Presence Of Dolomite Research Articles

On discrimination between carbonate and silicate inputs to Himalayan rivers

We review new and published analyses of river waters, bedloads and their constituent minerals from the Dhauli Ganga and Alaknanda, headwaters of the Ganges in Garhwal, and the Marsyandi in Nepal and their tributaries. These data are used to discriminate between the inputs of major cations and Sr from silicate and carbonate sources. Methods of estimating the proportion of the carbonate and silicate inputs to river waters using mixing arrays in Sr-Ca-Mg-Na-K-87Sr/86Sr space are shown to suffer from systematic correlations between the magnitude of the precipitation of secondary calcite and the fraction of the silicate component. This results in factor-of-two overestimates of the fractions of silicate-derived Ca, Mg and Sr. To correct for this the magnitude of secondary calcite precipitated and relative fractions of silicate and carbonate-derived cations are instead calculated by modeling the displacement of water compositions from the compositions of the carbonate and silicate components of the bedload in subsets of Sr-Ca-Mg-Na-K-87Sr/86Sr space. The compositions of the carbonate and silicate end-members in the bedload are determined by sequential leaching. The results of this modeling are compared with modeling of the modal mineral inputs to waters where mineral compositions are derived from electron-microprobe analyses of the minerals in the bedload. In the upper Marsyandi catchment, which drains low-grade Tethyan Sedimentary Series formations, a set of mainstem samples collected over a two-year period define tight correlations in Sr-Ca-Mg-Na-K-87Sr/86Sr space. Modeling of the magnitude of secondary carbonate precipitation and fractions of silicate-derived Ca, Mg and Sr in Sr-Ca-Mg-87Sr/86Sr space gives self-consistent results that are compatible with both the calculations of mineral modes and published Mg-isotopic compositions, if the ratio of chlorite to biotite weathering is high or if there is another silicate source of Mg. These calculations imply that between 12 and 31 percent of the Sr and 44 and 72 percent of the Mg is derived from silicate minerals where the range reflects the seasonal change in the ratio of silicate-derived to carbonate-derived cations. Modeling in Sr-Ca-Na and/or K space is inconsistent with the Sr-isotopic and Mg-isotopic constraints and we conclude that in this catchment dissolution of Na and K are incongruent relative to Sr-Ca-Mg. Potassium is preferentially retained in micas whereas the controls on Na are unclear. Modeling of the catchments underlain by High Himalayan Crystalline and Lesser Himalayan Series in Garhwal is complicated by the presence of dolomite as well as calcite in the carbonate and the results imply that dolomite dissolves faster in the acetic acid leaches than in nature. Up to 60 percent of the Sr in the catchment on High Himalayan Crystalline Series and 20 to 30 percent of Sr in the catchments on Lesser Himalayan Series are estimated to be derived from silicates. However it should be noted that the element budgets are not all self-consistent and the use of bedrock-element ratios to model the sources of chemical inputs to river waters remains subject to uncertainties.

Effects of temperature and CO2 on the frictional behavior of simulated anhydrite fault rock

AbstractThe frictional behavior of anhydrite‐bearing faults is of interest to (a) the safety and effectiveness of CO2 storage in anhydrite‐capped reservoirs, (b) seismicity induced by hydrocarbon production, and (c) natural seismicity nucleated in evaporite formations. We performed direct shear experiments on simulated anhydrite fault gouges, at a range of temperatures (80–150°C) and sliding velocities (0.2–10 µm s−1), under a fixed effective normal stress of 25 MPa. Four types of experiments were conducted (1) dry experiments, (2) experiments pressurized with water, (3) dry experiments pressurized with CO2, and (4) wet experiments pressurized with CO2. Fluid pressures of 15 MPa were used when applied. Over the temperature range investigated water‐saturated samples were found to be up to 15% frictionally weaker than dry equivalents. Wet samples containing CO2 were also up to 15% weaker than CO2‐free equivalents. Dry sample strength without CO2 was independent of temperature, whereas wet samples without CO2 strengthened 10% from 80 to 150°C. Samples containing CO2 weakened by 4% (dry) and 10% (wet) from 80 to 150°C. Under the P‐T conditions investigated, only dry anhydrite fault gouge showed velocity‐weakening behavior above 120°C, required for faults to potentially generate earthquakes. Assuming natural fault gouges are wet in situ, seismicity is unlikely to nucleate in anhydrite‐rich faults, though the presence of dolomite or (reaction‐produced) calcite may change seismic potential. CO2 penetration into wet anhydrite‐rich faults may trigger slip on critically stressed faults due to the observed short‐term CO2 weakening effects (excluding possible formation of secondary minerals), but is not expected to influence slip stability.

