Calcite Dolomite Research Articles

Formation Water Genesis Mechanism of Deep Tight Sandstone Gas Reservoirs in the Southern Ordos Basin and Its Indication for Development.

By analyzing the chemical characteristics of the formation water in the tight sandstone reservoirs of the P2x8 and P1s1 in the southern Ordos Basin, combined with rock mineral composition, reservoir physical properties, and well gas testing data, the genesis mechanism of formation water and its guiding role in gas reservoir development were discussed. The results show that the formation water is derived from the mixture of syngenetic seawater and meteoric water and has undergone remarkable modification by water-rock interactions, showing characteristics of Ca2+ enrichment and Mg2+ and SO4 2- depletion. The albitization of plagioclase in reservoir rock components causes Ca excess and Na deficiency in formation water, while the chloritization of albite leads to the increase of Na+. The dolomitization of calcite contributes to the decrease of Mg2+ in the formation water, while later ankerite formation makes the correlation of Ca excess-Mg deficit worse. In addition, the chloritization of dolomite and the formation of calcified debris by the metasomatism of ferrocalcite further increase the Ca2+ content of the formation water. Fe reduction and pyrite formation in reservoir minerals reduce the concentration of SO4 2-. The study also show that reservoirs endowed with Ca-Cl type formation water has more production potential. Chlorite fill, argillaceous debris, and calcareous debris are negatively correlated with face rate, porosity, and permeability. It is innovatively proposed that the specific formation chemical characteristics combinations and can effectively characterize reservoir porosity and permeability, while combinations and are strongly correlated with gas production and water production. In conclusion, the hydrochemical characteristics of geological formations are important references for reservoir evaluation and development indicators, which is helpful to accurately evaluate the development potential of reservoirs and guide exploration strategies of gas reservoirs.

Iron-rich Ca[sbnd]Mg skarns from the SW East European Craton (Lithuania): Microstructural study, mineral reactions and direct age constraints of ore-forming events using LA-ICPMS

The Varena Iron Ore deposit in the SW East European Craton is a significant ore body that occurs within metamorphosed and hydrothermally reworked Paleoproterozoic dolostones. We have performed microstructural investigations supplemented with mineral chemistry and geochronological investigations (LA-ICP-MS) to obtain age constraints on the ore-forming event(s) and improve the understanding of the conditions during mineralization process. Mineral chemistry and textures suggest a drop in pressure after the event of peak metamorphic skarn formation. Influx of oxidized, iron-rich H2O fluids resulted in (1) Mg mobility that caused secondary dolomitization of calcite, (2) dissolution of metamorphic magnetite and formation of a new, inclusion-rich (Mag-1) and inclusion-poor (Mag-2) magnetite, and (3) replacement of the peak skarn assemblages. During these fluid-related processes, accessory phases of monazite, baddeleyite, and zircon were formed. Their UPb dating yield individually robust ages of 1721 ± 9 Ma (monazite, 23 spots), 1703 ± 10 Ma (baddeleyite, 18 spots) and 1706 ± 54 Ma (zircon, 14 spots), respectively. The weighted mean age of 1713 ± 7 Ma (2σ internal) is considered to represent the best age estimate of the iron-ore mineralization in the Varena Iron Ore deposit, and possibly also dates influx of P, REEs etc. into the system. This mineralization event is contemporaneous with ca. 1.73–1.70 Ga metamorphic reworking of the host rocks in the region and may be linked to regional continental-margin type Transscandinavian Igneous Belt (TIB) magmatism in south-central Sweden.

Metasomatic ijolite, glimmerite, silicocarbonatite, and antiskarn formation: carbonatite and silicate phase equilibria in the system Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–O2–CO2

