Calcite Type Research Articles

Hydrothermal vein distribution in skarn type alteration zone of area X at PT. Freeport Indonesia

Kucing Liar is an economic skarn altered deposited located in Tembagapura, Papua. This deposit was found on Late Cretaceous to Miocene sedimentary rocks of Kembelangan Group and Papua New Guinea Limestone Group. The alteration from this deposit can be divided into groundmass alteration, named penetrative alteration, and selvage alteration forming hydrothermal veins. The penetrative alteration is divided into 9 zones, meanwhile the hydrothermal veins are classified by its mineral composition into 5 types of anhydrite veins, calcite, quartz, sulphide, and gypsum veins. Each vein type will associate the most with different penetrative alteration zone due to its protolith composition and on what stage the vein formed. The anhydrite and quartz veins are found to be associated the most with calc-silicate hornfels zone with the anhydrite sources came from calcite and quartz sources came from the surrounding rocks which the alteration fluid passed through. The sulphide and calcite veins are found to associate the most with dolomitization zone with calcite sources came from the surrounding rock and sulphide deposited filling the open spaces, such as fracture, in crystalline dolostone. Gypsum veins are found to associate the most with fault zone because it formed from the alteration of calcite by faulting process.

Middle Jurassic–Lower Cretaceous glendonites from the eastern Barents Shelf as a tool for paleoenvironmental and paleoclimatic reconstructions

Glendonites are carbonate pseudomorphs after ikaite which use as indicators of near-freezing temperatures. We describe the first glendonites of Middle–Late Jurassic to Early Cretaceous age from the Barents Shelf, including the first glendonites of Late Barremian–Early Aptian age ever discovered on Earth and provide the detailed mineralogical-geochemical and isotopic studies. Mesozoic glendonites are well-known across the Arctic realm, however the ikaite-calcite transformation and implication of glendonite findings are still debatable. Pseudomorphs are mainly composed of calcite. Cathodoluminescence and scanning electron microscopy studies reveal three types (I-III) of calcite: type I - elongated, rounded and irregular calcite; type II - blocky, fibrous and needle-like calcite/siderite; type III - blocky calcite in pores. Elemental analyses distinguish geochemical differences between the calcite types: type I comprises pure CaCO3; type II calcite contains Mg and P (in all studied samples), Fe (Bajocian–Callovian), S (Middle Volgian) or Sr (Upper Barremian–Lower Aptian); type III calcite is depleted in Mg, P and Fe. Concentrations of Mn, Fe, Sr and calculated Mn/Ca, Fe/Ca and Sr/Ca ratios are suggestive of diagenetic alteration. Bulk δ18O values range from −5.39 to −1.71‰ VPDB, supporting overprinting of primary values during burial diagenesis, while bulk δ13C values range from −33.3 to −22.6‰ VPDB, providing the influence of organic matter on ikaite-glendonite formation. However, 87Sr/86Sr values range from 0.7070 to 0.7110, mainly corresponding to Jurassic–Cretaceous seawater. Rare-earth elements characterize porewater REE-patterns, with slight middle REE-enrichment and depletion in light and heavy REE. Weak positive and negative Ce anomalies indicate fluctiating from anoxic to oxic conditions during ikaite-glendonite formation. Our new biostratigraphic data refine the ages of glendonite-bearing horizons in the Barents Shelf region, allowing a more definitive correlation with coeval glendonite occurrences across the Arctic realm and with global climatic changes during the Jurassic–Cretaceous.

Combined In Situ Chemical and Sr Isotopic Compositions and U–Pb Ages of the Mushgai Khudag Alkaline Complex: Implications of Immiscibility, Fractionation, and Alteration

