Meteoritic zircon – Occurrence and chemical characteristics

In common with the remarkable variation in the bulk rock Zr content of distinct meteorite groups, ranging from <1 ppm to >800 ppm, the occurrence and abundance of accessory zircon is also highly diverse and limited to certain meteorite classes. A detailed literature study on the occurrence of meteoritic zircon, along with other Zr-bearing phases reveals that lunar rocks, eucrites and mesosiderites are the prime sources of meteoritic zircon. Rare zircon grains occur in chondrites, silicate-bearing iron meteorites and Martian meteorites, with grain sizes of >5 μm allowing chemical and chronological studies at high spatial resolution using secondary ion mass spectrometry (SIMS) technique. Grain sizes, crystal habits, structural and chemical characteristics of zircon grains derived from various meteorite types, including their REE abundances, minor element concentrations, and Zr/Hf values is diverse. Superchondritic Zr/Hf values (47 ± 8; s.d. with n = 97), i.e., typical for zircon in eucrites and mesosiderites, indicate crystallization from a fractionated, incompatible-element-rich (residual) melt. Differences in REE abundances, occurrence or absence of Ce- and Eu-anomalies, and overall REE patterns that are often fractionated with a depletion in LREE, might be primarily controlled by variable formation conditions of individual grains and/or differences in the residual melt compositions on a small, local scale within single samples. Subsequent fractionation/modification of the chemical fingerprint of meteoritic zircon can involve high-temperature annealing processes during thermal metamorphic reactions and/or impact events along with mixing of lithic fragments since many samples are breccias.     

The distribution of halogens and carbon in PGE-bearing ultramafics of the Acoje ophiolite block, Zambales, Philippines

Evidence for redistribution of Pt and Pd in the Acoje ultramafic rocks led to an investigation of the role of Cl, Br, F, I and C in Pt and Pd transport in hydrothermal solution. Anomalously high contents of 300–1000 ppm Cl, 3 ppm Br, up to 50 ppm F, 180–380 ppm I and 300–3300 ppm C are characteristic of the Acoje ultramafic rocks. The Cl and Br concentrations are restricted to serpentinized dunites and a positive correlation between Br and Cl indicate their common origin and their introduction during serpentinization. The ratios Br/Cl,F/Cl, and I/Cl correspond to those of sediments that contain seawater which suggests that Cl, Br and I were partly expelled from deep sea sediments during emplacement of the ophiolite. Fluorine could have been derived from mantle material.Carbon occurs in fluid inclusions in olivines as CO₂, CO or CH₄ and/or submicroscopic graphite. The high C content in serpentinized dunites suggests that C, at least in part, is also of serpentinization origin.Chlorine is mainly incorporated into Fe-rich serpentines and Ca-amphiboles. Very low F concentration in hydrous phases is common, except in serpentines from pyroxenes, pargasites and edenites. Brucite is finely dispersed in serpentines derived from olivines, indicating low CO₂-activity during brucite formation and a pH of about 11.The presence of Pt and Pd tellurides, arsenides and bismuthides and the absence of selenides, in spite of elevated Se concentrations in bulk analyses of about 5 ppm, indicates that the stability conditions for selenide formation were not obtained during alteration. The formation of Pt and Pd halogen complexes, requiring highly oxidizing (f_O2 > hematite-magnetite boundary (HM)) and acid environments is not favoured for Pt and Pd transport in Acoje ultramafics. An redistribution caused by the solubility reduction of Pt and Pd by Te, Bi and As and a precipitation of their intermetallic phases is proposed. No correlation between Cl and PGE-bearing rock units was observed, which indicates the minor role of halogens during redistribution of Pt and Pd in the Acoje ophiolite.     

Halogen contents of eclogite facies fluid inclusions and minerals: Caledonides,western Norway

Primary multiphase brine fluid inclusions in omphacite and garnet from low‐ to medium‐temperature eclogites have been analysed for Cl, Br, I, F, Li and SO₄. Halogen contents and ratios provide information about trapped lower crustal fluids, even though the major element (Na, K, Ca) contents of inclusion fluids have been modified by fluid–mineral interactions and (step‐) daughter‐crystal formation after trapping. Halogens in the inclusion fluids were analysed with crush–leach techniques. Cl/Br and Cl/I mass ratios of eclogite fluids are in the range 31–395 and 5000–33 000, respectively. Most fluids have a Cl/Br ratio lower than modern seawater and a Cl/I ratio one order of magnitude lower than modern seawater. Fluids with the lowest Cl/Br and highest Cl/I ratios come from an eclogite that formed by hydration of granulite facies rocks, and may indicate that Br and I are fractionated into hydrous minerals. Reconstructions indicate that the inclusion fluids originally contained 500–4000 ppm Br, 1–14 ppm I and 33–438 ppm Li. Electron microprobe analyses of eclogite facies amphibole, biotite, phengite and apatite indicate that F and Cl fractionate most strongly between phengite (F/Cl mass ratio of 1469 ± 1048) and fluid (F/Cl mass ratio of 0.008), and the least between amphibole and fluid. The chemical evolution of Cl and Br in pore fluids during hydration reactions is in many ways analogous to Cl and Br in seawater during evaporation: the Cl/Br ratio remains constant until the a_H2O value is sufficiently lowered for Cl to be removed from solution by incorporation into hydrous minerals.     