Silicocarbonatites are carbonatite rocks containing > 20% silicate minerals. Their formation is not well understood due to low silica solubility in carbonatite melts and negligible amounts of silicate minerals on carbonatite melt cotectics at upper crustal conditions. We explore whether silicocarbonatites can be thought of as antiskarns: rocks formed by leaching of SiO2 from siliceous wall rocks by carbonatite melts, and its deposition as solid silicate minerals by reaction with chemical components already present in the carbonatite melt. Solid state thermodynamic modelling at 1–5 kbar and 500–800 °C predicts that calcite–dolomite–magnetite assemblages will transform to dolomite-free silicocarbonatites with an increase in silica contents. In sodic systems, the formation of aegirine and alkali amphiboles suppresses silica activity despite elevated silica contents. Therefore, dolomite remains stable, but Fe3+ is consumed, firstly from magnetite breakdown, and secondly by coupled Fe oxidation and reduction of CO2 to CO, CH4, and graphite, particularly at higher pressures. Despite a net increase in Fe3+/Fe2+, the system evolves to increasingly lower oxygen fugacity. In aluminous systems, nepheline indicates high temperatures whereas alkali feldspars form at lower temperatures. Modelling of potassic systems demonstrates stability of mostly phlogopite-rich biotites, leading to Fe2+ increase in all other carbonate and silicate phases. We find that perthites are expected in high pressures whereas two feldspars are more likely in lower pressures.Aspects of the clinopyroxene natural compositional trend (diopside to hedenbergite to aegirine) of carbonatite systems can be explained by silica contamination. Ferrous clinopyroxenes typically require low alumina and are predicted in potassic or low temperature sodic systems, primarily at mid to high pressures. Silica contamination permits the formation of silicocarbonatite-like assemblages in a way that is not limited by SiO2 solubility in carbonatite melts. Glimmerites and clinopyroxene-rich rocks (such as the ijolite series) that often occur around carbonatite rocks at the contact with silica-oversaturated wall rocks can be explained as the extreme end of silica contamination of carbonatite melts. Therefore, these clinopyroxenites and glimmerites can form solely via metasomatic processes without the presence of a silicate melt.

Disconformity-controlled hydrothermal dolomitization and cementation during basin evolution: Upper Triassic carbonates, UAE

Petrography, fluid-inclusion microthermometry, stable isotope analyses, and radiometric (206Pb/238U) dating of Upper Triassic dolostones, saddle dolomite, and quartz and calcite cements were used to constrain the timing and conditions of dolomitization and cementation in the context of the tectonic evolution of a basin in the northern United Arab Emirates. Dolomitization (ca. 152.4 Ma) and precipitation of saddle dolomite (ca. 146.8 Ma), calcite (ca. 144.6 Ma), and quartz cements are attributed to focused synrifting flow of hot basinal brines into grain-supported limestones in which permeability was enhanced by incursion of meteoric waters beneath a disconformity surface. Another calcite cement generation (ca. 99.7 Ma) was formed by flow of hot brines during tectonic compression related to the obduction of Oman ophiolites in the Late Cretaceous. Thus, this paper provides new insights into (1) stratigraphic controls on and timing of hydrothermal (hot basinal brines) dolomitization, (2) the origin of closely associated intraformational limestones and dolostones, and (3) linkages between diagenesis and thermochemical modifications of basinal brines during tectonic evolution of sedimentary basins.

Cu and Au Mineralization of the Tolparovo Ore Occurrence: Evidence for the Formation of Redbed Copper Occurrences in Neoproterozoic Deposits of the Southern Urals

The mineralization and geochemical features of the Tolparovo ore occurrence are studied to reveal the contribution of diagenetic and epigenetic processes in the formation of copper mineralization in redbed deposits. The methods of electron microscopy, ICP MS, X-ray fluorescence, X-ray phase, atomic absorption, thermogravimetric analyses, and C and O isotopic composition were used. The ore is confined to the fault zone and feathering dolomite–calcite veins, having formed at temperatures of ~330–200 °C and pressures of 0.8–0.2 kbar. Similar to other copper redbed occurrences of the Bashkirian uplift, the Tolparovo copper ore occurrence is confined to basal Neoproterozoic deposits. Siliciclastic and carbonate deposits of this level were accumulated at low paleoequator latitudes in arid climates of continental and coastal–marine environments close to evaporite ones. Rocks of this stratigraphic interval demonstrate increased background concentrations of copper (~2–5 times exceeding the clark), which explains the stratification of redbed copper ore occurrences, indicating a predominantly sedimentary copper source. However, most of the redbed copper ore occurrences of the Bashkirian uplift are located in tectonic zones and are associated with the dikes of the Inzer gabbrodolerite complex. This connects the generation of ore occurrences with the formation of the Southern Urals Arsha Large Igneous Province (707–732 Ma) and the activity of postmagmatic fluids. Magmatic processes were presumably activated due to the collapse of the Rodinia supercontinent. It is shown that copper mineralization in stratiform deposits may result from a joint manifestation of dia- and epigenesis processes.