The Mushgai Khudag complex consists of numerous silicate volcanic-plutonic rocks including melanephelinites, theralites, trachytes, shonkinites, and syenites and also hosts numerous dykes and stocks of magnetite-apatite-enriched rocks and carbonatites. It hosts the second largest REE–Fe–P–F–Sr–Ba deposit in Mongolia, with REE mineralization associated with magnetite-apatite-enriched rocks and carbonatites. The bulk rock REE content of these two rock types varies from 21,929 to 70,852 ppm, which is much higher than that of syenites (716 ± 241 ppm). Among these, the altered magnetite-apatite-enriched rocks are characterized by the greatest level of REE enrichment (58,036 ± 13,313 ppm). Magmatic apatite from magnetite-apatite-enriched rocks is commonly euhedral with purple luminescence, and altered apatite displays variable purple to blue luminescence and shows fissures and hollows with deposition of fine-grained monazite aggregates. Most magmatic apatite within syenite is prismatic and displays oscillatory zoning with variable purple to yellow luminescence. Both magmatic and altered apatite from magnetite-apatite-enriched rocks were dated using in situ U–Pb dating and found to have ages of 139.7 ± 2.6 and 138.0 ± 1.3 Ma, respectively, which supports the presence of late Mesozoic alkaline magmatism. In situ 87Sr/86Sr ratios obtained for all types of apatite and calcite within carbonatite show limited variation (0.70572–0.70648), which indicates derivation from a common mantle source. All apatite displays steeply fractionated chondrite-normalized REE trends with significant LREE enrichment (46,066 ± 71,391 ppm) and high (La/Yb)N ratios ranging from 72.7 to 256. REE contents and (La/Yb)N values are highly variable among different apatite groups, even within the same apatite grains. The variable REE contents and patterns recorded by magmatic apatite from the core to the rim can be explained by the occurrence of melt differentiation and accompanying fractional crystallization. The Y/Ho ratios of altered apatite deviate from the chondritic values, which reflects alteration by hydrothermal fluids. Altered apatite contains a high level of REE (63,912 ± 31,785 ppm), which are coupled with increased sulfur and/or silica contents, suggesting that sulfate contributes to the mobility and incorporation of REEs into apatite during alteration. Moreover, altered apatite is characterized by higher Zr/Hf, Nb/Ta, and (La/Yb)N ratios (179 ± 48, 19.4 ± 10.3, 241 ± 40, respectively) and a lack of negative Eu anomalies compared with magmatic apatite. The distinct chemical features combined with consistent Sr isotopes and ages for magmatic and altered apatite suggest that pervasive hydrothermal alterations at Mushgai Khudag are most probably being induced by carbonatite-evolved fluids almost simultaneously after the alkaline magmatism.

Control of Crystal Size and Morphology of Calcium Carbonate Crystal Polymorphism

Calcium carbonate, the main component of lime, has been widely used in industry due to its stability and economy. Calcium carbonate has three types of crystalline polymorphism, calcite, aragonite and vaterite, each with different properties. Therefore, the control of crystal polymorphism is required for industrial applications. In addition, the control of crystal size and shape is similarly required for different applications. In this study, the effect of SrCO3 on the size control of fine aragonite-type calcium carbonate crystals by uniform urea precipitation and the effect of SrCO3 addition was investigated by adding solid strontium carbonate and dissolved strontium carbonate. The addition of solid strontium carbonate affected the crystal polymorphism and size of the calcium carbonate produced, depending on the properties of the solid particles and the amount of SrCO3 added. Experiments on the addition of dissolved SrCO3 showed that the supersaturation formation rate could be controlled to control the crystal polymorphism.

Facies, stratigraphic architecture, and faults - The controls on the cement distribution in the Devonian Sappington Formation in southwestern Montana

Diagenesis has a profound effect on the porosity and permeability of sediments, and it is necessary to holistically evaluate the diagenetic history in the context of depositional, stratigraphic, and structural frameworks. This outcrop study from the late Devonian to early Mississippian Sappington Formation of southwestern Montana, USA, investigates the complex interplay of these different geologic factors and their controls on the distribution of diagenetic alterations.Our results suggest that the principal control on the distribution of diagenetic minerals is the thickness of the Lower, Middle, and Upper Sappington Shale Members, respectively. The sedimentary architecture plays a secondary role as clinoform boundaries and stratigraphic surfaces compartmentalized fluid flow. Structural features are of local importance and depositional facies, other than the previously mentioned shales, display little effect on the distribution of diagenetic minerals.Six dominant cement types were recognized in the Sappington Formation. Quartz and clay cements are the earliest cements and formed on the surfaces of detrital grains during early diagenesis and are relatively minor phases (<5% vol). These are postdated by a series of carbonate cements that dominate the diagenetic mineral assemblage (>60% vol) and include two types of dolomite, and two types of calcite. Dolomite is the most abundant diagenetic mineral and is observed as zoned, euhedral to subhedral rhombs with a nearly stoichiometric core and a series of ferroan rims and as subhedral to anhedral ferroan rhombs without zonation. Calcite cements are most common as a rim on the outer extents of dolomite rhombs but also occur as a replacement of dolomite or detrital feldspar.The outcrop-based model presented here – the first comprehensive diagenetic model of the Sappington Formation in SW-Montana, USA – can serve as a guide to hydrocarbon development in tight hybrid plays, such as the Bakken Formation in the Williston Basin, USA. It provides a more holistic understanding of the relationship between the depositional architecture and the diagenetic alterations and helps to decrease uncertainty in the second and third dimensions.