Deep pre-eruptive storage of silicic magmas feeding Plinian and dome-forming eruptions of central and northern Dominica (Lesser Antilles) inferred from volatile contents of melt inclusions

Volatiles contribute to magma ascent through the sub-volcanic plumbing system. Here, we investigate melt inclusion compositions in terms of major and trace elements, as well as volatiles (H₂O, CO₂, SO₂, F, Cl, Br, S) for Quaternary Plinian and dome-forming dacite and andesite eruptions in the central and the northern part of Dominica (Lesser Antilles arc). Melt inclusions, hosted in orthopyroxene, clinopyroxene and plagioclase are consistently rhyolitic. Post-entrapment crystallisation effects are limited, and negligible in orthopyroxene-hosted inclusions. Melt inclusions are among the most water-rich yet recorded (≤?8 wt% H₂O). CO₂ contents are generally low (<?650 ppm), although in general the highest pressure melt inclusion contain the highest CO₂. Some low-pressure (<?3 kbars) inclusions have elevated CO₂ (up to 1100–1150 ppm), suggestive of fluxing of shallow magmas with CO₂-rich fluids. CO₂-trace element systematics indicate that melts were volatile-saturated at the time of entrapment and can be used for volatile-saturation barometry. The calculated pressure range (0.8–7.5 kbars) indicates that magmas originate from a vertically-extensive (3–27 km depth) storage zone within the crust that may extend to the sub-Dominica Moho (28 km). The vertically-extensive crustal system is consistent with mush models for sub-volcanic arc crust wherein mantle-derived mafic magmas undergo differentiation over a range of crustal depths. The other volatile range of composition for melt inclusions from the central part is F (75–557 ppm), Cl (1525–3137 ppm), Br (6.1–15.4 ppm) and SO₂ (<?140 ppm), and for the northern part it’s F (92–798 ppm), Cl (1506–4428 ppm), Br (not determined) and SO₂ (<?569; one value at 1015 ppm). All MIs, regardless of provenance, describe the same Cl/F correlation (8.3?±?2.7), indicating that the magma source at depth is similar. The high H₂O content of Dominica magmas has implications for hazard assessment.     

Volatile composition of microinclusions in diamonds from the Panda kimberlite, Canada: Implications for chemical and isotopic heterogeneity in the mantle

In order to better investigate the compositions and the origins of fluids associated with diamond growth, we have carried-out combined noble gas (He and Ar), C and N isotope, K, Ca and halogen (Cl, Br, I) determinations on fragments of individual microinclusion-bearing diamonds from the Panda kimberlite, North West Territories, Canada. The fluid concentrations of halogens and noble gases in Panda diamonds are enriched by several orders of magnitude over typical upper mantle abundances. However, noble gas, C and N isotopic ratios (³He/⁴He = 4-6 Ra, ⁴⁰Ar/³⁶Ar = 20,000-30,000, δ¹³C = −4.5‰ to −6.9‰ and δ¹⁵N = −1.2‰ to −8.8‰) are within the worldwide range determined for fibrous diamonds and similar to the mid ocean ridge basalt (MORB) source value. The high ³⁶Ar content of the diamonds (>1 × 10⁻⁹ cm³/g) is at least an order of magnitude higher than any previously reported mantle sample and enables the ³⁶Ar content of the subcontinental lithospheric mantle to be estimated at ∼0.6 × 10⁻¹² cm³/g, again similar to estimates for the MORB source. Three fluid types distinguished on the basis of Ca-K-Cl compositions are consistent with carbonatitic, silicic and saline end-members identified in previous studies of diamonds from worldwide sources. These fluid end-members also have distinct halogen ratios (Br/Cl and I/Cl). The role of subducted seawater-derived halogens, originally invoked to explain some of the halogen ratio variations in diamonds, is not considered an essential component in the formation of the fluids. In contrast, it is considered that large halogen fractionation of a primitive mantle ratio occurs during fluid-melt partitioning in forming silicic fluids, and during separation of an immiscible saline fluid.     

