Temperatures Of Mineral Formation Research Articles

Metals pre–enrichment during the syn–sedimentary period of Mengxing Pb–Zn Deposit, western Yunnan, SW China: Evidence on LA–ICP–MS trace elements and S isotopes of lamellar sphalerite

The Mengxing Pb–Zn deposit, which contains up to 1.02 Mt of Pb + Zn metal with an average Pb + Zn grade of ca. 12.13 %, is a representative of sedimentary–reworked deposit in western Yunnan. The orebodies, which are strata–bound and veined, occur in the Silurian Shangrenheqiao formation. The mineralization process has been divided into sedimentary stage and hydrothermal stage. Previous research has primarily focused on the economic ores enriched during the hydrothermal stage. However, the formation of syn–sedimentary ore, responsible for metal pre–enrichment, has been largely ignored. To solve the issue above, the in–situ trace elements and mapping, as well as in–situ S isotopes analyses, were conducted on lamellar sphalerite ore, which retains the characteristics of the syn–sedimentary ore. Analysis of the trace elements revealed that the sphalerite at Mengxing are rich in Ge, Cd, As, Sb and poor in Fe, Mn, In, Sn and Co overall, suggesting a metallogenic environment of medium–low temperature. The LA–ICP–MS trace elemental mapping graph indicated that colloidal sphalerite exhibits the obvious oscillation belts. The dark zonal band of sphalerite is more enriched in Fe, Mn, Cu, Ge, As, Ag, Sb, and Pb, and depleted in Ga, Cd, and Sn, compared to the light zonal band, suggesting the various formation temperature. Based on the equation of the first principal component (PC1*) relating trace elements to mineral formation temperature, it is estimated that ore in the sedimentary stage occurred at relatively lower temperatures (174.74℃ – 203.18℃), while that of the hydrothermal stage occurred at higher temperatures (209.78℃ – 240.18℃). The S isotopic composition of sphalerite indicated a significant distinction between the sedimentary stage (δ34SVCDT = 13.29 ‰ – 37.06 ‰, with an average value of 27.97 ‰) and the hydrothermal stage (δ34SVCDT = −6.45 ‰ – 31.57 ‰, with an average of 9.01 ‰). It is hypothesized that sulfur during the early stage originated primarily from thermochemical sulfate reduction (TSR) of seawater sulfate, while sulfur during the hydrothermal stage was likely influenced by hydrothermal fluid from the deep. In conclusion, the early lamellar ores formed during the Silurian period exhibit characteristics consistent with SEDEX type mineralization, leading to initial metal pre–enrichment, followed by further enrichment of ore grade by superimposed fluid during the hydrothermal stage.

Calcination of sewage sludge-based sulphoaluminate cement clinker: Mineral formation mechanism and heavy metal transition behaviors

Utilizing sewage sludge (SS) to calcinate sulphoaluminate cement (SAC) is a promising technology for low-carbon transition of cement industry, but the unclear effects of SS-contained heavy metals limit the application of this technology. In this study, the effects of SS addition on the calcination of SAC clinker and the transformation of heavy metals were studied from the aspects of mineral phase change, microstructure evolution and heavy metal speciation respectively, covering the mineral formation temperature 900–1250 °C. The results show that the added SS will reduce the formation temperature and change the reaction pathways of mineral phases. When the content of SS increases from 10% to 25%, the compositions of mesophases CaO·Al2O3 and 4CaO·2SiO2·CaSO4 increase by 6.33% and 9.73%, respectively. Meanwhile, the formation of minerals will solidify Zn, Ni, Mn, Cu, Cr, and convert them into a more stable fraction (residual fraction), indicating a lower probability to harm the environment. Moreover, heavy metals present different migration behaviors. After calcination, Mn migrates from SS to 4CaO·Al2O3·Fe2O3 (52.48%), while Zn prefers to enter 3CaO·3Al2O3·CaSO4 (43.74%) and 4CaO·Al2O3·Fe2O3 (38.06%). This study offers new insights into the mineral formation mechanism and heavy metal transition behaviors of sewage sludge-based SAC.

