Composition Of Dolomite Research Articles

Reservoir Quality Under the Control of Gravity Flows in the C7 Member of Yanchang Formation in the Jinghe Oilfield, Ordos Basin, China

The late Triassic sandstone reservoir in the C7 member of the Jinghe oilfield southern Ordos basin is a typical deep-water gravity flow tight oil reservoir. Sedimentary microfacies, physical properties, and petrographic analysis were being examined for quality determination. Pore structure and physical properties data together combined with, thin sections, and scanning electron microscope and core images were used to identify factors controlling reservoir physical properties. The depositional system under debates of different gravity flows including debris flow, seismite slumping, and turbidity flows. Among which sandy debris flow facies shows a better distribution of porosity and permeability followed by seismite-slump, where turbidity facies are the poorest. The petrophysical analysis shows that the study oil interval is a typical tight sandstone reservoir with an average porosity of 9% and permeability average being 0.025mD. The rock classification criteria of the C7 sandstone reveal the sub-categories of lithic feldspar sandstone and feldspar lithic sandstone. Average quartz sandstone contents of 48.25%, average feldspar sandstone content being 25%, and lithic fragments content of 29%. The formation lithology comprises mostly fine-grained sandstone and small pore size, which disclose that the porosity-permeability distribution increases proportional to the average and median pore throat radius, and decreases with average and median pressure. The microfacies distribution shows that the depositional facies controlled physical properties. The sandstone primary pores are affected by the mineral composition of quartz, feldspar, illite, smectite, kaolinite, calcite, and dolomite. Features such as dissolved pores and intergranular pore filling by feldspar, silky-like aggregates of illite-smectite intergranular pore filling and most diagenetic minerals influenced the sandstone pores beside the compaction.

Stable isotope geochemistry evidences from fossil carbonate and sulfur minerals on the origin of geothermal water, Kızıldere Geothermal Field, Western Turkey

The Kızıldere geothermal field, located at the eastern part of the Büyük Menderes graben in Western Turkey, is the most important geothermal reservoir suitable for electricity generation. Current and fossil fumaroles and alteration zones are directly related to the tectonic zones influenced by N-S directional extension since Miocene period. Associated to fossil geothermal activities carbonate (calcite, dolomite) and sulfate (gypsum, anhydrite) minerals were occurred in the form of void/crack fill and bands/lenses parallel to bedding of Neogene clastic and carbonate rocks. The carbon (δ13CPDB ‰) and oxygen (δ18OPDB ‰) isotope compositions of hydrothermal calcites and dolomites and sulfur (δ34SCDT) and oxygen (δ18OSMOW) isotope compositions of gypsum and anhydrites are analyzed first time and correlated current geothermal water composition. The carbon and oxygen isotope data of calcites and dolomites have similar carbon but different oxygen isotope composition which increases in the direction of surface calcite – drill cuttings calcite – drill cuttings dolomite – surface dolomite. The isotope compositions of calcite and dolomite minerals range between limestone and marble host rock compositions and indicate the carbonate mineral-forming fluids originated from dissolution of carbonate rocks during the circulation of hot geothermal waters. According to the calcite-CO2 and dolomite-CO2 isotopic fractionation data for the 0–300 °C temperature range, the fossil isotope composition is higher than the composition of current CO2 and reflects relatively lower temperature conditions. The isotope compositions of gypsum and anhydrite minerals indicate that hot thermal waters dissolved terrestrial evaporites and formed a sulfur-rich geothermal solution, and hydrothermal gypsum and anhydrite precipitated from this solution. The δ34SCDT compositions of hydrothermal gypsum and anhydrites are similar to the current geothermal water compositions. Stable isotope geochemistry data of hydrothermal carbonate and sulfate minerals in the Kızıldere geothermal field have shown that the fluids forming these minerals were originated from host rocks instead of magmatic volatiles.

Seismic faulting and CO2-rich fluid interactions: Evidence from carbonate spherulitic grains in ultramafic fault damage zones

Faults and shear zones in the metamorphic ultramafic rocks of the Voltri Massif (Ligurian Alps, NW Italy) are often accompanied by intense or complete carbonation of the host rocks. One of these fault zones, hosted in peridotite and serpentinite, is characterized by distinctive structural features that can be related to a fluid-assisted multistage brittle deformation, indicative of paleoseismic activity. The fault rocks contain cataclasite and breccias with layers of coseismic spherulitic grains of dolomitic composition, silica/calchedony veins and cement, and saponite bearing gouge. The fault is part of a system of regional structures associated with gold mineralization in quartz veins and various stages of hydrothermal alterations.Here we present a multiscale study of this fault zone combining field observations, microstructural analysis, SEM-EDS, and electron backscattered diffraction (EBSD). Focus is on the microstructures of the fault core and the significance of the characteristic carbonate spherulite layers in association with silica/chalcedony cement and veins. Our results show that these structures are indicative of the interaction between CO2-rich fluids released during coseismic and interseismic phases of faulting, i.e., during cycles of fluid pressure build-ups, faulting, fluid flushing, and mineral precipitation and sealing during seismic failure of the fault.

