Enrichment Of Cs Research Articles

Enrichment of negative elements in molten quasi-binary nitrates

For the recovery of the electrochemically negative elements, such as alkali and alkaline-earth used in molten salt, it is important to separate them selectively each other. The results of electromigration in molten nitrate system allow us to conclude that the divalent cations were separated from the monovalent ones, because alkaline-earth nitrates were concentrated in the migration tube before the enrichment of Cs. In addition, we have investigated the internal mobilities of Cs in order to estimate the limitation of the enrichment degree. The results enable us to demonstrate that it is feasible to enrich CsNO 3 up to x Cs = 0.38 in molten LiNO 3–KNO 3 eutectic. Especially, it was effective to enrich these species under the high current density during electromigration.

Magmatic characteristics of the Paleocene Cerro Nevazón region and other Late Cretaceous to Early Tertiary calc-alkaline subvolcanic to plutonic units in the Neuquén Andes, Argentina

Voluminous Late Cretaceous–Early Tertiary calc-alkaline magmatism in the northwest part of the Neuquén province, Argentina, is characterized by a NS-trending belt of olivine basalt-augitic andesite volcanic and amphibole-rich diorite subvolcanic facies that were grouped in the Neuquén-Mendoza volcanic province. Of samples associated with skarn mineralization in the Cerro Nevazón area, two were dated by K/Ar in amphibole and one by Ar/Ar in plagioclase; together, they yield ages between 60.1±1.6 and 56.0±1.7 Ma. The igneous rocks contain normally zoned plagioclase (64–74%), amphibole (magnesiohastingsite and edenite; 15–20%), biotite (5–10%), quartz (4–18%), minor enstatite–ferrosilite (Wo 2.5–3En 71–73Fs 24–25), and augite (Wo 42–43En 42–43Fs 14–15), with accessory magnetite, minor ilmenite, apatite, sphene, and traces of zircon. The fractionation of calcic plagioclase+olivine+pyroxene±magnetite±ilmenite is responsible for the evolution of the parental magmas, which originated in approximately 10% melting of a mantle source contaminated by fluids from the oceanic subducted lithosphere, with sparse or no residual garnet. The gabbro rare earth element patterns are similar to those of the Antuco volcano (37°25′S) and other Quaternary basaltic rocks from the southern volcanic zone (CSVZ) of the Andes (37–41°5′S) emplaced in a relatively thin continental crust (≈30 km). Although the Cerro Nevazón granitoids share some geochemical signatures with the Paleogene Caicayén igneous units, also located in the northwestern region of Neuquén, they have different evolutionary styles, as expressed by the lack of amphibole fractionation and less Cs enrichment in the Caicayén rocks. With similar SiO 2 contents, the Upper Cretaceous–Paleocene Campana Mahuida subvolcanic rocks from the same region are richer in incompatible trace elements (K, Rb, Sr, Ba, Nb, La, Ce, Yb, Th, and U) than either the Nevazón or Caicayén units, which suggests that their parental magmas were contaminated with crustal material. The low Fe 2O 3/FeO ratios in the Nevazón igneous rocks, combined with the presence of ilmenite in most rocks and the low Mg/(Mg+Fe +2) ratios in mafic minerals, suggest that the Nevazón magmas evolved under more reduced conditions than did the Caicayén or Campana Mahuida magmas.

Temperature dependence of the electric properties of molten ternary chlorides by MD simulation

The electric properties are simulated in the temperature region of 800–1100 K for molten ternary mixtures (Li, Na, Cs)Cl of various compositions by molecular dynamics simulation in order to investigate the temperature dependence of the Chemla crossing points and the limit of the degree of enrichment of Cs. In addition, the self-diffusion coefficient, self-exchange velocity and the electric conductivities were calculated in molten LiCl–NaCl eutectic mixtures containing CsCl. From the results, it is concluded that the self-diffusion coefficients and self-exchange velocities of Li +, Na +, and Cs + with reference to Cl − show very similar tendencies with increasing temperature for each composition and the most appropriate temperature of Cs is 800–900 K for enrichment up to x Cs=0.5–0.6 in molten LiCl–NaCl eutectic.