Lake level and climate records of the last 90 ka from the Northern Basin of Lake Van, eastern Turkey

Sedimentary, geochemical and mineralogical analyses of the ICDP cores recovered from the Northern Basin (NB) of Lake Van provide evidence of lake level and climatic changes related to orbital and North Atlantic climate system over the last 90ka. High lake levels are generally observed during the interglacial and interstadial periods, which are marked by deposition of varved sediments with high total organic carbon (TOC), total inorganic carbon (TIC), low detrital influx (high Ca/F) and high δ18O and δ13C values of authigenic carbonate. During the glacial and stadial periods of 71–58kaBP (Marine Isotope Stage 4, MIS4) and end of last glaciation–deglaciation (30–14.5kaBP; MIS3) relatively low lake levels prevailed, and grey homogeneous to faintly laminated clayey silts were deposited at high sedimentation and low organic productivity rates.Millennial-scale variability of the proxies during 60–30kaBP (MIS3 is correlated with the Dansgaard–Oeschger (D–O)) and Holocene abrupt climate events in the Atlantic. These events are characterized by laminated sediments, with high TOC, TIC, Ca/Fe, δ18O and δ13C values. The Lake Van NB records correlate well in the region with the climate records from the lakes Zeribar and Urmia in Iran and the Sofular Cave in NW Anatolia, but are in general in anti-phase to those from the Dead Sea Basin (Lake Lisan) in the Levant.The relatively higher δ18O values (0 to −0.4‰) for the interglacial and interstadial periods in the Lake Van NB section are due to the higher temperature and seasonality of precipitation and higher evaporation, whereas the lower values (−0.8 to −2‰) during the glacial and stadial periods are caused mainly by relative decrease in both temperature and seasonality of precipitation. The high δ18O values (up to 4.2‰) during the Younger Dryas, together with the presence of dolomite and low TOC contents, supports evaporative conditions and low lake level. A gradual decrease in the δ18O values from an average of −0.4‰ during the humid early Holocene to an average of −3.5‰ during the more arid late Holocene suggests an increasing contribution of winter precipitation. The changes in the seasonality of precipitation in eastern Anatolia are probably caused by changes in the temperatures of North Atlantic and Mediterranean and in the strength of Siberian High.

Effect of CaMg(CO3)2 on hydrate assemblages and mechanical properties of hydrated cement pastes at 40 °C and 60 °C

The effect of additions of limestone and dolomite powder on the properties of blended cements cured at 40 and 60°C was investigated using a multi-method approach. The presence of limestone leads to the formation of hemi- and mono-carbonate and to the stabilization of ettringite at 40°C. An increase of temperature to 60°C results in the destabilization of ettringite and formation of monosulfate in the limestone cement. The dolomite is almost depleted in the cementitious matrix over the hydration time at the studied temperatures. As a result, the formation of hydrotalcite is observed which binds part of the alumina from clinker dissolution. At 60°C, no monosulfate is found and the CSH contains less alumina in the presence of dolomite in comparison to when limestone is present. The dolomite dissolution increases the strength at higher temperatures as a result of the additional hydrotalcite formation.

Geochemistry, microfacies and diagenetic evidences for original aragonite mineralogy and open diagenetic system of Lower Cretaceous carbonates Fahliyan Formation (Kuh-e Siah area, Zagros Basin, South Iran)

