Equiv Wt Research Articles

A preliminary geological and geochemical study of the Xiangquan thallium deposit, eastern China: the world’s first thallium-only mine

Here we report the first example of a thallium-only deposit, which was discovered in the northeast margin of the Yangtze block, eastern China, in the transition zone between the Yangtze Block, North China Block and Dabie orogenic belt. Ore from the Xiangquan deposit will be mined, ore-dressed and smelted independently for thallium. The ore deposit is hosted in Lower Ordovician micrite, calcilutite and marl within the Dalongwang Mountain Xiao Mountain anticline. The ore zones are fold and fault controlled. Thallium occurs mainly in pyrite but minor amounts form as lorandite (TlAsS2) and hutchinsonite (TlFeS2). Fluid inclusion studies of two stages of fluorite intimately associated with ore-forming pyrite yielded homogenization temperatures of 120 to 220 °C with a salinity of 1.5 to 6.0 equivalent wt.% NaCl. Thallium was originally derived by hydrothermal emanations onto the sea floor and deposited in calcareous sediments. Subsequently in the Early Cretaceous (Yanshanian period) these source beds were reworked to form thallium enriched minerals in hydrothermal veins.

ANALYSIS OF EVAPORATE MOUNDS AS A COMPLEMENT TO FLUID-INCLUSION THERMOMETRIC DATA: CASE STUDIES FROM GRANITIC ENVIRONMENTS IN NOVA SCOTIA AND PERU

The bulk composition of fluid inclusions is generally determined by using the temperature of ice melting (i.e., freezing-point depression of H2O–NaCl) and relating this to the ice-melting curve in the two-component system H2O–NaCl. In reality, natural systems are more complex. Therefore, the bulk composition is referred to as equivalent wt.% NaCl to account for the presence of other, generally undetermined, cations (e.g., K, Ca, Fe, Mn, Mg). Inferences of a more complex chemical composition are generally made on the basis of the depression of the eutectic temperature for the H2O–NaCl system (–21.2°C), the other common solutes being CaCl2, MgCl2, and FeCl2. Such an approach is qualitative at best, and the inherent problem of metastability invites caution. An alternative, relatively simple and cost-effective method among the many analytical methods available, is to artificially decrepitate fluid inclusions and analyze the resulting evaporate mounds with an electron microprobe equipped with an imaging system. To illustrate the potential of the method, three granitic environments, in Nova Scotia and in Peru, were chosen, two mineralized (Sn, Cu, Zn) and one barren (tourmaline pegmatite). Standard fluid-inclusion thermometric data have been integrated with compositions determined from evaporate mounds in the same suite of samples. The following points emerge: (1) the inclusions are invariably multi-component, being dominated by Na–K–Ca, but in consistently different proportion that reflect protracted fluid:rock interaction and mixing of reservoirs; (2) the low first-melting temperatures (i.e., <–50°C) do not unequivocally indicate the presence of CaCl2 in solution; (3) high concentrations of Fe and Mn are common within the mineralized systems examined, in addition to lesser amounts of Sr, Ba, P and Zn, and (4) the two methods complement each other, together providing a much more comprehensive account of the nature of the fluid and its evolution in space and time.

Geology and Genesis of the Ta'ergou Skarn ‐ Quartz Vein Tungsten Deposit in the North Qilian Caledonian Orogenic Belt, Northwest China