Structural and morphological characterization of scale deposits on the reverse osmosis membranes: Case of brackish water demineralization station in Morocco

Present study reports on the characterization of the fouling of reverse osmosis process membrane at brackish water demineralization station of Khang Lahmam in Tan Tan, Morocco, which clearly revealed difficulties related to the loss of performance of the membranes. Thus, to highlight a new anti-fouling method, a well-developed reverse osmosis module was autopsied and analyzed. The scale samples over membrane surfaces were collected from different sites and were further characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersion spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), X-ray fluorescence spectrometry (XRF)and thermogravimetric and differential scanning calorimetry analysis (TG/DSC).Obtained results were thus clearly indicated that the scales were uneven over membrane sites, and the regions near feed were found to be more seriously affected. Moreover, the integrated DRX, EDS and XRF spectra suggested that the scale was mainly inorganic matter (Ca, O, and C). In addition, the FTIR spectra and TG/DSC analysis of clogged reverse osmosis membranes reveal that the constituents of scale were mainly inorganic compounds with a significant loss of mass. Moreover, the SEM images indicated that the scale deposited samples were crystalline, and then the mapping images clearly revealed the uniformity of elemental distribution over the scale. Finally, it was concluded that there is a mineral fouling (scaling) and the different tartar samples were found to have similar nature, along with indicating the calcite type calcium carbonate (CaCO3) crystal deposition over reverse osmosis membrane surface sites.

High‐Resolution Mg/Ca and δ18O Patterns in Modern Neogloboquadrina pachyderma From the Fram Strait and Irminger Sea

AbstractNeogloboquadrina pachyderma is the dominant species of planktonic foraminifera found in polar waters and is therefore invaluable for paleoceanographic studies of the high latitudes. However, the geochemistry of this species is complicated due to the development of a thick calcite crust in its final growth stage and at greater depths within the water column. We analyzed the in situ Mg/Ca and δ18O in discrete calcite zones using laser ablation‐inductively coupled plasma‐mass spectrometry, electron probe microanalysis, and secondary ion mass spectrometry within modern N. pachyderma shells from the highly dynamic Fram Strait and the seasonally isothermal/isohaline Irminger Sea. Here we compare shell geochemistry to the measured temperature, salinity, and δ18Osw in which the shells calcified to better understand the controls on N. pachyderma geochemical heterogeneity. We present a relationship between Mg/Ca and temperature in N. pachyderma lamellar calcite that is significantly different than published equations for shells that contained both crust and lamellar calcite. We also document highly variable secondary ion mass spectrometry δ18O results (up to a 3.3‰ range in single shells) on plankton tow samples which we hypothesize is due to the granular texture of shell walls. Finally, we document that the δ18O of the crust and lamellar calcite of N. pachyderma from an isothermal/isohaline environment are indistinguishable from each other, indicating that shifts in N. pachyderma δ18O are primarily controlled by changes in environmental temperature and/or salinity rather than differences in the sensitivities of the two calcite types to environmental conditions.