Magnesium isotopic compositions and origin of Neogene dolomites in Xisha Islands, South China Sea

A common consideration of dolomite-based records for paleoseawater geochemistry reconstruction is the process of dolomite precipitation, which is closely related to the source of relevant elements. “Island dolomite” has been proposed as having great potential for recording paleoseawater geochemical characteristics, however, dolomitization should be strictly constrained in advance. As a major element in dolomites, magnesium (Mg) and its isotopes are critically involved in dolomitization, which may serve as a tool for providing direct insights into this process. Here, we report the Mg isotopic compositions of reef dolomites from the well Xike−1 reef core in Xisha Islands, South China Sea. The geochemical and mineralogical characteristics suggest that these reef dolomites experienced limited diagenetic alteration, and retained primary geochemical characteristics after dolomitization was complete. These reef dolomites reached chemical equilibrium with contemporaneous seawater during dolomitization, which were buffered by coeval seawater. Our results suggest that the development of carbonate platform and the formation of reef dolomites in Xisha Islands were related to tectonic subsidence. These reef dolomites were deposited during periods of decreasing tectonic subsidence rate. Then, dolomitization model for these reef dolomites was established, which provides an effective basis for reconstructing the chemical characteristics of paleoseawater. The occurrence of near-invariant seawater δ26Mg value during the past ∼23 Myr was subsequently verified via cross-checks provided by different seawater δ26Mg archives in this and previous studies. Our results highlight the great potential of seawater-buffered dolomites with limited postdepositional diagenetic alteration for constructing paleoseawater geochemistry though the geological history.

The covariation between Mg[sbnd]C isotopes and trace elements in dolostones: Implications for reconstructing the seawater chemistry

Magnesium isotopes of marine dolomites have the potential to reconstruct the Mg isotopic signals of coeval seawater. However, a massive dolostone sequence can form via the coupling effects of multiple dolomitization events, which can potentially reset the Mg isotopic compositions of dolomites during each migration of the dolomitization fluid. How to distinguish changes of seawater chemistry and early diagenetic effects which have been recorded in dolomites is crucial for the reconstruction of seawater Mg isotopic signals. Here we studied the Mg-Sr-C-O isotope systematics and trace elements of a dolostone sequence from the Qiangtang Basin in the hinterland of Tibet. Multiple lines of evidence consistently indicate the lack of deep-burial diagenesis and high-temperature alteration in the carbonates. The stratigraphic variations of isotopic and elemental compositions of the dolostone profile are generally characterized by the co-variation between MgC isotopes and trace element contents. Our modeling results indicated that a single downward dolomitization can cause the large Mg isotopic variability of dolomites, ca. 1 ‰, within a dolomitization front. However, when the limestones in the profile were completely dolomitized, the coupling effects of multiple downward dolomitizations will homogenize the δ26Mg values of dolostones. Therefore, we attribute the observed co-variation in isotopic and elemental signals in the dolostone sequence to the changes in the chemistry of evolved seawater within the platform. The reconstructed seawater δ26Mg values from the Carnian to Early Jurassic are lower than previous model-based estimations. This result implies an overestimation of the production of shallow-water carbonate in literature during Late Triassic to Early Jurassic. Our study highlights the importance of utilizing multiple geochemical proxies to identify the controlling factors driving Mg isotope variability in dolomites.

Heavy Li isotopic compositions of the terminal Ediacaran dolostones in the Tarim Basin and their possible link to dolomitizations