Abstract. The Ta'ergou tungsten deposit in Gansu province, northwestern China, is located in the western part of the North Qilian Caledonian orogen, and consists of scheelite skarn bodies and wolframite quartz veins. The tungsten‐bearing skarn developed by the replacement of carbonate layers intercalated in the Precambrian schist and amphibolite whereas wolframite‐quartz ore veins developed along a group of fractures that cut through horizontal skarns. The Ta'ergou tungsten deposit is genetically related to the Caledonian Yeniutan granodiorite intrusion and occurs ca. 500 m wide in the exo‐contact zone 300 ∼ 500 m apart from the intrusion. The granodiorite displays a lower grade of differentiation, low content of SiO2 and high contents of mafic components.There are three types of fluid inclusions in the wolframite‐quartz vein systems, i. e. aqueous, CO2‐H2O and CO2‐rich. The homogenization temperature of aqueous inclusion ranges from 140 to 380d̀C and their salinities from 6.4 to 17.4 equivalent wt% NaCl. Laser Raman spectroscopy shows that the inclusions contain a relatively high content of CO2. The δ34S values of skarn type sulfides range from +8.1 to +12.7 per mil and those of quartz vein sulfides from +9.3 to +14.9 per mil, similar to sulfides of the granodiorite with from +6.0 to +11.7 per mil. The δ18O values of quartz are between +10.5 and +13.3 per mil and those of wolframite between +3.4 and +5.1 per mil. The δ18O water values of ore forming fluids range from +0.6 to +6.4 per mil and suggest the mixture of magmatic fluids with meteoric water formed the ore‐forming fluids.It has been proved that Precambrian strata in the west sector of North Qilian region are enriched in tungsten. We propose the strata were remelted to be tungsten‐granitoid during subduction. The polymetallic tungsten was gradually accumulated into the roof pendants of the granite intrusion by fractional crystallization and then was deposited by hydrothermal fluids during metasomatism and infilling along fractures. On the other hand, the granite intrusion also acted as “heating machine” to make hydrothermal fluids leach out the metals from Precambrian strata and these metals joined the ore‐forming hydrothermal system.

An efficient method for removal of ruthenium byproducts from olefin metathesis reactions.

[reaction: see text] Sequential treatment of the ring-closing metathesis reaction products with silica gel, activated carbon (50 equiv wt relative to the crude products), and column chromatography on silica gel efficiently removed dark brown ruthenium byproducts from the reaction mixture. After this treatment, colorless compounds could be obtained with a ruthenium level of 0.06-0.53 microg per 5 mg of product.

Fluid-inclusion Data for Vein-type Cu-Ni-PGE Footwall Ores, Sudbury Igneous Complex and Their Use in Establishing an Exploration Model for Hydrothermal PGE-enrichment Around Mafic-Ultramafic Intrusions

Cu-Ni-PGE footwall ore deposits were studied in the McCreedy East and Whistle mines along the North Range, and the Lindsley and Little Stobie mines along the South Range of the Sudbury Igneous Complex. The footwall ores in these localities differ from typical magmatic Fe-Ni-Cu-PGE deposits in the Sudbury mining camp: they have higher Cu/Ni ratios, higher PGE content, vein-like appearance and ubiquitous association of ore with hydrous silicates. Results of comparative fluid inclusion petrography and microthermometry of footwall ores indicate that high temperatures (300°C to 480°C) and heavy-metal rich saline (up to about 40 NaCl equivalent wt% salinity) fluids were associated with the formation of the PGE-rich footwall ores at moderately high pressures (around 2 kbars). However, several, possibly independent fluid circulation stages were also found at the different localities and there also are differences in detailed characteristics for ore-forming fluids especially comparing data from the North Range and the South Range. Thus, in addition to the high temperature and salinity of fluids, there are local variations in the nature of hydrothermal processes. These differences may be related to the diverse origin of fluids (magmatic, metamorphic, and formational brines) and their differing extents of interaction with the compositionally different footwall lithologies.

Electrically facilitated molecular transport. Analysis of the relative contributions of diffusion, migration, and electroosmosis to solute transport in an ion-exchange membrane.

Electrically facilitated molecular transport in an ion-exchange membrane (Nafion, 1100 equiv wt) has been studied using a scanning electrochemical microscope. The transport rates of ferrocenylmethyltrimethylammonium (a cation), acetaminophen (a neutral molecule), and ascorbate (an anion) through approximately 120-micron-thick membranes were measured as a function of the iontophoretic current passed across the membrane (-1.0 to +1.0 A/cm2). Transport rates were analyzed by employing the Nernst-Planck equation, modified to account for electric field-driven convective transport. Excellent agreement between experimental and theoretical values of the molecular flux was obtained using a single fitting parameter for each molecule (electroosmotic drag coefficient). The electroosmotic velocity of the neutral molecule, acetaminophen, was shown to be a factor of approximately 500 larger than that of the cation ferrocenylmethyltrimethylammonium, a consequence of the electrostatic interaction of the cation with the negatively charged pore walls of the ion-exchange membrane. Electroosmotic transport of ascorbate occurred at a negligible rate due to repulsion of the anion by the cation-selective membrane. These results suggest that electroosmotic velocities of solute molecules are determined by specific chemical interactions of the permeant and membrane and may be very different from the average solution velocity. The efficiency of electroosmotic transport was also shown to be a function of the membrane thickness, in addition to membrane/solute interactions.

