Stable isotopic compositions of Recent freshwater cyanobacterial carbonates from the British Isles: local and regional environmental controls

Recent (<50 years old) freshwater cyanobacterial carbonates from diverse environments (streams, lakes, waterfalls) throughout Britain and Ireland were analysed for their stable carbon and oxygen isotope compositions. The mean δ¹⁸O value of ?5–9‰ PDB for river and stream data represents calcite precipitation in equilibrium with the mean oxygen isotopic composition of precipitation in central Britain (?7–5‰SMOW) assuming a mean water temperature of 9°C. The mean δ¹⁸O of lake data, ?4–5‰ PDB, is statistically different, reflecting the effects of residence time and/or variations in the oxygen isotopic composition of rainfall. Carbon isotopes have wide variations in both fluviatile and lake data sets (+ 3 to ?12‰ PDB). These variations are principally controlled in the fluviatile samples by contribution of isotopically light ‘soil zone’ carbon relative to isotopically heavier carbon from limestone aquifer rock dissolution. Lake samples have the heaviest carbon isotope values, reflecting a trend toward isotopic equilibrium between atmospheric CO₂ and aqueous HCO^?₃. We infer that isotopic compositions of ancient cyanobacterial carbonates should also record environmental information, although the effects of stabilization and diagenesis on primary δ¹⁸O values will need careful consideration. Primary carbon isotope compositions should be well preserved, although in marine samples values will be buffered by the isotopic composition of aqueous marine bicarbonate.     

The use of environmental markers to identify groundwater salinization sources in a Neogene basin, Kert aquifer case, NE Morocco

Environmental isotopes data of oxygen and hydrogen of natural water and sulphur and oxygen of dissolved sulphate as well as characteristics of d-excess are used to illustrate the salinity origin in Kert aquifer NE Morocco. In this study, 14 groundwater samples and surface water of the Kert River were collected in the Kert plain during December 2008, and were combined with previously collected hydrochemical data. The isotope compositions of these waters range from ?5.74 to ?4.51 ‰ for oxygen and from ?40.8 to ?34.1 ‰ for hydrogen. In Kert River these values are ?6.47 ‰ for oxygen and ?47.56 ‰ for hydrogen. All the samples with a slope <8 do not fall on the meteoric water line indicating a light evaporation. Water has low and different d-excess values (ranging from +1.37 to +9.82 ‰), reflecting different climatic conditions. Based on the nitrate concentration water in the Kert aquifer comes from the modern precipitation. The isotope compositions range from ?2.2 to +16 ‰ for sulphur and from +5.02 to +13.86 ‰ for oxygen. In Kert River these values are ?4.6 and +5.3 ‰ for sulphur and oxygen, respectively. There are fairly constant difference between oxygen of water and the oxygen of sulphate suggesting a dominant control of this latter in sulphate sources. At least three major sulphate sources were identified by the isotope data from sulphate in these waters: (1) dissolved marine sulphate from the underlying upper Miocene unit; (2) dissolved sulphate from Kert River; (3) sulphate derived from oxidation of sulphur compounds in the metamorphic massif of Temsamane. The latter has a dilution role. The isotopic variations of these waters and sulphate concentration therein reflect mixing of these sources in the aquifer.     

Oxygen isotope zoning in garnets from Franciscan eclogite blocks: evidence for rock–buffered fluid interaction in the mantle wedge

The oxygen isotope compositions of eclogite and amphibolite garnets from Franciscan Complex high-grade blocks and actinolite rinds encasing the blocks were determined to place constraints on their fluid histories. SIMS oxygen isotope analysis of single garnets from five eclogite blocks from three localities (Ring Mountain, Mount Hamilton, and Jenner Beach) shows an abrupt decrease in the δ¹⁸O value by ~1–3 ‰ from core to rim at a distance of ~120 ± 50 μm from the rim in nine out of the 12 garnets analyzed. In contrast, amphibolite garnets from one block (Ring Mountain) analyzed show a gradual increase in δ¹⁸O value from core to rim, implying a different history from that of the eclogite blocks. Values of δ¹⁸O in eclogite garnet cores range from 5.7 to 11.6 ‰, preserving the composition of the eclogite protolith. The abrupt decrease in the δ¹⁸O values of the garnet rims to values ranging from 3.2 to 11.2 ‰ suggests interaction with a lower δ¹⁸O fluid during the final stages of growth during eclogite facies metamorphism (450–600 °C). We hypothesize that this fluid is sourced from the serpentinized mantle wedge. High Mg, Ni, and Cr contents of actinolite rinds encasing the blocks also support interaction with ultramafic rock. Oxygen isotope thermometry using chlorite and phengite versus actinolite of rinds suggests temperatures of 185–240 °C at Ring Mountain and Mount Hamilton. Rind formation temperatures together with the lower δ¹⁸O garnet rims suggest that the blocks were in contact with ultramafic rock from the end of garnet growth through low-temperature retrogression. We suggest a tectonic model in which oceanic crust is subducted at the initiation of subduction and becomes embedded in the overlying mantle wedge. As subduction continues, metasomatic exchange between high-grade blocks and surrounding ultramafic rock is recorded in low δ¹⁸O garnet rims, and later as temperatures decrease, with rind formation.     

