Calcite Samples Research Articles

A fluid inclusion and stable-isotope study of hydrothermal vein mineralization, Schwarzwald district, Germany

A combined fluid inclusion and stable isotope study has been carried out on over 180 individual samples from 89 post-Variscan hydrothermal veins (Pb-Zn-Cu-bearing fluorite-barite-quartz veins, Co-Ni-Ag-Bi-U-bearing barite-fluorite-quartz veins and barren barite-fluorite-quartz veins) from the Schwarzwald district, Germany. The salinities of fluid inclusions in post-Variscan primary fluorite, calcite, barite and quartz are in the range of 22–25 wt.% equivalent (eqv.) NaCl, and the eutectic temperatures range between –57 and –45°C, indicating the presence of H2O-NaCl-CaCl2 fluids. Homogenization temperatures vary from 130 to 180°C. A low-salinity fluid (0 to 15 wt.% eqv. NaCl) was observed in some late stage fluorite, calcite and quartz samples, which were trapped similar temperature, range of high salinity fluids.
 Raman microprobe analyses show that the only detectable volatile in the vapour is CO2. Almost all δ18O (n=86) measurements of quartz from the fluorite-bearing post-Variscan veins range between +11.1 and +20.9 ‰. The calculated δ18OH2O values are between –11.0 and +4.4 ‰, using known quartz-water fractionation and fluid inclusion homogenization temperatures. The δ18OH2O values of directly extracted fluid inclusion water of fluorites range from –11.6 to +1.1 ‰, very consistent with the calculated values. The δD values of fluid inclusion water in calcites (extracted from primary and late calcite samples) lie in a narrower range between –26 and –15 ‰. The extracted fluid inclusion water from quartz samples has significantly more variable δD values between –63 and +9 ‰. The δ13C and δ18O values of fluid inclusion gas (CO2) range between –21.4 and –6.7 ‰ and between –16.3 to –7.1 ‰, respectively.
 Calculations for fluorite-barite-quartz veins combining oxygen isotope equilibria with microthermometric data result in quartz precipitation temperatures of 120–170°C at pressures between 0.3 to 0.5 kbar. The δ18OH2O and δD data, particularly the observed wide range in hydrogen isotopic compositions, indicate that the hydrothermal mineralization formed through large-scale mixing of a basement-derived saline NaCl-CaCl2 brine with meteoric water.

Macaque fossils (Cercopithecidae: Papionini) from the Kumok Cave, Sungho County, North Hwanghae Province, the Democratic People's Republic of Korea

ABSTRACTThe recently discovered macaque fossils, including mandible, maxilla fragments and isolated teeth, from the Kumok Cave, Sungho County, the Democratic People's Republic of Korea can be identified as Macaca mulatta. They represent the first recognised occurrence of fossil M. mulatta in the Kumok Cave. The Kumok Cave sediments include seven layers, of which the macaque fossils were found only in the third layer. Thermoluminescence dating on a calcite sample from Layer 3 is about 86.1 ± 7.7 ka, and geochronology by the accompanying mammal fauna belongs to the Late Pleistocene, Thus, it indicates that Layer 3 was represented by a warm phase at the end of the pre‐Würm interglacial Epoch. The Kumok fossils also contribute to the growing primate fossil record in DPRK, and indicate the need for increased research into fossil primates in that country.

Isotopic signals in fracture-filling calcite showing anaerobic oxidation of methane in a granitic basement