The Fahliyan Formation is an important reservoir unit of Cretaceous strata in the south of Iran (Zagros Mountains). This formation with the age of Lower Cretaceous overlies unconformably the Hith Formation and is conformably covered by the Gadvan Formation in the studied area. To evaluate the original carbonate mineralogy, paleotemperature, and diagenetic environment in Kuh-e Siah anticline in Boushehr Province, the Fahliyan Formation was investigated by petrographic and geochemical analyses. Petrographic studies led to the recognition of 25 microfacies that were deposited in four facies belts: tidal flat, lagoon, and shoal in inner ramp and shallow open marine in mid-ramp environment. Of these microfacies, twenty-one belong to inner ramp and four are located in the mid ramp. Calcareous algae and benthic foraminifera are abundant in the shallow-marine carbonates of the Fahliyan Formation. Evidences such as absence of calciturbidite deposits and reefal facies, the occurrence of widespread tidal flat deposits, gradual facies changes, and abundant micrites indicate that the Fahliyan Formation was deposited in a homoclinal carbonate ramp environment. Abundant aragonite skeletal and non-skeletal components and presence of dolomites in Fahliyan carbonates indicate original aragonite mineralogy. Radial ooids generated in low-energy environments similar to modern aragonitic forms. Deformed and spalled ooids as well as shattered micritic envelopes indicate aragonite dissolution during meteoric diagenesis. Isopachous and fibrous sparry calcite cements resemble modern aragonite morphologies. Micritization, geopetal fabric, bioturbation, neomorphism, compaction, cementation, dissolution, dolomitization, dedolomitization, and fracturing are diagenetic processes in the Fahliyan Formation, occurring in marine to meteoric and burial diagenetic environments. Cementation, dissolution, and dolomitization are the main diagenetic processes that affected the original texture. Values of major (Ca and Mg) and minor (Sr, Na, Fe and Mn) elements (such as high Sr value) and δ18O and δ13C designate that the Fahliyan carbonates were deposited in a shallow warm-water sub-tropical environment and aragonite was the original carbonate mineralogy. Variations of Sr/Ca and δ18O values versus Mn suggest that diagenetic alteration must have occurred in an open diagenetic system, with high water–rock interaction. Dolomitization, dissolution and cementation are the main diagenetic features observed in the Fahliyan Formation of Kuh-e Siah and confirm high water–rock interaction in open diagenetic system. Dissolution as leaching is the most important diagenetic event in the evolution of porosity, particularly where green algae and other benthic foraminifera are abundant. This may indicate that the original carbonate mineralogy of the mentioned bioclasts might be aragonite, rather than low-Mg calcite. Temperature calculation based on the oxygen isotope value of the least-altered sample, using Anderson and Arthur (Stable isotopes in sedimentary geology, vol 10. Society of Economic Paleontologists and Mineralogists. Short Course, pp 1–151, 1983) equation, indicates paleotemperature to be around 29.1 °C.

The Mianwali and Tredian Formations: An Example of the Triassic Progradational Deltaic System in the Low-Latitude Western Salt Range, Pakistan

The Nammal Gorge, Salt Range, Pakistan, preserves a record of the interacting Triassic open-marine carbonate sedimentation, cyclic siliciclastics progradation and fluctuating relative sea level. The sediments at the bottom in the Mianwali Formation, show bivalves and ammonoids rich wacke- to packestone lithofacies (i.e. ML 1 and ML 2), which indicates an open-marine depositional setting. The overlying shale of the Mianwali Formation (i.e. ML 3), has ammonoids and gastropods, the lower part of which indicates a relatively deep-marine depositional setting. Upwards, the ML 3 grades into the sandstones and shales (i.e. ML 4), which show ripple marks, mudcracks, bioturbation, graded, and cross bedding and syndepositional deformation. These features indicate deposition in delta lobe/shoreline sub-environments, with a high siliciclastic input. The lower part of the overlying Tredian Formation contains interbedded shale and sandstone (i.e. TL 1), having large scale slumps, which indicate deposition in cyclic, proximally located varied sub-environments of the delta topsets/channels and in the flood plain environments. The overlying thick, coarse, conglomeratic sandstone (i.e. TL 2) has planar, trough cross bedding and lenticular channelized bedding, which indicates a fluvial to continental environment. Further up, in the Tredian Formation, the presence of dolomite (i.e. TL 3) represents marine transgression. The facies association in the Mianwali and Tredian formation indicates many coarsening upward cycles representing the progradation of individual delta lobes. This study therefore proposes that, subsequent to the Permian-Triassic paraconformity, an open-marine depositional setting established in this area that gradually built up into a progradational deltaic system.