Control of the biofouling bryozoan, Plumatella repens, using pulsed chlorine treatment

Bryozoans are common biofoulers of under-drain filter nozzles in rapid gravity filters in water treatment works. A potential method for controlling bryozoan biofouling is the use of chlorine in backwash water. Repeatedly exposing bryozoan colonies with chlorine for 20 min every 24 h in an experimental setting, to replicate what would occur if the backwash was chlorinated, caused significant reduction in colony growth and size. After 10 days repeated treatment in good conditions for bryozoan propagation, the EC₅₀ (the chlorine concentration required to decrease growth such that treated colonies were half the size of control colonies) was 1.6 ppm (SE 0.3). In sub-optimal conditions for propagation, the impact of chlorine was greater. The majority of colonies treated with 1 ppm and above did not grow or even decreased in size over 5 days. However, a chlorine concentration of 5 ppm was necessary, even in sub-optimal conditions, to ensure all colonies decreased in size over 5 days of treatment; this is too high to be acceptable to water companies due to the risk of carcinogenic by-products. Nevertheless, the observed decline in feeding activity of bryozoans exposed to chlorine levels >1 ppm suggests that repeated backwashing with chlorine may cause colony death over time, especially in sub-optimal conditions. Chlorine backwashes may therefore be an effective long-term control strategy, especially in locations such as rapid gravity filters where it is suggested that upstream processes are likely to create sub-optimal conditions for bryozoan growth.     

Factors influencing methane-derived authigenic carbonate formation at cold seep from southwestern Dongsha area in the northern South China Sea

This paper carried out mineral and geochemical studies on a profile through a diagenetic methane-derived authigenic carbonate sample that was collected from southwestern Dongsha area of the northern South China Sea. Five samples locating in the cross-sectional middle mainly consist of dolomite and quartz, and two samples close to the surface have a small amount of Mg-calcite. The δ¹³C values of the samples vary between ?30.59 and ?0.30 % VPDB, with δ¹⁸O values ranging from 3.07 to 3.59 % VPDB, δ^44/40Ca values ranging from 1.35 to 1.47 % SRM915a, indicating a contribution of methane to the carbon pool where the precipitation of authigenic carbonates occurred. Based on the isotope values alone, it can not be distinguished if the carbon source is thermogenic gas or a mixture of biogenic methane and marine dissolved inorganic carbon. The δ¹⁸O values are in general consistent with dolomite precipitation from a fluid similar to present seawater. The observed small variation might be related to the oxygen isotope composition of seep fluid. The relative small range in calcium isotope values suggests that relatively constant growth conditions and precipitation from seawater. The central part of the carbonate nodule formed under the strong influence of methane seepage, and the external part is less influenced by methane, either due to reduced methane flux to the surface or caused by erosional exhumation of the carbonate nodule from greater depth to the sediment surface.     

Hydrogen and oxygen isotope evidence for fluid–rock interactions in the stages of pre- and post-UHP metamorphism in the Dabie Mountains

Hydrogen and oxygen isotope studies were carried out on high and ultrahigh pressure metamorphic rocks in the eastern Dabie Mountains, China. The δ¹⁸O values of eclogites cover a wide range of −4.2 to +8.8‰, but the δD values of micas from the eclogites fall within a narrow range of −87 to −71‰. Both equilibrium and disequilibrium oxygen isotope fractionations were observed between quartz and the other minerals, with reversed fractionations between omphacite and garnet in some eclogite samples. The δ¹⁸O values of −4 to −1‰ for some of the eclogites represent the oxygen isotope compositions of their protoliths which underwent meteoric water–rock interaction before the high to ultrahigh pressure metamorphism. Heterogeneous δ¹⁸O values for the eclogite protoliths implies not only the varying degrees of the water–rock interaction before the metamorphism at different localities, but also the channelized flow of fluids during progressive metamorphism due to rapid plate subduction. Retrograde metamorphism caused oxygen and hydrogen isotope disequilibria between some of the minerals, but the fluid for retrograde reactions was internally buffered in the stable isotope compositions and could be derived from structural hydroxyls dissolved in nominally anhydrous minerals.     