Study on the Hydrothermal Superposition Period: Mineralization–Alteration Zoning Model and Zoning Mechanism of the Dahongshan Fe-Cu Deposit in Yunnan Province

The Dahongshan large-scale iron (Fe)–copper (Cu) polymetallic deposit is in the Proterozoic metallogenic domain on the western margin of the Yangtze Block. It is a typical representative of Fe-Cu polymetallic composite mineralization in the Kangdian area. The deposit comprises a group of layered orebodies formed by volcanic exhalation sedimentation and metamorphism, and a group of vein-like orebodies formed by hydrothermal superposition. The large-scale mapping of altered lithofacies in the deposit has resolved issues of weak links and unclear mineralization and alteration zoning of hydrothermal superimposed deposits within the study area. The mineralization type, hydrothermal alteration type and intensity, mineral assemblage, and mineral structure of the vein-type Cu polymetallic deposits during the hydrothermal superposition period are meticulously analyzed and studied. Finally, the zoning relationships of vein orebodies (mineralization) are summarized. On the basis of the results of the study of the distribution pattern of this mineral body, a mineralization alteration zoning model of the hydrothermal superposition period is constructed. The results show that the alteration is primarily silicification, carbonation, and chloritization, and the mineralization is chalcopyrite, bornite, chalcocite, and pyrite. The Dibadu anticline and the cutting layer faults and fractures strictly control the hydrothermal alteration zoning. The mineralization alteration zoning from the core to the flank is divided into coarse vein zone (I) → stockwork zone (II) → veinlet zone (III). The corresponding mineral assemblages are quartz–calcite–chalcocite–bornite–(native copper) (I) → calcite–dolomite–quartz–bornite–chalcopyrite–chlorite (II) → dolomite–quartz–chalcopyrite–(pyrite) (III), where the stockwork zone has the most substantial mineralization. The mineral assemblages of each alteration zone, the characteristics of rare earth elements of typical samples, and the test results on the fluid inclusions confirm that pH and Eh primarily control the zoning mechanism. This study has significance for deepening the understanding of the composite metallogenic system, guiding deep and peripheral prospecting, and providing significant enlightenment for the study of this type of deposit.

Geochemistry of Rocks at the Neskevara Rare-Metal Deposit of the Vuoriyarvi Alkaline–Ultramafic Complex, Kola Peninsula

The Vuoriyarvi Paleozoic alkaline–ultramafic complex with carbonatites is made up of a great diversity of rocks with various ore mineralization. The paper presents data on the geochemistry of pyroxenites, phoscorites, and carbonatites from the Neskevara deposit of rare metals. The pyroxenites of the rare-metal deposit are significantly enriched in Nb, Ta, and Th relative to the primitive mantle and the primary alkaline–ultramafic melt composition calculated for the Kola alkaline province and are characterized by high Nb/Ta, Zr/Hf, and Th/U ratios of 29, 35, and 14, respectively. HFSE are maximally enriched in the phoscorites and carbonatites of stages II and III, with the highest concentrations of Nb (16 000 ppm), Th (2800 ppm), and Zr (4000 ppm) found in the calcite–tetraferriphlogopite phoscorites, in which pyrochlore crystallization on the liquidus was identified. The rocks of the carbonatite series are strongly enriched in LREE relative to carbonaceous chondrite. The calcite–dolomite carbonatites of the late magmatic–carbothermal stage show REE enrichment up to 25 800 ppm. The chondrite-normalized REE patterns and (La/Yb)N ratio indicate that REE were systematically more strongly fractionated in the sequence pyroxenite (70)—phoscorite (90)—calcite (540) and dolomite (3790) carbonatites The crystallization sequence of minerals in the rare-metal phoscorites and carbonatites of intermediate stages indicates that magnetite and pyrochlore crystallized nearly simultaneously. The crystallization temperatures of such associations are, according to data of the magnetite–ilmenite thermometer, lower than 500–600°C, at ∆NNO = –0.3 and + 1.5 and corresponded to the temperature at which the rare-metal ore mineralization of the main stage was formed.

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.