Forms of presence, interrelation and genetic significance of Al and Li impurities in quartz of gold deposits of the Darasunsky ore field (Eastern Transbaikalia, Russia)

Research subject. The distribution regularities of Al and Li impurities in gold-ore quartz. Materials and methods. The quartz of the Darasun, Teremkinskoye and Talatuy gold deposits of the Darasun ore field was studied. The gross contents of Al and Li impurities in quartz were determined by the LA-ICP-MS method; substitutional Al impurity concentrations were studied by the EPR method. The forms of Al impurity in quartz were determined based on the results of studying its behavior during material recrystallization. The genetic significance of Al and Li impurities in quartz was estimated taking into account the genetic information obtained during the study of the distribution of substitutional Al and Ti impurity concentrations. Results. It was found that Al is present in quartz in two main forms, i. e., as a substitutional Al impurity and Al complexes localized in the areas of high mineral defectiveness. Li+ ions are located in the structural channels of the mineral, serving as compensating ions for both Al impurity forms. The composition of Al complexes is assumed to include three Al3+ ions and one H+ or Li+ ion. Two stages of quartz recrystallization occurring at different temperatures of mineral formation were identified. The first, low-temperature stage leads to quartz enrichment with substitutional Al impurities. The second, high-temperature stage causes the decomposition of Al complexes. The recrystallization stages can be identified by the type of relationship between the gross concentrations of Al and Li. The increased content of Al impurity in ore quartz was found to be related to the presence of a large number of Al complexes. An assumption is made that these complexes formed during mineral crystallization from solutions with a high content of metal ions. Conclusions. The results obtained indicate that high Al impurity concentrations can serve as a genetic sign of ore quartz. At the same time, the decomposition of Al complexes during quartz recrystallization should be taken into account. A method for estimating the initial concentration of Al complexes is proposed, which is a more reliable genetic indicator.

Conditions of formation and sources of fluids of the birthplace of barren residential quartz of hydrothermal-metamorphogenic-metasomatic and hydrothermal-metamorphogenic genesis (Middle and South Urals)

The paper considers the conditions of quartz formation of hydrothermal-metamorphogenic-metasomatic and hydrothermal-metamorphogenic genesis of deposits and manifestations of the Middle and Southern Urals based on the study of fluid inclusions by methods of thermobarogeochemistry, ion and gas chromatography. It is established that the studied quartz objects are formed in a wide temperature range, against the background of insignificant differences in pressure values. It is shown that the temperatures of mineral formation in deposits of hydrothermal-metamorphogenic-metasomatic genesis vary from 440-230 ° C at a pressure of 1.2-1.4 kbar. The formation of these veins occurred with the participation of K-Mg-Fe-chloride fluid with a salinity of 1.2-8.7 wt. % NaCl-eq., depleted Mg and Fe due to the deposition of magnesia-ferruginous carbonates. A typomorphic feature of hydrothermal-metamorphogenic-metasomatic quartz is the high values of boron associated with the placement of quartz veins among pegmatoids and the presence of boron-containing mineral inclusions on quartz-vein objects. Veins of hydrothermal-metamorphogenic genesis were formed when the crack system was filled with quartz with the participation of a substantially K-Na chloride fluid (0.2-15.5 wt. % NaCl-eq.), at homogenization temperatures of 435-335 ° C and a pressure of 1.3-2.3 kbar. In the composition of fluid inclusions of hydrothermal-metamorphogenic-metasomatic quartz, the sum of "harmful" components (H2O, CO2, CH4, Cl, B, Na, K, Mg and Li) is less than in hydrothermal-metamorphogenic quartz. The studied quartz deposits and veins were formed in the range of temperatures and pressures not higher than the green shale stage during several successive stages: the formation of quartz veins – in a more high-temperature hydrothermal stage, while subsequent changes in quartz veins occurred under the influence of metamorphism processes, with a decrease in temperature. Subsequent changes are associated with the appearance of fracturing, cataclysm and recrystallization of quartz bodies with a decrease in grain size.