2D Raman spectroscopy study of dolomite and cyanobacterial extracellular polymeric substances from Khor Al‐Adaid sabkha (Qatar)

Dolomite precipitation, limited at low temperature, appears to be impacted by microbial extracellular polymeric substances (EPS). The presence of dolomites has been reported in the extreme environments of Arabian Gulf sabkhas. Many of these sites are characterized by extensive growth of cyanobacterial mats that are recognized as key producers of EPS. However, no information has been gathered on the cyanobacterial EPS involvement in dolomite precipitation. The objective of this study was to obtain in situ information on the spatial distribution of cyanobacterial EPS and dolomite in Khor Al‐Adaid sabkha (Qatar) sediments by chemical mapping. For this purpose, in situ 2D Raman spectroscopy and atomic force microscopy were applied. Additionally, samples were analyzed with scanning electron microscopy and X‐ray diffraction.Raman fingerprints of dolomite (300, 725, and 1098 cm−1), cyanobacteria, and their EPS (1000, 1130, 1148, and 1508 cm−1) were observed widely distributed in the top 2 cm of the sabkhas sediments. 2D chemical imaging of sediment layers characterized minerals and organic matter of microbial origins at high spatial resolution. Raman mapping indicated small dolomite clusters (<2 µm) embedded in a dense cyanobacterial EPS matrix. The spatial distribution showed that small dolomite clusters are closely associated with cyanobacterial EPS and organic carbon. Our results prove that cyanobacterial molecules are closely related to dolomite in the sabkhas sediments. This study demonstrated that Raman mapping is a robust and sensitive technique for acquisition of in situ information on cell–mineral interactions. Copyright © 2013 John Wiley & Sons, Ltd.

Air and air-steam gasification of sewage sludge. The influence of dolomite and throughput in tar production and composition

The influence of throughput (TR), steam and the use of dolomite (as primary catalyst) over the sewage sludge gasification products was investigated. For this purpose, experiments were conducted in an atmospheric fluidised bed reactor using air and air+steam as gasifying agents. The analysis of the results was mainly focussed on the gas composition, the gravimetric tar production, and the GC-detectable tar composition (and dew point estimations). According to the obtained results, higher TRs decreased the H2 content of the produced gas and clearly increased the gravimetric tar production. The use of air+steam, especially in the presence of dolomite, increased the H2 content (between 20% and 36%) and decreased the gravimetric tar production over all the tested TR, reaching tar removal efficiencies of up to 71%. Regarding the GC-detectable tar, higher TRs increased the heavy polyaromatic hydrocarbons production, steam slightly increased the water soluble tar content while the use of dolomite decreased the yield of all the tar classes except light aromatic hydrocarbons. Under the tested gasification conditions, the gas dew point never dropped below 110°C, value far above the recommended temperature when the syngas is to be used for engine applications.

Features of Mineral and Chemical Composition of the Khamambettu Carbonatites, Tamil Nadu

Abstract The paper presents mineralogical features and EPMA results of the Khamambettu carbonatites. The mineralogical data suggest that these rocks have been generated in magmatic and hydrothermal stages. Mineral geothermometer for carbonatite give temperatures of 790°-980°C. Fluid inclusion measurements in monazite (hydrothermal stage) give temperatures of 220°-290°C. One of the features of the carbonatites is high content of magnesia that is defined by the presence of dolomite, olivine, spinel, phlogopite, Mg-rich ilmenite. Chloritization, serpentinization, amphibolization, silicification processes and occurrence of barite, monazite-(Ce), strontianite, celestine are related to hydrothermal stage. Hydrothermal minerals at the Khamambettu were formed by recrystallization of primary carbonatite minerals in the presence of Ba, (SO4)2−, REE and Si carried in solution by the hydrothermal fluid.

Determination of Calcite and Dolomite Content in Soils and Paleosols by Continuous Coulometric Titration

Quantitative determination of calcite/dolomite ratios in soil carbonate fractions is important for understanding the pedogenic history of a soil or paleosol. This is particularly relevant to stable carbonate‐carbon and ‐oxygen isotope analyses where the presence of dolomite in a carbonate fraction can lead to erroneous results and inaccurate interpretations of the paleoenvironment. The goal of this work was to develop and test an accurate method using coulometric titration combined with differential kinetic principles for determining calcite and dolomite fractions in a sample. An automated titrator was connected to a temperature‐controlled carbonate reactor where 2 M HClO4 was introduced to the sample and mixed by bubbling CO2–free air at a constant rate of 100 mL min−1. Samples were ground to <53 μm to control for differences in particle size and reactive surface area. The concentration of C released from the reaction was monitored and recorded every 6 s for the length of the reaction. Data were fit with both a pseudo‐first order kinetic model and a Weibull model for comparison. The latter outperformed the pseudo‐first order kinetic model and the Weibull parameter, λ, fit to titration data from unknown samples was compared to λ values fit to data from mixtures of known fractions of pure calcite and dolomite to quantitatively obtain the content of the two minerals. Dolomite fractions obtained by this method qualitatively compared well with values obtained by X‐ray diffraction. Our method allows a precise and accurate measurement for both total carbonate and the ratio of calcite to dolomite in a sample.