Mineralogical and fluid inclusion studies of low-sulfidation epithermal veins at Osilo (Sardinia), Italy

Several precious metal-bearing, low sulfidation epithermal veins occur in the rolling topography of the Osilo area, northern Sardinia. The Sa Pala de Sa Fae and the Sa Pedra Bianca veins were subject to intense diamond drilling exploration in the mid 1990 s. The veins extend for 1–3 km, dip steeply, and range from 1 to 10 m in width. High K-calc-alkaline volcanic deposits containing plagioclase phenocrysts (along with lesser pyroxene, amphibole, magnetite, olivine and sanidine) form the main host rocks. Gold grades in drill intersections range from 50 m from the vein, the assemblage albite + Fe-chlorite + illite + pyrite (± montmorillonite ± calcite ± K-feldspar) prevails regionally, and its formation is attributed to minor metasomatism of the country rock involving the addition of water, carbon dioxide and hydrogen sulfide. At distances <10 m from the vein, the assemblage quartz + K-feldspar + pyrite ± illite dominates, forming an alteration envelope that cross cuts regional alteration. Quartz and K-feldspar increase in abundance towards the vein. Quartz is the main vein mineral, and it displays a range of morphologies and textures including crustiform colloform banding, quartz pseudomorphs of platy calcite, breccias and coarse euhedral crystals. Electrum and argentite which are the main gold and silver minerals deposited during the early stages of vein mineralization with rhomb-shaped crystals of K-feldspar (adularia). Pyrite, plus lesser marcasite, arsenopyrite, stibnite and sphalerite, are the other sulfide phases in veins. Kaolinite ± halloysite ± jarosite form a late assemblage overprinting earlier hydrothermal alteration. It is mostly restricted to shallow depths of a few meters, except near veins. Most of this assemblage likely formed from weathering and oxidation of sulfides. Microthermometric measurements were made on quartz-hosted, two-phase (liquid + vapor) inclusions, containing ∼75% liquid; mean homogenization temperatures (∼750 measurements) range from 220 to 250 °C, and ice-melting temperatures (∼550 measurements) range from 0.0 to −2.3 °C. The presence of co-existing vapor-rich and liquid rich inclusions, with quartz pseudomorphs of platy calcite, indicate that boiling conditions existed. Slight vapor-bubble expansion of a few fluid inclusions subjected to crushing experiments indicates inclusion fluids contained variable but low concentrations of dissolved gas. This study shows that gold-silver mineralization formed in subvertical channels from ascending solutions at 250 °C at around 300 to 450 m below the paleo-water table in a typical low-sulfidation epithermal environment. Hydrothermal solutions that produced vein mineralization and related alteration were dilute (<4.1 equivalent wt.% NaCl and <4 wt.% CO2), near neutral pH, reduced and, at times, boiling.

Sol–gel derived pure and palladium activated tin oxide films for gas-sensing applications

Pure and Pd activated SnO 2 films on Corning 7059 substrates were prepared by the sol–gel dip coating method and used as active material in gas-sensing devices. SnCl 4 and Pd(CH 3COO) 2 were used for tin and palladium sources. The SnO 2 sol was prepared from 1:3:9:4 molar ratios of SnCl 4:H 2O:C 3 n H 7OH:C 4 i H 9OH. The 5 equivalent wt% PdO-95% SnO 2 sol was prepared by mixing the required amount of Pd acetate to the pure SnO 2 sol. The dried (110°C/0.5 h) films were heat-treated in air at 600°C for 1 h. Pure SnO 2 films showed ethanol gas sensing characteristics similar to most of the commercially available tin oxide sensors. An improvement in the sensitivity towards ethanol gas at relatively low temperature was observed in case of Pd activated SnO 2 films. The improvement of sensing properties of Pd activated films was due to high surface roughness/surface area, oxygen vacancies and presence of PdO microcrystallites.