Alteration Characteristics and Precious Metal Availability in Gunung Gembes & Surroundings, Jeruk Village, Pacitan Regency, East Java Province

The research area is located in the area of Mount Gembes, Jeruk Village in Pacitan (East Java). This study aims to determine the characteristic and temperature in the formation of alteration which refers to petrography with the help of samples taken in the study area. The petrographic observations carried out were thin section observations which were then analyzed for the mineral content contained in the sample rock. After knowing the minerals contained in the sample rock, it is then entered into the mineral formation temperature diagram (White & Hedenquist, 1995). The method used in this study includes primary data in the form of geological observations such as lithology, geological structure geomorphology, environmental geology and alteration observations and combined with secondary data. Alteration observations in this study were carried out descriptively (megascopic) and subjective (microscopic). The geomorphic unit that works is of volcanic origin, with high hilly sub-units of porphyry dacite intrusion (volcanic neck). Geological structures that develop in the study area are faults, namely the left horizontal fault of Jeruk 1, the left horizontal fault of Jeruk 2 and the interpretation of the oranges right horizontal fault. Geological resources or sources found in the research area are mineral potential resources that are economical, and negative sources are in the form of mass movement of debris flow type. The Zonation and the type of alteration that developed in the research area are the clay alteration zone and silicification. The clay zone is formed at a temperature >100⁰C-220⁰C with a pH of 3-5 and a silicification zone is formed at a temperature>100⁰C-300⁰C with a pH <2 which is directly controlled by the faults found in the study site.

PECULIARITIES OF THE COMPOSITION AND THERMODYNAMIC CONDITIONS OF FORMATION OF ENDERBITES OF THE HAIVORONSKYI COMPLEX (SOUTH-WESTERN PART OF THE UKRAINIAN SHIELD)

Mineralogical and petrographic features of enderbites of the Haivoronskyi complex in the south-western part of the Ukrainian Shield (the valley of the Pivdennyi Buh River from the town of Haivoron to the village of Zavallia) were studied. The complex of research included field geological observations on outcrops and in quarries and laboratory petrographic, mineralogical and petrogeochemical studies. Such minerals as quartz, plagioclase (albite–oligoclase, andesine– bytownite), K-feldspar (microcline), rhombic (ferrosilite) and monoclinic (diopside, augite) pyroxenes, garnets, biotite, apatite, ilmenite, monazite, carbonates (calcite, dolomite) have been described. The temperature of mineral formation was calculated using garnet-biotite, garnetorthopyroxene and two-feldspar geothermometers according to the data of various authors using theoretical calculations and a graphic method. The thermodynamic conditions for the formation of enderbites during three stages were determined on the basis of the conducted research and literature data.

Trajectory and timescale of oxygen and clumped isotope equilibration in the dissolved carbonate system under normal and enzymatically-catalyzed conditions at 25 °C

The abundance of 18O isotopes and 13C-18O isotopic “clumps” (measured as δ18O and Δ47, respectively) in carbonate minerals have been used to infer mineral formation temperatures. An inherent requirement or assumption for these paleothermometers is mineral formation in isotopic equilibrium. Yet, apparent disequilibrium is not uncommon in biogenic and abiogenic carbonates formed in nature and in synthetic carbonates prepared under laboratory settings, as the dissolved carbonate pool (DCP) from which minerals precipitate is often out of δ18O and Δ47 equilibrium. For this, a complete understanding of both equilibrium and kinetics of isotopic partitioning and 13C-18O clumping in DCP is crucial. To this end, we analyzed Δ47 of inorganic BaCO3 samples from Uchikawa and Zeebe (2012) (denoted as UZ12), which were quantitatively precipitated from NaHCO3 solutions at various times over the course of isotopic equilibration at 25 °C and pHNBS of 8.9. Our data show that, although the timescales for δ18O and Δ47 equilibrium in DCP are relatively similar, their equilibration trajectories are markedly different. As opposed to a simple unidirectional and asymptotic approach toward δ18O equilibrium (first-order kinetics), Δ47 equilibration initially moves away from equilibrium and then changes its course towards equilibrium. This excess Δ47 disequilibrium is manifested as a characteristic “dip” in the Δ47 equilibration trajectory, a feature consistent with an earlier study by Staudigel and Swart (2018) (denoted as SS18). From the numerical model of SS18, the non-first-order kinetics for Δ47 equilibration can be understood as a result of the difference in the exchange rate for oxygen isotopes bound to 12C versus 13C, or an isotope effect of ~25‰. We also developed an independent model for the Exchange and Clumping of 13C and 18O in DCP (ExClump38 model) to trace the evolution of singly- and doubly-substituted isotopic species (i.e., δ13C, δ18O and Δ47). The model suggests that the dip in the Δ47 equilibration trajectory is due largely to kinetic carbon isotope fractionation for hydration and hydroxylation of CO2. We additionally examined the BaCO3 samples prepared from NaHCO3 solutions supplemented with carbonic anhydrase (CA), an enzyme known to facilitate δ18O equilibration in DCP by catalyzing CO2 hydration (UZ12). These samples revealed that, while CA effectively shortens the time required for Δ47 equilibrium in DCP, the overall pattern and magnitude of the dip in the Δ47 equilibration trajectory remain unchanged. This suggests no additional isotope effects due to the CA enzyme within the tested CA concentrations. With the ExClump38 model, we test various physicochemical scenarios for the timescales and trajectories of isotopic equilibration in DCP and discuss their implications for the Δ47 paleothermometry.