Variations in extent, distribution and impact of dolomitization on reservoir quality of Upper Cretaceous foreland-basin carbonates, Abu Dhabi, United Arab Emirates

Petrography, petrophysics, and geochemistry of an Upper Cretaceous, foreland-basin carbonate reservoir, Abu Dhabi, United Arab Emirates, are used to constrain the spatio-temporal variations in the extent of dolomitization and its impact on reservoir quality. Dolomitization in highstand systems tracts (HST) is attributed to repeated tidal and evaporative pumping as well as seepage reflux of penesaline brines during restriction of the platform due to 4th and 5th order cycles of relative sea-level fall and particularly below parasequence boundaries. This interpretation is supported by the presence of rare poikilotopic gypsum cement and scattered laths and micro-nodules of calcitized gypsum in the dolomitized peritidal dolostones. Dolomitization along bioturbation sites, which is most common in the transgressive systems tracts (TST), is attributed to the development of suitable localized geochemical conditions (e.g., microbial sulfate reduction and related increase in carbonate alkalinity). Porosity and permeability of the dolostones are strongly controlled by depositional textures of precursor limestones and by subsequent diagenetic evolution. Dolomitization of mudstones, wackestones and matrix-rich packstones has resulted in the formation of micropore-dominated microcrystalline dolostones whereas dolomitization of the shoal grainstones resulted in the formation of coarse-crystalline dolostones with abundant well-connected intercrystalline and moldic macropores. Mesogenetic alterations of the dolostones, which are attributed to the flow of hot basinal brines along steep faults, include dolomite cementation and, subsequently, dissolution and calcitization of dolomite (dedolomitization) and calcite cementation. The lack of systematic differences in porosity and permeability of dolostones between the oil and water-saturated dolostones suggest that most diagenesis occurred prior to completion of oil emplacement and/or reflect the shallow maximum burial depths of the formation (around 1.3 km). This study demonstrates that variations in the distribution and extent of dolomitization within a sequence stratigraphic context across an oilfield should be considered as primary control on the spatio-temporal reservoir lithology and heterogeneity in carbonate successions.

The NaCl–CaCO3–MgCO3 System at 3 GPa: Implications for Mantle Solidi

Abstract—Alkaline chlorides are important constituents of carbonatitic inclusions in magmatic minerals from kimberlites and lamproites, mantle xenoliths from kimberlites, and diamonds from kimberlites and placers around the world. This indicates the participation of alkali chlorides, along with carbonates, in the processes of melting of mantle rocks, which makes it important to study chloride–carbonate systems at mantle pressures. In this work, we studied the phase relations in the NaCl–CaCO3–MgCO3 system at 3 GPa in the range of 800–1300 °С using a multianvil press. It has been found that the NaCl–CaCO3 and NaCl–MgCO3 binaries have the eutectic type of T–X diagram. The halite–calcite eutectic is situated at 1050 °C and Na2# = 36, while the halite–magnesite eutectic is located at 1190 °C and Na2# = 77, where Na2# = 2NaCl/(2NaCl + CaCO3 + MgCO3) · 100 mol.%. In the NaCl–CaCO3–MgCO3 ternary, subsolidus assemblages are represented by halite and calcium–magnesium carbonates. Just below solidus, two assemblages are stable: halite + magnesite + dolomite and halite + dolomite–calcite solid solution. The minimum on the liquidus/solidus surface corresponds to the halite–Ca0.84Mg0.16CO3 dolomite eutectic, located at about 1000 °С with Na2#/Ca# = 34/84, where Ca# = Ca/(Ca + Mg) · 100 mol.%. At Ca# ≤ 73, the melting is controlled by the halite + dolomite = magnesite + liquid ternary peritectic, located at 1050 °C with Na2#/Ca# = 31/73. According to the data obtained, it can be assumed that at 3 GPa the solidi of NaCl-bearing carbonated peridotite and eclogite are controlled by the peritectic reaction halite + dolomite = magnesite + liquid, located at about 1050 °C. The melting is accompanied by the formation of a chloride–carbonate melt containing (wt.%): NaCl (35), CaCO3 (56), and MgCO3 (9).