Contrasting Carbon and Oxygen Isotopic Evolution in Metacarbonates from the Kerala Khondalite Belt,Southern India

The Kerala Khondalite belt is a Proterozoic metasupracrustal granulite facies terrain in southern India comprising garnet-biotite gneiss, garnet-sillimanite gneiss and orthopyroxene granulites as major rock types. Calc-silicate rocks and marbles, occurring as minor lithologies in the Kerala Khondalite Belt, show different mineral assemblages and reaction histories of which indicate a metamorphic P-T-fluid history dominated by internal fluid buffering during the peak metamorphism, followed by external fluid influx during decompression. The carbon and oxygen isotopic compositions of calcite from three representative metacarbonate localities show contrasting evolutionary trends. The Ambasamudram marbles exhibit carbon and oxygen isotope ratios (δ¹³C ∼ 0‰ and δ¹⁸O ∼ 20‰) typical of middle to late Proterozoic marine carbonate sediments with minor variation ascribed to the isotopic exchange due to the devolatilization reactions. The δ¹³C and δ¹⁸O values of ∼ −9‰ and 11‰, respectively, for calcite from calc-silicate rocks at Nuliyam are considerably low and heterogeneous. The wollastonite formation here, possibly corresponds to an earlier event of fluid infiltration during prograde to peak metamorphism, which resulted in decarbonation and isotope resetting. Further, petrologic evidence supports a model of late carbonic fluid infiltration that has partially affected the calc-silicate rocks, with subsequent isotope resetting, more towards the contact between calc-silicate rock and charnockite. At Korani, only oxygen isotopes have been significantly lowered (δ¹⁸O ∼ 13‰) and the process involved might be a combination of metamorphic devolatilization accompanied by an aqueous fluid influx, supported by petrologic evidence. The stable isotope signatures obtained from the individual localities, thus indicate heterogeneous patterns of fluid evolution history within the same crustal segment.     

A Nd- and O-isotope study of the REE-rich peralkaline Strange Lake granite: implications for Mesoproterozoic A-type magmatism in the Core Zone (NE-Canada)

It is well established that A-type granites enriched in high field strength elements, such as Zr, Nb and the REE, form in anorogenic tectonic settings. The sources of these elements and the processes controlling their unusual enrichment, however, are still debated. They are addressed here using neodymium and oxygen isotope analyses of samples from the 1.24 Ga Strange Lake pluton in the Paleoproterozoic Core Zone of Québec-Labrador, an A-type granitic body characterized by hyper-enrichment in the REE, Zr, and Nb. Age-corrected εNd values for bulk rock samples and sodic amphiboles (mainly arfvedsonite) from the pluton range from ?0.6 to ?5.7, and ?0.3 to ?5.3, respectively. The εNd values for the Napeu Kainiut quartz monzonite, which hosts the pluton, range from ?4.8 to ?8.1. The ¹⁴⁷Sm/¹⁴⁴Nd ratios of the suite and the host quartz monzonite range from 0.0967 to 0.1659, large variations that can be explained by in situ fractionation of early LREE-minerals (Strange Lake), and late hydrothermal HREE remobilization. Oxygen isotope analyses of quartz of both Strange Lake and the host yielded δ¹⁸O values between +8.2 and +9.1, which are considerably higher than the mantle value of 5.7 ± 0.2‰. Bulk rock oxygen isotope analyses of biotite-gneisses in the vicinity of the Strange Lake pluton yielded δ¹⁸O values of 6.3, 8.6 and 9.6‰. The negative εNd values and positive δ¹⁸O values of the Strange Lake and Napeu Kainiut samples indicate that both magmas experienced considerable crustal contamination. The extent of this contamination was estimated, assuming that the contaminants were sedimentary-derived rocks from the underlying Archean Mistinibi (para-) gneiss complex, which is characterized by low εNd and high δ¹⁸O values. Mixing of 5–15% of a gneiss, having an εNd value of ?15 and a δ¹⁸O value of +11, with a moderately enriched mantle source (εNd = +0.9, δ¹⁸O = +6.3) would produce values similar to those obtained for the Strange Lake granites. Based on analogies between the Nain Plutonic Suite and the Gardar alkaline igneous province (SW-Greenland), we conclude that the Strange Lake pluton and associated REE-mineralized anorogenic bodies formed from a combination of subduction-induced fertilization of the sublithospheric mantle, crustal extension and in situ magma evolution.     