The evaporite–coal transition: Chemical, mineralogical and organic composition of the Late Triassic Abu Ruweis Formation, NW Jordan—Reference type of the “Arabian Keuper”

The Abu Ruweis Formation, NW Jordan, was studied with regard to its chemical (major, minor elements, REE, S-, O-, C isotopes, organic chemistry), mineralogical compositions (rock-forming minerals), coal petrography (maceral analyses) and palynology (age determination and palaecosystem) for the evaporite–coal facies transition which is very rarely found. The palynomorphs point to a Late Triassic/Carnian age of formation. Strong evaporation in the series is demonstrated by the presence of dolomite, gypsum and celestite. Mg, Ca, F, Cl, S, Sr and Ba reflect the variation of evaporation during basin subsidence. A detrital influx is characterized by the abundance of Si, Ti, Al, Fe, Mn Ce, Co, Cr, V, Y and the (Zr+Rb)/Sr ratio. Salinity variation may be characterized by the fractionation of LREE (La) and HREE (Lu). The element triplet Zn, Cu and Pb offers a clue to the redox regime and supports the idea of mineralogical-based proximity indicators: Zn (Eh≪0)⇒Cu (Eh≤0)⇒Pb (Eh≤0). Oxygen isotope composition (δ18O −8.3 to −0.9‰) of the carbonate fraction resulted in uniform isotope formation temperatures near 50°C. Temperature data obtained during coal petrography yielded maximum paleotemperatures of 100°C for the black shale and about 70°C for the remaining coal samples that are likely to reflect hot brine activity in some parts of the basin. The carbon isotopic composition (δ13C −12.4 to −3.9‰) of the carbonate fractions indicates a biogenic 12C-enriched CO2 source, which probably was admixed to marine pore water bicarbonate (with δ13C near 0‰) during early diagenesis. The S isotope composition (sulfide fraction −28.9 to −24.0‰) is typical of sulfides formed in the course of bacterial reduction with some sulfate (sulfate fraction +7.5 to +11.6‰) resulted from later re-oxidation of the sulfides. Phosphate distribution is a measure for the aridity while high-sulfur contents in the coal-bearing sediments point to brackish or alkaline waters. The results of the organic chemistry are interpreted in terms of a bloom of algae which were preserved during dysaerobic conditions in the course of early diagenesis. Sesqui- and diterpenoids are most probably derived from precursor molecules abundant in leaf resins of conifers. Phenanthrene and its methylated analogues derived from combustion products of fossil fuels generated by wild fires. Among the maceral types, textinites A and B represent xylem features of tree trunks and the crassi-cutinite upper leaf cuticles. The data allow for a definition of a special geological setting called the “Arabian Keuper Facies”. This facies type is characterized by an evaporite–coal transition which translates into a geodynamic setting positioned between the fully marine “Alpine Triassic Facies” of the Tethyan Ocean where submarine brines were responsible for the Alpine-type MVT Pb–Zn deposits and the epicontinental “Germanic Keuper Facies” that lacks both hydrothermal activity and major marine incursions.

Thermal, mineralogical and spectroscopic study of plasters from three post-Byzantine churches from Kastoria (northern Greece)

Several plaster samples were collected from the wall paintings of post-Byzantine monuments from Kastoria town, northern Greece. They were analysed mainly by simultaneous thermal analysis (TG-DTG/DTA) and X-ray diffraction and supplementary by electron microscope (ESEM-EDX) and Raman spectroscopy. Whitish and dark plaster layers were evident in most cases. Calcite, micas, and quartz were the dominant minerals, while dolomite, gypsum, and feldspar were detected as minor phases in most of the samples. Hydromagnesite and chlinochlore were also determined in a few samples. The utilisation of the results for chronological purposes (i.e. for assignment of different painting periods) was also suggested and the presence of dolomite and hydromagnesite could be characteristic for the provenance of the raw material. Gypsum was regarded mainly as a weathering product due to sulfation process, and secondly as a binding material of the plaster. The thermoanalytical results are in good agreement with the mineralogical data. The white plasters are categorized as hydraulic lime mortars, while the dark ones as natural pozzolanic mortars. Calcite and gypsum correlates well with their respective mass losses at certain temperature ranges and their Raman spectra are clearly detected. ESEM-EDX revealed fine calcareous components with aluminolisilicate aggregates and the application of the fresco technique either as a multi-layer or a single-layer plaster. The deterioration caused by salts (gypsum, halite, and nitratine) and micro-organisms was also determined. The detrimental effect of the salt crystallization and dissolution was also confirmed using the so-called Peltier-stage experiment.