The F,Cl, Br and I Contents of Reference Glasses BHVO‐2G,BIR‐1G,BCR‐2G,GSD‐1G,GSE‐1G,NIST SRM 610 and NIST SRM 612

Halogen contents for the widely distributed reference glasses BHVO‐2G, BIR‐1G, BCR‐2G, GSD‐1G, GSE‐1G, NIST SRM 610 and NIST SRM 612 were investigated by pyrohydrolysis combined with ion chromatography, total reflection X‐ray fluorescence analysis, instrumental neutron activation analysis, the noble gas method, electron probe microanalysis and laser ablation‐inductively coupled plasma‐mass spectrometry. Glasses BHVO‐2G, GSD‐1G and GSE‐1G have halogen contents that can be reproduced at the 15% level by all bulk techniques and cover a significant range in halogen mass fractions for F (~ 20–300 μg g^?1), Cl (~ 70–1220 μg g^?1) and Br (~ 0.2–285 μg g^?1) and I (~ 9–3560 ng g^?1). The BIR‐1G glass has low F (< 15 μg g^?1), Cl (~ 20 μg g^?1), Br (15 ng g^?1) and I (3 ng g^?1). The halogen contents for the silica‐rich NIST SRM 610 and 612 glasses were poorly reproduced by the different techniques. The relatively high Cl, Br and I abundances in glasses GSD‐1G and GSE‐1G mean that these glasses are well suited for calibrating spatially resolved micro‐analytical studies on silicate glasses, melt and fluid inclusions. Combined EPMA and laser ablation‐inductively coupled plasma‐mass spectrometry data for glass GSE‐1G demonstrate homogeneity at the 10% level for Cl and Br.     

Geochemical evolution of halogen-enriched granite magmas and mineralizing fluids of the Zinnwald tin-tungsten mining district,Erzgebirge, Germany

We remelted and analyzed crystallized silicate melt inclusions in quartz from a porphyritic albite-zinnwaldite microgranite dike to determine the composition of highly evolved, shallowly intruded, Li- and F-rich granitic magma and to investigate the role of crystal fractionation and aqueous fluid exsolution in causing the extreme extent of magma differentiation. This dike is intimately associated with tin- and tungsten-mineralized granites of Zinnwald, Erzgebirge, Germany. Prior research on Zinnwald granite geochemistry was limited by the effects of strong and pervasive greisenization and alkali-feldspar metasomatism of the rocks. These melt inclusions, however, provide important new constraints on magmatic and mineralizing processes in Zinnwald magmas.The mildly peraluminous granitic melt inclusions are strongly depleted in CAFEMIC constituents (e.g., CaO, FeO, MgO, TiO₂), highly enriched in lithophile trace elements, and highly but variably enriched in F and Cl. The melt inclusions contain up to several thousand ppm Cl and nearly 3 wt% F, on average; several inclusions contain more than 5 wt% F. The melt inclusions are geochemically similar to the corresponding whole-rock sample, except that the former contain much more F and less CaO, FeO, Zr, Nb, Sr, and Ba. The Sr and Ba abundances are very low implying the melt inclusions represent magma that was more evolved than that represented by the bulk rock. Relationships involving melt constituents reflect increasing lithophile-element and halogen abundances in residual melt with progressive magma differentiation. Modeling demonstrates that differentiation was dominated by crystal fractionation involving quartz and feldspar and significant quantities of topaz and F-rich zinnwaldite. The computed abundances of the latter phases greatly exceed their abundances in the rocks, suggesting that the residual melt was separated physically from phenocrysts during magma movement and evolution.Interactions of aqueous fluids with silicate melt were also critical to magma evolution. To better understand the role of halogen-charged, aqueous fluids in magmatic differentiation and in subsequent mineralization and metasomatism of the Zinnwald granites, Cl-partitioning experiments were conducted with a F-enriched silicate melt and aqueous fluids at 2,000 bar (200 MPa). The results of the experimentally determined partition coefficients for Cl and F, the compositions of fluid inclusions in quartz and other phenocrysts, and associated geochemical modeling point to an important role of magmatic-hydrothermal fluids in influencing magma geochemistry and evolution. The exsolution of halogen-charged fluids from the Li- and F-enriched Zinnwald granitic magma modified the Cl, alkali, and F contents of the residual melt, and may have also sequestered Li, Sn, and W from the melt. Many of these fluids contained strongly elevated F concentrations that were equivalent to or greater than their Cl abundances. The exsolution of F-, Cl-, Li-, ± W- and Sn-bearing hydrothermal fluids from Zinnwald granite magmas was important in effecting the greisenizing and alkali-feldspathizing metasomatism of the granites and the concomitant mineralization.Editorial Handling: B. Lehmann     