Investigation on the electrical properties of molten quaternary systems (Li, Na, K, Cs)Cl and (Li, Na, K, Cs)F by MD simulation

For the pyrochemical reprocessing of spent metallic fuels in molten salts, it is of importance to estimate the degree of enrichment of Cs. Molecular dynamics simulation has been carried out on molten quaternary systems (Li, Na, K, Cs)Cl at 625 K and (Li, Na, K, Cs)F at 727 K for the various compositions in order to investigate the electrical properties, i.e. the electrical conductivity, the self-diffusion coefficient, the self-exchange velocity and the relative differences in the internal cation mobilities of Cs in molten LiCl–NaCl–KCl eutectic mixtures and in the FLINAK melts. These results allow us to conclude that the electrical conductivities, the self-diffusion coefficients and the self-exchange velocities of Li +, Na +, K + and Cs + with reference to Cl − and F − show almost the same tendencies for each composition. We demonstrated that it was possible to enrich Cs up to x Cs=0.38 in molten LiCl–NaCl–KCl eutectic as well as in the LiCl–KCl system and up to x Cs=0.42 in the FLINAK melts as well as in the molten FLINA system. In addition, the sequence of the simulated electrical conductivity in molten quaternary alkali chloride and fluoride systems was in fair agreement with that of the current simulated self-exchange velocities and self-diffusion coefficients.

Extremely Metal-poor Stars. IX. CS 22949-037 and the Role of Hypernovae

We have obtained high-resolution spectra of the extremely metal-poor star CS 22949-037 ([Fe/H] = -3.79) in the region of the ultraviolet NH bands at 3360-3370 Å, which confirm our earlier report that it exhibits extreme nitrogen enhancement. We find [N/Fe] = 2.3 ± 0.4. The star is also known to have large relative overabundances, of order 0.5-1 dex, of carbon and the α-elements. This abundance pattern is not explained by any standard Galactic chemical enrichment model of which we are aware. The large N enhancement is, however, predicted by the zero heavy element, M ≳ 200 M☉, hypernova models of Woosley & Weaver and Fryer, Woosley, & Heger. If the rotating models of Fryer et al. are relevant to the enrichment of CS 22949-037, one might expect it to possess a large overabundance of oxygen, with a mass fraction similar to or larger than that of nitrogen, and an [O I] λ6300.3 line strength of ~2-8 mÅ.

The composition of suspended matter from Ganges–Brahmaputra sediment dispersal system during low sediment transport season

Suspended matter supplied from the Ganges–Brahmaputra river system was sampled in waters of the adjacent shelf area in times of low suspended matter load (November/December 1997). The absolute amount of suspended matter ranges between >500 mg/l near the river mouth and <1 mg/l on the outer shelf. Chemical and mineralogical analyses of the suspended matter show changes in its composition with distance from the source. Compositional changes are based on grain size partitioning; quartz and heavy minerals are precipitating sooner, leaving the suspended matter from the outer shelf depleted in quartz, REE, Zr, Hf, Nb, Ta, W, U, Th, Y, and Ca. The other part of the compositional changes is based on the reaction of suspended matter with seawater. Manganese hydroxide is producing coatings on suspended matter grains, and adsorbing elements out of the seawater. As a consequence, enrichment of Mn, Zn, Ni, Cr, Co, Li, Cs, As, Sb, Pb, Tl, and Cd can be observed in the suspended matter from the outer shelf. Arsenic is accumulating on the inner shelf by a factor of 2. Chemical partitioning in sequential leaching experiments shows that arsenic does not follow the enrichment mechanism of manganese and other transition metals. More than 90% of the total arsenic is bound to nearly insoluble phases of the suspended matter (e.g., crystalline iron oxides, residual minerals). For comparison with suspended matter, adjacent surface sediments were sampled and analysed. In this sediment, the dominating phase is the one which settled down during the times of high suspended load, with more quartz and heavy minerals and consequent chemical composition. The enrichment of manganese oxide and adsorbed transition metals gets lost; because of anaerobic conditions in the bottom-near seawater, they dissolve from the sediment and get recycled in seawater. Arsenic is found in nearly insoluble parts of the sediment, as it is the case in the suspended matter

Estimation of the Enrichment of Cs in Molten Chloride and Fluoride Systems by Molecular Dynamics Simulation

Abstract For the pyrochemical reprocessing of spent metallic fuels in molten salt baths it is of importance to estimate the enrichment degree of Cs. A molecular dynamics simulation has been executed on molten (Li, Na, Cs)Cl at 900 K and (Li, Na, Cs)F at 925 K for various compositions in order to calculate the relative differences in the internal cation mobilities of Cs in molten LiCl-NaCl equimolar mixtures and the LiF-NaF eutectic. According to these results the self-exchange velocities of Li+, Na+ and Cs+ with respect to Cl- and F- have similar tendencies at each composition, and Cs can be enriched effectively up to xCs = 0.5 -0.6 in LiCl-NaCl melts. In addition, the sequence of the calculated self-diffusion coefficients for various compositions was in a fair agreement with that of the obtained self-exchange velocities.