Synthesis of GdBO3:Eu3+ nanophosphors via acetylacetone assisted aqueous sol–gel route: Effect of some synthesis parameters

Abstract Nano-sized Eu3+ -doped GdBO3 vaterite type nanophosphors have been synthesized successfully via acetylacetone assisted aqueous sol–gel route. Systematic investigation of the influence of Eu3+ ion content and pH value of the suspension of precursors on structural, morphological and luminescence spectroscopic properties has been performed. X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, field emission-scanning electron microscopy (FE-SEM), Thermogravimetric and differential thermal gravimetry (TG/DTA), room temperature steady and time resolved photoluminescence (PL) spectroscopy techniques were employed to characterize the obtained powder samples. It has been found that the Eu3+ ion content and pH value precursors suspension have important effect on the structural, morphology and emission properties. The XRD analysis reveals that GdBO3: 10% mol Eu3+ synthesized at pH = 2 and pH = 10 exhibit the quasi-purest P63/mmc vaterite structure. The vibrational absorption of (BO3)3- group is assigned to the GdBO3 with calcite type or other vaterite structure namely triclinic and monoclinic. The morphologies of GdBO3 particles size increases with increasing of pH value. All sample present only the orange-red colors emission from 5D0 levels to the 7FJ levels (J = 0–3) of Eu3+ ion. Furthermore, it was found that 10% concentration of Eu3+ presents the quenching of emission in GdBO3. Also, it was that the emission intensity was affected by the pH value and sample with pH = 10 exhibits the highest emission intensity. The asymmetry ratio parameter R between red and orange emission intensities in function of Eu3+ content and pH value is determinate and discussed.

The origins of carbonate minerals of a source-controlled lacustrine carbonate succession in the Shulu sag, Bohai Bay Basin: Implications for porosity development and paleoenvironment

Lacustrine carbonates are widely distributed in the third member of the Eocene Shahejie Formation (Es3L) of the Shulu sag and other rift basins in the Bohai Bay Basin, which can act as reservoirs for hydrocarbon and provide insights into paleoenvironment. However, the origins of lacustrine carbonate deposition and their implications for porosity development and paleoenvironment are not well understood. Based on micropetrological characteristics, X-ray diffraction (XRD), stable carbon and oxygen isotope analyses, and organic geochemistry data, four types of calcite (calcite debris; calcareous biological detritus; micrite in fine-grained marlstone; fibrous sparry calcite) and two types of dolomite (dolomite debris; rhombic euhedral dolomite) with distinctly different characteristics and origins are identified. The δ13C and δ18O values of calcite and dolomite debris are consistent with that of the Cambrian-Ordovician carbonate rock in the provenance area, suggesting that the carbonate debris was sourced from the surrounding Cambrian-Ordovician carbonate bedrock. Microcrystalline calcites are commonly developed in organic-rich marlstones with a large number of algae. The δ13C values of the microcrystalline calcites are higher than that of carbonate debris and the positive excursion of the δ13C value is along with the increase of TOC content. These indicate that origin of the microcrystalline calcite was authigenic calcite and was formed by biochemical process. Bedding-parallel fibrous sparry calcite occurs in intervals with high TOC contents and within the thermally mature zone of hydrocarbon generation, indicating that oil generation should be responsible for the sparry calcite formation. Rhombic euhedral dolomite commonly occurs as isolated micro-crystals with euhedral to subhedral rhombs shape. Micro-sized spherule-like dolomite in the early stage of crystal growth were also present. Rhombic euhedral dolomite are commonly associated with organic matter and developed in organic-matter rich intervals with plenty of fossilized bacterial filaments and framboidal pyrite. These suggest that rhombic euhedral dolomite were probably microbially mediated dolomite. Mineral components can affect reservoirs quality. The porosities of samples show a positive correlation with dolomite content and the porosities of fibrous sparry calcite-bearing intervals are higher than non-parry calcite-bearing intervals. The increase in authigenic microcrystalline calcite content reflects a rise in lake level and an increase in water depth and primitive productivity.