Upper crustal abundances of trace elements: A revision and update

We report new estimates of abundances of rarely analyzed elements (As, B, Be, Bi, Cd, Ge, In, Mo, Sb, Sn, Te, Tl, W) in the upper continental crust based on precise ICP-MS analyses of well-characterized upper crustal samples (shales, pelites, loess, graywackes, granitoids and their composites) from Australia, China, Europe, New Zealand and North American. Obtaining a better understanding of the upper crustal abundance and associated uncertainties of these elements is important in placing better constraints on bulk crust composition and, from that, whole Earth models of element cycling and crust generation. We also present revised abundance estimates of some more commonly analyzed trace elements (Li, Cr, Ni, and Tm) that vary by > 20% compared to previous estimates. The new estimates are mainly based on significant (r² > 0.6) inter-element correlations observed in clastic sediments and sedimentary rocks, which yield upper continental crust elemental ratios that are used in conjunction with well-determined abundances for certain key elements to place constraints on the concentrations of the rarely analyzed elements. Using the well-established upper crustal abundances of La (31 ppm), Th (10.5 ppm), Al₂O₃ (15.40%), K₂O (2.80%) and Fe₂O₃ (5.92%), these ratios lead to revised upper crustal abundances of B = 47 ppm, Bi = 0.23 ppm, Cr = 73 ppm, Li = 41 ppm, Ni = 34 ppm, Sb = 0.075, Te = 0.027 ppm, Tl = 0.53 ppm and W = 1.4 ppm. No significant correlations exist between Mo and Cd and other elements in the clastic sediments and sedimentary rocks, probably due to their enrichment in organic carbon. We thus calculate abundances of these elements by assuming the upper continental crust consists of 65% granitoid rocks plus 35% clastic sedimentary rocks. The validity of this approach is supported by the similarity of SiO₂, Al₂O₃, La and Th abundances calculated in this way with their upper crustal abundances given in Rudnick and Gao [Rudnick, R., Gao, S., 2003. Composition of the continental crust. In: Rudnick, R.L. (Ed.), The Crust. In: Holland, H.D., Turekian, K.K. (Eds.), Treatise on Geochemistry, vol. 3. Elsevier–Pergamon, Oxford, pp. 1–64.]. The upper crustal abundances thus obtained are Mo = 0.6 ppm and Cd = 0.06 ppm. Our data also suggest a  20% increase of the Tm, Yb and Lu abundances reported in Rudnick and Gao [Rudnick, R., Gao, S., 2003. Composition of the continental crust. In: Rudnick, R.L. (Ed.), The Crust. In: Holland, H.D., Turekian, K.K. (Eds.), Treatise on Geochemistry, vol. 3. Elsevier–Pergamon, Oxford, pp. 1–64.].     

Origin of salinity of deep groundwater in crystalline rocks

Deep groundwater in fractured crystalline basement has been reported from deep mines and from scientific deep wells. Highly saline brines have been described from several km depth in the continental basement of the Canadian, Fennoscandian and Ukrainian shields and elsewhere in the world. The origin of salinity is unknown and many different possibilities have been presented. We compare the compositional evolution of deep waters in the Black Forest basement, SW Germany, with those of other deep crystalline waters, and use halogen systematics (e.g. Cl/Br ratios) and other parameters of the waters to deduce the origin of their salinity. In the Black Forest the composition of deep thermal waters results from chemical interaction of surface water with the rock matrix (mainly weathering of plagioclase and mica) and from mixing of the reacted water with stagnant saline deep water. Here we show by Na/TDS-and Cl/TDS-investigations, by molality-ratios of the Na and Cl concentrations, and by Cl/Br systematics that these deep saline waters have a marine origin. The Cl/Br ratios in deep crystalline waters are very close to normal marine ratios (Cl/Br = 288 ppm basis). In contrast, Cl/Br ratios of other possible sources of salinity show distinctly different Cl/Br ratios: water derived from dissolved Tertiary halite deposits of the rift valley is in the order of Cl/Br = 2400 and water from dissolved Muschelkalk halite deposits has values of about Cl/Br = 9900. Leaching experiments on crystalline rocks, on the other hand, show that the average Cl/Br ratio of crystalline rocks is far below Cl/Br = 100.     

Mixed messages in iron oxide–copper–gold systems of the Cloncurry district,Australia: insights from PIXE analysis of halogens and copper in fluid inclusions

Proterozoic rocks of the Cloncurry district in NW Queensland, Australia, are host to giant (tens to hundreds of square kilometers) hydrothermal systems that include (1) barren regional sodic–calcic alteration, (2) granite-hosted hydrothermal complexes with magmatic–hydrothermal transition features, and (3) iron oxide–copper–gold (IOCG) deposits. Fluid inclusion microthermometry and proton-induced X-ray emission (PIXE) show that IOCG deposits and the granite-hosted hydrothermal complexes contain abundant high temperature, ultrasaline, complex multisolid (type 1) inclusions that are less common in the regional sodic–calcic alteration. The latter is characterized by lower salinity three-phase halite-bearing (type 2) and two-phase (type 3) aqueous inclusions. Copper contents of the type 1 inclusions (>300 ppm) is higher than in type 2 and 3 inclusions (<300 ppm), and the highest copper concentrations (>1,000 ppm) are found both in the granite-hosted systems and in inclusions with Br/Cl ratios that are consistent with a magmatic source. The Br/Cl ratios of the inclusions with lower Cu contents are consistent with an evaporite-related origin. Wide ranges in salinity and homogenization temperatures for fluid inclusions in IOCG deposits and evidence for multiple fluid sources, as suggested by halogen ratios, indicate fluid mixing as an important process in IOCG genesis. The data support both leaching of Cu by voluminous nonmagmatic fluids from crustal rocks, as well as the direct exsolution of Cu-rich fluids from magmas. However, larger IOCG deposits may form from magmatic-derived fluids based on their higher Cu content.     

