Geochemistry of ground ice,saline groundwater,and brines in the cryoartesian basins of the northeastern Siberian Platform

We present results of a comprehensive study of ground ice, saline waters, and brines in the cryoartesian basins of the northeastern Siberian Platform. The composition of major geochemical types of ground ice is considered. The specifics of the hydrogeochemical zonation of the cryoartesian basins are the regional distribution of chloride saline waters and brines. Study of stable isotopes (¹⁸O, D, ³⁷Cl, ⁸¹Br, and ⁸⁷Sr/⁸⁶Sr) led us to the conclusion that the chloride brines resulted either from the leaching of halogen rocks or from the metamorphism of bittern connate water. The drainage brine reserves (hydromineral resources) of the Udachnaya kimberlite pipe in the Olenek cryoartesian basin are assessed.     

Concentrated brines of Siberian Platform and their counterparts in Asia,Europe, Africa and America

The brines, found throughout the world, occupy the interior parts of intermontane basins at depths between 400 and 3000 m. They exhibit the entire range of concentration, through twophase salt water systems, and are found in rocks representing every interval of geologic time Brines with high calcium chloride concentrations are restricted to those cross-sections which include abundant sulfates.     

Isotopic composition of oil-field brines from Kettleman North Dome,California, and their geologic implications

Deuterium and O¹⁸ analyses were made on 25 formation-water samples from Miocene (Temblor Formation) and Eocene (McAdams Formation) reservoir rocks at Kettleman North Dome oil field, California, and on three surface water samples from Reef Ridge located about three miles to the west of the field. The δO¹⁸ values obtained generally increase with depth and most probably are due to temperature controlled exchange reactions with carbonate cement and dissolved carbonate species. The δD values obtained seem to be controlled primarily by the membrane behavior of shales modifying the assumed original values. The contribution of isotopic exchange between water and clays cannot be evaluated at present.The isotopic data support the conclusions based on a detailed study of geology, hydrodynamics, and formation water geochemistry (Kharaka, 1971) which indicate that:1. The Temblor Formation waters are probably meteoric in origin concentrated chemically and isotopically by shale membranes, and 2. The McAdams Formation waters were most probably obtained by squeezing the original interstitial marine connate waters of deposition from the underlying Mesozoic sediments.     

B, Sr, O and H Isotopic Compositions of Formation Waters from the Bachu Bulge in the Tarim Basin

In order to elucidate the origin and migration of basinal brines in the Bachu Bulge, Tarim Basin, we have carried out analyses on chemical composition, and boron, hydrogen and oxygen isotopes of formation waters together with the XRD of clay minerals from the Paleozoic strata. The waters show Ca, B, Li and Sr enrichment and SO4 depletion in the Carboniferous and Ordovician and K enrichment in part of the Ordovician relative to seawater. The relationship between δD and δ^18O shows that all the data of the waters decline towards the Global Meteoric Water Line with the intersection of them close to the present-day local meteoric water, suggesting that modern meteoric water has mixed with evaporated seawater. The ^87Sr/^86Sr ratios range from 0.7090 to 0.7011, significantly higher than those of the contemporary seawater. The δ^11B values range from ＋19.7 to ＋32.3‰, showing a decrease with the depth and B concentrations. The results suggest that isotopically distinct B and Sr were derived from external sources. However, since the percentages of illite are shown to increase with depth among clay minerals in the study area, i.e., illite is due to precipitation rather than leaching during deeper burial, it is unlikely for illite to have contributed a significant amount of B to the waters. Thus, B with low δ^11B values is interpreted to have been added mainly from thermal degradation of kerogen or the basalts in the Cambrian and Lower Ordovician.     

Zur Kristallstruktur des Strontiumhydroxyd-Oktohydrat,Sr(OH)2.8H2O

Ohne ZusammenfassungMit 3 Textabbildungen.     