Molecular dynamics analysis of moisture effect on asphalt-aggregate adhesion considering anisotropic mineral surfaces

The objective of this work is to analyze the effect of moisture on the bonding and debonding behaviors between asphalt and aggregates based on molecular dynamics (MD) simulation, considering the anisotropic characteristics of mineral surfaces. Full atomistic models adopted for MD simulations were constructed using the 12-component asphalt model and two types of representative minerals, α-quartz and calcite. Anisotropic wettability was studied by simulating the dynamic processes of a water nano-droplet spreading on anisotropic mineral surfaces. An improved energy ratio (ER) considering the residual adhesion between asphalt and aggregates in a moist state was established to evaluate the moisture susceptibility of asphalt mixtures. It was found that (1) anisotropic mineral surfaces have a significant influence on the bonding properties and moisture susceptibilities of asphalt mixtures; (2) the concentrated hydroxyl groups on the hydroxylated α-quartz surfaces significantly increase surface hydrophilicity and reduce the resistance to water damage; (3) freshly-cleaved calcite surfaces contribute the most to moisture susceptibility, while un-hydroxylated α-quartz surfaces contribute the least among the mineral surfaces studied. This simulation work provides insights to better understand the moisture damage mechanisms of asphalt mixtures at a microscopic level.

Geological and geochemical implications of the complicated carbonate diagenetic process in the Lower Ordovician buried hills of the eastern Tazhong Low Rise, NW China, using Well M1 as an example

There are many structural buried hills in the east of Tazhong Low Rise that have significantly valuable for oil/gas exploration and research. In this work, geochemical and geological methods were used to research the complicated diagenetic process of Yingshan carbonate. The Yingshan carbonate underwent four diagenetic stages with three types of calcite, which diagenetic environment was complex and variable. During the Early Ordovician of syndiagenetic stage, the high-magnesium CI calcite develops along the micro-fracture and has no or very weakly cathodoluminescence color. In the following early diagenetic, the Yingshan carbonate subsided and developed the CIII calcite along the corroded fissure and pressolved sutures. After the M1 buried hill formed during the Late Silurian, the Yingshan carbonate experience the supergene stage, and suffered the weathering and denudation for a long period. During the Carboniferous karst, two cave horizons developed in the M1 buried hill, corresponding with two sets of Carboniferous carbonate rocks by the stratigraphic correlation. The cement CII calcite contains less Sr, Na, Mg, and more Mn and Fe than sea water, showing bright red in the cathodoluminescence. During the following middle and late diagenetic stage, M1 buried hill underwent a process of persistent burial and slight uplifting with CIII calcite cementing from the formation water. During the Permian, the hydrothermal fluid intensely influenced the buried hill, leaving the hydrothermal minerals.

Morphotropism of Rare-Earth Orthoborates RBO3

A diagram in the coordinates “temperature-ionic radius” is built for polymorphic and morphotropic transitions in a series of REE orthoborates. The stability fields are determined for the structural types of calcite, aragonite, vaterite, pseudo-vaterite, H-LaBO3, and L-SmBO3. The temperatures of some metastable phase transformations are estimated.

Rare Earth Elements Geochemistry and C–O Isotope Characteristics of Hydrothermal Calcites: Implications for Fluid-Rock Reaction and Ore-Forming Processes in the Phapon Gold Deposit, NW Laos

The Phapon gold deposit is located in the northern Laos and the northern segments of the Luang Prabang–Loei metallogenic belt. The lode-gold orebodies consist of auriferous calcite veins in the middle, and the surrounding siderite alteration and hematite alteration zones in red color. This deposit is hosted in Lower Permian limestone and controlled by a NE-trending ductile–brittle fault system, and it is characterized by the wallrock alteration of carbonatization and lack of quartz and metal sulfides. The hydrothermal calcite from auriferous calcite veins and red alteration zone, as well as the wall rocks of limestone and sandstone were selected for rare earth elements (REE) and C–O isotope analyses. The two types of calcite and limestone have generally consistent REE patterns and δEu and δCe values, which are completely different from those of sandstone. Calcites from the auriferous vein show slight light rare earth elements (LREE)-depleted patterns and higher Tb/La and Sm/Nd ratios than the ones from the red alteration zone with slight LREE-enriched patterns. These values indicate that the calcites from the auriferous veins and the red alteration zones are products of homologous fluids, but the former ones are generally likely to form later than the latter ones. The hydrothermal calcites have C–O isotope compositions within the range of marine carbonate, and markedly different from the magmatic or mantle reservoir values. Taking the Y/Ho–La/Ho and Tb/Ca–Tb/La variations into consideration, we believe the hydrothermal calcites could be formed from remobilization and recrystallization of the ore-hosted limestone, and the fluid-wallrock interaction played a major role in the gold mineralization in Phapon. In combination with the regional and local geology, the ore-forming process is suspected to be primarily associated with dehydration and decarbonisation of the Lower Permian limestone and Middle–Upper Triassic sandstones. The Phapon gold deposit could have been formed during the Late Triassic–Jurassic regional dynamic metamorphism driven by Indochina–Sibumasu post-collisional magmatism. A number of features in Phapon are similar to epizonal orogenic deposit, but it is still a unique calcite vein type gold deposit in the Luang Prabang-Loei metallogenic belt.