Dolostones are promising archives for recording paleo-seawater Li isotope compositions, and are especially important for the Cambrian and Precambrian periods when limestones are scarce. However, the effect of dolomitization on carbonate Li isotopes is unclear, limiting their application in tracking (Pre-)Cambrian seawater Li isotopes. Research on Li isotopes in dolostone sections may resolve this issue. We present the Li isotope compositions of dolostones from the terminal Ediacaran Chigebrak Formation (NW Tarim Basin). The dolostone Li isotopes are ∼17 ± 5 ‰ heavier than contemporaneous seawater, indicating significant Li isotope fractionations during dolomite formation. Given that the formation of clay minerals may enrich the porewater with heavier Li isotopes and promote the dolomite formation, we argue that the clay-catalyzed dolomite formation would probably result in heavier Li isotope compositions of dolomites. Moreover, assuming a fixed fractionation factor (∼15 ‰) for the clay-catalyzed dolomitizations, we obtain the seawater δ7Li variations in the terminal Ediacaran, which show similar declining trends with the carbonate 87Sr/86Sr record. Using a simple ocean Li-Sr box model, we propose a reduced weathering scenario during the terminal Ediacaran (∼549 Ma) to explain the seawater Li-Sr isotope covariations. Our study suggests considerable fractionations of Li isotopes (∼17 ± 5 ‰) during clay-catalyzed dolomite formation and a reduced-weathering scenario during the terminal Ediacaran. This large Li isotope fractionation factor indicates the Li isotope fractionation factors during dolomitizations may vary widely and should be considered based on the type of dolomitization. More comparative studies on Li isotopes among coeval carbonates are expected to further explore the potential of dolostones in recording paleo-seawater Li isotopes.

PRE‐, SYN‐ AND POST‐TECTONIC DIAGENETIC EVOLUTION OF A CARBONATE RESERVOIR: A CASE STUDY OF THE LOWER CRETACEOUS FAHLIYAN FORMATION IN THE DEZFUL EMBAYMENT, ZAGROS FOLDBELT, SW IRAN

Lower Cretaceous carbonates of the Fahliyan Formation form prolific reservoir rocks at oilfields in the Dezful Embayment, central Zagros fold‐thrust belt, SW Iran. The carbonates have undergone significant diagenetic alteration in phases which can in general be linked to the pre‐, syn‐ and post‐tectonic evolution of the fold‐thrust belt. This paper investigates the impact of diagenetic processes on the reservoir quality of the carbonates using integrated petrographic, geochemical and sedimentological analyses of subsurface and outcrop samples of the formation. Diagenetic alterations include:(i) pre‐tectonic eogenesis in the marine and shallow‐burial realm, which resulted in micritization of allochems and cementation by equant and isopachous calcite rims and framboidal pyrite together with limited dolomitization and dissolution of metastable bioclasts. The isotopic compositions of micrite and early calcite cement depart from postulated values of Lower Cretaceous marine carbonates, signifying early stabilization of precursor metastable carbonate minerals and the possible effects of the incursion of meteoric waters and/or increasing burial temperatures;(ii) mesogenesis during the subsequent syn‐tectonic phase, which included Late Cretaceous ophiolite obduction at the northern margin of the Arabian Plate and the later Zagros orogeny in the Miocene‐Pliocene. Diagenetic modifications included the emplacement of hydrocarbons, the development of stylolites and fractures, and the precipitation of saddle dolomite, replacive rhombic dolomite, discrete pyrite, microcrystalline quartz, kaolin and anhydrite. The average stable isotope compositions of saddle dolomite (δ18O: ‐6.9 ‰ ± .9 and δ13C 0.5 ‰ ± 1.6, respectively) also reflects the influence of high temprature basinal fluids;and (iii) “late” (telogenetic, post‐tectonic) uplift‐related modification starting in the Pliocene, when the incursion of meteoric waters resulted in the formation of vugs, the calcitization of dolomite, and cementation by fracture‐filling blocky calcite. The negative δ18O and δ13C stable isotope values (average: ‐5.5 ‰ ± 1.5; and ‐3.6 ‰ ± 5.9, respectively) of late blocky calcite cement suggest the incursion of meteoric water into the system.This study demonstrates that diagenetic processes in carbonates in the Fahliyan Formation, which exerted a significant control on the distribution of secondary porosity, can be related to the tectonic evolution of the central Zagros fold‐thrust belt. Thus, constraining the diagenetic history of carbonate successions within the context of their wider tectonic evolution is important for the prediction of the spatial and temporal distribution of reservoir quality.