Isotopic (Sr,Nd, O) systematics of the high Sr-Ba Late Miocene granitoid intrusions from the Caucasian Mineral Waters region

This paper is dedicated to the interpretation of isotope-geochemical data on high Sr-Ba granitoids exemplified by their typical representatives—Late Miocene laccoliths of the Caucasian Mineral Waters (CMW). These massifs are made up of amphibole granites, granosyenites, syenites, and leucogranites, which show particular behavior of Sr, Nd, and O isotope systems. The syenites and granosyenites are characterized by δ¹⁸O variations from 8 to 10‰. As compared to them, the amphibole granites have lowered (up to 7‰), while leucogranites, elevated (up to 12.5–13.7‰) oxygen isotope compositions. The (⁸⁷Sr/⁸⁶Sr)_8.3 ratio in the granitoids accounts for 0.7083–0.7086, whereas σ_Nd(T) varies from −4.2 to −2.1.     

Hydration properties of bentonites from Cabo de Gata (SE, Spain). Isotopic study (O/O; H/H) of the hydration water

The aim of this study is to determine the isotopic composition (δ¹⁸O and δ²H) of interstitial water in bentonites. The study had been carried out from adsorbed vapour in homoionic bentonites. We have worked with the fraction <20 μm of a bentonite from Serrata de Níjar (Almería, Spain). Homoionic sodium and calcium bentonites were prepared as well as variable quantities of exchangeable Na/Ca (75Ca/25Na; 50Ca/50Na; 25Ca/75Na), by mixing pure sodium and calcium suspensions in the appropriate quantities. To carry out the hydration of the samples, every one of them was previously dried at 300 °C overnight, they were subjected to controlled saturation conditions in an atmosphere of different relative humidity and at a constant temperature of 20 °C, until equilibrium was achieved. The different vapour pressures were: P/P_o = 0.05; P/P_o = 0.078; P/P_o = 0.15; P/P_o = 0.32; P/P_o = 0.45; P/P_o = 0.63; P/P_o = 0.8; P/P_o = 1, obtained from the saturated solutions of different salts or sulphuric acid.The saturation water was extracted for isotopic analysis from an aliquot of a saturated sample. The technique used was vacuum extraction based on a modification of the one described by Araguás-Araguás et al. (1995).The differentiation between the isotopes of ¹⁸O and ²H from interstitial water in the bentonite samples, depending on the different relative humidity, may affect the ions diffusion in the interstitial solutions, since in those from low relative humidities, there could be a higher diffusion velocity as they are formed by molecules of light isotopes, versus interstitial solutions from higher relative humidities or those near saturation. This fact should be taken into account in studies on cation and solute transport from these solutions inside bentonite, even though it is important to continue studying and corroborating it with a larger number of solutions isotopically marked.     

Multi-proxy approach (H/H, O/O, C/C and Sr/Sr) for the evolution of carbonate-rich groundwater in basalt dominated aquifer of Axum area, northern Ethiopia

Isotopic and chemical composition of groundwater from wells and springs, and surface water from the basalt-dominated Axum area (northern Ethiopia) provides evidence for the origin of water and dissolved species. Shallow (depth < 40 m) and deep groundwater are distinguished by both chemical and isotopic composition. Deep groundwater is significantly enriched in dissolved inorganic carbon up to 40 mmol l⁻¹ and in concentrations of Ca²⁺, Mg²⁺, Na⁺ and Si(OH)₄ compared to the shallow type.The δ²H and δ¹⁸O values of all solutions clearly indicate meteoric origin. Shifts from the local meteoric water line are attributed to evaporation of surface and spring water, and to strong water–rock interaction. The δ¹³C_DIC values of shallow groundwater between −12 and −7‰ (VPDB) display the uptake of CO₂ from local soil horizons, whereas δ¹³C_DIC of deep groundwater ranges from −5 to +1‰. Considering open system conditions with respect to gaseous CO₂, δ¹³C_DIC = +1‰ of the deep groundwater with highest PCO₂ = 10^−0.9 atm yields δ¹³C_CO2(gas) ≈ −5‰, which is close to the stable carbon isotopic composition of magmatic CO₂. Accordingly, stable carbon isotope ratios within the above range are referred to individual proportions of CO₂ from soil and magmatic origin. The uptake of magmatic CO₂ results in elevated cations and Si(OH)₄ concentrations. Weathering of local basalts is documented by ⁸⁷Sr/⁸⁶Sr ratios of the groundwater from 0.7038 to 0.7059. Highest values indicate Sr release from the basement rocks. Besides weathering of silicates, neoformation of solids has to be considered, which results in the formation of, e.g., kaolinite and montmorillonite. In several solutions supersaturation with respect to calcite is reached by outgassing of CO₂ from the solution leading to secondary calcite formation.     