Geochemistry, mineralogy, and technological properties of the main Stephanian (Carboniferous) coal seams from the Puertollano Basin, Spain

This study is focused on the occurrence and distribution of mineral matter and major and trace elements in the high volatile bituminous coal from Puertollano (south-central Spain). The relationship between ash behaviour and inorganic composition, as well as the possible formation of fouling and slagging deposits in boilers during the conversion process, were investigated. The Puertollano coals do not exhibit plastic properties, despite their rank, probably because of their high ash and inertinite contents. The Puertollano coal has medium to low total S content (0.48% to 1.63% db, with a mean of 1.0% db) and is characterised by relatively high contents of Si, Pb, Sb, and Cs. Some elements such as As, Cd, Co, Cr, Cu, Ge, Li, Mn, Ni, W, and Zn are also present in relatively high contents. The enrichment in a number of heavy metals could be attributed to the common sulphide ores occurring near the Puertollano coal deposit. The following trace elements affinities are deduced: (a) sulphide affinity: As, Co, Cd, Cu, Ni, Sb, Tl, and Zn; (b) aluminum–silicate affinity: K, Ti, B, Co, Cr, Cs, Cu Ga, Hf, Li, Nb, Rb, Sn, Ta, Th, V, Zr, and LREE; (c) Carbonate affinity: Ca, Mg, Mn, and B; (d) organic affinity: B. The very high Si levels and the anomalous enrichment in Cs, Ge, Pb, Sb, and Zn shown by the Puertollano coals account for the high contents of these elements in the Puertollano fly ash when compared with the other Spanish coal fly ashes. The chemical composition of the high temperature ash (HTA) is consistent with the trend shown by the ash fusion temperatures (AFT) and also with the predictive indices related to slagging and fouling propensities. Thus, the ash fusion temperatures increase with high values of Al 2O 3 as well as with the decrease in Fe 2O 3, CaO, and MgO.

Compared geochemical signatures and the evolution of Menez Gwen (37°50′N) and Lucky Strike (37°17′N) hydrothermal fluids, south of the Azores Triple Junction on the Mid-Atlantic Ridge

During the DIVA 1 cruise in May 1994, a series of 19 dives was conducted using the French submersible Nautile at the topographic highs of three volcanic segments centered at 37°17′N, 37°50′N and 38°20′N, respectively, south of the Azores Triple Junction (ATJ) on the Mid-Atlantic Ridge (MAR). Hydrothermal fluids were collected at the Lucky Strike (LS) hydrothermal field, discovered at 37°17′N in 1993, and at a new hydrothermal site called Menez Gwen (MGw) discovered at 37°50′N during this cruise. Both systems are relatively shallow compared to other MAR systems with seafloor depths of 1700 and 850 m, respectively, characteristics which make them unique among the already known sites on the MAR. The characteristics of the LS fluids are the same as in 1993 and include temperatures ranging from 170°C to 324°C, variable chlorinities lower than seawater, low hydrogen sulfide (<3.0 mmol/kg), high Ba concentrations (up to 80 μmol/kg), low metal concentrations and high gas contents, and distinct chemical end-members indicative of significant geographic control of the venting system. In contrast, the very clear MGw fluids at 37°50′N show a rather uniform exit temperature (285°C) and chemical compositions with chlorinities (360–380 mmol/kg) lower than at LS and corresponding lower concentrations of cations, H 2S (1.8 mmol/kg), metals and silica (8–11.5 mmol/kg), due to the lower temperature ( T) and pressure ( P) of the system. In the two systems, fluid chemistry is strongly affected by phase separation. At the low-pressure conditions of these sites, phase relations in the NaCl–H 2O system dictate production of an extremely low salinity. The higher salinities observed in fluids thus indicate that mixing of extremely low salinity vapor with single-phase hydrothermal seawater is the dominant process controlling Cl concentrations. Depletions and enrichments of elements in solutions are also explained by the involvement of fluid-rock reactions. The enrichment of Ba, K, Cs and Rb in the fluids is linked to the enriched character of these elements in basalts. Relatively high pH and Ca, low Li, Sr and metals are related to the highly altered basaltic substrate in the reaction zone. Low Sr/Ca and high Ca/Na ratios are explained by albitization within the crust. The increase of degassing when approaching the Azores may be related to the carbon-enriched basaltic crust near the Azores hot spot. Isotopic ratios show that CO 2, CH 4 and helium gases have a magmatic signature. Compared to other deeper sites on the MAR, all fluids collected at LS and MGw are gas-enriched, except for H 2S and helium, whose both concentration and isotopic ratio compare well with other hydrothermal fluids. The high CH 4 concentration associated with unsaturated hydrocarbons and the high CH 4/ 3He ratios also suggest a contribution of CH 4 generated by serpentinization of ultramafic rocks by Fischer–Tropsch catalysis of CO 2 reduction.