Lithium isotope composition of Ediacaran dolostones from the Nuccaleena and Doushantuo formations

The end of the Cryogenian glaciations undoubtedly affected the chemistry of the Neoproterozoic oceans, with potential consequences for the evolution of life; the duration and extent of this influence are poorly constrained. Lithium (Li) isotopes in carbonates can be used to investigate past weathering events and riverine input into the oceans. Here, we report the Li isotope (δ7Li) composition of the Ediacaran cap dolostones (Marinoan) from the Nuccaleena Formation, South Australia and the Doushantuo Formation, South China to investigate changes in weathering during the aftermath of the Marinoan glaciation. The origin of dolomite formation is still hotly debated, and the inability to precipitate dolomite at ambient temperatures (the ‘dolomite problem’) has not yet been resolved. The dominant hypothesis for the presence of marine dolomite is that it is of secondary origin, owing to diagenetic replacement of calcium carbonate, but a second hypothesis is that it forms as a result of primary marine deposition; both are plausible hypotheses. Using carbon isotopes (δ13C) and ratios of manganese and strontium (Mn/Sr), we suggest that diagenesis may not have significantly altered the δ7Li composition of the primary dolomite, but this cannot be discounted without further diagenetic modelling. As a result, we cannot infer the δ7Li composition of the Ediacaran oceans, as further work must be done to address the impact of diagenesis on the δ7Li values. Nevertheless, this dataset contributes to a Li isotope chemostratigraphic record of the Proterozoic, which is a key element to understanding the emergence of complex life.

Triassic gypsum layers in Keban Metamorphics, eastern Tauride Belt, Southeastern Turkey: New data about Triassic rifting in northern Tethys margin

ABSTRACT A gypsum interlayer with 100 m thick was identified within the Early-Middle Triassic shelf type clastic and carbonates of the Keban Metamorphics, along the shore of the Fırat River, ~500 m west of Keban district (Elazığ, southeast Turkey). Gypsum layers have thickness of 15–50 cm, and exhibit the original sedimentary bedding intercalated with dolomitic carbonate rocks. They were subjected to hydrothermal alteration related to late Cretaceous magmatic intrusions. Hydrothermal activity caused the dissolution and recrystallization of gypsum, as well as occurrences of secondary gypsum, elemental sulphur and quartz (amethyst). The geochemical (trace element and sulphur and oxygen isotope) compositions of gypsum and dolomites indicate typical marine evaporite compositions. The δ34S and δ18O values of the Keban gypsum correspond to Early Triassic evaporites, based on Early-Middle Triassic seawater sulphate composition. Keban gypsum represents Triassic rifting along the northeastern margin of Gondwana and exhibits similar age (Early-Middle Triassic) and palaeogeographic setting to Kemer (Antalya, Turkey) gypsum, associated with opening of the Neotethyan Ocean between Gondwana (Pangea) and the Cimmerian microcontinent. However, the Keban gypsum is different from the late Triassic Honaz-Denizli and Nusaybin-Gaziantep gypsum representing the southern margin of the Paleo-Tethys Ocean (Tauride Belt) and southern margin of the Neo-Tethys (Arabian Plate). The presence of gypsum is observed on both passive continental margins of Neo-Tethys means that their deposition took place before the subduction of the Neo-Tethys Ocean during Late Triassic-Jurassic period.

Chronology of detrital carbonate events in Baffin Bay reveals different timing but similar average recurrence time of North American-Arctic and Laurentide ice sheet collapse events during MIS 3

Baffin Bay Detrital Carbonate (BBDC) layers represent periods of elevated discharge of terrigenous sediments, icebergs and freshwater originating from the North American Arctic-ice sheet complex. Distinct from Heinrich event layers in their dolomitic composition, these sedimentary deposits are found throughout Baffin Bay. They are considered a signature of large-scale instability of the ice sheets discharging into the Baffin Bay, akin to the Heinrich events of the North Atlantic. However, the precise timing of and potential forcing mechanisms for the North American Arctic-ice sheet instabilities remains elusive. Previous work suggests that BBDC events were not in phase with Heinrich events originating from the Hudson Strait, but this hypothesis could not be tested without rigorous chronological constraints. By combining radiocarbon ages and relative paleointensity (RPI) dating in a central western Baffin Bay marine sedimentary sequence, we were able to derive a new chronology for BBDC events covering a large part of MIS3. Sedimentological and elemental data indicate the occurrence of seven distinct BBDC events over the last 52 ka. These events occur during both glacials (stadials) and interglacials (interstadials) and have no consistent phase relationship with Heinrich events. However, the mean duration and mean recurrence time of BBDC events appears similar to Heinrich events. We conclude that BBDC events reflect repeated ice sheet instability periods, with similar statistical properties but different timing compared to the Heinrich events. This implies that episodic instability was an intrinsic property of the North American Arctic-ice sheet complex as well, but over the studied period of MIS3, instabilities of the Arctic and the Laurentide Ice sheets did not appear to have been linked.

New analytical method for the evaluation of heterogeneity in cation compositions of dolomites by micro-XRF and Raman spectroscopies.