Understanding the long-term redox conditions and the related carbon cycle in groundwater is essential for long-term safety assessment because they affect the performance of barrier systems and radionuclide transport in geological disposal. However, it is difficult to identify those long-term changes directly. To help understand this, we conducted a paleohydrogeological study on calcite mineralization associated with fracture-controlled groundwater flow-paths in the Toki Granite in central Japan, focusing on its carbon and oxygen stable isotope characteristics. Previous studies revealed four generations of fracture-filling calcite in the Toki Granite. Therefore, we conducted isotopic analysis on both bulk samples of calcite and spatially-resolved microsamples of discrete generations of calcite within zoned crystals. The δ18OVPDB of calcite ranging between −32.7‰ to −0.59‰ revealed that the groundwater that precipitated the calcite was derived from various origins over the geological history of the area, including early hydrothermal fluids associated with the late-stage cooling of the granite (less than −17.2‰); freshwater invasion from the surface following regional uplift (−18.5‰∼ −8.3‰), and; seawater that penetrated during periods of marine transgression (−8.7‰ ∼ −0.3‰). The range in δ13CVPDB values (−56.5‰ ∼ +6.0‰) was wider than the isotopic range of dissolved inorganic carbon (DIC) that originated from hydrothermal, meteoric, and seawater sources (−25‰ ∼ +2‰). Calcite with low δ13CVPDB values less than −25‰ is believed to have precipitated from groundwater with DIC that was provided by anaerobic oxidation of methane (AOM), whereas calcite with δ13CVPDB higher than +2‰ is believed to have precipitated from groundwater containing 13C-enriched DIC as a carbon source derived during methanogenesis. These processes influencing the formation of calcite mineralization in the Toki Granite are comparable to those at other crystalline rock sites in European countries. The AOM calcite and calcite associated with methanogenesis in the Toki Granite precipitated during the transition of the groundwater origin from meteoric to seawater. Understanding these redox processes and the related carbon cycle in granitic groundwater can provide important insights into processes relevant to assessing the long-term evolution of geoenvironmental systems.

An integrated petrophysical analysis based on NMR, organic geochemistry and mineralogy. The Vaca Muerta source rock-unconventional play at different thermal maturities

The Vaca Muerta Formation (Upper Jurassic–Lower Cretaceous) of the Neuquén Basin, Argentina is a world-class source rock and renowned as an unconventional reservoir for both oil and gas. The present study examines rotary sidewall cores representative of the oil and gas windows to analyze correlations between nuclear magnetic resonance (NMR T2 and T1-T2 maps at 2 MHz), Gas Filled Porosity (GFP), Rock-Eval programmed pyrolysis and quantitative X-ray diffraction (XRD) mineralogy. Shale samples are characterized by high present-day total organic carbon contents ranging from 3 to 7.20% (mean: 4.30%) for Well A at the oil window and, 0.72 to 11.77% (mean: 5.86%) for Well B at the gas window. The analyzed set also covers a wide compositional spectrum from carbonate-rich (> 50% of calcite and minor dolomite), mixed carbonate-siliciclastic (30 to 50% of calcite), to siliciclastic-rich (< 30% of calcite) samples. Notably, the clay fraction is dominated by interstratified illite-smectite minerals with less than 10% of expandable layers. Total porosity, calculated from Gas Filled Porosity plus NMR T2 Cumulative Distribution, is in the range of 10 to 20 porosity units. In this work we also present a new NMR sequence to detect solid-like organic matter with NMR at 2 MHz in an integrated workflow to characterize petrophysical properties of the Vaca Muerta Formation.

A natural calcite reference material for microbeam Sr isotope analysis

A natural calcite sample MNP is prepared as a potential reference material for in situ Sr isotope analysis.

Systematic Evaluation for the Impact of the Geological Conditions on the Adsorption Affinities of Calcite as an Adsorbent of Zn2+ Ions from Aqueous Solutions: Experimental and Theoretical Studies

Three samples of calcite (calcite crystal (CA), calcite of limestone (L.CA), and metamorphosed calcite (marble) (M.CA)) were assessed as adsorbents of Zn (II) to consider the impact of the different geological conditions. The three samples exhibit remarkable changes in their Zn (II) retention capacities (Qsat = 384.6 mg/g (CA), 274.5 mg/g (L.CA), and 512.6 mg/g (M.CA)). The retention systems of the three calcite samples were described on the basis of the suggested statistical physics-based equilibrium studies as well as the traditional kinetic and isotherm models. However, the M.CA samples exhibited the best retention capacity, the steric properties reflecting a higher active site density of CA (Nm (Zn) = 113.46 mg/g) than both M.CA (Nm (Zn) = 82.8 mg/g) and L.CA (Nm (Zn) = 52.4 mg/g) at 323 K. This was assigned to the controlling effect of the sequestered numbers of Zn (II) per site on the surfaces of the calcite phase (n(Zn) = 3.39 (CA), 5.24 (L.CA), and 6.19 (M.CA)) in addition to the higher surface area and ion exchange of the metamorphosed and deformed M.CA. The previous n(Zn) values suggested the retention of Zn (II) by a multi-ionic mechanism in a vertical orientation. The Gaussian energies (8 to 16 KJ/mol) and retention energies (˂40 KJ/mol) of Zn (II) by CA and L.CA suggested complex physical and weak chemical mechanisms involving ion exchange, hydrogen bonding, dipole bonding forces, electrostatic attractions, and van der Waals forces. The thermodynamic properties were illustrated on the basis of the internal energy, free enthalpy, and entropy functions, which validate the endothermic and spontaneous nature of the Zn (II) retention system by the three calcite samples.