Fluid inclusion characteristics of mesothermal gold deposits in the Xiaoqinling district, Shaanxi and Henan Provinces, People's Republic of China

Fluid inclusions were studied in quartz samples from early (stage I) gold-poor quartz veins and later (stage II) gold- and sulphide-rich quartz veins from the Wenyu, Dongchuang, Qiangma, and Guijiayu mesothermal gold deposits in the Xiaoqinling district, China. Fluid inclusion petrography, microthermometry, and bulk gas analyses show remarkably consistent fluid composition in all studied deposits. Primary inclusions in quartz samples are dominated by mixed CO2-H2O inclusions, which have a wide range in CO2 content and coexist with lesser primary CO2-rich and aqueous inclusions. In addition, a few secondary aqueous inclusions are found along late-healed fractures. Microthermometry and bulk gas analyses suggest hydrothermal fluids with typically 15–30 mol% CO2 in stage I inclusions and 10–20 mol% CO2 in stage II inclusions. Estimates of fluid salinity decrease from 7.4–9.2 equivalent wt.% NaCl to 5.7–7.4 equivalent wt.% NaCl between stage I and II. Primary aqueous inclusions in both stages show consistent salinity with, but slightly lower Th total than, their coexistent CO2-H2O inclusions. The coexisting CO2-rich, CO2-H2O, and primary aqueous inclusions in both stage I and II quartz are interpreted to have been trapped during unmixing of a homogeneous CO2-H2O parent fluid. The homogenisation temperatures of the primary aqueous inclusions give an estimate of trapping temperature of the fluids. Trapping conditions are typically 300–370 °C and 2.2 kbar for stage I fluids and 250–320 °C and 1.6 kbar for stage II fluids. The CO2-H2O stage I and II fluids are probably from a magmatic source, most likely devolatilizing Cretaceous Yanshanian granitoids. The study demonstrates that gold is largely deposited as pressures and temperatures fall accompanying fluid immiscibility in stage II veins.

Effect of streptozotocin-induced diabetes on rat brain sulfonylurea binding sites

Both high and low affinity sulfonylurea receptors (SURs) reside on glucose responsive neurons where they influence cell firing and neurotransmitter release via the adenosinetriphosphate (ATP)-sensitive K + (katp) channel. Here, the effect of diabetes on [ 3H] glyburide binding to SURs was assessed in male obesity-resistant Sprague-Dawley rats rendered diabetic with streptozotocin (65 mg/kg, i.p.). Additional streptozotocin-treated rats were supplemented with insulin (1.5 U/kg/ day). Streptozotocin reduced plasma insulin to 13% of control associated with hyperglycemia (25.3 ± 1.7 mmol/1), while insulin lowered plasma glucose (9.56 ± 1.78 mmol/l) to near control levels (7.65 ± 0.22 mmol/l). Over 7 days, all streptozotocin-treated rats lost 12% of their initial body wt. while controls gained 1%. Despite equivalent wt. loss, streptozotocin-induced diabetes selectively increased high affinity [ 3H] glyburide binding in the hypothalamic dorsomedial nuclei (DMN) and ventromedial nuclei (VMN) and lateral area (LH). This was prevented by insulin injections. Low affinity binding was similarly increased in the DMN and VMN, as well as two amygdalar subnuclei but decreased in the substantia nigra, pars compacta. Insulin fully prevented these changes only in the DMN and one amygdalar nucleus and the substantia nigra. Therefore, binding to (SURs) appears to be generally upregulated in the face of hypoinsulinemia with hyperglycemia and this is prevented by insulin treatment. These and other data suggest that this combination of abnormalities in diabetes should have an adverse effect on the glucose sensing capacity of the brain.