Exploring the use of silica sands and calcite from natural deposits to prepare bioactive glasses

Abstract Nowadays bioactive glasses represent one of the most successful bioceramics used for bone tissue restorations. In this work, three types of silica sands (White, Yellow and Gray Sands) and calcite from Cuban natural deposits were employed to synthesize glasses from the system SiO2–CaO–Na2O. The ions released from glasses were evaluated through in vitro tests in Tris-HCl and in simulated body fluids. All sands had purity around 99.2% of SiO2 and contained traces (ppm) of Zr, Cr, Ba, Ce and Sr ions, while calcite raw material had traces of Sr, Cr, Zr, Ce and Zn. All glasses induced a pH change in Tris-HCl from 7.4 to 9 after 24 h; they had similar ion-release behavior in the in vitro solutions tested and showed a significant bioactive performance after 5 h. This work illustrates the potentialities of the use of natural resources to develop medical products when recognized trademark materials are not available.

Suitability of the Iraqi natural clay for the preparation of Al-Fe pillared-clays

Some organic pollutant in aqueous wastewater inhabitant biological treatment, catalyst wet air oxidation is a method to treat this waste. Al-Fe pillared Iraqi clays with different Fe content were prepared. Aluminum was mixed with iron in different molar ratio Fe/Al (1:9- 2:8- 3:7- 4-6- 5:5) for each regions. These clays collected from different location in Iraq (Anbar, Erbil, Mosel, Baghdad, and Basra), the results of some properties studied for natural and pillared clay, from X-Ray- Fluorescence (XRF) show that iron cation replaces some Ca in the clay, and from X-Ray Diffraction (XRD) show the Calcite types of Iraqi clays. constructs clusters of active ingredient which dramatically clear on the catalytic surface for all catalyst types show through photos of catalysts by Scanning Electron Microscopy (SEM), the best molar ratio of Fe/Al in which give strong interaction between Fe and Al in the pillared were (0.5-0.4-0.3-0.3 and 0.2) for (Mosul-Basra -Anbar-Baghdad and Erbil) respectively. This ratio gives high surface area, and pore size in mesopore. It is concluded that clay and silty clay (Mosul clay) consider the best catalyst due to higher activity and stability through experiment of CWAO in batch reactor, with operation condition 150°C, 2.5 Mpa, Ccat equal to 7 mg/l.

Cryptic serpulid-microbialite bioconstructions in the Kakoskali submarine cave (Cyprus, Eastern Mediterranean)

The biostalactites from the Kakoskali cave in Cyprus represent a new example of the complex biotic relationships between skeletal organisms and microbial communities in building bioconstructions of cryptic marine environments. Biostalactites are mainly constituted of polychaetes of the family Serpulidae and, to a lesser degree, foraminifers and bryozoans. Within the skeletal framework of these organisms, two types of microcrystalline calcite (micrite) have been recognized: autochthonous and detrital micrite. The autochthonous fraction is syndepositionally lithified and occurs as clotted peloidal and, subordinately, aphanitic (structureless) textures, suggesting the presence of heterotrophic microbial activities thriving on decaying metazoan organic matter. This fraction is limited to the protected portions of the bioconstructions, especially in the inner and lower parts. The presence of iron and manganesiferous oxidizing bacteria is suggested by the deposition of ferromanganesiferous crusts and Frutexites-like structures. These microbial-induced biomineralizations are the main evidence of carbonatogenetic and Fe–Mn, autotrophic and chemoheterotrophic, bacterial activities. The Kakoskali cave is frequently visited by divers who, during their immersions, resuspend the fine bottom sediment, which later covers the surface of the bioconstructions, disturbing the delicate equilibrium of the biotic association. This perturbation, which is also caused by strong waves and currents, during winter months, reflects on the bioconstruction morphologies, community composition, and colonization pattern. Bioconstructions exhibit an upper smooth surface, produced by few taxa (e.g., polychaetes, foraminifers), hosting a low number of living individuals, and a lower comparably rough surface, colonized by a more abundant community showing a higher species richness. The ratio surface roughness/smoothness is related to micrite sediment type: the upper part is mainly characterized by loose detrital micrite while the internal and lower parts by syndepositional cemented autochthonous micrite.