Constraints from high-pressure veins in eclogites on the composition of hydrous fluids in subduction zones

Hydrous high-pressure veins formed during dehydration of eclogites in two paleo-subduction zones (Trescolmen locality in the Adula nappe, central Alps and Münchberg Gneiss Massif, Variscan fold belt, Germany) constrain the major and trace element composition of solutes in fluids liberated during dehydration of eclogites. Similar initial isotopic compositions of veins and host eclogites at the time of metamorphism indicate that the fluids were derived predominantly from the host rocks. Quartz, kyanite, paragonite, phengite, zoisite and omphacite are the dominant minerals in the veins. The major element compositions of the veins are in agreement with experimental evidence indicating that the composition of solutes in such fluids is dominated by SiO 2 and Al 2O 3. Relative to N-MORB, the veins show enrichments of Cs, Rb, Ba, Pb, and K, comparable or slightly lower abundances of Sr, U, and Th, and very low abundances of Nd, Sm, Zr, Nb, Ti and Y. The differential fractionation of highly incompatible elements such as K, U and Th in the veins, as well as the presence of hydrous minerals in the eclogites rule out partial melting as a cause for vein formation. These results confirm previous suggestions that fluids derived from subducted basalt may have low abundances of high field strength elements, rare earth elements and Y. Variable vein-eclogite enrichment factors of incompatible alkalis and to a lesser extent Pb appear to reflect mineralogical controls (phengite, epidote-group minerals) on partitioning of these elements during dehydration of eclogite in subduction zones. However, abundance variations of incompatible elements in minerals from eclogites suggest that the composition of fluids released from eclogites at temperatures <700°C may not reflect true equilibrium partitioning during dehydration. Simple models for the trace elements U and Th indicate the relative importance of the basaltic and sedimentary portions of subducted oceanic crust in producing the characteristic chemical signatures of these elements in convergent plate margin volcanism.

THE GENESIS OF PYROXENITE-RICH PERIDOTITE AT CABO ORTEGAL (NW SPAIN). INFERENCES FROM GEOCHEMICAL, MINERAL AND PB-SR ISOTOPIC DATA

THE GENESIS OF PYROXENITE-RICH PERIDOTITE AT CABO ORTEGAL (NW SPAIN). INFERENCES FROM GEOCHEMICAL, MINERAL AND PB-SR ISOTOPIC DATA

Burning radionuclide question: What happens to iodine, cesium and chlorine in biomass fires?

Fires can mobilize radionuclides from contaminated biomass through suspension of gases and particles in the atmosphere or solubilization and enrichment of the ash. Field and laboratory burns were conducted to determine the fate of I, Cs and Cl in biomass fires. Straw, wood, peat, dulse (seaweed) and radish plants were combusted with temperatures varying from 160 to 1000°C, representing the normal range of field fire temperatures. Loss to the atmosphere increased with fire temperature and during a typical field fire, 80–90% of the I and Cl, and 40–70% of the Cs was lost to the atmosphere. The remainder was left behind in the ash and was soluble. Typically, the ash was enriched in I by a factor of two to three, with higher enrichments of Cs and lower enrichments of Cl, when compared to the initial fuel concentration during field burns. Most of the I was lost to the atmosphere as a gas. If the elements were radioactive isotopes, such as 129I, 137CS and 36C1, fires could cause an increased radiological dose to people through inhalation, exposure to ash, or ingestion of plants because of increased uptake of ash leachate.

Experimental partitioning of Rb, Cs, Sr, and Ba between alkali feldspar and peraluminous melt

Hydrous partial melting experiments performed between 650 and 750 °C at 200 MPa (H20) on synthetic metapelite compositions (quartz + albite + muscovite + biotite mineral mixtures) doped with Ba, Sr, Rb, and Cs yielded alkali feldspar crystals with a wide range of compositions in equilibrium at their rims with peraluminous melt. Measured partition coefficients for normally trace lithophile elements between feldspar and melt [D(M)FSP/gl, M = Ba, Sr, Rb, Cs] do not depend on either temperature or bulk composition of melt for the compositions studied. Values of D(Sr)FSP/gl are between 10 and 14 and appear to be independent of the albite and orthoclase contents of the feldspar crystals. In contrast, values of D(Ba)FSP/gl and D(Rb)FsP/glare strongly dependent on the orthoclase content of feldspar, relationships that can be expressed by the following linear equations: D(Ba)FSP/gl = 0.07 + 0.25(orthoclase) and D(Rb)FsP/gl= 0.03 + 0.0 1(orthoclase), where orthoclase is in mole percent. These equations reproduce the range of previously reported values for D(Ba) and D(Rb) determined on natural and synthetic samples. A single partition coefficient for Cs was also determined at D(CS)Fsp/gl = 0.13. These data can be used in conjunction with recently published partition coefficients for muscovite, biotite, and plagioclase feldspars (Blundy and Wood 1991; Icenhower and London 1995) to model quantitatively the trace element signatures of peraluminous magmas during anatexis and crystallization. Depending on bulk composition and pressuretemperature trajectories during episodes of partial melting, Ba and Sr (and to a lesser extent, Rb) are retained at the source while Cs and Li are enriched in the first melts. These results explain why peraluminous granitic magmas with S-type (sedimentary) sources carry a distinctive enrichment in Li and Cs.