Calcite U-Pb, pyrite Re-Os geochronological and fluid inclusion and H-O isotope studies of the Dafang gold deposit, South China

The Dafang gold deposit is one of the representative gold mineralization in southern Hunan province, South China. The gold orebodies mainly occur in the contact zones between late Jurassic granodiorite porphyry and late Paleozoic limestone as well as the fractures in them. Three primary mineralizing stages have been identified: pyrite + arsenopyrite ± chalcopyrite + quartz (stage I), pyrite + gold + calaverite + polymetallic sulfides + quartz (stage II), and pyrite + arsenopyrite + quartz + calcite (stage III). Pyrite samples separated from stage II yielded a Re-Os isochron age of 149 ± 16 Ma. Calcite samples from stage III demonstrated a U-Pb age of 157.7 ± 6.5 Ma. The above ages are similar to the zircon U-Pb ages of the local granodiorite porphyry although field evidences did not support a genetic link between them. The newly obtained mineralizing ages for Dafang indicate that this deposit is most likely related to deep or nearly late Jurassic intrusions (e.g., the Baoshan porphyry intrusion) and that this gold mineralization is synchronous with the large-scale W-Sn mineralization (160–150 Ma) for the Nanling Range in South China. The measured δDH2O (−103.5 to −81.4 ‰) and calculated δ18OH2O (−4.1 to + 4.9 ‰) isotope compositions for different stage vein quartz suggest that the Dafang ore-forming fluids were initially dominated by magmatic water, and were diluted by meteoric water in the late stage. Fluid inclusion studies indicate that the ore fluids belong to the H2O-NaCl-CO2-CH4 system, which cooled during its evolution (e.g., 230–337 °C, 150–246 °C, and 91–178 °C for stages I to III, respectively) with varied fluid salinity (4.7–9.2, 4.7–23.3, and 2.1–9.9 wt% NaCl eqv. for stages I to III, respectively). Fluid inclusions assemblages with different vapor and liquid phase ratios in a single quartz growth, and their similar homogenization temperatures with varying fluid salinities supported the fact that fluid boiling occurred in ore stage II. Combined with geological occurrences and the results from this study, we propose that gold was mainly transported in a reducing condition, and fluid boiling and host-rock sulfidation are the key factors for gold deposition at Dafang.

Isotopic time-series (δ13C and δ18O) obtained from the columnar layer of Permian brachiopod shells are a reliable archive of seasonal variations

In this paper, we develop a robust palaeo-proxy technique for inferring seasonal fluctuations in Phanerozoic seawater temperature. Specifically, we report δ13C and δ18O values across the columnar layer (inner shell) of Permian brachiopods, including five genera of the Order Spiriferida (Ingellarella, Martinia, Permophricodothyris, Cartorhium, and Trigonotreta) and two genera of the Order Athyridida (Araxathyris and Comelicania). These brachiopod specimens are inferred to have inhabited varied palaeo-depths, based on facies analysis, and were collected from low, middle and high palaeolatitudes. To obtain high-resolution ontogenetic isotopic time-series, a handheld microdrill was used to collect low-magnesium calcite samples along the longitudinal axis of the mid-valve for each specimen. Intrageneric and intergeneric comparison of statistics (mean values, variance, and range) reveals that δ18O values are consistent within and between genera although δ13C values are more variable. In specimens obtained from low palaeolatitudes (Julfa Formation, Iran; Bellerophon Formation, Italy; Late Permian), the range of δ18O values is small and consistent with weak seasonal temperature variations, irrespective of water depth. In specimens obtained from middle palaeolatitudes (Qarari Formation, Oman; Early-Middle Permian), we found a range of δ18O values dependent on inferred water depth, possibly reflecting a change in thermocline structure between warm and cold seasons. In specimens obtained from high palaeolatitudes (Wasp Head and Wandrawandian Siltstone formations, Australia; Early-Middle Permian), brachiopods from glacial and interglacial climate phases show significant variations of δ18O values, probably caused by seasonal changes in the seawater surface temperature. Based on these findings, the technique developed in this paper appears to provide reliable paleoclimate and paleoenvironmental data for Permian sites, and should be also applicable for Phanerozoic studies in general. However, we caution that δ18O values vary dependent on the growth direction, resulting in differences of up to 5 °C in seawater paleotemperature calculations, and emphasise that a consistent sampling strategy accounting for shell structure and growth direction is required.