Solute chemistry of inclusion fluids from sparry dolomites and magnesites in Middle Cambrian carbonate rocks of the southern Canadian Rocky Mountains

Middle Cambrian carbonate rocks of the southern Canadian Rocky Mountains are host to widespread units of white, sparry, hydrothermal, replacement, and open-space filling dolomite. Contained within the dolomites are occurrences of talc and Mississippi Valley type Pb-Zn (the former Kicking Horse and Monarch mines) mineralization and economic concentrations of magnesite (Mount Brussilof mine). Results of studies of solute chemistry of saline (18-25 equivalent wt.% NaCl) inclusion fluids reveal distinctly low Na/Br (55-220) and Cl/Br (95-340) values. These values indicate that the brines which formed the dolomite originated from seawater that had deposited large amounts of halite in an evaporitic environment. Low I/Br ratios for the dolomite-magnesite inclusion fluids are consistent with their derivation from seawater and contrast sharply with the high I/Br ratios of Laramide-age fluids, which formed veins throughout the Rocky Mountains. Variations in F/Br ratios between texturally early and late magnesites indicate the involvement of a second fluid in the formation of the late magnesites. Results of the study of solute chemistry of inclusion fluids from hydrothermal dolomites, magnesites, and associated mineralization are consistent with a model of the pre-Laramide formation of these materials from seawater that had undergone extensive evaporation and halite deposition. Distinct differences in I/Br, total salinity, and delta D values between the dolomite-magnesite depositing fluids and Laramide-age vein-forming fluids clearly indicate the lack of the involvement of Laramide-age fluids in the genesis of the dolomites, magnesites, and associated mineralization.

Holocene stromatolites and microbial laminites associated with lenticular gypsum in a marine‐dominated environment, Ras El Shetan area, Gulf of Aqaba, Egypt

Field and petrographic investigations of Holocene evaporites in the Ras El Shetan area, Gulf of Aqaba, Egypt, indicate the presence of microbial mats either in the form of laminites or stromatolites. The morphology of microbial mats and gypsum crystal size characterize the following lithofacies: (1) slump‐stromatolitic gypsarenite, (2) random gypsrudite, (3) stromatolitic gypsarenite, and (4) microbially laminated gypsrudite. These evaporite lithofacies are formed above pre‐evaporitic mudstones rich in disrupted cyanobacterial filaments, burrows and cerithid gastropods. The morphology of the gypsum crystals is mainly lenticular, indicating enrichment of dissolved organic compounds in the depositional environment. The difference in size of the lenticular gypsum crystals is related to minor changes in salinity and temperature of the parent brine. Fluid inclusions in gypsum crystals indicate their formation at low temperature (&lt;50°C) in a seawater sourced brine that evaporated to gypsum saturation or higher. The brine salinities range from 10·62 to 12·99 equivalent wt% NaCl, and the brine densities range from 1·08 to 1·11 g/cm3. The change in morphology of the microbial mats (stromatolites and laminites) is related mainly to changes in water depth, from a very shallow salina to a coastal sabkha. Lenticular gypsum nucleated displacively in the microbial mats from saline, oxygenated groundwater that seeped from the sea through a barrier.

Microthermometric Study of Silicate Melt Inclusions in Variscan Granites from SE Germany: Volatile Contents and Entrapment Conditions

Melt inclusions in granitic rocks are generally crystalline and must be homogenized to glass before analysis. We employ a simple kinetic technique with microthermometry to estimate total volatile contents and P–T conditions of trapping of the melts from their homogenization behaviour. This information complements chemical data from microprobe or ion probe analysis, and can be obtained from inclusions too small for direct analysis. We present here values for volatile contents (as equivalent wt % H2O), trapping temperatures and trapping pressures derived from studies of melt inclusions in some Variscan granites of the Erzebirge, Fichtelgebirge and Oberpfalz, Germany. The volatile concentrations range from 3 to 10 equiv. wt % H2O. Microprobe analysis shows that the most volatile-rich inclusions contain up to 8 wt % F. Estimates of trapping pressures ad temperatures suggest that crystallization began at an emplacement level of 3–6.5 km near 700°C with ‘normal’ biotite and two-mica granites, and ended with topaz–albite granite (∼650°C) and pegmatitic phases down to 520°C. This wide range of trapping temperatures and volatile contents is a general feature of melt inclusions in granites. Many of the granites studied are highly evolved geochemically, but the extreme volatile enrichment typical for these also occurs locally in the ‘unspecialized’ granites.