Sr,Nd and O Isotopic Studies on the Genesis of the Huashan Granite Complex1

Abstract Systematical Sr, Nd and O isotopic studies were made on the Huashan granite complex in Guangxi. In combination with the studies of geological, petrological and geochemical data, it is believed that the complex consists of granites of three stages, with different geneses and different source materials. They are not the products of differentiation and evolution of one single consanguineous magma. Granites of the 1st stage are of the Indosinian syntectic type or I type, also derived from a mixed mantle-crustal source. Those of the 2nd stage are of the early Yanshanian syntectic type or I type, also derived from a mixed mantle-crustal source, and those of the 3rd stage are of the late Yanshanian transformed type or S type, derived from a crustal source.     

Magmatic Nature of Mineralizing Fluids in the Solnechnoye Sn Deposit (Russia) Deduced from Isotopic (H,O) Compositions of Tourmaline

In this paper, we present new isotopic (H, O) data of fluids in tourmalines from the large Sn deposit at Solnechnoye (Far East Russia). These data indicate that the deposit formed by fluid‐rock interactions in a hydrothermal system where the mineralizing fluid was mainly magmatic and to a lesser extent meteoric. This is in agreement with a magmatic fluid model. Our interpretation of the new isotopic data is consistent with earlier findings of the studies on fluid‐rock interactions that magmatic fluids form larger Sn deposits than exogenic fluids. We propose that isotopic (H, O) data of fluids in tourmaline, rather than those in quartz, muscovite, or chlorite, support robust interpretation on the nature of mineralizing fluids associated with Sn deposits.     

Nd, Sr and O Isotopic Study on Spilite-Keratophyre in Xiqiu,,Zhejiang Province, China

Nd, Sr and O isotopic study on the spilite-keratophyre sequence in Xiqiu shows that its ∈_(Nd) values are inthe range of 4.02-5.26, and its ∈_(Sr) values, +1.4-2.6. According to the points of these data in the ∈_(Nd)-T,∈_(Sr)-T and ∈_(Nd)-∈_(Sr) diagrams, the spilite-keratophyre is interpreted as being slightly contaminated by crustalmaterials. Its δ~(18)O values are 3.9-5.0‰. The depletion of ~(18)O in the rocks resulted from the influence ofseawater hydrothermal alteration during or soon after the rock formation. Based on the isotopic characteristicsand available geochemical data, it is believed that the spilite-keratophyre was formed in the well-developedisland-arc environment during the Late Proterozoic subduction of the palaeo-Pacific plate beneath thesoutheastern margin of the Yangtze massif.     

Geochemical and Isotopic (O, Nd, Pb and Sr) Constraints on A-type Granite Petrogenesis Based on the Topsails Igneous Suite, Newfoundland Appalachians

The voluminous, bimodal, Silurian Topsails igneous suite consistsmainly of ‘A-type’ peralkaline to slightly peraluminous,hypersohnis to subsolvus granites with subordinate syenite,onzonite and diabase, plus consanguineous basalts and highsilicarhyolites. _Nd(T) values from the suite range from –1.5to +5.4; most granitoid components exhibit positive _Nd(T) values(+1.1 to +3.9). Granitoid initial ⁸⁷Sr/⁸⁶Sr and most ¹⁸ O valuesare in the range expected for rocks derived from mantle-likeprotoliths (0.701–0.706 and +6 to +80/). Restricted ²⁰⁷Pb/²⁰⁴Pbvariation is accompanied by significant dispersion of ²⁰⁶Pb/²⁰⁴Pband ²⁰⁸Pb/²⁰⁴Pb. Superficially, petrogenesis by either direct(via fractionation from basalt) or indirect (via melting ofjuvenile crust) derivation from mantle sources appears plausible.Remelting of the granulitic protolith of Ordovician are-typegranitoids can be ruled out, because these rocks exhibit negative_Nd(T) and a large range in ²⁰⁷Pb/²⁰⁴Pb. Geochemical and isotopicrelationships are most compatible with remelting of hybridizedlithospheric mantle generated during arc-continent collision.A genetic link is suggested among collision-related delaminationor slab break-off events and emplacement of ‘post-erogenic’granite suites. A-type granites may recycle previously subductedcontinental material, and help explain the mass balance notedfor modern arcs. However, they need not represent net, new,crustal growth. KEY WORDS: A-type granites; juvenile crust; isotopes; Newfoundland ^*Telephone: (613) 995-4972. Fax: (613) 995-7997. e-mail: jwhalen{at}gsc.emr.ca     