Clumped isotope geochemistry of island carbonates in the South China Sea: Implications for early diagenesis and dolomitization

Studying the diagenesis of island carbonates can be hampered by the difficulty of accurately constraining the mineral formation temperature. The carbonate clumped isotope composition (measured as the Δ47 value) is based on the temperature-dependent binding of 13C to 18O, and offers a promising means of calculating the formation temperature. In this study, we report the Δ47 values of island carbonates from a ~1 km-long drill core from the Meiji Reef in the South China Sea, which are integrated with petrography, carbon (δ13C) and oxygen isotope (δ18O) compositions, and trace element contents to constrain the diagenetic environment. We find that most of the digenetic alteration of the initial carbonates likely occurred above a water depth of ~200 m below sea level at temperatures between ~15 and 28 °C, and that the fluids involved during the formation of the diagenetic calcites and dolomites have similar δ18O values to modern seawater. Considering the estimated secular variation in seawater δ18O, the dolomite likely formed from an evaporative fluid source via a brine reflux mechanism and with a high convection rate during the late Miocene. Although isotopic compositions of the reef carbonates were overprinted by early diagenetic alteration, the Δ47 values can reflect the temperature of their depositional environment if the diagenesis occurred at depths similar to the depositional depth. These results can help refine the existing dolomitization model of tropical islands and increase the utility of Δ47 values of diagenetic reef carbonates in shallow burial settings as valuable records of the shallow water and climate conditions.

Gold composition and conditions of Southern Ak-Dag gold-sulfide-quartz ore occurrence formation (Western Tuva)

Research subject. The paper presents data on the mineralogical, geochemical and fluid inclusion features of the Southern Ak-Dag gold-sulphide-quartz ore occurrence in Western Tuva.Methods. Mineral formation temperatures, salt composition and fluid salinity were examined using a Linkam TMS-600 cryostage and an Olympus BX 51 microscope. The chemical composition of samples was identified using a MIRA 3 LMU (Tescan Orsay Holding) scanning electron microscope equipped with INCA Energy 450+XMax 80 and INCA Wave 500 microanalysis systems; BSE photos were taken by Tescan Vega 3 and Hitachi ТМ-1000 SEM instruments.Results. The ores under study were found to contain both high-grade and medium-grade gold with an Ag content of up to 17.05 wt %. The average gold fineness comprised 904 ‰, ranging from 830 to 928 ‰. According to fluid inclusion data, gold-sulphide-quartz veins were formed at temperatures of 280–240 °C and pressures of 0.8–1.2 kbar from aqueous fluids having a salinity of 8.6–6.4 wt % NaCl eq. The narrow range of fluid salinity at decreasing temperatures and the prevalence of high-grade gold in sulphide-quartz veins indicate a relatively high rate of mineral formation in a narrow permeable zone without any significant interaction with host rocks or mixing with meteoric waters.Conclusions. Gold mineralization in the Southern Ak-Dag ore occurrence, which was formed within one ore substage, corresponds to the type of gold-galena-chalcopyrite with barite. The established similarity of native gold in the Southern Ak-Dag occurrence and other deposits in the Aldan-Maadyr ore cluster in terms of P-T parameters of ore formation and mineralogical and geochemical features, as well as association of the ore mineralization with beresites, indicate the possibility of discovering industrial ore deposits in the region and confirm its paragenetic relation with Devonian magmatic activity.