Titanium Nitride/Carbon Coatings on Graphite Fibers

Titanium nitride (TiN) coatings were applied to graphite‐fiber tows by dip coating desized (900°C in nitrogen) fibers in hexane solutions containing 0.5, 1, or 2 equivalent wt% TiN as the precursor, [Ti(NMe2)x(μ–NCHMe2)4−2x]n. The precursor was characterized by thermogravimetric analysis (TGA), chemical analysis, and nuclear magnetic resonance. Bulk samples of precursor were heated to selected temperatures in argon. Based on microstructural and chemical analyses, two pyrolysis temperatures— 900°C and 1200°C— were selected for more‐detailed studies predicated on fiber oxidation‐resistance behavior. At 900°C, the bulk material exhibited a powder X‐ray diffractometry (XRD) pattern consistent with microcrystalline TiN, although some free carbon remained. XRD analysis of the samples pyrolyzed to 1200°C indicated a higher degree of crystallinity and some carbon incorporation in the TiN lattice; e.g., a TiCN solid solution forms, as supported by chemical and TGA analyses. Fibers coated with precursor were heated at a rate of 10°C/min in argon to selected temperatures, followed by a hold for 1 h, and the resulting coatings were characterized by scanning electron microscopy, X‐ray photoemission spectroscopy, and oxidation resistance at 700°C for 2 h in air. Coated fibers pyrolyzed to 900° and 1200°C were studied in detail. Fibers heat treated at 900°C exhibited better oxidation resistance than fibers pretreated at 1200°C, as determined by mass loss. Uncoated fiber tows fully oxidized after 80 min. The oxidation‐resistance studies on fiber tows pretreated at 900°C and coated with 0.5, 1, and 2 equivalent wt% TiN indicated that the sample with a coating of 1 wt%, with thicknesses of 0.1–0.2 μm, was the most stable. The coatings of 0.5 equivalent wt% TiN were irregular, whereas the coatings of 2 equivalent wt% TiN exhibited process‐related cracking, leading to poor oxidation resistance.

Curing characteristics ofo-cresol novolac epoxy resin modified by bismaleimide

Curing characteristics of o-cresol novolac epoxy resin modified by 4,4-diaminodiphenylmethane bismaleimide (DDM-BMI) using FTIR were investigated and the glass transition temperature was measured. With the addition of DDM as hardener, the relative curing reaction conversion of DDM-BMI increased with equivalent weight ratio [R1 = (equiv wt summation of epoxy and DDM-BMI)/equiv wt of DDM] and weight ratio of epoxy and DDM-BMI (R2 = wt of epoxy resin/wt of DDM-BMI). Using phenol novolac resin (PN) as hardener, the curing reaction conversion of DDM-BMI was hardly changed, but the variation of that in the epoxy resin was observed with R2 change. © 1996 John Wiley & Sons, Inc.

Variation in Salinity Tolerance in Sunflower (Helianthus annum L.)

AbstractForty‐five accessions of sunflower collected from different countries were screened for salinity tolerance after 2 weeks growth in sand culture salinized with 150 meq l−1 of NaCl2+ CaCl2 (1:1 ratio equivalent wt. basis) in half strength Hoagland's nutrient solution. The results for plant biomass of 45 accessions show that there was considerable variation in salinity tolerance.In a further greenhouse experiment, the salinity tolerance of three tolerant (HO‐1, Predovik, Euroflor) and two sensitive (SMH‐24, 9UO‐985) lines (selected on the basis of their performance in the seedling experiment) was assessed at the adult stage to evaluate the consistency of salinity tolerance at different growth stages. All three salt tolerant accessions produced significantly greater plant biomass, seed yield and seed oil content than the salt sensitive accessions. The tolerant accessions accumulated less Cl− and more K+ in the leaves under saline conditions compared with the salt sensitive accessions. The salt tolerant accessions also maintained relatively high leaf K:Na ratio and K+ versus Na+ selectivity. Although statistically nonsignificant, all three tolerant accessions had greater soluble carbohydrates, soluble proteins, total free amino acids and proline in the leaves than the sensitive accessions. A field trial conducted in a salt‐affected field confirmed the greenhouse results of the selected accessions.This study shows that salinity tolerance of sunflower does not vary with stage of plant cycle, so selection for increased salt tolerance can be carried out at the initial growth stage. Secondly, it is found that there is great variation of salt tolerance in sunflower. Low uptake of Cl−, high uptake of K+, and maintenance of high K:Na ratios and K+ versus Na+ selectivity in the leaves and possibly the accumulation of organic osmotica such as soluble carbohydrates, soluble proteins, proline and free amino acids seem to be the important components of salt tolerance in sunflower.