Dolomite (CaMg(CO3)2) is an abundant carbonate mineral contained in sedimentary rocks and plays significant roles in water and carbon cycle in geo/cosmochemical environments. Since the cation compositions of carbonates are sensitive to the aqueous environment where they were precipitated and persisted, quantitative analysis of their cation compositions provides valuable information on the aqueous environments and their changes. The difficulty for the analysis of natural dolomite is that Mg2+ is continuously substituted by Fe2+ or Mn2+, and hence they sometimes possess micrometer-scale heterogeneity. Such heterogeneity carries quite important information on the gradual changes in aqueous environments due to changes in thermodynamic conditions and/or aqueous chemical compositions. In the present study, we explored a new quantitative scale to assess such heterogeneity of cation composition in natural dolomite and ferroan dolomite by combining X-ray fluorescence (XRF) and Raman spectroscopy. While the Fe + Mn content differed spot-by-spot, it was found that the Raman wavenumber and Fe + Mn content linearly correlated with each other. Since the spatial resolution of micro-Raman spectroscopy is as high as 1μm, it does not require vacuum conditions, and is free from so-called matrix effect faced in other methods utilizing X-Rays and electron beams, the proposed qualitative analytical scale can provide a useful tool to assess the cation compositions in dolomites found in nature.

Oxygen isotopic composition of Paleoproterozoic seawater revealed by clumped isotope analysis of dolomite, Vempalle Formation, Cuddapah, India

The Paleoproterozoic (∼2.0–1.9 Ga) Vempalle Formation, in the south-western part of the Cuddapah Basin, is a well-studied Paleoproterozoic succession. Detailed descriptions of sedimentological features, micro-textures, and isotopic compositions of dolomite in the stromatolites and associated lithologies suggest that the succession was deposited on a carbonate ramp. Early burial diagenesis of the dolomite modified the original isotopic signatures. Nonetheless, here we discern evidence for two distinct depositional events based on clumped isotopic signatures preserved within dolomitic stromatolite and the underlying dolomite mud. Dolomitic muds within cherty precipitate record original thermometry signatures from these rocks. Clumped isotope analyses suggest that the lowest temperature of the Paleoproterozoic seawater was 21.8 ± 2 °C, and that its isotopic composition (δ18OVSMOW) during dolomite precipitation at equilibrium was −9.6 ± 0.1‰, which is lighter than that of present-day ocean water. The overlying stromatolitic dolomite exhibits a temperature range of 70.7–109.8 °C, reflecting late-stage diagenetic processes and hydrothermal activity. Hydrothermal fluids were isotopically enriched (up to 4.9‰) suggesting their mantle origin and interaction with evaporative seawater. We evaluated the degree of water-rock interaction with water of heavier isotopic composition that was responsible for the precipitation of late phase dolomite found in the strata overlying carbonate mud.

Numerical studies and analysis on reaction characteristics of limestone and dolomite in carbonate matrix acidizing

Carbonate reservoirs with abundant oil and gas resources are mainly composed of limestone and dolomite. As the acid-rock reaction progresses, limestone is gradually consumed and more acid gradually reacts with the slower dolomite. However, the existing acid rock-reaction models do not consider the competition between limestone and dolomite with acid, and cannot objectively describe the degree of contribution of limestone and dolomite to wormholes at each stage of acidizing. Here, an acidizing model was developed to study and analyze the effect of the reaction characteristics of limestone and dolomite on the carbonate acidizing. In this study, the probability of limestone and dolomite contact with acid is assumed to be related to the content of limestone and dolomite, and a new acid-rock reaction model is proposed by considering the reaction rate and reaction sequence of limestone and dolomite. The acid-rock reaction model is coupled with the porous medium heat transfer model and the two-scale continuum model, and a comprehensive carbonate acidizing model is established. The model can respond to the competition between limestone and dolomite in each stage of acidizing at different temperatures and quantitatively characterize the dynamic change of different mineral contents. Based on the model, this work studies and analyzes the effects of the temperature, dolomite characteristics (uniform, blocky, and columnar) and distribution orientation on wormholes propagation and acidizing efficiency. The simulation results show that the comprehensive carbonate acidizing model can accurately reveal the higher contribution of limestone to the wormhole when the temperature is less than 338 K. As the temperature increases, the difference of reaction rate between limestone and dolomite gradually decreases, and the contribution of dolomite to the wormholes increases. When the temperature is 418 K, the dissolution of limestone and dolomite in the wormholes and the area around the wormholes is almost the same. Moreover, when the temperature is 298 K, the smaller size and density of blocky and columnar dolomite can make the wormholes tortuous and complicated, thus reducing the acidification efficiency. When the size and density are larger, the presence of dolomite can hinder the generation of branching wormholes and guide the propagation of wormholes, enhancing the acidizing efficiency. In addition, the orientation of dolomite does not change the propagation distance of wormholes, but it changes the propagation orientation of wormholes. This study privates a guide for the acidizing treatment of carbonate reservoirs with the different mineral compositions of limestone and dolomite.