Conditions of the Formation of Unique Mineralization with Yushkinite V1 – xS · n[(Mg,Al)(OH)2] in Quartz–Calcite Veins, Pai-Khoi Ridge: Evidence from Study of Fluid Inclusions

The results of the study of fluid inclusions in quartz from quartz–calcite veins with unique yushkinite mineralization are reported. For the first time, it was proved that their formation occurred under sharply reducing conditions. The mineral formation medium was enriched in calcium and magnesium chlorides and hydrogen sulfide. The temperature of mineral formation was ~120–150°С.

Mineralogical and Geochemical Features and Formation Conditions of the Tardan Gold–Sulfide–Quartz Deposit (Northeastern Tuva)

Abstract —We studied the mineralogical and geochemical features and formation conditions of productive mineral assemblages of the Tardan gold–sulfide–quartz deposit located in the endo-/exocontact zone of the Kopto–Bai-Syut gabbro-diorite–plagiogranite pluton of the Early Ordovician Tannu-Ola complex (O1tn). Postskarn mineralization of vein–dissemination type in skarns, quartz diorites, and carbonate rocks is limited by tectonic crushing zones and conjugated with beresitization and listwanitization of the ore-bearing rocks. Mineralogical and geochemical research has shown the formation of ultrahigh-fineness (986–952‰) and high-fineness (947–918‰) gold at the first productive gold–quartz–calcite substage, of high-fineness gold (918–904‰) → medium-fineness gold (896–809‰) → low-fineness gold (798–756‰) ± hessite Ag2Te ± volynskite AgBiTe2 at the second productive gold–telluride–sulfide–quartz–carbonate substage, and of medium-fineness gold (897–802‰) → low-fineness gold (799–717‰) → electrum (691–612‰) → mercurian electrum (471–451‰) ± hessite Ag2Te ± acanthite Ag2S ± matildite AgBiS2 at the third productive gold–sulfosalt–sulfide–quartz substage. High- and medium-fineness gold prevails in the ores, ultrahigh- and low-fineness gold is subordinate, and electrum and mercurian electrum are scarce. The fineness of native gold in the ores varies from 451 to 986‰, averaging 858‰. The productive mineral assemblages of the Tardan deposit formed from aqueous fluids containing Mg, Na, and K chlorides (salinity of 6.1–12.9 wt.% NaCl eq.), with a decrease in the mineral formation temperature from 380 to 150 ºC and variations in fO2, fS2, fSe2, and fTe2.

The subseafloor thermal gradient at Iheya North Knoll, Okinawa Trough, based on oxygen and hydrogen isotope ratios of clay minerals

We measured the oxygen and hydrogen isotope ratios of smectite, chlorite, and illite in hydrothermally active sediments at the Iheya North Knoll, Okinawa Trough, obtained by seafloor drilling of active hydrothermal fields during the Integrated Ocean Drilling Program (IODP) Expedition 331. Formation temperatures calculated from oxygen isotope data were compared to the downhole temperatures that were measured during the same expedition. The δ18O values ranged from +9.9‰ to +13.3‰ for smectite, +1.3 to +3.0‰ for chlorite or chlorite/smectite mixed-layer mineral, and +2.1‰ to +5.1‰ for illite or illite/smectite mixed-layer mineral with minor chlorite. For samples of illite that contained minor chlorite, δ18O values for illite or illite/smectite mixed-layer mineral of +4.4‰ to +6.1‰ were calculated, based on the proportion of the two clay minerals calculated from chemical composition of the individual mineral and the mixture determined by TEM-EDS and EPMA. We estimated the formation temperatures of the minerals using oxygen isotope fractionation data and assumed values of 0 to +1.2‰ for the fluid that was equilibrated with the minerals, based on the reported values of the seawater and vent fluid measured in previous studies. The temperature range calculated was 111–175 °C for a shallow layer less than about 25 m below seafloor (mbsf) that contained smectite and a minor kaolinite component, 177–297 °C for a deeper layer between about 25 and 40 mbsf that was dominated by chlorite or chlorite/smectite mixed-layer mineral, and 220–314 °C for the deepest layer between about 40 and 120 mbsf that contained illite or illite/smectite mixed-layer mineral with less chlorite. The temperatures of mineral formation calculated from the oxygen stable isotope data were slightly higher at some depths, but both calculated and measured temperatures demonstrated a steep, step-wise thermal gradient below the active hydrothermal field, where temperatures of >200 °C were determined at as little as 50 mbsf. Hydrogen isotope values mostly ranged between −40 and −55‰ and did not vary significantly or systematically between the layers, except in the clay fractions containing smectite above 25 mbsf that had relatively low values between −65 and −72‰. Hydrogen isotope results of the clay minerals were problematic to interpret and not consistent with interpretation of the oxygen data. Calculated temperatures from illite and smectite were mostly negative, whereas temperatures calculated from chlorite were more positive (average 145 °C), but lower than those from the oxygen isotope data. Additional work is still required to determine the hydrogen isotope fractionation between clay minerals and water with respect to temperature.