Hydrothermal processes and shifting element association patterns in the W—Sn enriched granite of Regoufe, Portugal

Combined research in geochemistry and mineral chemistry of the hydrothermally altered W-Sn specialized granite of Regoufe and its derivatives in Portugal was undertaken to gain insight in the mineralogical changes associated with hydrothermal processes within a single granite cupola. Over 1000 unpolished rock sections were analyzed by automated X-ray fluorescence spectrometry (XRF). On the basis of the XRF data, a small number of these same sections was selected for investigation by electron probe microanalysis. The study focuses on fourteen elements of interest that are measurable with the chosen techniques. Major pervasive alteration within the Regoufe granite is virtually contemporaneous with mineralization in the form of Sn- or W-bearing quartz veins. Two phases of hydrothermal activity are discerned, characterized by different element associations. Fluids of the first phase were especially rich in Sn, Cs and F, whereas the second phase was marked by a W-Ta-Nb-Rb association and presumably carried less F. Phosphorus probably was an important fluid component in both phases. The fluids are inferred to have fractionated from a related granitic magma at depth. Tin, W, Nb and Ta are mainly found as substitutions or inclusions in biotite in the least altered part of the Regoufe granite. Tantalo-niobian rutile is an important control for the distribution of Nb. Tin occurs in rutile and rarely as cassiterite. Muscovitization caused leaching of Ti and Zr from the granite. Tin, supplied or mobilized by the hydrothermal fluids, behaves differently from W, Nb and Ta. In the most altered rocks, muscovite hosts significant amounts of Sn. Whereas Sn is still related to Cs and Ti, elements that probably represent altered biotite, W, Ta and Nb are related to newly formed Rb-rich muscovite. Columbitetantalite was detected embedded in late muscovite. In contrast to Sn, the fluid-supplied W was predominantly deposited as wolframite in quartz veins and the altered granite is not enriched in W compared to the relatively unaltered rocks. Strontium is preferentially hosted by K-feldspar in the least altered granite; Ca in this rock is still partly contained in albite. With increasing albitization and muscovitization, Sr and Ca were released and are partly bound in newly formed apatite. The primary magmatic apatites have near-ideal formula compositions, but mobilization of P during hydrothermal activity resulted in the formation of Mn-rich apatite in all parts of the granite, and Sr- and probably Li-rich varieties in the most altered rocks. Eosphorite, and scorodite as the oxidation product of arsenopyrite, were also formed as a result of P mobilization. In the least altered rocks, Cs is mainly contained in biotite. In the most altered granite and aplitic rocks, enrichment of Cs and Rb is evenly distributed over K-feldspar and micas. The processes that lead to increased Rb are partly independent of Cs enrichment, and apparently related to the W-Nb-Ta mineralization event, separate from the preceding Sn mineralization.

Crustal contamination in early Basin-and-Range hawaiites of the Los Encinos Volcanic Field, central México