Effect of Epsom Salt Concentration and Dry-Mix Composition on Bonding Properties of Magnesium Oxysulfate

Non-hydraulic magnesium oxysulfate cement has many superior properties than ordinary portland cement and it draws much research interest due to energy saving and environment protection considerations. It is formed by the exothermic reaction between lightly calcined MgO and MgSO4·7H2O (epsom salt) solution. This heat is responsible for cracking and makes the product unsound. The incorporation of inert filler can overcome this problem by absorbing the excess heat. In present work, a parametric study was conducted to investigate the effect of dry-mix composition (MgO: inert filler) and gauging solution epson (MgSO4·7H2O) concentration on cementing properties of magnesium oxysulfate cement. The results show that a 1:1 dry-mix composition of MgO and dolomite with 25º Be concentration of magnesium sulfate works best in the cementing action of magnesium oxysulfate

Boom Clay pore-water geochemistry at the Mol site: Chemical equilibrium constraints on the concentrations of major elements

It is important to understand the mechanisms controlling the chemistry of the pore water in the Boom Clay, which has been studied as a reference host rock for the geological disposal of radioactive waste. The chemistry of the pore water and the related properties of the Boom Clay were investigated experimentally. This paper presents the results of equilibrium calculations and discusses the probable chemical constraints that control the concentrations of major elements in the pore water. The present-day Boom Clay pore water is a dilute NaHCO3 solution of 10–20 mM, and the concentration increases with the depth of the Boom Clay over a thickness of 65 m around the underground laboratory at approximately 200 m below sea level. The present-day NaHCO3 water is likely a result of freshwater infiltration, and the concentration profile observed must have been affected by waters from upper and lower aquifers. Among the minerals found in the Boom Clay, equilibrium calculations indicate that the pore water is in equilibrium with calcite, dolomite, siderite, pyrite, and quartz. Aluminium silicate minerals, kaolinite and chlorite, are also possibly in equilibrium, but their saturation states cannot be fully demonstrated mainly because of uncertainties associated with the pore-water concentration of aluminium. Cation exchange, an important property of clays, seems to be controlling only the pore-water concentration of potassium. Concentrations of other cation exchangeable elements, such as calcium and magnesium, are more likely regulated by the solubility of carbonate minerals. On clay surfaces, however, cation-exchange reactions are evidenced and control occupancies of all exchangeable cations. The cation-exchange pool on clay responds to the increase in NaHCO3 concentration with depth, and the surface occupancies vary according to the selectivity of exchangeable cations. Equilibrium calculations allow us to propose a Boom Clay reference model that is able to explain the observed pore-water chemistry. This model is compared to other models in the literature, such as those for the Opalinus Clay in Switzerland and Callovo-Oxfordian Clay in France, which have also been studied for the purpose of radioactive waste disposal. Future studies to improve our understanding of the Boom Clay pore-water geochemistry include i) accurate determination of the pore-water concentration of aluminium, which is crucial for studying the mineral saturation state of aluminium silicates; ii) improving understanding of the mineralogical composition of dolomite in the Boom Clay and its dissolution mechanisms; iii) reassessment of magnesium cation-exchange occupancy on clay surfaces; and iv) improving pore-water sampling and analysis techniques with respect to pH and pCO2 measurements to avoid perturbations to water samples so that the in situ conditions can be preserved to a maximum extent.

Conservative behavior of Mg isotopes in dolomite during diagenesis and hydrothermal alteration: A case study in the Lower Cambrian Qiulitage Formation, Gucheng area, Tarim Basin