The System KCl–CaCO3–MgCO3 at 3 GPa

Inclusions in mantle minerals and xenoliths from kimberlites worldwide derived from depths exceeding 100 km vary in composition from alkali-rich saline to carbonatitic. Despite the wide distribution of these melts and their geochemical importance as metasomatic agents that altered the mineralogy and geochemistry of mantle rocks, the P-T range of stability of these melts remains largely undefined. Here we report new experimental data on phase relations in the system KCl–CaCO3–MgCO3 at 3 GPa obtained using a multianvil press. We found that the KCl–CaCO3 and KCl–MgCO3 binaries have the eutectic type of T-X diagrams. The KCl-calcite eutectic is situated at K2# 56 and 1000 °C, while the KCl-magnesite eutectic is located at K2# 79 and 1100 °C, where K2# = 2KCl/(2KCl + CaCO3 + MgCO3) × 100 mol%. Just below solidus, the KCl–CaCO3–MgCO3 system is divided into two partial ternaries: KCl + magnesite + dolomite and KCl + calcite–dolomite solid solutions. Both ternaries start to melt near 1000 °C. The minimum on the liquidus/solidus surface corresponds to the KCl + Ca0.73Mg0.27CO3 dolomite eutectic situated at K2#/Ca# 39/73, where Ca# = 100∙Ca/(Ca + Mg) × 100 mol%. At bulk Ca# ≤ 68, the melting is controlled by a ternary peritectic: KCl + dolomite = magnesite + liquid with K2#/Ca# 40/68. Based on our present and previous data, the KCl + dolomite melting reaction, expected to control solidus of KCl-bearing carbonated eclogite, passes through 1000 °C at 3 GPa and 1200 °C at 6 GPa and crossovers a 43-mW/m2 geotherm at a depth of 120 km and 37-mW/m2 geotherm at a depth of 190 km.

Carbonate and Oxalate Crystallization Effected by the Metabolism of Fungi and Bacteria in Various Trophic Conditions: The Case of Penicillium chrysogenum and Penicillium chrysogenum with Bacillus subtilis

The present work contributed to the patterns of crystallization affected by the metabolism of fungi and bacteria in various trophic conditions and specifically covers the case of Penicillium chrysogenum and P. chrysogenum with Bacillus subtilis. The cultivation of microorganisms was carried out on the dolomitic calcite marble in liquid Czapek–Dox nutrient medium with glucose concentrations of 1, 10 and 30 g/L. The study of the crystal component of mycelium formed on the marble surface was supported through powder X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy; the quantitative content of the extracellular polymer substance (EPS) and low-molecular-weight organic acids (LMWOAs) in the medium was determined through chromatography–mass spectrometry (GC-MS). The results obtained clearly demonstrated the unique ability of the fungus P. chrysogenum to not only release organic acids (primarily oxalic), but the EPS also which significantly affected the pH of the culture liquid and, accordingly, the carbonate and oxalate crystallization. Carbonate crystallization manifested in the presence of Bacillus subtilis as well. The transition from oxalate crystallization to carbonate and vice versa could occur with a change in the species composition of the microbial community as well as with a change in the nutritional value medium. Under the conditions closest to natural conditions (glucose content of 1 g/L), through the action of P. chrysogenum, oxalate crystallization occurred, and through the action of P. chrysogenum with B. subtilis, carbonate crystallization was observed. The identified patterns can be used to reveal the role of fungi and bacteria in the oxalate–carbonate pathway.

Sawdust Recycling in the Development of Permeable Clay Paving Bricks: Optimizing Mixing Ratio and Particle Size

The permeable pavement system (PPS) has effectively contributed to stormwater management as a low-impact development (LID) technology. The suitability of clay bricks, consolidated with waste materials, for sustainable PPS applications in urban infrastructure needs further attention. In this study, several series of permeable clay paving bricks samples were prepared by mixing different ratios and particle sizes of sawdust (SD) with clay soil and firing at 900 °C. The raw soil and SD samples were characterized through sieve analysis, X-ray Fluorescence (XRF), X-ray diffraction (XRD), and Fourier-Transform Infrared Spectroscopy (FTIR). The bricks were tested for their compressive strength, bulk density, apparent porosity, water adsorption, permeability coefficient, and stormwater treatment efficiency. The clay soil comprised 17.5% clay/silt with appropriate amounts of SiO2 (50.47%), Al2O3 (19.14%), and fluxing agents (15.34%) and was suitable for brick manufacturing. XRD and FTIR analysis revealed that the soil predominantly comprises quartz, dolomite calcite, feldspar, kaolinite, illite, and chlorites. The SD samples were enriched with amorphous and crystalline cellulose. The compressive strength of the bricks decreased, while the permeability of the bricks increased with an increasing percentage of SD. An optimal percentage of 10% SD achieved a 21.2 MPa compressive strength and a 0.0556 m/s permeability coefficient, meeting the ASTM specifications for PPS. The optimal size of SD, between 0.5 and 1.0 mm, achieved the desired compressive strength of the bricks. The permeable bricks effectively removed the total suspended solids (TSS), turbidity, and BOD5 from the stormwater, which complies with the guidelines for wastewater reuse applications.

