameters such as feed solution compositions and concentrations, superficial velocities of the process streams (diluate, concentrate, and electrode rinse), applied electrical voltages, and types of IEMs. Thus, direct comparison of ED desalination performance of different IEMs is virtually impossible. While the use of different conventional IEMs in ED has been reported, the use of bioinspired ion exchange membrane has not been reported yet. The goal of this study was to evaluate the ED desalination performance differences between novel laboratory‑scale bioinspired IEM and conventional IEMs by determining (i) limiting current density, (ii) current density, (iii) current efficiency, (iv) salinity reduction in diluate stream, (v) normalized specific energy consumption, and (vi) water flux by osmosis as a function of (a) initial concentration of NaCl feed solution (diluate and concentrate streams), (b) superficial velocity of feed solution, and (c) applied stack voltage per cell-pair of membranes. A laboratory‑scale single stage batch-recycle electrodialysis experimental apparatus was assembled with five cell‑pairs of IEMs with an active cross-sectional area of 7.84 cm2. In this study, seven combinations of IEMs (commercial and laboratory-made) were compared: (i) Neosepta AMX/CMX, (ii) PCA PCSA/PCSK, (iii) Fujifilm Type 1 AEM/CEM, (iv) SUEZ AR204SZRA/CR67HMR, (v) Ralex AMH-PES/CMH-PES, (vi) Neosepta AMX/Bare Polycarbonate membrane (Polycarb), and (vii) Neosepta AMX/Sandia novel bioinspired cation exchange membrane (SandiaCEM). ED desalination performance with the Sandia novel bioinspired cation exchange membrane (SandiaCEM) was found to be competitive with commercial Neosepta CMX cation exchange membrane.

scholarly journals Analysis of Hydrothermal Systems Beneath Tayukeng through Long-Term Geochemical Signals of Hydrothermal Fluids in Tatun Volcano Group, Taiwan

2021 ◽  
Vol 18 (14) ◽  
pp. 7411
Author(s):  
Hsin-Fu Yeh ◽  
Hung-Hsiang Hsu
Keyword(s):  
Surface Temperature ◽  
Hydrothermal System ◽  
Hydrothermal Fluid ◽  
Thermal Water ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Geochemical Variations ◽  
Northern Taiwan

The Tatun Volcano Group (TVG) is located in northern Taiwan and consists of many springs and fumaroles. The Tayukeng (TYK) area is the most active fumarole site in the TVG. In this study, we analyzed the long-term geochemical variations of hydrothermal fluids and proposed a mechanism responsible for the variation in TYK. There are two different aquifers beneath the TYK area: a shallow SO42−-rich aquifer and a deeper aquifer rich in Cl−. TYK thermal water was mainly supplied by the shallow SO42−-rich aquifer; therefore, the thermal water showed high SO42− concentrations. After 2015, the inflow of deep thermal water increased, causing the Cl− concentrations of the TYK to increase. Notably, the inferred reservoir temperatures based on quartz geothermometry increased; however, the surface temperature of the spring decreased. We inferred that the enthalpy was lost during transportation to the surface. Therefore, the surface temperature of the spring does not increase with an increased inflow of deep hydrothermal fluid. The results can serve as a reference for understanding the complex evolution of the magma-hydrothermal system in the TVG.

Hydrothermal Sr contamination of the Dippin sill, Isle of Arran, Western Scotland

1984 ◽  
Vol 48 (348) ◽  
pp. 311-322 ◽  
Author(s):  
A. P. Dickin ◽  
C. M. B. Henderson ◽  
F. G. F. Gibb
Keyword(s):  
Stable Isotope ◽  
Hydrothermal Alteration ◽  
Closed System ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Drill Core ◽  
Sr Isotope ◽  
Core Section ◽  
High Silica ◽  
Isotope Measurements

Abstract The Dippin sill, which is emplaced into the Triassic sediments of SE Arran, is an alkaline basic sheet which displays pronounced hydrothermal alteration. The 40-m-thick sill has suffered pervasive contamination with radiogenic Sr, introduced from the Triassic sediments by hydrothermal fluids. Stable isotope measurements suggest that fluids were of meteoric origin, but were restricted to a small closed-system circulation. Initial 87Sr/86Sr ratios in the sill were raised from an original value of 0.7032 to a maximum of 0.7091, contamination being especially pronounced near the contacts at Dippin Head itself (localities 12 and 14) and in a drill core section through the sill above Dippin. Hydrothermal Sr was incorporated into an early-formed high-CaO, high-Sr analcime, which replaced unstable high-silica nepheline in interstitial patches. However, this high-CaO analcime, along with plagioclase, was later replaced by a low-CaO, low-Sr analcime, allowing Sr leaching from the margins of the sill. Hydrothermal fluids are thought to have migrated up to 1 km laterally, up the dip of the sill, mainly via tension joints forming in the cooling intrusion. Pooling of hot fluids at the upper end of the sill probably raised water/rock ratios in this region and allowed greater Sr contamination during mineralogical alteration. The undersaturated mineralogy of the sill accounts for its pervasive hydrothermal Sr contamination, which contrasts markedly with the relatively undisturbed Sr isotope compositions of Hebridean granites involved in hydrothermal systems.

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