Simultaneous Determination of Fluorine,Chlorine, Bromine and Iodine in Six Geochemical Reference Materials Using Pyrohydrolysis,Ion Chromatography and Inductively Coupled Plasma‐Mass Spectrometry

Concentrations of halogens (fluorine, chlorine, bromine and iodine) were determined in six geochemical reference materials (BHVO‐2, GS‐N, JG‐1, JR‐1, JB‐1b, JB‐2). Halogens were first extracted from powdered samples using a pyrohydrolysis technique, then hydrolysis solutions were analysed by ion chromatography for F and Cl and inductively coupled plasma‐mass spectrometry for Br and I. The detection limits in solutions were 100 μg l^?1 for both F and Cl and 10 ng l^?1 for Br and I. Considering the extraction procedure, performed on a maximum of 500 mg of sample and producing 100 ml of pyrohydrolysis solution, detection limits in rock samples were 20 mg kg^?1 for F and Cl and 2 μg kg^?1 for Br and I. The mean analytical errors on the studied composition ranges were estimated at 10 mg kg^?1 for F and Cl, 100 μg kg^?1 for Br and 25 μg kg^?1 for I. The concentration values, based on repeated (generally > 10) sample analysis, were in good agreement generally with published values and narrowed the mean dispersion around mean values. Large dispersions are discussed in terms of samples heterogeneity and contaminations during sample preparation. Basaltic RMs were found to be more suitable for studies of halogen compositions than differentiated rock material, especially granites – the powders of which were heterogeneous in halogens at the 500 mg level.     

The systematics of chlorine, fluorine, and water in Izu arc front volcanic rocks: Implications for volatile recycling in subduction zones

We studied the systematics of Cl, F and H₂O in Izu arc front volcanic rocks using basaltic through rhyolitic glass shards and melt inclusions (Izu glasses) from Oligocene to Quaternary distal fallout tephra. These glasses are low-K basalts to rhyolites that are equivalent to the Quaternary lavas of the Izu arc front (Izu VF). Most of the Izu glasses have Cl ∼400-4000 ppm and F ∼70-400 ppm (normal-group glasses). Rare andesitic melt inclusions (halogen-rich andesites; HRA) have very high abundances of Cl (∼6600-8600 ppm) and F (∼780-910 ppm), but their contents of incompatible large ion lithophile elements (LILE) are similar to the normal-group glasses. The preeruptive H₂O of basalt to andesite melt inclusions in plagioclase is estimated to range from ∼2 to ∼10 wt% H₂O. The Izu magmas should be undersaturated in H₂O and the halogens at their preferred levels of crystallization in the middle to lower crust (∼3 to ∼11 kbar, ∼820° to ∼1200°C). A substantial portion of the original H₂O is lost due to degassing during the final ascent to surface. By contrast, halogen loss is minor, except for loss of Cl from siliceous dacitic and rhyolitic compositions. The behavior of Cl, F and H₂O in undegassed melts resembles the fluid mobile LILE (e.g.; K, Rb, Cs, Ba, U, Pb, Li). Most of the Cl (>99%), H₂O (>95%) and F (>53%) in the Izu VF melts appear to originate from the subducting slab. At arc front depths, the slab fluid contains Cl = 0.94 ± 0.25 wt%, F = 990 ± 270 ppm and H₂O = 25 ± 7 wt%. If the subducting sediment and the altered basaltic crust were the only slab sources, then the subducted Cl appears to be almost entirely recycled at the Izu arc (∼77-129%). Conversely, H₂O (∼13-22% recycled at arc) and F (∼4-6% recycled) must be either lost during shallow subduction or retained in the slab to greater depths. If a seawater-impregnated serpentinite layer below the basaltic crust were an additional source of Cl and H₂O, the calculated percentage of Cl and H₂O recycled at arc would be lower. Extrapolating the Izu data to the total length of global arcs (∼37,000 km), the global arc outflux of fluid-recycled Cl and H₂O at subduction zones amounts to Cl ∼2.9-3.8 × 10¹² g/yr and H₂O ∼0.7-1.0 × 10¹⁴ g/yr, respectively—comparable to previous estimates. Further, we obtain a first estimate of global arc outflux of fluid-recycled F of ∼0.3-0.4 × 10¹²g/yr. Despite the inherent uncertainties, our results support models suggesting that the slab becomes strongly depleted in Cl and H₂O in subduction zones. In contrast, much of the subducted F appears to be returned to the deep mantle, implying efficient fractionation of Cl and H₂O from F during the subduction process. However, if slab devolatilization produces slab fluids with high Cl/F (∼9.5), slab melting will still produce components with low Cl/F ratios (∼0.9), similar to those characteristic of the upper continental crust (Cl/F ∼0.3-0.9).     