The provenance and evolution of thermal spring waters from the Dogai Coring area of Qiangtang basin in Tibet, China

Chemistry of major and minor elements, 87Sr/86Sr, δO, δD, and δ34S of thermal spring water, and 34S of gypsum were measured from Jurassic strata in the Qiangtang basin, China. The aim is to elucidate the provenance and evolution of thermal spring water, further to reveal geological information on the deep basin. Analysis results show that the spring waters are rich in K and Ca but deficient in Mg and Br. Most spring water samples have TDS within the range of 10–100 g/L, with a few containing 1–10 g/L TDS, and can be referred to as saline springs. High consistency of spring water data with seawater curves indicates that Na and Cl in spring water are derived from residual seawater sequestered in strata, or dissolution of self-evaporiting salts in strata. However, the mean Cl/Br value of spring water samples ranges from 1000 to 30,000, further indicating that solutes in spring water are derived from dissolved evaporites (e.g., NaCl) in strata. Sulfur isotopic characteristics indicate that thermal spring waters commonly dissolve Jurassic gypsum in strata and dolomitization of calcite is the mainly reason for Mg loss. The interpretation of Ca enrichment of spring waters of northwest Wan'an Lake (NWA), Yuanquan River (YQR), and east Thermal Spring (ETS) include: dissolution of gypsum and albitization of plagioclase. Spring waters of south Dogai Coring Lake (SDC) are enriched with more Ca than that at the NWA, YQR and east ETS, mainly due to dissolution of gypsum and dolomitization of calcite. The enrichment of K of spring waters at NWA, YQR and ETS can be attributed to albitization and dissolution of K-feldspar in groundwater. Relatively increased K in SDC spring waters are possibly derived from dissolution of potassium minerals (e.g., KCl). The 2nd member of Xiali Formation has 87Sr/86Sr values distributed in a consistent range with those of thermal spring waters in the Dogai Coring area, which is most likely the source horizon of salts (e.g., halite, gypsum, and sylvine). Modern meteoric water enter strata and dissolve ancient evaporites.

Extreme halophilic bacteria promote the surface dolomitization of calcite crystals in solutions with various magnesium concentrations

In this study, we conducted experiments on the transformation from calcite to protodolomite using bacteria. The surface dolomitization of calcite seed crystals was initiated by Vibrio harveyi J4, a newly isolated extreme halophilic bacterium, under increasing magnesium concentrations of 0, 0.05, 0.10, 0.15, to 0.20 mol L–1. The mineralogy, surface morphology, elemental composition, and lattice structure of the calcite crystals before and after bacterial treatment were analyzed by XRD, SEM-EDS, AFM and TEM, respectively. Organic functional groups within newly-formed minerals were determined by FTIR and XPS. The weight loss of minerals in the experimental group and control groups was measured by TGA and DSC. The experiments resulted in numerous nano-spheroidal-hemispheroidal precipitates being formed on the surface of the calcite seeds, whereas dissolution took place on the calcite crystal surfaces in control experiments with no bacteria. The nano-spheroids-hemispheroids were confirmed to be disordered protodolomite. The number of protodolomite spheroids on the calcite crystal surfaces increases dramatically with increasing concentration of magnesium. Since no calcium ions were added to the bioreactor, the protodolomite nano-spheroids-hemispheroids are considered to have been formed through some dissolution of the calcite to provide the Ca2+ ions in a local precipitation process. The mechanism of protodolomite precipitation is thought to be related to the presence of acidic amino acids and polysaccharides in the EPS of the extreme halophilic bacteria. These results suggest that in addition to promoting the precipitation of dolomite, micro-organisms may also play a key role in the dolomitization of calcite.