C and Sr isotope chemostratigraphy of Vendian-Lower Cambrian carbonate sequences in the central Siberian Platform

We propose a detailed δ¹³C curve for the Vendian and Lower Cambrian (Tommotian) strata of the central Siberian Platform. Two positive carbon isotope excursions identified near the base of the Yuryakh Formation (up to 5.5‰) and in the lower Bilir Formation (up to 5‰) are assigned to the lowermost and middle Tommotian, respectively. This correlation is supported by paleontological data, specific ⁸⁷Sr/⁸⁶Sr values (0.70845-0.70856), and similar C isotope record in coeval Early Cambrian basins. The documented minor vertical oscillations (a few meters) of these isotope excursions relative to the formation boundaries in remote boreholes is presumably caused by the spatiotemporal migration of facies. A high-amplitude negative δ¹³C excursion (-8 to -11‰) in the upper Nepa Regional Stage putatively corresponds to the global Shuram-Wonoka negative carbon isotope excursion (Middle Ediacaran). Carbonates of the lower Nepa Regional Stage (Besyuryakh Formation) demonstrate positive δ¹³C values (up to 5‰) and minimum ⁸⁷Sr/⁸⁶Sr ratios of 0.70796-0.70832. The C and Sr isotope record of the Nepa Regional Stage provides its robust correlation with the Dal’nyaya Taiga and Zhuya Groups of the Patom Foredeep. Micropaleontological data herein reported and glacial diamictites documented at the base of the Vendian sedimentary cover both in the central Patom Foredeep and on its periphery suggest a full stratigraphic volume of the Ediacaran System in the most stratigraphically complete sections of the central Siberian Platform.     

1Tc-Strontiohilgardit (Ca,Sr)2[B5O8(OH)2Cl] und seine Stellung in der Hilgarditgruppe X2/II[B5O8(OH)2Cl]

Zusammenfassung 1Tc-Strontiohilgardit (Ca, Sr)₂ [B₅O₈(OH)₂,Cl] mit Ca : Sr etwa 1 : 1 ist ein neues Mineral der Hilgarditgruppe. Fundpunkt: Reyersbausen (9° 59,7 E, 51° 36,6 N), Grube Königshall-Hindenburg, Flöz Staßfurt in sylvinitischer Ausbildung.Konstanten : triklin-pedial,a ₀=6,38 Å,b ₀=6,480 Å,c ₀=6,608 Å, =75,4°,=61,2°, =60,5°; tafelige-gestreckte Links- und Re chtskristalle, farblos, wasserunlöslich, piezoelektrisch. Härte 5–7, Dichte 2,99 g cm^–3;n =1,638,n =1,639,n =1,670; 2V =19°.Neue Daten für die Hilgarditgruppe : 2 M (Cc)-Calciumhilgardit (=Hilgardit) =4 Ca₂[B₅O₃(OH)₂Cl], Raumgruppe Cc.3Tc-Calciumhilgardit (=Parahilgardit) = 3 Ca₂[B₅O₃(OH)₂Cl]; trinklin-pedial, ₀=6,31 Å,b =6,484 Å,c ₀=17,50 Å; =84,0°,=79,6°, =60,9°.Die Polymorphiebeziehungen sind geometrisch deutbar durch eine spezielle Art der Polytropie (Stapelung von Links- und Rechtskristallen im Elementarbereich).     