The Effect of Experimental Cycles on the Traps Depths of Dosimetric Traps of Natural Calcite Minerals

A trap found in a solid state radiation dosimetry is characterized by kinetic parameters such as trap depth (Ea), frequency factor (s), kinetic order (b) and carrier concentration (no). Trap depth (Activation energy) is the required energy to release carriers in the trap. In this study, it is investigated that how the dosimetric trap depths of the traps found in the four natural calcite minerals are affected by reusable of them as a dosimeter. All samples were irradiated about 36 Gy beta dose and read out by a thermoluminescence dosimeter (TLD) reader. A computer glow curve deconvulation program (CGCD) was used to get the kinetic parameters. And the results are compared for the four calcite samples.

Characterization and Geological Implications of Precambrian Calcite‐Hosted Phosphate

AbstractConstraints on marine phosphate availability and cycling directly inform our understanding of long‐term biological evolution. However, early Earth phosphate records are sparse, biased toward siliciclastic samples, and susceptible to post‐depositional modification. Well‐preserved shallow marine inorganic carbonate precipitates provide a complementary yet understudied record of phosphate cycling. We combined micro‐X‐ray fluorescence mapping, X‐ray absorption, and Nuclear Magnetic Resonance spectroscopy on samples of Precambrian syndepositional herringbone calcite (HBC) and microspar to characterize phosphorus speciation and distribution in these carbonate fabrics. Phosphorus spectroscopy from synthetic calcite, HBC, and microspar, is qualitatively consistent with a disordered distribution of phosphate. These characteristics are diagnostic of calcite‐hosted phosphate, which is pervasive at low concentrations in HBC and microspar. This study provides evidence that ancient, well‐preserved carbonate fabrics retain phosphate sourced from seawater and highlights the potential for an unaltered archive of marine phosphate concentration over geologic time.

Controls on Timing of Hydrothermal Fluid Flow in South-Central Kansas, North-Central Oklahoma, and the Tri-State Mineral District

Paleozoic sedimentary rocks in the southern midcontinent of the United States have been affected by multiple events of deformation and fluid flow, resulting in petroleum migration, thermal alteration, Mississippi Valley-type mineralization, and a complex diagenetic history. This record is a hidden history of how cratonal settings respond to tectonic and non-tectonic drivers. The aim of this contribution is to better understand the controls on fluid migration in Paleozoic strata to evaluate whether hydrothermal activity is forced by tectonic or non-tectonic processes. This paper summarizes and vets the distribution of published dates related to thermal events in the southern midcontinent. In addition, we present new U-Pb dates obtained by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) on calcite cements that were formed from hydrothermal fluids. These are from three samples from the Berexco Wellington KGS 1-32 core in Sumner County, Kansas; an ore sample from the Tri-State Mineral District, Neck City, Missouri; and a core sample from the Blackbird 4-33 well in Osage County, Oklahoma. Previous studies of these calcite samples provided evidence for hydrothermal fluid flow, with one of the Wellington samples possibly recording vertical hydrothermal fluid flow out of the basement. The sample from the Tri-State Mineral District (Missouri) yields a mid-Cretaceous age of 115.6±3.1 Ma. This age falls into the timing of the Sevier Orogeny along the west coast and the development of its foreland basin in the midcontinent. Calcites from the Mississippian interval in the Wellington KGS 1-32 core yield dates of 305±10.5 Ma and 305.1±9.1 Ma. Calcite in Mississippian strata from the Blackbird 4-33 core yields a date of 308.6±2.5 Ma. These dates from Mississippian calcite cements indicate hydrothermal fluid flow in the Late Pennsylvanian that coincides with the timing of the Marathon-Ouachita Orogeny or the Ancestral Rocky Mountains Orogeny. A calcite sample from the Ordovician Arbuckle Group from the Berexco Wellington KGS 1-32 core yielded an age of 5.6±1.6 Ma, coinciding with a time after high elevation uplift of the Rocky Mountains was already far advanced. We propose that this hydrothermal fluid flow may have been associated with increased meteoric recharge and increased regional fluid pressure in a basement aquifer that activated local seismic events far into the continental interior. The distribution of ages of hydrothermal fluid flow confirms a syntectonic driver during the Ouachita Orogeny and Ancestral Rocky Mountains Orogeny deformation. Continuation of hydrothermal fluid flow well into the Permian and tailing off early in the Triassic indicates a post-tectonic driver, where uplifted areas continued to provide the recharge from gravity-driven fluid flow, until the mountains were mostly beveled by the early part of the Triassic. A dearth of Triassic and Jurassic hydrothermal events suggests Gulf of Mexico rifting and extension were less important. Rejuvenation of hydrothermal fluid flow in the Cretaceous and continuing into the Paleogene indicates that elevation and regional flexure from both the Sevier and Laramide events continued to drive hydrothermal fluid flow far from the main sites of mountainous uplift and deformation. Finally, hydrothermal fluid flow associated with more recent uplift of the Rocky Mountains may have been activated by recharge events that pressurized a regional basement aquifer and triggered seismic activity.