Oxygen isotope exchange and closure temperatures in cooling rocks

Retrograde exchange of oxygen isotopes between minerals in igneous and metamorphic rocks by means of diffusion is explored using a finite difference computer model, which predicts both the zonation profile of δ¹⁸O within grains, and the bulk δ¹⁸O value of each mineral in the rock. Apparent oxygen isotope equilibrium temperatures that would be observed in these rocks are calculated from the δ¹⁸O values of each mineral pair within the rock. In systems which cool linearly from a sufficiently high temperature or at a low enough cooling rate, such that the final oxygen isotope values are not dependent upon the initial oxygen isotope values ('slow cooling'), the apparent oxygen isotope temperature derived for a rock composed of a single mineral pair can be shown to be simply related to the Dodson closure temperatures ( T _c) for the two phases and the mode of the rock. Adding a third phase into a system which undergoes 'slow' cooling will cause the apparent temperature derived for the two minerals already present to differ from the simple relationship for a two-phase system. In some systems oxygen isotope reversals can be developed. If cooling is not 'slow', then the mineral δ¹⁸O values resulting from cooling will be partly dependent upon the initial temperature of the system concerned. The model successfully simulates the mineral δ¹⁸O values that are often observed in granitic rocks. Application of the model will help in assessing the validity of oxygen isotope thermometry in different geological settings, and allows quantitative prediction of the oxygen isotope fractionations that are developed in cooling closed systems.     

Organic carbon content and carbon isotope variations across the Permo-Triassic boundary in the Gartnerkofel-1 borehole,Carnic Alps,Austria

The Gartnerkofel borehole is one of the most thoroughly studied and described Permo-Triassic sections in the world. Detailed bulk organic carbon isotope studies show a negative base shift from ? 24‰ to ? 28‰ in the Latest Permian which latter value persists into the Earliest Triassic after which it decreases slightly to ? 26‰. Two strongly negative peaks of > ? 38‰ in the Latest Permian and a lesser peak of ? 31‰ in the Early Triassic are too negative to be due to a greater proportion of more negative organic matter and must be due to very negative methane effects. The overall change to more negative values across the Bulla/Tesero boundary fits the relative rise in sea level for this transition based on the facies changes. A positive shift in organic carbon isotope values at the Late Permian Event Horizon may be due to an increase in land-derived organic detritus at this level—a feature shown by all Tethyan Permo-Triassic boundary sections though these other sections do not have the same values. Carbonate carbon isotope trends are similar in all sections dropping by 2–3 units across the Permo-Triassic boundary. Gartnerkofel carbonate oxygen values are surprisingly, considering the ubiquitous dolomitization, compatible with values elsewhere and indicate reasonable tropical temperatures of 60 °C in the Latest Permian sabkhas to 20–40 °C in the overlying marine transition beds. Increased land-derived input at the Late Permian Event Horizon may be due to offshore transport by tsunamis whose deposits have been recognized in India at this level.     

Source rock potential of selected Cretaceous shales,Orange Basin,South Africa

Twenty Cretaceous shale samples from two wells in the Orange Basin of South Africa were evaluated for their source rock potential. They were sampled from within a 1400 m-thick sequence in boreholes drilled through Lower to Upper Cretaceous sediments. The samples exhibit total organic carbon (TOC) content of 1.06–2.17%; Rock-Eval S2 values of 0.08–2.27 mg HC/g; and petroleum source potential (SP), which is the sum of S1 and S2, of 0.10–2.61 mg HC/g, all indicating the presence of poor to fair hydrocarbon generative potential. Hydrogen index (HI) values vary from 7 to 128 mg HC/g organic carbon and oxygen index (OI) ranges from 37 to 195 mg CO₂/g organic carbon, indicating predominantly Type III kerogen with perhaps minor amounts of Type IV kerogen. The maturity of the samples, as indicated by T _max values of 428–446°C, ranges from immature to thermally mature with respect to oil generation. Measured vitrinite reflectance values (%Ro) of representative samples indicate that these samples vary from immature to mature, consistent with the thermal alteration index (TAI) (spore colour) and fluorescence data for these samples. Organic petrographic analysis also shows that amorphous organic matter is dominant in these samples. Framboidal pyrite is abundant and may be indicative of a marine influence during deposition. Although our Rock-Eval pyrolysis data indicate that gas-prone source rocks are prevalent in this part of the Orange Basin, the geochemical characteristics of samples from an Aptian unit at 3318 m in one of the wells suggest that better quality source rocks may exist deeper, in more distal depositional parts of the basin.     