Synthesis and Characterization of New Sr3(BO3)2 Crystal for Stimulated Raman Scattering Applications

A new kind of borate crystalline material Sr3(BO3)2 with a similar calcite type structure was designed and synthesized by solid state reaction method, moreover, the single crystal growth was attempted with traditional Czochralski pulling method. Crystal phase of Sr3(BO3)2 was investigated by using X-Ray powder diffraction (XRPD) at room temperature and found similar to Ca3(BO3)2 crystal with space group of R-3c. The phase stability was studied by means of thermogravimetric differential thermal analysis (TG/DTA) and high temperature XRPD up to 1350 °C, where an obvious endothermic peak was observed in DTA curve around 1250 °C, and weak splits of diffraction peaks were found at temperatures above 1250 °C, indicating the existence of structure transformation for Sr3(BO3)2 crystal. Raman properties were studied experimentally and theoretically by using density functional perturbation theory, though the strongest frequency shift of Sr3(BO3)2 crystal (900 cm−1) was comparable to that of Ca3(BO3)2 (927 cm−1), the line width of the strongest Raman peak obtained for Sr3(BO3)2 (5.72 cm−1) was much lower than Ca3(BO3)2 (7.01 cm−1), indicating a larger Raman gain for Sr3(BO3)2 crystal, which would be favorable for stimulated Raman scattering application.

Diagenesis of tight oil sand reservoirs: Upper Triassic tight sandstones of Yanchang Formation in Ordos Basin, China

Upper Triassic sandstones in the Ordos Basin, northern‐central China, comprise tight oil reservoirs. Using a combination of thin sections, SEM, BSE, EDS, XRD, and fluid inclusion analyses, 24 core samples from 13 wells were collected to study the petrology, paragenesis, and diagenetic processes and implications for reservoir quality. Quartz cement usually occurs as overgrowths or euhedral quartz. Extensive dissolution and albitization of K‐feldspar can be observed. Five types of carbonate cements, ferrocalcite, ankerite, dolomite, calcite, and siderite, occur during different diagenetic stages. Two main types of illite and 5 main habits of chlorite are observed in this study. Kaolinite mainly occurs as booklets and vermicular aggregates. Diagenetic illite, chlorite, biotite, mixed‐layer illite/smectite (I/S), and other minor minerals are also observed. The diagenetic processes include compaction, alteration of volcanic materials and mica, clay mineral transformation, cementation (silica, aluminosilicate, and carbonate), and dissolution of feldspars and rock fragments. Compaction was a significant porosity‐reducing agent, and the presence of carbonate cement exerts a dominant impact on the reduction of porosity. Quartz cement and authigenic clays are less important; however, it is worth mentioning that pore‐lining clays are conducive to porosity preservation. In this study, most of the porosity variation is caused by a combination of compaction, carbonate cements, quartz cement, and authigenic clays. This study gives insights into diagenetic alterations within tight sandstones and has implications for reservoir quality prediction in similar settings.

Fluid evolution in CM carbonaceous chondrites tracked through the oxygen isotopic compositions of carbonates