Chlorite chemistry, H-O-S-Pb isotopes and fluid characteristics of the Yuhai Cu-Mo Deposit in Eastern Tianshan: Implications for porphyry copper mineralization and exploration

The Yuhai porphyry Cu-Mo deposit, located in the Eastern Tianshan metallogenic belt, northwest China, is a new discovery in the eastern section of Dananhu-Tousuquan arc, hosted mainly by quartz diorite and granodiorite intrusions. Based on alteration and mineralization assemblages as well as crosscutting relationships, three stages of hydrothermal activities have been identified: 1) early mineralization stage characterized by potassic alteration and minor Cu-Mo mineralization; 2) main mineralization stage with phyllic and propylitic alterations and extensive Cu-Mo precipitation; and 3) late mineralization stage forming barren quartz and minor calcite, chlorite, and epidote minerals. Sulfur isotope compositions of the Yuhai chalcopyrite, pyrite, bornite and molybdenite record a narrow range of −3.4 to +0.4 ‰, indicating a deep source of magmatic sulfur. Lead isotope data of sulfides from our previous study display consistent 208Pb/204Pb and 207Pb/204Pb ratios, but distinguishable 206Pb/204Pb ratios from the Yuhai intrusions analysed in this work. Combined sulfur and lead isotopic signatures, we suggest that the ore-forming components (metals and sulfur) were derived from a mantle-derived magmatic reservoir with some crustal components. The δ18O values of quartz, chlorite, calcite, and sericite samples separated from different mineralization stages range from 1.5 to 8.2 ‰ (n = 11), with calculated δ18OH2O values of −2.2 to 4.5 ‰, and the δD values of fluids range from −92.7 to −68.7 ‰ (n = 4), indicating the ore-forming fluids are composed of magmatic fluid and meteoric water. Mineral chemistry of chlorite, fluid inclusions microthermometry, and petrographic evidences reveal that the ore-forming fluids evolved from a high fO2 to relative weak oxidized condition with decreasing temperature, and copper was largely precipitated at temperatures of <320 °C in a weakly oxidized system during main stage. All these observations demonstrate that Yuhai was formed by hydrothermal fluids related to the diorite magma, and that the fO2 and temperature decreasing plays a critical role for abundant depositions of Cu and Mo. The Paleozoic diorite complex formed in a subduction setting is suggested as a significant exploration target for porphyry-style Cu mineralization in the Eastern Tianshan.