Kinetic analyses of biomass tar pyrolysis using the distributed activation energy model by TG/DTA technique

Biomass tar pyrolysis behavior was investigated in absence and presence of catalyst-dolomite (10% mass) with different heating rates of 10, 20, 30 K min−1 under nitrogen atmosphere. Different kinetic methods such as distributed activation energy model (DAEM), Coats–Redfern method were used to analyze the TG/DTA data to identify reaction parameters. For Coats–Redfern method, first reaction order (n = 1) and two stages (volatilization and pyrolysis) reaction model was selected to calculate the kinetics parameters; for DAEM model, three different heating rates (10, 20, 30 K min−1) were selected to obtain the activation energy distribution (Ea). The peak values of Ea curves for biomass tar volatilization process are nearly 250 and 200 kJ mol−1 in absence and presence of dolomite, whereas, the value of Ea for pyrolysis stage gradually increase and varied from 70 to 200 and 40 to 100 kJ mol−1 with the mass loss, respectively, in absence and presence of dolomite. The application of the new DAEM model can show the variation trend of activation energy for the whole pyrolysis process.

Assessments of natural and anthropogenic controls on the spatial distribution of stream water quality in Southeastern Korea

Hydrogeochemical and geostatistical analyses were conducted to evaluate natural and anthropogenic effects using stream water data of Southeastern Korea acquired through the Hydrogeochemical Survey Program of the Korea Institute of Geoscience & Mineral Resources. The results of a variographic analysis of the spatial structure of stream water quality show that the semivarigrams of Ca, Mg, and HCO3 have similar patterns and regional distributions, reflecting the same geogenic source of Paleozoic, Tertiary, and Cretaceous sedimentary rocks. Although Ca and Mg originated from Paleozoic sedimentary rocks, the distribution of Mg is significantly different from that of Ca due to the presence of dolomite in northeastern area of Korea, which enhances the Mg concentration in stream water. Studies of mineralization and acid mine drainage resulting from previous mining activities reveal a high Ba in sedimentary rock from of Kyongsang basin, as well as anomalous concentration of Al, Fe, and SO4 in the Ogcheon and Tabaeksan mineralization areas. Saturation indices of barite determined using average Ba and SO4 concentrations in stream water suggest the existence of barite mineralization deposits in sedimentary rock of Kyongsang Group. Na, Cl, K, NO3, and Cl, exhibit effects of anthropogenic and marine sources in the stream water, with increasing values near residential, agricultural, and coastal areas. Cokriging analyses employing Ca-HCO3, Ca-Sr, Ba-SO4, and Na-Cl also revealed the nature of bedrock geology, mineralization, and anthropogenic and marine sources.

Microbial communities in Messinian evaporite deposits of the Vena del Gesso (northern Apennines, Italy)

The Vena del Gesso (Northern Apennines) is a 230 m-thick succession consisting of up to 16 gypsum-shale cycles belonging to the “Lower Evaporites” formed during the Messinian salinity crisis in theMediterranean. The study of the microbial communities preserved in the gypsum crystals of one complete cycle (6 th cycle at Monte Tondo quarry) showed abundant, regularly arranged filamentous forms that resemblemorphologically modern obligate phototrophes, cyanobacteria colonizing modern photic, shallow-water gypsum basins. At least four different bacterial populations have been recognized: a) filamentous type cyanobacteria with characteristic inserted funnel shaped structure resembling the modern Scytonematacean; b) Type 1 organisms consisting of filamentous structures impregnated by clay minerals containing pyrite grains in the outer sheath; c) Type 2 filaments filled by clay minerals with dolomite in the outer sheath; d) Type 3 filamentous organisms with a central hollow tube and an encrusted outer sheath mainly composed of calcium carbonate. These organisms were probably associated with other heterotrophic bacteria as suggested by the presence of dolomite and pyrite structures. The size and preservation suggest that most of these cyanobacteria were likely conducting oxygenic photosynthesis as presently observed in modern solar salt works. It follows that they were living in shallow water settings or settled down from the water column to the bottom of a relatively deep evaporite basin.