The Los Encinos Volcanic Field (LEVF) consists of Miocene (10.6–13.6 Ma) hawaiitic volcanic necks and lava-capped mesas that crop out sparsely over an area of 11,500 km2 at the eastern margin of the Mexican Basin and Range Province (BRP). The LEVF rocks are similar to other early extensional hawaiites from the southern BRP, and provide numerous contrasts with younger basanites and alkali basalts that erupted during the Quaternary at the Ventura and Santo Domingo Volcanic Fields about 100 km to the south. A suite of 18 LEVF hawaiites was studied in thin section, and analyzed for mineral compositions, whole-rock major and trace element compositions, and Sr, Nd, and Pb isotopic ratios. All samples contain the stable minerals plagioclase (An53–64), olivine (Fo61–88), clinopyroxene, titanomagnetite, and minor biotite. Most samples also contain a complex assemblage of resorbed and reacted xenocrysts and megacrysts. Some of these minerals appear to have crystallized slowly from related, but more differentiated magmas, but other xenocrysts were clearly derived from lower-crustal, high-grade orthogneisses and paragneisses that are found as large xenoliths in the nearby Quaternary volcanic fields. Quartz xenocrysts are especially common in many hawaiites (up to 3.9 vol.%) and show a wide range of reaction styles. One sample contains microxenoliths of sillimanite- and quartz-bearing paragneiss with fine-grained domains that are interpreted as coronal structures related to original garnet xenocrysts. The geochemical effects of crustal contamination in the LEVF hawaiites vary widely. Five samples appear to be essentially uncontaminated (type U). Aside from being somewhat differentiated from a more primitive parent, the type-U samples can be used to infer the geochemistry of the mantle that was melting during the early stages of basin-and-range rifting. Type-U samples range up to ɛNd and down to 87Sr/86Sr=0.70286 and 206Pb/204Pb=18.74, compositions that are more extreme than any of the nearby Quaternary volcanic rocks. The other 13 samples are divided into two contamination types, A and B. Both types show trends toward higher 87Sr/86Sr (to 0.7040) and 206Pb/204Pb (to 18.98), lower ɛNd (to +3.1), and elevated Yb, which appear to reflect bulk or AFC-style contamination by granulites, particularly garnet-bearing paragneisses. Type-A hawaiites also show selective enrichments in Cs, Rb, Th, Sb, U, Pb, K, and Si. These elements were probably transferred into the type-A hawaiitic magmas through mixing with low-degree partial melts from deep-crustal granulites. The enrichments of these elements in type-A hawaiites complement the depletions of many of these same elements in highgrade granulites worldwide and provide insight into the origin of those depletions. Mixing models between type-U hawaiites and paragneiss xenoliths indicate that up to 45% of the Pb found in type-A hawaiites is crustally derived. In comparison with more mafic Quaternary basanitic rocks from the volcanic fields to the south, which carried large peridotite and granulite xenoliths to the surface, the LEVF hawaiites are relatively differentiated and megacryst rich, but free of large xenoliths, and show a wide variety of petrographic and geochemical evidence for crustal contamination. These differences probably reflect the slow and interrupted ascent of the LEVF hawaiites during early stages of basin-and-range extension in the Miocene, when the crust had a somewhat lower density and the entire lithosphere was relatively thick and cool. We argue that Quaternary basanites were able to ascend significantly faster through the thinner, hotter, and more fractured and extended lithosphere, whose crust was made denser by mafic intrusions during the preceding magmatic episode. Consequently the Quaternary basanites rose without stagnating and interacting with crustal lithologies, and without losing their entrained peridotite xenoliths.

Fluorapatite fenitization and gold enrichment in sheeted trondhjemites within the Destor–Porcupine fault zone, Taylor Township, Ontario

Pronounced fluorapatite mineralization is present in sheeted trondhjemites near Timmins. The trondhjemites intrude a deformed ultramafic to Fe-tholeiite volcanic sequence disposed in the structural hanging wall of the Destor–Porcupine Fault, and they bound a domain of high-grade gold ore. Spinifex-textured ultramafic flows record variable intensities of secondary alteration to a carbonate–Cr-muscovite assemblage. They are characterized by chondritic Al2O3/TiO2 ratios (19 ± 1.7), enhanced Cr (1570–2090 ppm) and Ni (470–1070 ppm), together with low levels of the incompatible elements Ta, Nb, and Th.Fresh quartz–oligoclase trondhjemitic intrusions are compositionally coherent with respect to SiO2 (average 63 wt.%), Al2O3 (16.3 wt. %), and Na2O (6.7 wt. %), as well as to the alteration-insensitive elements V, Sc, Zr, and Hf. Whole-rock δ18O values of 10.0–10.6‰, combined with "magmatic" quartz–feldspar (0.8–0.9‰), signify that these are primary high-18O magmas, likely derived by partial melting of 18O-enriched mafic granulites. Albitic trondhjemites are characterized by enhanced Na2O (10.8 wt. %) and are systematically enriched by ~1‰ relative to fresh counterparts, due to a preferential positive 18O shift of albite, resulting in negative quartz–feldspar. Sodium enrichment coupled with isotopic disturbance is attributed to low-temperature spilitization in the presence of marine water.A domain of high-grade gold ore is focussed in an intensely silicified unit. The ore is composed of quartz, feldspar, muscovite, carbonate, graphite, pyrite, molybdenite, and gold, with corresponding pronounced enrichments of Si, K, Rb, Ba, Cs, S, C, As, Sb, Pb, and Mo. The lithology is compositionally diverse but uniform with respect to Al2O3/TiO2 (17–27) and Ti/Zr (60–73). These features, combined with variably elevated Cr (50–955 ppm) and Ni (60–570), low contents of the incompatible elements, and a flat REE distribution, collectively indicate Fe-tholeiite and basaltic komatiite precursors. The silicified unit is bounded by trondhjemites overprinted by a secondary muscovite–Fe-dolomite alteration assemblage, with associated anomalies of CO2, S, As, Sb, Mo, and Pb. Quartz is isotopically uniform (δ18O = 14.1 ± 0.2‰ (1σ), n = 15) throughout the diverse lithologies overprinted by alteration linked to gold mineralization. Quartz is shifted ~+3‰ and albite ~−1‰ relative to fresh trondhjemites, such that Δquartz–feldspar = 1.8 to 2.6‰ in ore. Fluids implicated in gold mineralization were characterized by ambient temperatures of 330 ± 20 °C and by [Formula: see text]. Carbon-isotope compositions of hydrothermal ferroan dolomite are constrained at δ13C = −2.5 ± 0.8‰, but they are systematically heavier in graphitic rocks. δCgraphite averages −20.8‰.Fluorapatite occurs as megacrysts superimposed on trondhjemites and as microveins in a narrow domain cospatial with the Destor–Porcupine Fault. Its modal abundance correlates directly with P2O5 and F, which attain levels of 6.8 wt.% and 6800 ppm, respectively. Fluorapatite is close to end-member composition and possesses extremely enhanced REE abundances: 87Sr/86Sr = 0.7012, a value similar to that for contemporaneous mantle. Rocks have been extensively stripped of Si, K, Na, and Al in domains of fluorapatite, signifying a process allied to fenitization.