Crystal chemistry and origin of REE-bearing mukhinite from carbonate veins of the Svetlinsky gold deposit, South Urals, Russia

AbstractA rare earth element (REE)-, Cr- and Mg-bearing variety of the vanadium epidote-group mineral mukhinite occurs in a calcite–dolomite carbonatite dyke cutting metamorphosed volcano-sedimentary rocks exposed in the walls of the quarry of the Svetlinsky gold deposit, South Urals. This mineral was found in a paragene assemblage including native sulphur, phlogopite and fluorophlogopite, together with accessory pyrite, other sulfides and sulfosalts, gold, Cr- and V-bearing muscovite, margarite, Cr- and V-bearing dravite, fluoro-tremolite, actinolite, fluoro-pargasite, anhydrite, apatite, uranium hydroxides, V-rich titanite, V- and Nb-rich rutile, spinel and corundum. The contents of ΣREE2O3 and V2O3 in mukhinite vary in the ranges of 4.01–9.69 and 5.34–7.46 wt.%, respectively. A Raman spectrum of REE-rich mukhinite is provided. The main schemes of isomorphic substitutions in mukhinite are ΣREE + Mg ↔ Ca + Al and V+Cr ↔ Al. The crystal structure of REE-rich mukhinite has been studied by single-crystal X-ray diffraction analysis. The mineral is monoclinic, with the space group P21/m, and unit-cell parameters are: a = 8.8972(11) Å, b = 5.6221(6) Å, c = 10.1519(12) Å, β = 115.169° and V = 459.60(11) Å3. The crystal structure of REE-rich mukhinite is similar to that of its synthetic analogue; the refined crystal-chemical formula of the sample studied is (Z = 2): {A1CaA2(Ca0.8REE0.2)}{M1(Al0.95Cr0.05)M2AlM3[(V,Cr)3+0.40Al0.35Mg0.25]}(Si2O7)(SiO4)O(OH).

Petrography and mineralogy of rinded ferrous‐carbonate concretions in the Middle Eocene carbonate rocks: A case study from the Avanah Formation in north‐east Erbil City, northern Iraq

The spherical rinded concretions in the carbonate rocks of the Avanah Formation (Middle Eocene) in the Gomaspan section, north‐east Erbil City, northern Iraq have been studied for the first time. They occur within the grey to yellow thick‐bedded marly dolomitic limestone interbedded with thin beds of grey shale in the lower part of the formation. Their diameter varies between 1 and 3 cm, are mostly spherical in shape, and characterized by brownish to dark grey isopachous rinds or cortex and brownish‐red centre. The microscopic study shows a similarity between the concretions and their host rocks in their microfacies and fossils contained. The main microfacies is dolomitized lime mudstone and contains Valvulina sp. and pelecypods. The concretions are affected by selective diagenesis that resulted in the colour changes between the centre and outer rims of the concretions. X‐ray diffraction (XRD) analysis of concretions and host rocks revealed the presence of dolomite, calcite, quartz, illite and haematite, the latter exists only in the concretions. Meanwhile, the scanning electron microscopy (SEM) and EDX analyses supported the results of (XRD) and show that the iron oxide (haematite) mainly was concentrated in the outer orange to red cortex. While the dark black inner cortex is characterized by containing less amount of Fe as compared with Ca, O, C and Mg in addition to illite, which also exists in the carbonate host rocks. Field observations, petrographic and mineralogical analyses revealed that the studied concretions had undergone four stages of formation, which consequently include dissolution of semi‐rounded fossils such as pelecypods and forming the moulds during the deposition of the carbonate rocks of the Avanah Formation, precipitation of calcite minerals in the moulds and formation of calcite concretions syn‐depositionally, partial dolomitization of calcite in meteoric‐marine mixed zone and formation of rinded iron oxide concretion by selective diagenesis in meteoric water conditions by the action of acidic water to form haematite.

Compositional Analysis of Conventional and Unconventional Permian Basin-Produced Waters: A Simple Tool for Predicting Major Ion Composition