Recovering the Mg isotopic composition of seawater using penecontemporaneous dolomite is possible; however, the Mg isotopic composition of dolomite may be changed by later diagenesis and hydrothermal activities. Solving this problem requires further research on the behavior of Mg isotopes in dolomitization systems. Diagenesis and hydrothermal fluids have significantly altered the considerable amount of dolomites in the Lower Cambrian Qiulitage Formation in the Gucheng region of the Tarim Basin. Thus, this formation is excellent for examining the behavior of dolomite Mg isotopes after diagnostic and hydrothermal alterations. The results of major and trace elements and C–O–Mg isotope analysis show that the dolomite of Qiulitage Formation is penecontemporaneous dolomite, and the Mg in dolomite is mainly from the Early Cambrian seawater. The dolomites of the Qiulitage Formation in the Gucheng area are formed by carbonate platform facies. The stratigraphic variability of Mg isotopes is small, averaging −2.08‰± 0.23‰, which indicates that the Mg isotope of the dolomitized fluid in the large-scale dolomitization process of the carbonate platform is uniform and balanced with the seawater in the same period. In addition, the Mg isotopic composition of dolomite is stable, and the δ26Mg value is not affected by burial diagenesis and hydrothermal fluid activities. we found that the Mg isotopic composition and stratigraphic age of the dolomites of the Lower Cambrian Qiulitage Formation are consistent with the simulated results, the δ26Mg value of the ancient seawater in the Early Cambrian is estimated to be about −0.08‰±0.23‰. This study shows that the δ26Mg of penecontemporaneous massive dolomite may have been used to invert the Mg isotopic composition of seawater during the same period, within a confidence range of ±0.2‰, using massive dolomite, and provided a new idea for quantitatively reconstructing the marine Mg cycle in the geological history.

Petrological, Geochemical and Mechanical Characteristics of Afghan White Marble

The aim of this article is to examine the Geological, Geochemical, Mineralogical, and Physical-Mechanical characteristic of Afghan White Marble deposit in Nangahar province Afghanistan. The objective of the article includes information about the value, quantity & quality of the marble mine. In addition, this study summarizes information related to the marble mining methods, Processing and production tools technologies used for extracting of Marble in Afghanistan. To achieve, the aim of the research, library, field and Laboratory methods have been used. The library result shows the general information related to Geology, Tectonic and Magmatic of the study areas. A fieldwork was conducted in the study area and appropriate measurements i.e. Geographical location and reserve estimation were taken and also 10 sample of marble were collected from the mine of Ghondy n Mamakhail for lab analyses. The collected samples were analyzed by using different analytical methods such as XRF, Electron polarizing microscope and mechanical tests such as compressive strength, specific gravity, absorption, and unit weight. ASTM standard is used to interpret and compare the results from the above mechanical analyses. The XRF and microscopic analyses show that the marble from Nangrhar Province Shirzad district Kodikhel have dolomite composition. The results from different mechanical and physical tests showed that these marbles have high consistency against any types of applied pressure, and have high value, which can be used in various construction’s affairs. In Summary, you need to focus on the results and interpretation of those analyses.

Origin of the dolomite in the Buqu Formation (Mid-Jurassic) in the south depression of the Qiangtang Basin, Tibet: Evidence from petrographic and geochemical constraints

The Qiangtang Mesozoic sedimentary basin is a new field of hydrocarbon exploration, in which the Buqu Formation dolostone reservoirs have attracted increasing attention in recent years. To determine the origin of these reservoirs, petrographic study, fluid inclusion thermometry dating, and C-O and Sr isotopic dating were performed. The results revealed the genesis and evolution of different types of dolomite matrix and cement, as follows: 1) The dolomite texture in the study area is closely related to its formation environment and process and can be categorized as primary fabric well-preserved dolomite (Rd1), primary fabric poorly-preserved dolomite, and dolomite filling. The primary fabric-poorly-preserved dolomite includes fine-grained euhedral dolomite (Rd2), fine-grained planar subhedral dolomite (Rd3), and medium-to coarse-grained anhedral dolomite (Rd4). The dolomite filling includes fine-grained planar subhedral cave-filling dolomite (Cd1) and medium-to coarse-grained anhedral, saddle dolomite (Cd2). 2) Rd1 has δ13C‰PDB of 3.42‰–4.23‰, δ18O‰PDB from −4.22‰ to −3.37‰, and 87Sr/86Sr of 0.707654–0.708176 and was formed in the contemporaneous or penecontemporaneous stage at low temperatures by mimic replacement related to seawater evaporation. Abundant supersaturated dolomitization fluids favored the preservation of its primary dolomite texture. 3) Rd2 has δ13C‰PDB of 3.18‰–4.11‰, δ18O‰PDB from −4.56‰ to −4.23‰, and 87Sr/86Sr (0.707525–0.708037), while Rd3 has δ13C‰PDB of 2.72‰–4.42‰, δ18O‰PDB from −6.57‰ to −5.56‰, and 87Sr/86Sr of 0.707432–0.707990. Both were formed at low temperatures in the shallow-burial stage, when the dolomitization fluid was mainly derived from seawater. Excessive dolomitization during the late shallow-burial stage caused the destruction of the dolomite crystals from euhedral to subhedral. 4) Rd4 has δ13C‰PDB of 3.24‰–4.14‰, δ18O‰PDB from −8.22‰ to −6.37‰, and 87Sr/86Sr of 0.707234–0.707884 and resulted from dolomitization or recrystallization at high temperatures in the medium-to deep-burial stage. The crystal curvature was caused by high environmental temperatures. 5) Cd1 has δ13C‰PDB of 3.02‰, δ18O‰PDB of −5.13‰, and 87Sr/86Sr of 0.708147 and was formed during cavern filling before the shallow-burial stage. Cd2 has δ13C‰PDB of −0.09‰−3.38‰, δ18O‰PDB from −10.41‰ to −8.56‰, and 87Sr/86Sr of 0.708180–0.708876 and was related to the collisional orogeny between the Lhasa termite and the Qiangtang Basin in the late Early Cretaceous. Fluids in the overlying and underlying clastic strata of the Buqu Formation were driven by the thermal hot spot during compressional tectonic setting. These fluids caused negative shifts in the oxygen isotope compositions of the earlier dolomite.