Nature of serpentinization and carbonation of ophiolitic peridotites (Eastern Desert,Egypt): constrains from stable isotopes and whole-rock geochemistry

Serpentinites are widespread in the Arabian-Nubian Shield (ANS) of the Eastern Desert of Egypt and usually enclose a tremendous carbonate alteration. Combined investigation of the stable isotope compositions of both O-H in serpentines and O-C in the whole-rock and the chemistry of the fluid-mobile elements (FMEs) in whole-rock serpentinites from Wadi (W.) Alam, Gabal (G.) El-Maiyit, and W. Atalla (Eastern Desert of Egypt) allowed to better understand the subsequent fluid sources of serpentinization and carbonation, as well as impact of these processes on the geochemistry of protolith ultramafic rocks. δ ¹⁸O values of W. Alam and W. Atalla serpentine minerals are close to the unaltered mantle and propose a lower temperature serpentinization if compared with those of G. El-Maiyit rocks. Moreover, δD values of W. Alam and W. Atalla serpentines (? 94 to ? 65‰) correspond to an igneous source that might be hydrothermal solutions mixed with the seawater in the mid-ocean ridge-arc transition setting. On the other hand, G. El-Maiyit serpentine is more depleted in ¹⁸O (with lower δ ¹⁸O values = 4.08–4.85‰), and its δD values (? 73 to 56 ‰) are most probably caused by an interaction with metamorphic fluids, acquired during on-land emplacement of oceanic peridotites or during burial in fore-arc setting. In addition, the oceanic oxygen isotope composition of most studied ophiolitic serpentinites points to the preservation of the pre-obduction δ ¹⁸O signatures and thus local-scale fluid flow at low water/rock ratios. Serpentinization fluids were CO₂-poor and the carbonation of the serpentinites resulted from infiltration of externally derived fluids. δ ¹⁸O_VSMOW values of carbonates in the studied serpentinites vary between heavier oxygen isotope composition in G. El-Maiyit samples (av. = 25.32‰) to lighter composition in W. Alam samples (av. = 19.43‰). However, δ ¹³C values of all serpentinites point mantle source of carbon. This source might have been evolved in mid-ocean ridge (W. Atalla) and subduction zone (W. Alam and G. El-Maiyit) settings. The studied serpentinites are usually enriched in FMEs, particularly Pb, Sr, Cs, and U. These enrichments were most probably the result of serpentinization and/or carbonation.     

Carbon and oxygen isotope fractionation in scleractinian corals: a review

The present theories on the fractionation of stable isotopes in scleractinian corals are critically discussed in the light of data available on primary productivity, respiration and stable isotope chemistry. These data support a model of fractionation in which the carbon and oxygen isotopes are decoupled. Calcification occurs from a reservoir of carbon dioxide derived from both organic and inorganic sources. Photosynthesis preferentially fixes¹³C and thereby leaves behind¹³C. Increases in the rate of photosynthesis therefore also enrich the carbon isotope ratio of the skeleton. From theoretical considerations, photosynthesis has little effect on the oxygen isotope ratio of the skeleton, a fact confirmed by available data. The process of respiration adds depleted carbon and oxygen to the calcification reservoirs. The varying correlations between carbon and oxygen isotopes seen in hermatypic corals are caused by changes in the relationship between photosynthesis and respiration at different geographical localities. The isotopic compositions in the skeletons of non-zooxanthellate corals, which show a consistent positive correlation, can also be explained by the above scenario.     