Quantification of Cl,Br and I in Geological Materials by NH4F Digestion: Comparison with Rapid Acid Digestion

The lack of analytical techniques for halogens in geological materials is mainly due to the loss of analytes during sample preparation. This study describes a rapid bulk rock digestion method (NH₄F digestion) for determination of the abundances of Cl, Br and I in geological materials by SF-ICP-MS. During high temperature (200–240 °C) digestion, NH₃ released from the decomposition of molten NH₄F can effectively prevent the loss of halogens released from geological samples. Chlorine, Br and I were not lost during NH₄F digestion at 220 °C for 0.25–6 h. The limits of quantitation for NH₄F digestion were 2.8, 0.018 and 0.003 μg g^-1 Cl, Br and I, respectively. Most results for halogens in geological reference materials by NH₄F digestion were in agreement with their certified values, confirming that the high-performance rapid bulk rock NH₄F digestion has sufficient digestion capability to extract Cl, Br and I from rocks, sediments and soils. In comparison, results obtained following acid digestion showed that HNO₃ + HF digestion could effectively extract Br and I from soil and sediment samples, and that HNO₃ acid digestion is only suitable to use for the determination of Br and I in soil samples.     

Halogens and noble gases in sedimentary formation waters and Zn–Pb deposits: A case study from the Lennard Shelf,Australia

Halogen ratios (Br/Cl and I/Cl) and concentrations provide important information about how sedimentary formation waters acquire their salinity, but the possible influence of organic Br derived from sedimentary wall-rocks is rarely quantified. Here, it is demonstrated that Br/Cl versus I/Cl mixing diagrams can be used to deconvolve organic Br contributions; that organic matter has a limited range of Br/I ratios; and that organic Br is a more significant component in Zn–Pb deposit ore fluids than previously recognised. The significance of these findings is illustrated for the Lennard Shelf Zn–Pb deposits of Western Australia.Fluid inclusions related to Lennard Shelf Zn–Pb mineralisation have variable salinity and hydrocarbon contents. The halogen data from these fluid inclusions require mixing of three fluid end-members: (1) an evaporated seawater bittern brine (30 wt.% NaCl equiv.) with greater than seawater Br/Cl ratio; (2) a lower salinity pore fluid (?5 wt.% NaCl equiv.) with moderately elevated Br/Cl and I/Cl; and (3) fluids with Br/Cl ratios of ～5 times seawater and extremely elevated I/Cl ratios of ～11,500 times seawater. The first two fluids have ⁴⁰Ar/³⁶Ar of 300–400 and greater than air saturated water ³⁶Ar concentrations that are typical of fluid inclusions related to Zn–Pb mineralisation. The third ‘organic-rich’ fluid has the highest ⁴⁰Ar/³⁶Ar ratio of up to 1500 and a depleted ³⁶Ar concentration.Mineralisation is interpreted to have resulted from mixing of Zn-rich evaporitic brines and H₂S present in hydrocarbons. It is suggested that aqueous fluids acquired organic Br and I from hydrocarbons, and that hydrocarbons exsolving from the aqueous fluid removed noble gases from solution. Interaction of variably saline brines and hydrocarbons could account for the variable Br/Cl and I/Cl composition, and ³⁶Ar concentrations, recorded by Lennard Shelf fluid inclusions. The distinct ⁴⁰Ar/³⁶Ar signature of the fluid with the highest I/Cl ratio suggests the hydrocarbons and brines were sourced independently from different parts of the sedimentary basin. These data indicate the complementary nature of halogen and noble gas analysis and provide new constraints on important mixing processes during sediment-hosted Zn–Pb mineralisation.     

The origins of the Mengye potash deposit in the Lanping–Simao Basin,Yunnan Province,Western China

The Lanping–Simao Basin (LSB) is a Mesozoic–Cenozoic continental margin rift basin in Western China. It formed during the opening and closing of the Tethys Ocean. This basin is also known as a “metal belt” as it hosts several metal deposits, besides, the Mengye potash deposit. However, the exact dates of the formation either in the Paleocene or the Cretaceous, and thus the origins of the marine, continental or mixed origins of the Mengye deposits, remain disputed. Based on the basin's evolution, materials of marine origin and/or remnant seawater should be present, but instead the salt layers of the Mengye potash deposit present typically continental lithological features. This study examines and reviews evaporative minerals, Br/Cl and I/Cl molar ratios, and isotopes of S, B, and Sr·I and I/Cl data for this area has not been previously reported. The basin's evaporative minerals are dominated by halite and sylvite. The amounts of anhydrite, chlorocalcite, langbeinite, glaserite, tachyhydrite and glauberite are small. All of these form in both marine and continental environments. The values of I and the I/Cl molar ratios of halite and sylvite are from 0.07 to 0.27 ppm, and from 0.03 to 0.11 × 10^− 6, respectively, dependent on organic substances. Br and molar Br/Cl values are from 89.08 to 555.45 ppm and from 0.06 × 10^− 3 to 0.38 × 10^− 3, respectively. All of the Br/Cl molar ratios are lower than those of seawater, and most of them are < 0.1, suggesting continental or mixed origin. Previously published δ³⁴S, δ¹¹B and ⁸⁷Sr/⁸⁶Sr values for evaporative minerals indicate a continental origin for the Mengye potash deposit. However, materials of hydrothermal origin are widely distributed in the basin and may have played an active role for the formation of the potash deposit. Thus the Mengye potash deposit could be of continental origin, with a remnant seawater trace.     