A Geochemical Process Model for the Mount Isa Copper Orebodies

In this paper we present new data and review existing data on the distribution, lithochemistry and paragenesis of copper ore at Mount Isa and provide the first description of a body of anhydrite, dolomite, barite, and hematite recently intersected at the northern end of the copper system. It has been previously proposed that the extraordinary spatial coincidence of giant copper and lead-zinc deposits at Mount Isa is due to the emplacement of copper into host rocks made chemically favorable for copper mineralization by enrichment in dolomite and/or pyrite and mechanically favorable by the presence of preexisting layers of ductile lead and zinc sulfide ore. Several recent studies, however, suggest that copper and much if not all of the lead and zinc were deposited contemporaneously. We provide evidence that high-grade (>2.5%) copper is associated with fractured and silicified rocks. Early breccia-cementing quartz is commonly euhedral and contains numerous growth zones defined by disordered carbon and brine inclusions containing CH4. This quartz is inferred to have been deposited from a cooling brine (“basement brine”) that equilibrated with rocks beneath the level of the deposit. Consistent with earlier studies, we have noted that there is often late dolomite (dolomite II) infilling of vuggy porosity defined by this euhedral quartz. Chalcopyrite, however, postdates both phases and there is textural evidence of both dolomite and quartz dissolution during chalcopyrite formation. The nature of the copper-bearing fluid (“basinal brine”) was deduced from the intimate association of chalcopyrite and anhydrite and from previous fluid inclusion studies. This brine was oxidized and sulfur rich but undersaturated in quartz, consistent with this fluid being introduced from above as proposed in several previous studies. New reaction path modeling suggests that reduction of the oxidized brine by the carbonaceous and Urquhart Shale was the most likely depositional process. Many other rock types in the region also had the capacity to reduce oxidized ore-forming brines, thus ore can be anticipated in these other units, provided that sufficient porosity and permeability existed during ore formation. The modeling further suggests that the presence of dolomite is not a prerequisite to economic copper grades, although carbonate dissolution possibly contributed (with fracturing) to enhanced porosity and permeability. Furthermore, sulfide-rich rocks were no more effective at precipitating copper than sulfide-absent rocks, consistent with several lines of evidence demonstrating that pyrite or other sulfide minerals were not consumed during ore formation. Mixing of the basinal and basement brines could also have caused precipitation of copper, but the predicted gangue assemblages differ from those observed in nature. Various radiometric ages are consistent with formation of the Mount Isa copper deposits after initiation of the unconformable South Nicholson basin, although we recognize that more precise and accurate dating of the ore and fluid-flow events are required. Basal red-bed sediments of the South Nicholson basin would have provided suitable aquifers for the oxidized, copper-rich basinal brines. We speculate that the driving force for brine flow was the development of topography to the east of Mount Isa.

Mineralogical and geochemical changes in the sediments of the Okhotsk Sea during deglacial periods in the past 500 kyrs

Characterized by extended seasonal sea-ice cover, the Okhotsk Sea is widely considered one possible source of the North Pacific Intermediate Water (NPIW). Therefore, reconstructing the characteristics of the sediments that resulted from the ice-melting pulses of this northeastern Asian sea during glacial–interglacial cycles is crucial to understanding past climatic changes and NPIW formation in the northwest Pacific Ocean. Here, we produced the detailed mineralogy and geochemistry of the upper 20 m of the sediments of IMAGES Core MD012414, which was drilled in the central part of the Okhotsk Sea. This depth covers the last 500 kyrs. The mineralogical data show that in glacial periods, the sediments were predominantly composed of quartz and plagioclase with a volume of about 80%, indicating that they were mainly from the surrounding landmasses. During interglacial periods, however, biogenetic calcite and amorphous opal drastically increased from less than 5% to a remarkable 40–60%, while the element ratios Mg/Al, Ca/Al and Si/Al also had anomalous increases from 0.2 to 0.5, 0.12 to 1.2 and 3.5 to 10, respectively. These characteristics of the sediments in interglacial periods strongly suggest that the melting of permanent ice opened a gateway, thereby letting the northwest Pacific warmer water flow into the Okhotsk Sea, which subsequently increased biogenetic productivity during the deglacial periods. In addition, in early interglacial periods, the bottom water became anoxic, as evidenced by the presence of dolomite and the enrichment of the Mn/Al and P/Al ratios more than 25 to 200 times. The fact that these trends did not occur in stage 7 strongly suggests that stage 8 may have been a warmer glacial period.