Stable Isotope Investigations on the Granulite Facies Terrains of Brazil: A Review

Stable isotope data from three areas in the granulite facies terrains of Brazil are assembled and discussed. All the three areas (Jequié, Guaxupé and São José do Rio Pardo) are from the São Francisco Craton. The carbon isotope composition of the fluid inclusion CO₂ in the Archean granulite terrain of Jequié indicate the participation of two distinct sources, an upper mantle source and an internal source of Archean organic matter. The isotope data may be interpreted in terms of the granulite genesis due to the intrusion of magma in the lower crust. The singularly uniform carbon isotope data for CO₂ fluid inclusion of plutonic granulites is a clear indication of the magmatic addition of CO₂-rich volatiles from deeper crustal sources. In the São José do Rio Pardo area sulfur and carbon isotope data of scapolites from the granulites imply the derivation of volatiles from internal sources. The whole rock oxygen isotope data of the amphibolite and granulite facies gneisses from Guaxupé indicate a small scale variation of d¹⁸O values, compatible with the chemical data, suggesting the preservation of pre-metamorphic oxygen isotope composition. The isotope data of the granulites from São Francisco Craton indicate non-pervasive fluid flow during metamorphism.     

南京孔山剖面早二叠世冰川旋回期内氧碳同位素演化特征及其环境意义

在南京孔山地区早二叠世的碳酸盐岩沉积序列中系统地采集了样品并进行了氧、碳同位素分析 ,同时作了有关海平面变化的研究。结果表明 ,处于浅水和近岸环境的碳酸盐岩的氧同位素值系“全球冰川效应”和区域的淡水掺混两种作用相互平衡的结果。它的变化特征虽然可以忠实地记录原生沉积环境的变迁 ,但不能简单套用远洋沉积物中所总结出的模式。碳同位素亦非古代海平面变化的简单函数。有机碳埋藏速率及与之相关的氧化 -还原环境应是 δ1 3 C值的最终控制因素     

Trace element contents and C-O isotope geochemistry of the different originated magnesite deposits in Lake District (Southwestern Anatolia), Turkey