Formation conditions of host rocks and veins productive deposits of the Astrakhan gas-condensate field

This study examines one- (gas) and two-phase (aqueous solution–gas) inclusions in the calcite of the Cheremshanskian Horizon of the Bashkirian stage at a depth of 4,215–4,217 m in the Pravoberezhnaya-1 well. Homogenizing temperature is within 100–134 °C, which is likely close to the temperature of mineral formation. Calcite vein formation involves calcium bicarbonate fluid enriched in Mg chloride. It was established the calcite inclusions contain carbon dioxide, methane, and hydrogen sulfide. The gas composition of the inclusions in limestone is distiuguished of its high carbon dioxide concentration but rather low methane and hydrogen sulfide concentration.

Coexisting Bournonite–Seligmannite and Tennantite–Tetrahedrite Solid Solutions of the Darasun Gold Deposit, Eastern Transbaikalia, Russia: Estimation of the Mineral Formation Temperature

Mineral associations, intergrowth features, chemical composition and Sb and As distribution in coexisting fahlore and bournonite-seligmanite solid solutions in the Darasun gold deposit were studied. For the first time the almost complete solid solution was found between bournonite and seligmanite with a continuous isomorphism between Sb and As in the range of Sb/(Sb + As) ratios from 0.21 to 1.00 in the Darasun deposit by EMPA. The composition of the fahlore coexisting with bournonite varies widely: Sb/(Sb + As) ratios 0.03-0.96 and Fe/(Fe + Zn) ratios 0.36-0.87. The coupled compositional evolution from early antimony to late arsenic in coexisting solid solutions has been established. Based on the investigation of the Sb and As distribution between coexisting fahlore and bournonite-seligmanite, the temperatures of their joint deposition and, as a result, of the productive stage, in which they are closely associated with native gold and tellurides (90–335 °С), are estimated.

Formation Conditions of Host Rocks and Veins of Productive Deposits of the Astrakhan Gas–Condensate Field

One- (gas) and two-phase (aqueous solution plus gas) inclusions are studied in calcite taken from the Cheremshan horizon of the Bashkirian stage at a depth of 4215–4217 m in the Pravoberezhnaya-1 borehole. It is established that their homogenization temperatures are within 100–134°С, which is possibly close to the mineral formation temperature. Calcite veinlets were formed with the participation of a hydrocarbonate–calcium fluid enriched in magnesium chlorides. Inclusions in calcite mainly contain CO2, CH4, and H2S. The gas composition of the inclusions in limestone differs in an elevated CO2 content and the presence of CO with subordinate CH4 and H2S.