MICROFACIES OF LATE PLEISTOCENE TRAVERTINE DEPOSITS IN JORDAN

The Late Pleistocene travertine outcrops from Deir Alla, Suwayma, and Az Zara were investigated, and their microfacies were identified. The microfacies of the Deir Alla travertines include micrite and spar groundmass, shrubs, crystalline crusts, a stromatolite-like structure, peloids, and cements. Shrub travertine includes spar calcite-coated stems with probably microbial micritic clumps. The crystalline crust travertine displays an alternation of micrite and sparite laminae. The micritic laminae are dark-coloured. Bundles of radial spar crystals are associated locally with micritic groundmass. The crystalline crust developed where biogenic activity is limited. Peloidal microfacies are less than 0.25 mm in diameter, cryptocrystalline, pale-dark green in colour, elliptical to spherical in shape, and usually associated with microorganisms. The microfacies of the Suwayma and Az Zara travertines include crystalline calcite rhombs and other composite scalenohedral crystals. They occur as small anhedral-subhedral crystals, monocrystalline to some polycrystalline, corroded, subrounded, and mainly coated with iron oxide and/or clay minerals. Peloids, ooids, and oncoids are common. They are dark-green coloured, cryptocrystalline to microcrystalline carbonates of spherical and ellipsoidal shape with less than 1 mm in diameter. Rich flora travertines include reed and paper-thin rafts with leaf impressions encrusted on moss cushions. The flora observed in the upper part of the Suwayma section was identified as charophyte oospores (gyrogonites). A few grains of quartz are present as small subhedral-euhedral crystals, monocrystalline, corroded, rounded, and mainly coated with iron oxide. The iron is irregularly distributed among the laminae and voids and is occasionally replaced by carbonates. The described macrophyte encrustation structures probably represent algae, cyanobacteria, or bryophytes. All samples of micrite and spar calcite appear as groundmass.

Metallogenesis of Ni–Co–Fe-arsenide type mineralization in the Purísima-Rumicruz deposit, Jujuy, Argentina

The Purísima-Rumicruz vein system is a Ni–Co–Fe-arsenide type or Five-Element deposit located in the Cordillera Oriental, northwestern Argentina. The host rocks are Ordovician black shales of the Acoite Formation. Three vein types, were identified (a) sulfides/sulfoarsenides + carbonates ± quartz; (b) barite; and (c) crystalline quartz veins. Sulfide-carbonate veins are narrow and exhibit multi-episode infill and are NW-SE and E-W oriented. Four successive stages of mineral precipitation were established. The first stage, sulfide-rich, comprises galena, pyrite, chalcopyrite, bornite, and Zn-rich tetrahedrite-tennantite. A second stage corresponds to native silver, arsenides, Ni-sulfarsenides and pitchblende, indicative of a rise in the As/S ratio in the hydrothermal fluids. The third stage evidences a decrease in the As/S ratio with sulfide precipitation of silver sulfides, chalcocite, chalcopyrite, tetrahedrite-tennantite, bornite and millerite. Finally, a supergene event with covellite, digenite, limonite and Cu-carbonates occurred. Microthermometric studies of Stage 1 quartz yield Th between 185 and 276 °C and 5.2–12 wt% eq. NaCl. Salinities. Stage 3 calcite yield Th 110-240 °C and salinities in two ranges, 1–11 and 16.8–24 %wt. NaCl eq. The δ34S values in chalcocite and galena range between +5.8 and + 7‰, and the δ18OSMOW values from quartz, are between +6.2 and + 9.0‰. δ18OSMOW and δ13CPDB values in calcite samples range between +10.9 and +14.7‰, and −3.05 to −4.07‰, respectively. Isotope data indicate a cortical source of the fluids, probably from connate waters. Early Cretaceous rifting produced a thermal anomaly and direct faults and fractures. Deep-seated brines mixed with connate fluids of the Acoite Formation led to the formation of the Purísima-Rumicruz veins.

Experimental evidence of static disorder of carbonate ions in Ba-doped calcite

Incorporation of structurally incompatible Ba2+ into calcite by crystallization via amorphous calcium carbonate induces extinction of 113 reflection in X-ray diffraction patterns even at room temperature. Recently, this phenomenon has been hypothesized as deriving from the static disorder of CO32− in Ba-doped calcite, creating a marked increase in the unit-cell volume. To clarify this hypothesis by experiments, behaviors of CO32− and local structures in Ba-doped calcite samples were investigated. Powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC) indicate that CO32− ions in Ba-doped calcite are disordered, even at 91K. 13C MAS NMR spectra suggest that Ba atoms in calcite are substituted randomly for Ca atoms. The Ca K-edge X-ray absorption fine structure (XAFS) and the IR absorption spectra indicated reduction of CO32− symmetry with increasing Ba content. These local structure changes by incorporation of incompatible Ba2+ into calcite cause static disorder of CO32− at room temperature.