Vein-stockwork magnesite in the Madenli area, sedimentary huntite-magnesite in the A?a??t?rtar area, and lacustrine hydromagnesite in the Salda Lake area are located in the Bey?ehir-Hoyran and Lycian nappe rocks around Isparta and Burdur, Southwest Anatolia. The aim of this study is to understand trace element contents and carbon-oxygen isotope ratios in different originated magnesite, magnesite bearing huntite, and hydromagnesite deposits. Also, the element contents and isotope ratios of the magnesite occurrences are to compare with each other and similar magnesite occurrences in Turkey and world. It is found that the Madenli magnesite occurrences in the ?arkikaraa?aç ophiolites, A?a??t?rtar magnesite bearing huntite deposits in the lacustrine rocks of the Miocene-Pliocene, and the Salda hydromagnesite deposits in lacustrine basin on the Ye?ilova ophiolites. The paragenesis contains a common carbonate mineral magnesite, less calcite, serpentine, smectite, dolomite, and talc in the Madenli magnesite occurrences, mostly huntite and locally magnesite, dolomite, calcite, illite, quartz, and smectite in the A?a??t?rtar huntite-magnesite occurrences, and only hydromagnesite mineral in the Salda Lake hydromagnesite occurrences. Vein and stockwork Madenli magnesite deposits were recognized by higher total iron oxide concentrations (mean 1.10 wt%) than sedimentary A?a??t?rtar magnesite bearing huntite (mean 0.13 wt%) and lacustrine Salda hydromagnesite (mean 0.22 wt%) deposits. It is suggested that high Fe content (up to 5%) in the magnesite associated with ultramafic rocks than those from sedimentary environments (≤1% Fe). Based on average Ni, Co, Ba, Sr, As and Zr contents in the magnesite deposits, average Ni (134.63 ppm) and Co (15.19 ppm) contents in the Madenli magnesite and Salda hydromagnesite (36.85 ppm for Ni, 3.15 ppm for Co) have higher values than A?a??t?rtar huntite + magnesite (7.67 ppm for Ni and 0.89 ppm for Co). Average Ni-Co contents of these deposits can have close values depending on ophiolite host rock. Average Ba values of the Madenli (108.09 ppm) and A?a??t?rtar (115.88 ppm) areas are higher than those of Salda hydromagnesite (13.15 ppm). Sediment-hosted A?a??t?rtar magnesite-huntite deposits have the highest Sr contents (mean 505.81 ppm) as reasonably different from ultrabasic rock-related Madenli magnesite (mean 38.76 ppm) and Salda hydromagnesite (mean 36.70 ppm). The highest Sr content of sedimentary A?a??t?rtar deposits reveals that Sr is related to carbonate rocks. As and Zr contents have the highest average values (As 52.76 ppm and Zr 9.67 ppm) in the A?a??t?rtar deposits different from Madenli magnesite (As 0.54 ppm and Zr 1.67 ppm) and Salda hydromagnesite (As 0.5 ppm and Zr 2.58 ppm) deposits. High As and Zr concentrations in the A?a??t?rtar magnesite-huntite deposits may come from volcanic rocks in near country rocks. The δ ¹³C (PDB) isotope values vary between ?10.1 and ?11.4‰ in the Madenli magnesite, 7.8 to 8.8‰ for huntite, 1.7 to 8.3‰ for huntite + magnesite and 4.0‰ for limestone + magnesite in the A?a??t?rtar huntite-magnesite deposits, and 4.4 to 4.9‰ for Salda Lake hydromagnesite. The sources of the CO₂ are hydrothermal solutions, meteoric waters, groundwater dissolved carbon released from fresh water carbonates and marine limestone, soil CO₂, and plant C3 in the Madenli magnesite, and may be deep seated metamorphic reactions in limestone and shales of rich in terms of organic matter. The sources of CO₂ in A?a??t?rtar huntite and Salda hydromagnesite were meteoric water, groundwater dissolved inorganic carbon, fresh water carbonates, and marine limestone. The δ ¹⁸O (SMOW) isotope composition ranges from 26.8 to 28.1‰ in the Madenli magnesite, 30.4 to 32.4‰ for huntite and 29.8 to 35.5‰ for huntite + magnesite and 26.9‰ for limestone + magnesite in the A?a??t?rtar area, and 36.4 to 38.2‰ in the Salda Lake hydromagnesite. The Salda Lake hydromagnesite has heavier oxygen isotopic values than others. The sources of oxygen in the Madenli magnesite deposits are hydrothermal solutions, meteoric water, freshwater carbonates, and marine limestone, but the sources of oxygen of the A?a??t?rtar magnesite-huntite are meteoric water, fresh water carbonates, and marine limestone. The Salda Lake hydromagnesite has very high δ¹⁸O isotope values indicating a strong evaporitic environment. Magnesium (Mg⁺²) and silica are released by disintegration of very weathered-serpentinized ultrabasic rocks of all magnesite deposits and from partly dolomite and dolomitic limestone in the A?a??t?rtar magnesite bearing huntite deposits. In the A?a??t?rtar area, calcium (Ca⁺²) for huntite mineralization is provided by surrounding carbonate rocks. Based on isotopic data, host rocks, petrographic properties of the Madenli magnesite can be described as an ultramafic-associated hydrothermal vein mineralization corresponding to “Kraubath type” deposits, but A?a??t?rtar ve Salda Lake deposits are sedimentary mineralization (lacustrine/evaporitic) corresponding to “Bela Stena type” deposits. The estimated temperature using average δ¹⁸O isotope values is about 33.51 °C for Madenli magnesite, 48.33 °C for A?a??t?rtar huntite-magnesite, and 25 °C for Salda hydromagnesite. Based on isotope data, we can be say that the Madenli magnesite, A?a??t?rtar magnesite-huntite, and Salda hydromagnesite occur at low to moderate-low temperature water and alkaline (pH 8.5–10.5) under surface or near-surface conditions.     

Geochemistry of Altungol cap dolostones from the Tarim Basin,NW China

The Snowball Earth hypothesis postulates that the whole earth was covered by ice sheets for millions of years in the Neoproterozoic. In Tarim Basin, there are four intervals of glacial deposits recorded in the Quruqtagh area during the Neoproterozoic. In chronological order, they are Bayisi, Altungol, Tereeken, and Hankalchough glaciations. In this study, we analyzed carbon, oxygen, and strontium isotopes; whole-rock geochemistry; and acid-insoluble residua of the ～5-m-thick Altungol cap dolostone (ten samples) in Quruqtagh unit of the Tarim basin. The geochemical data of whole rock are used to explain the ocean environmental changes, while the geochemical data of acid-insoluble residua reflect the changes of the continental environment. The δ¹³C_PDB of cap dolostone varies from ?2.5 to ?1 ‰, which is likely due to the influence of organics. From the bottom to the top of the Altungol cap dolostones, the chemical index of alteration of acid-insoluble residua rises from 72 to 77, but the index of chemical variation drops from ～3 to ～1. Ni, Zn, Cu, and Y contents of acid-insoluble residua are enriched in 2.5 m. The values of iron maintain at a high level in all of the whole-rock samples (>5.15 %), but in the samples of acid-insoluble residua, the values of iron are higher than in the whole rock (19～60 %) below 1.5 m. The variations in chemical composition were probably associated with the changes of continental weathering. The geochemistry suggests that ocean and continent environmental variations had taken place after the Altungol glaciation, including the destruction of ocean stratification and the changes of chemical weathering. During this period, the source of this area had changed. At first, the weathering residues of the parent rocks were exhausted by meltwater. Then, the vigorous weathering of freshly exposed continental crust provided a new source.     