Geochemistry of High-silica Peralkaline Rhyolites, Naivasha, Kenya Rift Valley

The Recent ( 5 per cent phenocrysts. Phenocryst minerals are quartz-sanidine-ferrohedenbergite-fayalite-titanomagnetite-ilmenite-riebeckite-arfvedsonite-aenigmatite-biotite-zircon. Ferrohedenbergite and zircon are restricted to less peralkaline, and amphibole, aenigmatite, and biotite to more peralkaline, rocks.The comendites show unusually strong enrichment in Cs, F, Hf, Nb, Rb, REE, Ta, Th, U, Y, Zn, and Zr, and extreme depletion in Mg, Ca, Ba, Co, and Sr. REE patterns are moderately LREE-enriched, with large, negative Eu anomalies. Values of LIL/HFS element ratios, such as Th/Ta and Rb/Zr, are unusually high for peralkaline rhyolites, and are consistent with a substantial crustal component in the comendites. Parameters such as LREE/HREE and Zr/Nb ratios indicate that the Naivasha rhyolites represent several pulses of closely related, but subtly different, magmas. Sanidine/glass partition coefficients for Ba, Pb, Rb, Sr, U, and the REE are presented for one specimen.Major and trace element modelling, and feldspar-rock relationships, show that closed system crystal fractionation cannot alone account for the overall compositional variations in the comendites. A model involving partial melting of variable crustal source rocks and migration of dissolved volatile-metal complexes may be appropriate at Naivasha.