Summary Treatment methods for produced water (PW) are significantly affected by a high concentration of total dissolved solids (TDS), a summation of dissolved organic and inorganic compositions. Understanding the constituents of TDS to eliminate or prevent chemical reactions is critical in the design optimization of the treatment processes. In this paper, two PW geochemical data sets generated from conventional and unconventional reservoirs in the Permian Basin were analyzed to correlate constituents with TDS. Compositional data sets from over 115,000 PW samples originally reported by the U.S. Geological Survey (USGS) and 45 oil and gas operations were analyzed. Data preprocessing, culling, systematized- and meta-analysis, and statistical techniques were adapted to associate the data. Subcompositional geochemical data were transformed into isometric log ratios and are presented in bivariate and multivariate plots. Results indicate that Na+ and Ca2+ were the dominant cations and Cl− was the dominant anion. No observable trend differences in the Na+, Cl−, Ca2+, Mg+, and SO42− concentrations between PW from conventional and unconventional wells were registered. Variations in the isometric log ratio of Na/Cl and Ca/SO4 with TDS revealed that Na/Cl was nearly constant over the range of TDS, suggesting mineral buffering or a lack of significant water/rock reactions involving Na and Cl, and that Ca/SO4 increased with TDS, indicating that low-salinity fluids may have dissolved anhydrite producing a value near zero, with Ca gain and/or SO4 loss with increasing salinity. In all 10 counties and 8 formations investigated in this work, the ln (Ca/SO4) denotes Ca gain/SO4 loss relative to their composition in anhydrite or Permian seawater. Likely mechanisms leading to elevated ln (Ca/SO4) include sulfate reduction, dolomitization of calcite, Na/Ca cation exchange, albitization, and anhydrite precipitation from Ca-rich fluids. Results from this work are important as it is revealed that Ca/SO4 and Na/Cl can potentially be predicted from PW TDS concentrations. This information was combined to create a reservoir or location-specific model to estimate Na, Cl, Ca, and SO4 concentrations in Permian Basin PW, a powerful tool to improve treatment and reuse options in areas with few direct data.

Influence of seawater intrusion on the hot springs in a coastal area: The case of the Anak-Sinchon Uplift, Korean Peninsula

Temperatures and chemical compositions of hot springs are decisive of their roles in heating, power-generation, therapeutic applications and recreational activities. However, the influence of seawater intrusion on hot springs are still not fully understood. Typical ten hot springs in and around the Anak-Sinchon Uplift in a coastal area of the northern Korean Peninsula were investigated. All the hot springs were near-neutral to weakly alkaline. High TDS value of 25300 mg/L was found at the hot spring closest to the coastline. TDS values, and concentrations of Na+, K+, Ca2+, Cl− and SO42− in the hot spring waters near the coast showed decreasing trends with the distance from the coastline. According to the calculation of seawater fraction, three hot springs near the coast were contaminated by seawater. Temperatures of the geothermal reservoir were estimated to range from 103 to 170 °C, which were interpolated by thin plate spline to predict the local trend of the reservoir temperature distribution. Mg2+ concentration was used to determine the time order between the heating process and seawater intrusion. Among the three seawater-contaminated hot springs, very low Mg2+ concentrations in two hot spring waters probably indicate that they were mixed with seawater before being heated in the geothermal reservoir and not affected by seawater intrusion again afterwards; relatively high Mg2+ concentration in the hot spring water closest to the coastline likely indicates that it was mixed with seawater again during the ascent from the geothermal reservoir. The geochemical modeling performed with PHREEQC indicates that dolomitization of calcite and precipitation of anhydrite were the dominant water-rock interactions for the seawater-contaminated hot spring waters.

Relationship among paleosol types, depositional settings, and paleoclimates in Tetori group (Lower Cretaceous, central Japan)

AbstractOne of the key areas and periods for dinosaur evolution is considered to be Early Cretaceous East Asia, of which paleoclimate, that affected dinosaur diversity, needs to be accurately estimated. This study reconstructed paleoenvironmental information from two paleosol sections of the Lower Cretaceous Tetori Group in Hokuriku province, Japan. Elemental and isotopic compositions indicate that the two sections (Sections K5 and T1) formed under similar mean annual temperature (MAT) and mean annual precipitation (MAP) but exhibit significantly different paleosol colors (red in the Section K5, and gray in the Section T1) and mineralogy of carbonate nodules (dolomite–siderite in the Section K5, and dolomite–calcite in the Section T1). In addition, the oxygen isotopic ratio of carbonate minerals in the Section K5 was significantly low. The differences in sedimentary features and isotopic composition were considered to reflect the differences of seasonal climatic factors (e.g., monsoon) and local settings (e.g., drainage condition) despite the two sections exhibiting similar MAT and MAP. The results of this study suggest that the northeastern margin of East Asia, where the Tetori Group was deposited, had temperate and humid climate with monsoonal contrast in humidity during Aptian to Albian.