Oxygen isotope fractionation during smithsonite formation from aqueous solutions

Oxygen isotope fractionation between carbonate minerals and water is used as an environmental proxy to estimate mineral formation temperatures or isotopic composition of precipitating fluids. To date no experimental data on the oxygen isotope fractionation factor between smithsonite (ZnCO3) and water, α(18O)smithsonite-water = (18O/16O)smithsonite / (18O/16O)water, exist. Therefore, in the present study experimental work on smithsonite synthesis in the temperature range between 25 and 80 °C is coupled with ab-initio based theoretical calculations.Laboratory precipitation experiments took place in titanium reactors at elevated pCO2 (~10 atm) in order to induce the formation of smithsonite from hydrozincite (Zn5(CO3)2(OH)6), which is the precursor phase initially formed at 25 °C and low pCO2 (pH ~ 6.8). The constant α(18O)smithsonite-water = (1000 + δ18Osmithonite) / (1000 + δ18Owater) value reached at a reaction time ≥ 10,000 min (7 days) suggests near equilibrium conditions. Based on the experimentally obtained temperature relation of α(18O)smithsonite-water at 25, 40, 60, and 80 °C the integrated equation can be linearly described by the function:103lnα18Osmithsonite−water=2.79∗106/T2–0.95±0.06∗106/T2+0.60where the temperature is in Kelvin. The ab initio calculations suggest that this relation can be described in the temperature range from 0 to 100 °C as:103lnαsmithsonite−liquid water=3.21∗106/T2–3.63±0.025∗106/T2+0.90The α(18O)smithsonite-water values from the experimental approach fit within error to the theoretical relationship from the literature and the above ab initio calculations. Difference in slope between the experiment and theoretical obtained equation likely reflects modeling inaccuracies, whereas kinetic effects cannot be completely ruled out in the experimental approach.The obtained α(18O)smithsonite-water values match with the general sequence of Zn2+ < Fe2+ < Mn2+ < Ca2+ for mono-cation trigonal Me-carbonate minerals suggesting incorporation of lighter oxygen isotopes in the carbonate mineral at increasing cation radius as indicated from thermodynamic considerations. Potential applications of oxygen isotope fractionation during smithsonite formation for natural aqueous surroundings are discussed.

Assessment of Factors Controlling Clumped Isotopes and δ18O Values of Hydrothermal Vent Calcites

AbstractThe clumped isotope composition of CaCO3 (Δ47) is a geochemical proxy that can provide mineral formation temperatures and, together with measured carbonate δ18O, inferred fluid δ18O values. Under natural conditions, carbonates form within a relatively wide pH range and varying growth rates which are typically not reflected in laboratory‐based calibrations (mostly ∼pH 8, moderate growth rates). A pH and growth‐rate dependence is known for oxygen isotopes and was also postulated for clumped isotopes. Theoretical predictions suggest that Δ47 values could lie between the carbonate equilibrium value and the value inherited from the dissolved inorganic carbon (predicted offset: +0.04‰ pH &lt; 4 and −0.025‰ at high pH &gt; 12). Here we test whether pH (in addition to temperature) is recorded in the carbonate clumped isotope composition using modern calcites from natural travertine‐forming streams and scales precipitated in pipes of deep geothermal wells from Italy, Hungary, and Turkey (pH: 6.1–7.5, T: 33–100°C). Although a comparison of all samples with expected equilibrium values in this pH range and known formation temperatures reveals only an insignificant Δ47 offset (0.006 ± 0.004‰, 1SE, n = 9), the clumped isotope values of samples with the highest growth rates (0.014 ± 0.007‰, 1SE, n = 5) are consistent with the theoretical prediction attributable to pH of 0.01‰. Similarly, deviations in δ18O of up to −2‰ follow a growth‐rate dependence. This field‐based study shows that pH‐related effects are mostly small for Δ47 in the subsurface environment at lower pH and that high mineral growth rates control the magnitude of this disequilibrium.

Modeling the effects of diagenesis on carbonate clumped-isotope values in deep- and shallow-water settings

The measurement of multiply isotopically substituted (‘clumped isotope’) carbonate groups provides a way to reconstruct past mineral formation temperatures. However, dissolution-reprecipitation (i.e., recrystallization) reactions, which commonly occur during sedimentary burial, can alter a sample’s clumped-isotope composition such that it partially or wholly reflects deeper burial temperatures. Here we derive a quantitative model of diagenesis to explore how diagenesis alters carbonate clumped-isotope values. We apply the model to a new dataset from deep-sea sediments taken from Ocean Drilling Project site 807 in the equatorial Pacific. This dataset is used to ground truth the model. We demonstrate that the use of the model with accompanying carbonate clumped-isotope and carbonate δ18O values provides new constraints on both the diagenetic history of deep-sea settings as well as past equatorial sea-surface temperatures. Specifically, the combination of the diagenetic model and data support previous work that indicates equatorial sea-surface temperatures were warmer in the Paleogene as compared to today. We then explore whether the model is applicable to shallow-water settings commonly preserved in the rock record. Using a previously published dataset from the Bahamas, we demonstrate that the model captures the main trends of the data as a function of burial depth and thus appears applicable to a range of depositional settings.