Fluid infiltration into fault zones: Chemical, isotopic, and mechanical effects

Fluid infiltration into fault zones and their deeper-level counterparts, brittle-ductile shear zones, is examined in diverse tectonic environments. In the 2.7 Ga Abitibi greenstone belt, major tectonic discontinuities, with lateral extents of hundreds of kilometres initiated as listric normal faults accommodating rift extension and acted as sites for komatiite extrusion and locally intense metasomatism. During reverse motion on the structures, accommodating shortening of the belt, these transcrustal faults were utilised as a conduit for the ascent of trondhjemitic magmas from the base of the crust and of alkaline magmas from the asthenosphere and for the discharge of thousands of cubic kilometres of hydrothermal fluids. Such fluids were characterised by δ18O=+6±2, δD=−50±20, δ13C=−4±4, and temperatures of 270 to 450°C, probably derived from devolatilisation of crustal rocks undergoing prograde metamorphism. Hydrothermal fluids were more radiogenic (87Sr/86Sr=0.7010 to 0.7040) and possessed higher μ than did contemporaneous mantle, komatiites or tholeiites, and thus carried a contribution from older sialic basement. A provinciality of87Sr/86Sr and δ13C is evident, signifying that fault plumbing sampled lower crust which was heterogeneous at the scale of tens of kilometres. Mineralised faults possess enrichments of large ion lithophile (LIL), LIL elements, including K, Rb, Ba, Cs, B, and CO2, and rare elements, such as Au, Ag, As, Sb, Se, Te, Bi, and W. Fluids were characterised by XCO 2≈0.1, neutral to slightly acidic pH, low salinity ≤3 wt-%, K/Na=0.1, they carried minor CH4, CO, and N2, and they underwent transient effervescence of CO2 during decompression. Clastic sediments occupy graben developed at fault flexures. The40Ar/39Ar release spectra indicate that fault rocks experienced episodic disturbance on time scales of hundreds of millions of years. At the Grenville front, translation was accommodated along two mylonite zones and an intervening boundary fault. The high-temperature (580°C) and low-temperature (430 to 490°C) mylonite zones, formed in the presence of deep-level crust-equilibrated fluids of metamorphic origin. Late brittle faults contain quartz veins precipitated from fluids with extemely negative δ18O (−14 per mil) at 200 to 300°C. The water may have been derived from downward penetration into fault zones of precipitation of low18O on a mountain range induced by continental collision, with uplift accommodated at deep levels by the mylonite zones coupled with rebound on the boundary faults. Archean gneisses overlie Proterozoic sediments along thrust surfaces at Lagoa Real, Brazil; the gneisses are transected by brittle-ductile shear zones locally occupied by uranium deposits. Following deformation at 500 to 540°C, in the presence of metamorphic fluids and under conditions of low water-to-rock ratio, shear zones underwent local intense oxidation and desilication. All minerals undergo a shift of −10 per mil, indicating discharge of meteoric-water-recharged formation brines in the underlying Proterozoic sediments up through the Archean gneisses, during overthrusting; ≈1000 km3 of solutions passed through these structures. The shear zones and Proterozoic sediments are less radiogenic (87Sr/86Sr=0.720) than contemporaneous Archean gneisses (0.900), corroborating the transport of fluids and solutes through the structure from a large external reservoir. Major crustal detachment faults of Tertiary age in the Picacho Cordilleran metamorphic core complex of Arizona show an upward transition from undeformed granitic basement through mylonitic to brecciated and hydrothermally altered counterparts. The highest tectonic levels are allochthonous, oxidatively altered Miocene volcanics. This transition is accompanied by an increase of 12 per mil in δ18O, from +7 to +19, and a 400°C decrease in temperature. Lower tectonic levels acted as aquifers for the expulsion of large volumes of higher-temperature reduced metamorphic fluids and/or evolved formation brines. The Miocene allochthon was influenced by a lower-temperature reservoir inducing oxidative potassic alteration; mixing occurred between cool downward-penetrating thermal waters and the hot, deeper aqueous reservoir. In general, flow regimes in these fault and shear zones follow a sequence, from conditions of high temperature and pressure with locally derived fluids at low water-to-rock ratios, during initiation of the structures, to high fluxes of reduced formation or metamorphic fluids along conduits as the structures propagate and intersect hydrothermal reservoirs. Later in the tectonic evolution and at shallower crustal levels there was incursion of oxidising fluids from near-surface reservoirs into the faults. In general, magmatism, tectonics, and fluid motion are intimately related.

Isotope enrichment of Cs +, Ba 2+ and Zn 2+ ions in a competitive uptake from aqueous solutions by zeolite-4A

Selective sorption of the radionuclides 134Cs +, 133Ba 2+ and 65Zn 2+ from aqueous solutions using zeolite-4A is reported. A mutual suppression in the uptake of individual cations was observed. Under the experimental conditions there exists a direct correspondence between the rate contant ( k) and the final amount of uptake ( Q ∞) of a cation from a binary mixture. The order of Q ∞ values with respect to the three cations was Q ∞[Cs + (mix)] > Q ∞[Ba 2+ (mix)] > Q ∞[Zn 2+ (mix)]. The influence of ionic mobility upon k is discussed.

Selective concentration of cesium in analcime during hydrothermal alteration, Yellowstone National Park, Wyoming

Chemical and mineralogical studies of fresh and hydrothermally altered rhyolitic material in Upper and Lower Geyser Basins, Yellowstone National Park, show that all the altered rocks are enriched in Cs and that Cs is selectively concentrated in analcime. The Cs content of unaltered rhyolite lava flows, including those from which the altered sediments are derived, ranges from 2.5 to 7.6 ppm. The Cs content of analcime-bearing altered sedimentary rocks is as high as 3000 ppm, and in clinoptilolite-bearing altered sedimentary rocks Cs content is as high as 180 ppm. Altered rhyolite lava flows which were initially vitrophyres, now contain up to 250 ppm Cs, and those which were crystallized prior to hydrothermal alteration contain up to 14 ppm. Mineral concentrates of analcime contain as much as 4700 ppm Cs. The Cs must have been incorporated into the analcime structure during crystallization, rather than by later cation substitution, because analcime does not readily exchange Cs. The Cs Cl of the fluids circulating through the hydrothermal system varies, suggesting that Cs is not always a conservative ion and that Cs is lost from upflowing thermal waters due to water-rock interaction resulting in crystallization of Cs-bearing analcime. The source of Cs for Cs enrichment of the altered rocks is from leaching of rhyolitic rocks underlying the geyser basins, and from the top of the silicic magma chamber that underlies the area. Analcime is an important natural Cs sink, and the high Cs concentrations reported here may prove to be an important indicator of the environment of analcime crystallization.