Early Devonian volcanics of southeastern Gorny Altai: Geochemistry,isotope (Sr,Nd, and O) composition,and petrogenesis (Aksai complex)

Geological, geochemical, and isotope (Sr, Nd, and O) parameters of Early Devonian (405 Ma) volcanics of southeastern Gorny Altai (Aksai and Kalguty volcanotectonic structures) are discussed. The studied igneous rock association comprises magnesian andesitoids, Nb-enriched andesite basalts, and A-type peraluminous silicic rocks (dacites, rhyolites, granites, and leucogranites). Magnesian andesitoids (mg# > 50) are characterized by a predominance of Na among alkalies (K₂O/Na₂O ≈ 0.1-0.7), medium contents of TiO₂ (~ 0.8-1.3 wt.%) and Al₂O₃ (~ 12-15 wt.%), enrichment in Cr (up to 216 ppm), and low Sr/Y ratios (4-15). The Nb-enriched (Nb = 10-17 ppm) andesite basalts have high contents of TiO₂ (1.7-2.7 wt.%) and P₂O₅ (0.4-1.4 wt.%). The A-type granitoids are characterized by high contents of K(K₂O/Na₂O ≤ 60) and alumina (ASI ≤ 2.9) and depletion in Ba, Sr, P, and Ti. The magnesian andesitoids and Nb-enriched andesite basalts are products of melts generated in the metasomatized lithospheric mantle; silicic magmas were formed through the melting of Cambrian-Ordovician metaturbidites of the Gorny Altai Group and, partly, Early-Middle Cambrian island-arc metabasites. The above rock association might have resulted from a plume impact on the lithospheric substrates of the continental paleomargin during the evolution of the Altai-Sayan rift system.     

Environmental isotopes (18O, 2H, and 87Sr/86Sr) as a tool in groundwater investigations in the Keta Basin, Ghana

Analyses of environmental isotopes (¹⁸O, ²H, and ⁸⁷Sr/⁸⁶Sr) are applied to groundwater studies with emphasis on saline groundwater in aquifers in the Keta Basin, Ghana. The ⁸⁷Sr/⁸⁶Sr ratios of groundwater and surface water of the Keta Basin primarily reflect the geology and the mineralogical composition of the formations in the catchments and recharge areas. The isotopic compositions of ¹⁸O and ²H of deep groundwater have small variations and plot close to the global meteoric water line. Shallow groundwater and surface water have considerably larger variations in isotopic compositions, which reflect evaporation and preservation of seasonal fluctuations. A significant excess of chloride in shallow groundwater in comparison to the calculated evaporation loss is the result of a combination of evaporation and marine sources. Groundwaters from deep wells and dug wells in near-coastal aquifers are characterized by relatively high chloride contents, and the significance of marine influence is evidenced by well-defined mixing lines for strontium isotopes, and hydrogen and oxygen stable isotopes, with isotopic compositions of seawater as one end member. The results derived from environmental isotopes in this study demonstrate that a multi-isotope approach is a useful tool to identify the origin and sources of saline groundwater. Electronic Publication     

Isotope geochemistry (S,C, O,Sr, Pb) of the Chaudfontaine mineralization (Belgium)

Investigations on S, C, O, Sr, and Pb isotopes in ores, gangue, and country rocks of the Chaudfontaine ore deposit confirm that interbedded barite and white sparry calcites are cogenetic. They emphasize the marine origin of S and the nonmarine origin of the metals. They underline the important role played by the bacterial reduction at the site of deposition. Hypotheses concerning the source of the metals and the nature of the brines involved in their transportation are briefly discussed.     

Multistage Alterations of Pre-Vendian Oil-Bearing Rocks of the Baikit Anteclise (Siberian Platform) Based on Rb–Sr and K–Ar Data

Riphean carbonate rocks of the Baikit Anteclise with hydrocarbon raw material reserves exhibit a complicated block structure. Therefore, correlation of sections of even adjacent wells and general understanding of the geological structure of the territory are extremely hampered. The problem becomes more complicated because of multiple epigenetic reworking of Riphean rocks. Study of Rb–Sr and K–Ar systems based on materials from three boreholes drilled on the Baikit Anteclise reveal at least three stages of such reworking dated at about 1400, 1000, and 700 Ma, respectively. Rocks of the whole penetrated pre-Vendian section are assumed to be Early Riphean or even pre-Riphean. Brines saturating them are likely to be related to Vendian–Cambrian saliferous rocks.