A study on A-type granites in Suzhou,China

The Suzhou granite suite is the anorogenic product, which is located on the inactive continental margin of east China. It was emplaced about 141 Ma ago, occurring as a stock with a polygonal outline on the surface, belonging to alkali potash-feldspar granites with K₂O > Na₂O, Reit’s alkali coefficient = 0.694, SiO₂ = 74.95, and Al₂O₃/(K₂O + Na₂O)mol= 1. Besides K and Na, Li and Rb are also rather high. Highlycharged metals such as Zr, Nb, REE, Y, Sn, Th, Ga and Zn are 10, or even 50 times higher than those in the ordinary granites. Halogen elements such as F and Cl are high in abundance with F = 2700 ppm and Cl = 170 ppm on average. The abundances of deep-source elements such as Ti, Al, Ca, Mg and P are relatively low, with A1₂O₃ = 12.65% and Ca + Mg < 1%. High Ga and low Al contents are typomorphically characteristic of A type granites. Biotite in the rocks is, for the most part, annite, usually filling in quartz and feldspar crystals, indicating that the crystallization of magma proceeded under relatively anhydrous condition. More than 40 kinds of accessory minerals have been identified, of which the mantle-derived mineral chrompicotite and moissanite is of great interest. Two different intrusions, the major and supplementary intrusions, can be distinguished in the granite suite. The rock-forming temperature is estimated to be 810°C, pressure 2.5 kbars, pH 8.1,¹⁸O/¹⁶O low(δ¹⁸O_WR = 6.19‰), and_fo₂= 10⁻¹⁶. The abundances of REE are high and Eu depletion is remarkable (δEu = 0.24). A variety of mineral deposits related to the Suzhou granite suite have been recognized.     

High Precision Sr‐Nd‐Hf‐Pb Isotopic Compositions of USGS Reference Material BCR‐2

The Lamont‐Doherty Earth Observatory radiogenic isotope group has been systematically measuring Sr‐Nd‐Pb‐Hf isotopes of USGS reference material BCR‐2 (Columbia River Basalt 2), as a chemical processing and instrumental quality control monitor for isotopic measurements. BCR‐2 is now a widely used geochemical inter‐laboratory reference material (RM), with its predecessor BCR‐1 no longer available. Recognising that precise and accurate data on RMs is important for ensuring analytical quality and for comparing data between different laboratories, we present a compilation of multiple digestions and analyses made on BCR‐2 during the first author's dissertation research. The best estimates of Sr, Nd and Hf isotope ratios and measurement reproducibilities, after filtering at the 2s level for outliers, were ⁸⁷Sr/⁸⁶Sr = 0.705000 ± 11 (2s, 16 ppm, n = 21, sixteen digestions, one outlier), ¹⁴³Nd/¹⁴⁴Nd = 0.512637 ± 13 (2s, 25 ppm, n = 27, thirteen digestions, one outlier) and ¹⁷⁶Hf/¹⁷⁷Hf = 0.282866 ± 11 (2s, 39 ppm, n = 25, thirteen digestions, no outliers). Mean Nd and Hf values were within error of those reported by Weis et al. (2006, 2007) in their studies of RMs; mean Sr values were just outside the 2s uncertainty range of both laboratories. Moreover, a survey of published Sr‐Nd‐Hf data shows that our results fall within the range of reported values, but with a smaller variability. Our Pb isotope results on acid leached BCR‐2 aliquots (n = 26, twelve digestions, two outliers) were ²⁰⁶Pb/²⁰⁴Pb = 18.8029 ± 10 (2s, 55 ppm), ²⁰⁷Pb/²⁰⁴Pb = 15.6239 ± 8 (2s, 52 ppm), ²⁰⁸Pb/²⁰⁴Pb = 38.8287 ± 25 (2s, 63 ppm). We confirm that unleached BCR‐2 powder is contaminated with Pb, and that sufficient leaching prior to digestion is required to achieve accurate values for the uncontaminated Pb isotopic compositions.     