Formation of the Rock Canyon Creek carbonate-hosted REE–F–Ba deposit, British Columbia, Canada: Constraints from Mg-Sr isotopes of dolomite, calcite, and fluorite

The Rock Canyon Creek REE–F–Ba deposit is a carbonate-hosted REE deposit located in the Alkaline Province of British Columbia, Canada, which hosts most REE mineralization. It shares tectonic, stratigraphic and structural similarities with nearby Mississippi Valley-type deposits. To constrain the dolomitization and mineralization processes, the δ26Mg, 87Sr/86Sr, and elemental compositions of dolomite, calcite, and fluorite were determined. The δ26Mg values of dolomite from the unmineralized zone (−1.83 ‰ and −1.67 ‰) are consistent with marine evaporative dolomite, but those from the mineralized zone (−0.97 ‰ to −0.17 ‰) are higher and more variable. The linear 87Sr/86Sr–Sr/Mg relationships, both in the dolomite and calcite from the unmineralized zone, suggest dolomitization in an evaporative marine environment. The high δ26Mg values with large variation and the non-stoichiometric Ca/Mg ratios in the dolomite from the mineralized zone suggest that this dolomite interacted with a relatively low-temperature hydrothermal fluid (<200 °C). Considering the Na, Ca, Sr, Ba, and LREE-enrichment and low 87Sr/86Sr signature in the dolomite from the mineralized zone as well as mineral paragenesis in the deposit, the most plausible scenario for the formation of the deposit is that marine-evaporitic dolomite re-equilibrated with basinal fluids along permeable zones, and at a later stage, carbohydrothermal REE-bearing fluids infiltrated into the Rock Canyon Creek brecciated zone and deposited the REE mineralization. Late-stage, post-mineralization calcite veins and iron oxides formed in the upper part of the deposit under supergene conditions, as suggested by combination of textural observations, REE patterns, and differences in isotopic compositions between dolomite and calcite from the mineralized zone. This study demonstrates that δ26Mg, 87Sr/86Sr, and element/Mg ratios in carbonate minerals are useful for characterizing mineralizing fluids in carbonate-hosted deposits, and discriminating mineralization-related dolomite from marine evaporative dolomite and unmineralized hydrothermal dolomite.

Effect of Value Added Admixture Zeolite on Setting Time and Compressive Strength of Magnesia Cement

In 1867,S. T. Sorel discovered Magnesia Cement in an aqueous solution by reacting magnesium chloride with magnesia. In comparison to Portland cement, this has versatile cementing characteristics. As an inert filler to absorb the heat evolved during the exothermic formations of magnesia cement Dolomite is used. Authors in this research paper have prepared Dry-mixes composition of magnesia and dolomite (inert filler) in the ratios of (1s And then these are gauged with 24oBegauging -solutions MgCl2 and the impact of admixture on their setting time -initial and final and compressive strength can be found. The initial and final setting time was observed to be increasing remarkably. With increase in percentage of admixture (zeolite) time of the cement blocks increased in the initial and final setting time also ratio of inert filler (dolomite) in the each dry-mix composition was observed and recorded. In the results it was found that to the percentage composition of admixture (zeolite) both initial and final setting time of cement blocks and also the ratio of inert filler in the dry-mix composition itis directly proportional. Quantity of magnesia cement drastically increases with Incorporation of zeolite and this further remarkably increases and improves strength of the cement. Magnesia cement could in fact act as carbon sinks, acting to favorably reduce greenhouse gas emissions. It is eco friendly cement.