Mineralogical and geochemical (stable C and O isotopes) variability of marbles from the Moldanubian Zone (Bohemian Massif,Czech Republic): implications for provenance studies

Metacarbonates of the Moldanubian Zone (Bohemian Massif, Czech Republic) were studied to obtain qualitative and quantitative mineralogical-petrographic as well as stable isotopic data for the purpose of stone provenance studies, potentially applicable in material research studies of cultural heritage artefacts. Twenty-six samples from twelve different historical quarries, as well as two samples from historical artefacts, were analysed by both mineralogical-petrographic and geochemical methods including: polarizing microscopy, cathodoluminescence, scanning electron microscopy with microanalysis, petrographic image analysis, powder X-ray diffraction, and isotope ratio mass spectrometry. The petrographic characteristics allowed for the discrimination of groups of (1) calcitic marbles, (2) dolomitic marbles, and (3) carbonate–silicate rocks. These groups exhibit characteristic features such as (1) the presence/abundance of major rock-forming minerals, (2) grain geometric characteristics (specifically, mean carbonate grain size and index of grain size homogeneity), and (3) the presence of specific accessory phases. The content of non-carbonate minerals, some rock fabric parameters, as well as the carbon and oxygen isotope data exhibited significant variability, even within a single quarry in the case of some impure marbles and carbonate–silicate rocks. Although the carbon and oxygen isotopic ranges displayed overlaps among the quarries studied, the isotopic signatures throughout the Moldanubian Zone allowed for discrimination of a group of white calcitic marbles with high carbon and oxygen depletion, as well as white dolomite–calcitic marble with higher carbon isotope values when compared with other marble resources of the Bohemian Massif. A combination of the isotopic signature with detailed mineralogical-petrographic characteristics seems to provide sufficient information for discrimination of the Moldanubian marbles from one another. The provenance of the Vrchotovy Janovice artefact is very probably from the Rabí quarry, among the Moldanubian marbles. The provenance of the artefact from the Prague Klementinum was not definitively assigned; however, the Nehodiv quarry was considered its probable source locality.     

Study of Metallogenic Fluid Sources of Five Gold Deposits in Zhangjiakou,China

It is very important to define the type and composition of metallogenic fluid in terms of the hydrogen and oxygen isotope data in the study of ore-forming mechanism.In the long past,the method to discriminate metallogenic fluid sources by comparing the δD-δ^18 O diagram with the standard values in not valid when the hydrogen and oxygen isotope values are plotted between the meteoric water line and the magmatic water area.Based on their hydrogen and oxygen isotope information of five gold deposits(Shuijingtun,Xiaoyingpan,Dongping, Zhongshangou and Jinjiazhuang)in the Zhangjiakou area,this paper details the metallogenic fluid sources and presents water/rock ratios in the vie gold deposits and the principle of water/rock exchange.     

Hydrogeochemical investigation of geothermal springs in Erzurum,East Anatolia (Turkey)

Geothermal water sources located within The Erzurum province were identified and hot water samples were taken from four different geothermal areas. The results of in situ and hydrogeochemical analyses of these hot water samples were interpreted and the properties of hot water, water–rock associations, estimated reservoir temperature and hot water usage areas were determined. The temperatures of the samples collected from the study area vary between 26.2 and 57.7 °C, while pH values change from 6.09 to 7.33, EC values obtained from in situ measurements are between 1829 and 9480 µS/cm and Eh values are (??190) to (26.3) mV. Total dissolved solids of the hot waters have a range from 838.7 to 3914.1 mg/l. The maximum estimated reservoir temperature is calculated as 250 °C by applying chemical geothermometers. However, considering the actual temperatures of Pasinler, Köprüköy, Horasan and Il?ca thermal waters and wells, the most reliable temperature range depending on the applied geothermometers’ results indicate minimum and maximum reservoir temperatures 85–158.9 °C, respectively, taking in account the errors. According to the isotope analysis, the waters circulating within the geothermal system are of meteoric origin and modern waters. In addition, two samples taken from clayey levels observed in the field were analyzed and the mineralogy of the clays was evaluated.