Occurrence of Taeniidae in a Middle Pleistocene speleothem of the Bàsura cave (Toirano, Liguria, Italy)

ObjectiveThis study aims to (i) analyse whether speleothems may contain fossil parasitic worm eggs and, if so, (ii) identify the pathogens involved, and (iii) place them in geological, palaeontological, and chronological contexts to know the zoonoses that could affect human and animal populations during the Middle Pleistocene. MaterialsA sample of calcite dated to the beginning of MIS 9 and MIS 8 from the Bàsura cave (Liguria, Italy) was analysed. MethodsThe chemical protocol applied is characterised using hydrochloric acid, the reduction of hydrofluoric acid application time, and by the absence of the use of base, dense liquor or acetolysis. ResultsAn embryophore of a taeniid was recovered. ConclusionsEndoparasitic worm eggs can be found in speleothems. A taeniid embryophore was found in a calcite level dated to MIS 9. Zoonoses related to the Taeniidae family existed 300,000 years ago in the northern Mediterranean region and may have affected Middle Pleistocene predators, carnivores, or humans. Speleothems are good tools for paleoparasitological studies. SignificanceThis is the oldest taeniid recovered and identified. LimitationsA more precise determination of the genus of this taeniid is not possible in the absence of more precise palaeontological data. Suggestions for further researchAn application of this approach to other Pleistocene speleothems could broaden the spectrum of parasites and their zoonoses over remote Pleistocene periods.

Calcite trace element geochemistry of Au deposits in the Singu-Tabeikkyin Gold District, Myanmar: Implications for the sources of ore-forming fluids

The Singu-Tabeikkyin gold district is one of the largest gold districts in Myanmar. The gold mineralization is represented by several tens of quartz lodes, which are hosted by a metamorphic sequence of marbles, calc-silicate rocks, gneisses, and migmatites. Trace- and rare earth element (REE) concentrations of successive generations of hydrothermal calcites from gold deposits of the Singu-Tabeikkyin gold district were analyzed in order to determine the origin of the ore fluids. Calcite samples contain variable concentrations of REE (3–1051 ppm) and Y (1–219 ppm). The chondrite-normalized rare earth element and yttrium (REEY) patterns of ore-stage calcites show three different trends which are (1) being strongly enriched in light REE (LREE) with positive Eu anomalies, (2) being enriched in heavy REE (HREE) with negative Eu anomalies, and (3) being enriched in middle REE (MREE) with no distinct Eu anomalies. The first trend, which is representative of the majority of ore-stage calcites, is in agreement with ore fluids originating from a magmatic origin at high temperature (>250 °C). This is consistent with previous geochronological and geochemical data, demonstrating that the ore fluids are primarily associated with the Miocene magmatism. HREE- and MREE-rich REEY patterns of some hydrothermal calcites from Te-rich deposits are interpreted to represent the minor involvement of additional fluids.

Key oil accumulation periods of ultra-deep fault-controlled oil reservoir in northern Tarim Basin, NW China

A giant fault-controlled oilfield has been found in the ultra-deep (greater than 6000 m) Ordovician carbonate strata in the northern Tarim Basin. It is of great significance for hydrocarbon accumulation study and oil exploitation to determine the key oil accumulation periods. Based on detailed petrographic analysis, fluid inclusion association (FIA) in calcite samples filling in fractures from 12 wells were analyzed, and key accumulation periods of the strike-slip fault-controlled oilfield was studied by combining oil generation periods of the source rocks, formation periods of the fault and traps, and the fluid inclusion data. (1) There are multiple types of FIA, among them, two types of oil inclusions, the type with yellow fluorescence from the depression area and the type with yellow-green fluorescence from the uplift area with different maturities indicate two oil charging stages. (2) The homogenization temperature of the brine inclusions in FIA is mostly affected by temperature rises, and the minimum temperature of brine inclusions symbiotic with oil inclusions is closer to the reservoir temperature during its forming period. (3) FIA with yellow fluorescence all have homogenization temperatures below 50 °C, while the FIA with yellow-green fluorescence have homogenization temperatures of 70–90 °C tested, suggesting two oil accumulation stages in Middle–Late Caledonian and Late Hercynian. (4) The Middle–Late Ordovician is the key formation period of the strike-slip fault, fracture-cave reservoir and trap there. (5) The oil generation peak of the main source rock of the Lower Cambrian is in the Late Ordovician, and the oil accumulation stage is mainly the Late Ordovician in the depression area, but is mainly the Early Permian in the uplift area. The key oil accumulation period of the strike-slip fault-controlled reservoirs is the Late Caledonian, the depression area has preserved the primary oil reservoirs formed in the Caledonian, while the uplift area has secondary oil reservoirs adjusted from the depression area during the Late Hercynian. Oil reservoir preservation conditions are the key factor for oil enrichment in the strike-slip fault zone of northern Tarim, and the Aman transition zone in the depression is richer in oil and gas and has greater potential for exploration and development.