Fluidised bed co-gasification of coal and olive oil industry wastes

Co-gasification of bagasse wastes mixed with coal is technically feasible, without major installation changes. The effect of experimental conditions on co-gasification process was analysed, to enhance gas production and improve its composition and energetic content. The rise of bagasse content increased tars and gaseous hydrocarbons contents, which can be reduced by increasing gasification temperature and/or air flow rate. The rise of temperature till 890 °C favoured hydrocarbons further reactions and allowed an increase of 45% in hydrogen release and a decrease in gaseous hydrocarbons of 55%. A reduction of around 30% in gaseous hydrocarbons was also achieved by rising O 2/fuel ratio till 0.6 g/g daf, which decreased gas heating value, due to nitrogen diluting effect. Though no significant changes in gaseous hydrocarbons composition were obtained, the presence of dolomite in the fluidised bed had the benefit of decreasing tars content and rising gas yield, being the gas richer in hydrogen content.

Palygorskite in the uppermost Cretaceous–Eocene rocks from Marrakech High Atlas, Morocco

Uppermost Cretaceous–Eocene series of the Marrakech High Atlas consist of alternations of marl, dolomite, limestone, gypsum and phosphatic beds. The rocks were deposited in a shallow, coastal marginal basin characterised by rapid changes in salinity. Palygorskite occurs as interwoven fibrous mats forming fine laminae and as coatings and pore-filling, and pore-bridging cements in dolomitic marls. This textural evidence suggests a direct chemical precipitation, mostly post-dating dolomitization. A magnesium concentration in presence of dolomite was sufficient for palygorskite precipitation; the necessary Si and Al were derived by dissolution of silicates under alkaline conditions. The maximum development of palygorskite was near the top of the upper sedimentary system, which was deposited during a marine transgression.

Geochemistry of submarine warm springs in the limestone cavern of Grotta Azzurra, Capo Palinuro, Italy: evidence for mixing-zone dolomitisation

Subtidal springs in and around the submarine limestone cavern of Grotta Azzurra, at Capo Palinuro, Italy, discharge fluids which are warm (< 25°C), mildly acidic, depleted in Cl −, Na + and Mg 2+, and enriched in Si, alkalinity, Ca 2+, Sr 2+, Mn, NH 4 +, PO 4 3− and H 2S, relative to surrounding seawater. The compositions of the warm fluid samples collected in and around the cave define mixing lines which suggest dilution of a single thermal fluid ( T ≥ 23°C) by cool overlying seawater ( T= 17–17.6°C). The chemical data suggest that the proposed thermal fluid contains two components, one derived from seawater (< 90%) and the other from low-salinity groundwater (> 10%). Excess Si, alkalinity, Ca 2+, Sr 2+ and Mn relative to seawater are likely derived from the groundwater component or dissolution/hydrothermal alteration of the host rocks. Magnesium has been removed from the seawater component in exchange for Ca 2+, due to dolomitisation of the limestone and/or hydrothermal alteration reactions. Saturation-state calculations suggest that the vented fluids are near saturation with respect to calcite and supersaturated with respect to dolomite. This and the presence of dolomite in the host rocks and cave-floor sediments suggest that “mixing-zone” dolomitisation of the limestones is occurring, perhaps kinetically assisted by elevated temperature and/or bacterial mediation in the reducing subseafloor zone. One possible “end-member” condition is considered for the thermal fluid — zero-Mg — which suggests an end-member temperature of 50.5°C and a fluid composition derived from ∼ 38% seawater and ∼ 62% groundwater. The heat source for the circulating fluids is uncertain, but may involve warm underlying igneous rocks or heating via the geothermal gradient. A continuous in-situ record of vent-fluid temperature, salinity, pH and O 2 concentration collected within the cavern is consistent with our interpretation of the fluid origin, and suggests that tidal forcing affects circulation and venting of the warm fluids.