Evolution of Neoproterozoic Wonoka–Shuram Anomaly-aged carbonates: Evidence from clumped isotope paleothermometry

The Wonoka–Shuram Anomaly represents the largest negative carbon isotope excursion recognized in the geologic record and is associated with the emergence and diversification of metazoan life ca. 580 million years ago (Ma). The origin of the anomaly is highly debated, with interpretations ranging from primary to diagenetic, each having unique and potentially transformative implications for early life. Here, we apply carbonate clumped isotope thermometry to three sections expressing the anomaly in order to constrain mineral formation temperatures and thus directly calculate water oxygen isotope compositions (δ18Ow) with which carbonate minerals equilibrated. With δ18Ow known, it is possible to address previous hypotheses for the origin of the anomaly. In each section, precipitation temperatures correlate positively with reconstructed δ18Ow. Previous hypotheses, based on the covariance of δ18Ocarb vs. δ13Ccarb (uncorrected for temperature effects), suggested a meteoric diagenetic origin for the anomaly. However, reconstructed δ18Ow values do not covary with carbon isotope compositions (δ13Ccarb) within anomaly facies. Rather, the oxygen isotope and temperature data are consistent with carbonate recrystallization and equilibration under increasingly rock-buffered conditions. Based on simple modeling and comparison to modern formation fluids, recrystallization may have occurred in an environment far removed from the initial depositional or early diagenetic regime. In addition, although clumped isotope temperatures vary significantly and reach elevated values consistent with burial diagenesis, it is unclear to what degree, if at all, carbon isotope values were reset during recrystallization. Ultimately, these new data indicate that Wonoka–Shuram-aged carbonates experienced equilibration with fluids under increasingly closed-system conditions. The clumped isotope data do not provide a means to distinguish previous hypotheses outright, but provide additional context for the evaluation of geochemical signatures within these ancient carbonate rocks.

Laboratory calibration of the calcium carbonate clumped isotope thermometer in the 25–250 °C temperature range

Many fields of Earth sciences benefit from the knowledge of mineral formation temperatures. For example, carbonates are extensively used for reconstruction of the Earth’s past climatic variations by determining ocean, lake, and soil paleotemperatures. Furthermore, diagenetic minerals and their formation or alteration temperature may provide information about the burial history of important geological units and can have practical applications, for instance, for reconstructing the geochemical and thermal histories of hydrocarbon reservoirs.Carbonate clumped isotope thermometry is a relatively new technique that can provide the formation temperature of carbonate minerals without requiring a priori knowledge of the isotopic composition of the initial solution. It is based on the temperature-dependent abundance of the rare 13C–18O bonds in carbonate minerals, specified as a Δ47 value. The clumped isotope thermometer has been calibrated experimentally from 1°C to 70°C. However, higher temperatures that are relevant to geological processes have so far not been directly calibrated in the laboratory.In order to close this calibration gap and to provide a robust basis for the application of clumped isotopes to high-temperature geological processes we precipitated CaCO3 (mainly calcite) in the laboratory between 23 and 250°C. We used two different precipitation techniques: first, minerals were precipitated from a CaCO3 supersaturated solution at atmospheric pressure (23–91°C), and, second, from a solution resulting from the mixing of CaCl2 and NaHCO3 in a pressurized reaction vessel at a pressure of up to 80bar (25–250°C).The calibration lines of both experimental approaches overlap and agree in the slopes with theoretical estimates and with other calibration experiments in which carbonates were reacted with phosphoric acid at temperatures above 70°C. Our study suggests a universal Δ47-T calibration (T in K, Δ47 in ‰):Δ47=0.98(±0.01)·(-3.407·109/T4+2.365·107/T3-2.607·103/T2-5.880/T)+0.293(±0.004)This new Δ47-T calibration (given in the absolute reference frame), that extends the experimentally calibrated temperature range for clumped isotopes to 250°C, can be applied to carbonates that grew at intermediate temperatures (20–250°C).