The oxygen isotopic compositions of calcite grains in four CM carbonaceous chondrites have been determined by NanoSIMS, and results reveal that aqueous solutions evolved in a similar manner between parent body regions with different intensities of aqueous alteration. Two types of calcite were identified in Murchison, Mighei, Cold Bokkeveld and LaPaz Icefield 031166 by differences in their petrographic properties and oxygen isotope values. Type 1 calcite occurs as small equant grains that formed by filling of pore spaces in meteorite matrices during the earliest stages of alteration. On average, the type 1 grains have a δ18O of ∼32–36‰ (VSMOW), and Δ17O of between ∼2‰ and −1‰. Most grains of type 2 calcite precipitated after type 1. They contain micropores and inclusions, and have replaced ferromagnesian silicate minerals. Type 2 calcite has an average δ18O of ∼21–24‰ (VSMOW) and a Δ17O of between ∼−1‰ and −3‰. Such consistent isotopic differences between the two calcite types show that they formed in discrete episodes and from solutions whose δ18O and δ17O values had changed by reaction with parent body silicates, as predicted by the closed-system model for aqueous alteration. Temperatures are likely to have increased over the timespan of calcite precipitation, possibly owing to exothermic serpentinisation. The most highly altered CM chondrites commonly contain dolomite in addition to calcite. Dolomite grains in two previously studied CM chondrites have a narrow range in δ18O (∼25–29‰ VSMOW), with Δ17O ∼−1‰ to −3‰. These grains are likely to have precipitated between types 1 and 2 calcite, and in response to a transient heating event and/or a brief increase in fluid magnesium/calcium ratios. In spite of this evidence for localised excursions in temperature and/or solution chemistry, the carbonate oxygen isotope record shows that fluid evolution was comparable between many parent body regions. The CM carbonaceous chondrites studied here therefore sample either several parent bodies with a very similar initial composition and evolution or, more probably, a single C-type asteroid.

Petrography and geochemistry of fault-controlled hydrothermal dolomites in the Riópar area (Prebetic Zone, SE Spain)

The present paper reports the first detailed petrographical and geochemical studies of hydrothermal dolomites related to MVT Zn-(Fe–Pb) deposits in the Riópar area (Mesozoic Prebetic Basin, SE Spain), constraining the nature, origin and evolution of dolomitizing and ore-forming fluids. Mapping and stratigraphic studies revealed two stratabound dolostone geobodies connected by other patchy bodies, which replace carbonate units of Upper Jurassic to Lower Cretaceous ages. These dolostones are associated to the W–E trending San Jorge fault, indicating a main tectonic control for fluid flow. Seven different dolomite types were identified: i) matrix-replacive planar-s (ReD-I); ii) matrix-replacive planar-e (ReD-II); iii) planar-e sucrosic cement (SuD); iv) non-planar grey saddle dolomite cement (SaD-I) pre-dating Zn-(Fe–Pb) sulfides; v) non-planar milky to pinkish saddle dolomite cement (SaD-II) post-dating Zn-(Fe–Pb) ores; vi) ore-replacive planar-e porphyrotopic (PoD); and vii) planar-s cloudy cement (CeD). Meteoric calcite types were also recognized. The different dolomite types are isotopically characterized by: i) depleted δ18O (from +25.1 to +27.6‰ V-SMOW) and δ13C (from −2.3 to +0.9‰ V-PDB) values compared to Upper Jurassic to Lower Cretaceous limestone signature (δ18O: +27.6 to +30.9‰ V-SMOW; δ13C: +0.5 to +3.2‰ V-PDB); and ii) 87Sr/86Sr ratios for the main dolomitization phases (ReD and SuD: 0.70736–0.70773) close to the Jurassic and Cretaceous carbonate values (0.70723–0.70731) whereas more radiogenic values (0.70741–0.70830) for saddle dolomites (SaD) related to the Zn-(Fe–Pb) sulfide mineralization prevailed after fluid interaction with Rb-bearing minerals. Microthermometrical studies on two-phase liquid and vapor fluid inclusion populations in planar and non-planar dolomites and sphalerite show homogenization temperatures between 150 and 250 °C. These data indicate that both planar and non-planar dolomite textures formed at high-temperatures under hydrothermal conditions in deep-burial diagenetic environments. The main dolomitizing phase (ReD-I/ReD-II and SaD-I) shows low to moderate fluid inclusions salinity (5–14 wt.% eq. NaCl), whereas the dolomitization related to ore precipitation (sphalerite and SaD-II) spreads to higher salinity values (5–25 wt.% eq. NaCl). These data may respond to a mixing between a low salinity fluid (fluid A, less than 5 wt.% eq. NaCl) and a more saline brine (fluid B, more than 25 wt.% eq. NaCl) at different fluid proportions.