丹寨汞矿卤素元素地球化学特征

丹寨汞矿是产于碳酸盐岩地层中以汞为主伴生金的浅成低温层控矿床。本文对该矿床矿石及围岩中的卤素元素分布特征进行了一定的研究。研究结果表明,（１）矿区内Ｂｒ、Ｉ的富集程度远比Ｆ、Ｃｌ高,从远矿围岩→近矿围岩→汞矿石Ｂｒ、Ｉ含量呈增加趋势,金矿石中Ｂｒ、Ｉ含量比近矿及远矿围岩含量低,且Ｉ的富集系数小于１;（２）Ｆ在金矿化岩石及近矿围岩中含量较高;（３）Ｃｌ的变化规律不甚明显,且富集系统均小于１;（４）垂     

Solar-system abundances of the elements

A new abundance table has been compiled, based on a critical review of all C1 chondrite analyses up to mid-1982. Where C1 data were inaccurate or lacking, data for other meteorite classes were used, but with allowance for fractionation among classes. In a number of cases, interelement ratios from meteorites or lunar and terrestrial rocks as well as solar wind were used to check and constrain abundances. A few elements were interpolated (Ar, Kr, Xe, Hg) or estimated from astronomical data (H, C, N, O, He, Ne).For most elements, the new abundances differ by less than 20% from those of Cameron (1982a). In 14 cases, the change is between 20 and 50% (He, Ne, Be, Br, Nb, Te, I, Xe, La, Gd, Tb, Yb, Ta and Pb) and in 5 others, it exceeds 50% (B, P, Mo, W, Hg). Some important interelement ratios ($\text{Na}\text{K}$, $\text{Se}\text{Te}$, $\text{Rb}\text{Sr}$, $\text{Kr}\text{Xe}$, $\text{La}\text{W}$, $\text{Th}\text{U}$, $\text{Pb}\text{U}$, etc.) are significantly affected by these changes.Three tests were carried out, to see how closely C1 chondrites approximate primordial solar system abundances. (1) A plot of solar vs Cl abundances shows only 7 discrepancies by more than twice the nominal error of the solar abundance: Ga, Ge, Nb, Ag, Lu, W and Os. Most or all apparently reflect errors in the solar data or f-values. (2) The major cosmochemical groups (refractories, siderophiles, volatiles, etc.) show no significant fractionation between the Sun and C1's, except possibly for a slight enrichment of volatiles in Cl's. (3) Abundances of odd-A nuclides between A = 65 and 209 show an almost perfectly smooth trend, with elemental abundances conforming to the slope defined by isotopic abundances. There is no evidence for systematic fractionation of the major cosmochemical groups from each other. Small irregularities (10–15%) show up in the Ag-Cd-In and Sm-Eu regions; the former may be due to a ~ 15% error in the Ag abundance and the latter, to a 10–20% fractionation of Eu during condensation, to contamination of C1 chondrites with interplanetary dust during regolith exposure, or to a change from s-process to r-process dominance.It appears that the new set of abundances is accurate to at least 10%, as irregularities of 5–10% are readily detectable. Accordingly, Cl chondrites seem to match primordial solar-system matter to ? 10%, with only four exceptions. Br and I are definitely and B is possibly fractionated by hydrothermal alteration, whereas Eu seems to be enriched by nebular condensation or regolith contamination.     

Volcan Popocatepetl, Mexico. Petrology, Magma Mixing, and Immediate Sources of Volatiles for the 1994-Present Eruption

Volcán Popocatépetl has been the site of voluminousdegassing accompanied by minor eruptive activity from late 1994until the time of writing (August 2002). This contribution presentspetrological investigations of magma erupted in 1997 and 1998,including major-element and volatile (S, Cl, F, and H₂O) datafrom glass inclusions and matrix glasses. Magma erupted fromPopocatépetl is a mixture of dacite (65 wt % SiO₂, two-pyroxenes+ plagioclase + Fe–Ti oxides + apatite, 3 wt % H₂O, P= 1·5 kbar, f_O2 = NNO + 0·5 log units) and basalticandesite (53 wt % SiO₂, olivine + two-pyroxenes, 3 wt % H₂O,P = 1–4 kbar). Magma mixed at 4–6 km depth in proportionsbetween 45:55 and 85:15 wt % silicic:mafic magma. The pre-eruptivevolatile content of the basaltic andesite is 1980 ppm S, 1060ppm Cl, 950 ppm F, and 3·3 wt % H₂O. The pre-eruptivevolatile content of the dacite is 130 ± 50 ppm S, 880± 70 ppm Cl, 570 ± 100 ppm F, and 2·9 ±0·2 wt % H₂O. Degassing from 0·031 km³ of eruptedmagma accounts for only 0·7 wt % of the observed SO₂emission. Circulation of magma in the volcanic conduit in thepresence of a modest bubble phase is a possible mechanism toexplain the high rates of degassing and limited magma productionat Popocatépetl. KEY WORDS: glass inclusions; igneous petrology; Mexico; Popocatépetl; volatiles