Exploring deep carbonate reservoir samples: Anisotropy and correlation of static and dynamic Young’s moduli

In total, 14 limestone samples, drilled in the vertical and horizontal directions from a depth &gt;3 km, are analyzed to understand the correlation between static (operating at in-situ strain levels) and dynamic (at a sound wave strain level) Young’s moduli, [Formula: see text] and [Formula: see text], and also to investigate their directional dependence. Young’s moduli are measured simultaneously under a confining pressure of 30 MPa to a differential axial stress of 50 MPa using a triaxial frame with linear variable differential transformers: two axial and one radial calibrated with a standard aluminum slug. Static and dynamic moduli decrease with increasing porosity whereas the static moduli are typically less than the dynamic moduli. The static measurements exhibit significant hysteresis indicating a nonlinear (irreversible) regime, whereas the dynamic moduli, measured with low-strain amplitude, indicate a linear (reversible) regime. The static Poisson’s ratio increases with porosity, but the dynamic ratio remains unchanged over the whole range of porosity, which seems to not be sensitive enough to the heterogeneity in the pore structure. The induced microfractures, naturally developed under tensile stress after these deep samples were brought to the surface, are imaged in computer microtomography (micro-CT) scan experiments. The mineralogical composition is determined as higher than 95% calcite CaCO3and mapped out using quantitative evaluation of minerals by scanning electron microscopy. Elastic anisotropy is observed with increasing porosity, where the ratio [Formula: see text]/[Formula: see text] increases for the vertical but decreases for the horizontal samples. Likewise, a permeability anisotropy also is observed as porosity increases, where the ratio of the vertical to horizontal permeability [Formula: see text]/[Formula: see text] is higher than one, indicating a preferred vertical structure for fluid flow. Two linear correlations between [Formula: see text] and [Formula: see text] are developed for the studied calcite samples, and for samples composed of up to 30% dolomite CaMg(CO3)2reported in the literature.

Sm‐Nd isochron age and Sr‐Nd isotopes of the calcite from the Nibao gold deposit in the Youjiang Basin, SW China

AbstractThe Youjiang Basin in SW China is the second‐largest Carlin‐like goldfield in the world after Nevada, USA. However, the age and the hydrothermal origin of the gold mineralization are still in controversy, which leads to ambiguities in understanding the geodynamic setting and genetic mechanism of the gold deposition. Nibao is a large, stratabound, and fault‐controlled Carlin‐type gold deposit in the north of the Youjiang Basin. Three ore stages have been recognized in the evolution of the mineralizing hydrothermal fluid, with the stages being characterized by assemblages of the early quartz–porous pyrite, the main quartz–calcite‐apatite–sericite–pyrite–arsenopyrite‐gold, and the late quartz–calcite–fluorite–realgar–orpiment–stibnite. Calcite veins from the main and late ore stage at Nibao are enriched in middle rare earth elements, which is a distinctive characteristic of hydrothermal calcite veins associated with low‐temperature hydrothermal Au‐Sb deposits in the Youjiang Basin, and yield a Sm‐Nd isochron age of 138 ± 1 Ma. The vast majority of the ore stage calcite samples have narrow 87Sr/86Sr ratios and εNd(t) values ranging from 0.708119 to 0.708423 and − 1.1–−3.3, respectively, indicating that the gold‐bearing hydrothermal fluid could be derived from the mixing of mantle and crustal materials. Therefore, we proposed that the gold mineralization during the Early Cretaceous in the Youjiang Basin was triggered by the large‐scale lithosphere extension following the retreat of the subducted Paleo‐Pacific oceanic crust, and the hydrothermal fluid could be originated from the mantle and underwent the contamination of Yangtze upper continental crust.