Mississippi Valley-type Pb-Zn mineralization in eastern Belgium: Indications for gravity-driven flow

Mississippi Valley-type deposits are widespread in Carboniferous strata in eastern Belgium. Five successive Fe-rich, fracture-filling calcite generations have been recognized in the veins containing the Pb-Zn mineralization of Bleiberg. Fluid-inclusion evidence indicates that all the calcites formed from fluids with salinities between 16.0 and 23.1 equivalent wt% NaCl. The trapping temperature of the fluid inclusions decreases from ∼125 °C in the first two calcite generations to ≤50 °C in the last two vein cements. The δ 13 C values of the calcites vary between -0.1‰ and -8.3‰ relative to PDB (Peedee belemnite). The oxygen isotopic composition of the ambient fluids, calculated from the trapping temperature and the isotopic composition of the calcites, varies between -5.2‰ and +7.6‰ relative to SMOW (standard mean ocean water). The low δ 13 C values of the calcites are explained by the contribution of 12 C from CO 2 released during the oxidation of organic matter in the upper Carboniferous shales and the coupled reduction of sulfate in the mineralizing brine. The highly variable oxygen isotopic composition of the ambient fluids, the low δ 18 C value of the water from which one calcite cement precipitated, and the intense water-rock interaction necessary to leach metals indicate that the original fluids had a low δ 18 C, and that those fluids became enriched in 18 O by water-rock interaction. Waters with such low δ 18 C, values must have had a meteoric origin. Flow of these waters into the deeper subsurface was likely gravity driven and took place from the uplifted parts of the Variscan orogen toward the foreland basin.

Paleohydrogeology of the Canadian Rockies and origins of brines, Pb-Zn deposits and dolomitization in the Western Canada Sedimentary Basin

Results of stable isotopic and fluid-inclusion studies of Cambrian carbonate units in the southern Canadian Rockies indicate that, during the Late Devonian or Early Mississippian, a warm brine migrated from miogeoclinal shales in the western part of the Western Canada Sedimentary Basin into the eastern carbonate sequences. This fluid had a temperature of 150 ±25 °C, salinity values of 20 to 25 equivalent wt% NaCl, and isotopic values of δ 18 O = -7‰ to 0‰,δ 13 C = -1‰ ±2‰, δD = -70‰ ±19‰, and 87 Sr/ 86 Sr >0.710. The fluids formed large bodies of coarse, sparry dolomite, as well as Pb-Zn, magnesite and talc mineralizations in the Cambrian units. It is probable that this event was also responsible for the development of Pb-Zn mineralization (specifically Pine Point) in the Devonian units, as well as a component of the present-day basinal brines in the basin.

A fluid inclusion and light element stable isotope study of the gold-bearing quartz vein system, Falun, Sweden

The Falun gold quartz vein mineralization is located ca 230 km NW of Stockholm, Sweden, within the Early Proterozoic volcano-sedimentary sequence of Bergslagen. The mineralization consists of a system with subparallel quartz veins that crosscut the alteration zone to the Falun massive sulphide deposit. Early barren and late gold-bearing quartz veins follow tectonic structures postdating the formation of the massive sulphide ore. Both generations of veins are epigenetic to the massive sulphide ore and were formed by hydrothermal processes. Fluid inclusion study of the gold-bearing quartz veins indicates a low-moderately saline fluid (0.3 to 17.4 equiv wt% NaCl). Heterogeneous trapping is indicated by coexisting inclusions showing a variable CO2 content from 100% CO2 ± CH4 to 100% aqueous fluid. Temperatures of total homogenization also show a wide spread from 116–350°C with a slightly bimodal distribution with peaks at ca 180°C and 280°C. MeasuredδD values — 69 to — 63%0 (SMOW), of inclusion fluid and calculatedδ18O values of hydrothermal fluids — 7.5 to — 1.4%0 (SMOW), strongly suggest a meteoric origin for the fluids. The quite consistentδD values and the range inδ18O values indicate that major water-rock interaction led to the evolution inδ18O of the hydrothermal fluids.

Metasomatism during subduction: products and possible paths in the Catalina Schist, California

On Santa Catalina Island, southern California, lawsonite-albite to amphibolite facies metasedimentary, metamafic, and metaultramafic rocks show veining and chemical alteration that reflect fluid flow and mass transfer at 15 to 45 km depths in an Early Cretaceous subduction zone. In many exposures, multiple generations of cross-cutting syn- and post-kinematic veins record fluid transport and metasomatism during various stages of prograde metamorphism and uplift. Mineralogy and whole-rock compositions demonstrate chemical redistribution, especially of Si, Al, and alkali elements (Na, K), but also of many trace elements, particularly B and LILE (Rb, Cs, Sr, and Ba). Evidence exists for mass transfer, at both local and larger scales, via mechanical mixing, diffusional, and fluid-mediated transfer processes. Highest-grade, amphibolite facies rocks contain feldspar + quartz ± mica ± amphibole leucosomes and pegmatites attributed to migmatization; the leucosomes and pegmatites reflect high- P T mass transfer in felsic silicate liquids. Veining and replacement in blueschist grade rocks comprise three contrasting types of assemblages: (1) silica-saturated (quartz-rich), (2) potassic (white-mica ± quartz-rich), and (3) sodic and silica-undersaturated (albite/Na-amphibole-rich, quartz-absent). Evidence for silicification and alkali exchange also occurs in greenschist and amphibolite facies units. In all units, the evidence for metasomatism (e.g., veins; stable isotope homogenization; rinds on blocks) is particularly abundant in melange zones, in which melange matrix compositions resulting from mechanical mixtures of mafic, ultramafic, and sedimentary rocks were shifted by metasomatic additions and subtractions during melange formation. Geochemical evidence (particularly stable isotope data) indicates that the blueschist, greenschist, and amphibolite units exchanged with fluids of similar compositions. The diverse metasomatic features in the Catalina Schist provide evidence regarding fluid sources and paths. Based on the stable isotope data, the H 2O-rich, low-salinity (∼ 1 to 2 equivalent wt. % NaCl), C/1bO/1bH/1bS/1bN fluids are believed to have been derived from low-grade, largely sedimentary parts of the subduction zone (analogs for fluid sources are the low-grade units). Metasomatic changes could be driven by flow across boundaries between contrasting lithologies and by variations in pressure and temperature along the fluid flow paths. Simple predictions of mass changes along different P- T paths suggest that both mechanisms could be effective at producing the range of observed features, even though the required equilibrium constants are only poorly estimated at the relevant P- T conditions. Decreasing T and P favors fixing of K, Si, C, and H in rocks, whereas increasing T (± moderately decreasing P) should fix Na but leach most other components. The Si-rich, K ± Si-rich, and Na-rich/Si-poor assemblages are thus consistent with differing fluid P- T flow paths. Regular differences are expected in silica precipitation/dissolution, alkali exchange, and hydrogen-alkali exchange reactions, among others. Silica ± carbonate addition, consistent with the majority of veins observed, is likely the consequence of cooling ± decompression whereas sodic (± silica-undersaturated) assemblages would be expected for rarer, but geologically plausible up- T fluid flow paths. A composite fluid flow path, first up-grade, then down P and T. is indicated for the silica addition to the largely ultramafic amphibolite-facies melange. Although mass balance and physical constraints appear to preclude pervasive major element metasomatism on large scales, focussing of fluids would likely produce pervasive changes in significant volumes (e.g., up to km-scale melange zones). Vein mineralogy would record the paths even at small fluxes. Study of the Catalina Schist demonstrates the significance of metasomatism at all scales, but indicates that large-scale changes in vein mineralogy and bulk composition are in some cases attributable to fluid flow over large distances. Comparison with other areas and elementary theoretical considerations suggest that these processes may be widely developed and that their petrographic and geochemical effects potentially give insight into the dynamics of subduction zones.