Residual Fluids Research Articles

Pyrite Rb-Sr, Sm-Nd and Fe isotopic constraints on the age and genesis of the Qingchengzi Pb-Zn deposits, northeastern China

Sr-Nd-Fe isotopes are reported for pyrites and whole rocks of ores and associated rocks for the Qingchengzi Pb-Zn deposits in the northeasern China, to investigate the age, sources and processes of the Pb-Zn mineralization. Rb-Sr leaching isotopic dating of pyrites that crystallized coeval with galena and sphalerite from five subsamples of ores yields isochron ages of 143 ± 12 Ma to 159 ± 12 Ma with a weighted mean age of 151.8 ± 5.2 Ma. This age can be interpreted to be the timing of Pb-Zn mineralization, coeval with the emplacement of Late Jurassic granites in the region. The pyrites have negative εNd (152 Ma) values of −17.6 to –22.0, among the Neoarchean TTG rocks, Paleoproterozoic meta-sedimetary rocks (i.e., wall rocks) and granites, and Mesozoic mafic dykes and granites. However, the initial 87Sr/86Sr ratio of 0.7188 ± 0.0004 is similar to those of Late Jurassic granites and Paleoproterozoic rocks (0.7082–0.7183), distinct from those of mafic dykes (0.7069–0.7110), indicating the ore-forming materials (i.e., Pb and Zn) were mainly derived from wall rocks and Late Jurassic granites. Combined with the previously-published H-O isotopes, the new age and Sr-Nd isotopic data indicate that the mineralizaing fluids were mainly derived from dehydration of granitic magmas, interacted with meteoric water that extracted Pb and Zn from the wall rocks. The δ56Fe values of pyrites in the Pb-Zn ores and Paleoproterozoic meta-sedimentary rocks range from +0.23‰ to +1.09‰ and −0.49‰ to +0.17‰, respectively, distinct from those of Paleoproterozoic basement rocks and Mesozoic rocks (−0.03‰ to +0.28‰). Combined with Nd isotopes, the large range of δ56Fe values for pyrites would be the result of rapid precipitation of pyrites in the wall rocks and contemperal deposition of pyrites in the residual fluids during interaction between wall rocks and ore-forming fluids. Collectively, our new Sr-Nd-Fe isotopes of pyrites not only constrain the age and sources of Pb and Zn mineralization, but also reveal the detailed mineralization processes, providing a new method to constrain the genesis of hydrothermal Pb-Zn deposits.

Magnesium isotope fractionation during hydrothermal seawater-basalt interaction

Fluid-rock interactions in hydrothermal systems at or near mid-oceanic ridges (MOR) play a major role in determining the composition of the oceanic crust and seawater. To quantify the processes that govern cation exchange in these environments we have experimentally studied the isotopic evolution of δ26/24Mg in the fluid phase during seawater-basalt interaction at 250 and 290 °C. Mass balance constraints indicate that isotopically heavy Mg was preferentially incorporated into non-exchangeable (octahedral) sites in secondary clay minerals such as saponite (Mg-rich smectite), leaving residual fluids enriched in light Mg isotopes. The magnitude of fractionation observed during smectite precipitation in our experiments (εSmectite-Liquid26/24) ranged from 0.35‰ to 0.42‰. This observation, which contrasts with the preferential uptake of light Mg isotopes into biogenic and inorganic marine carbonates, highlights the potential utility of Mg isotopes as tracers of the precipitation dynamics of authigenic Mg-silicate and Mg-carbonate phases. Furthermore, although Mg isotopic fractionation is often masked by the almost complete removal of Mg in high temperature marine hydrothermal systems, our experiments demonstrate that it does become significant at lower temperatures where Mg removal by clay formation is incomplete. Under such conditions, this fractionation will create isotopically light fluids due to smectite precipitation, thus potentially represents an important component of the marine Mg isotope inventory.

Modeling of ex-situ dissolution for geologic sequestration of carbon dioxide in aquifers

Underground carbon dioxide (CO2) sequestration is considered to be one of the main methods to mitigate greenhouse gas (GHG) emissions. In this technology, pure CO2 is injected into an underground geological formation and since it is less dense than residual fluids, there is always a risk of leakage to the surface. To increase security of underground CO2 disposal, ex-situ dissolution can be implemented. When CO2 is dissolved in brine before injection, it significantly reduces the risks of leakage. In this approach, pure CO2 is dissolved on the surface before injection. Surface dissolution could be achieved in a pipeline operating under the pressure of a target aquifer into which the CO2 is injected. In a pipeline, CO2 droplets are dissolved being dispersed in a brine turbulent flow. In this paper, a comprehensive model of droplet dissolution along a pipeline is presented. The model accounts for droplet breakup and coalescence processes and is validated against available experimental data.

Fracturing fluid retention in shale gas reservoirs:mechanisms and functions

Shale gas reservoirs are characterized by nano-Darcy permeability, rich organic matter, ultralow water saturation, developed bedding, and micro-fractures, leading to multi-scale transportation of shale gas. Multistage fracturing of horizontal wells is the main development technology to stimulate shale gas reservoirs, and tens of thousands of cubic meters of fluids are injected into the reservoir. Retention and flowback of fracturing fluids on gas transfer plays an important role on the effect of hydraulic fracturing. Through the analysis of geological and engineering factors controlling water imbibition and diffusion in shale gas reservoirs, the mechanisms of low recovery of fracturing fluids and the reasons that some shale gas wells with low recovery of fracturing fluids have high gas production rate were revealed. This paper carried out a series of experiments of the fluid imbibition and fracture initiation in the shale selected from the Longmaxi Formation in Sichuan basin. In detail, this paper investigated imbibition and dispersion the fluid in shale and analyzed the mechanisms of the shale-water interactions causing the reduction of shale strength and fracture initiation and propagation. Based on the field case studies of well shut-in after fracturing, its influence on the well production was assessed. Formation damage caused by fracturing fluid is multi-scale, and the evaluation of formation damage caused by fracturing fluids should take the influence on the gas transmission capacity into consideration, and residual fracturing fluids may have a positive effect on gas transfer. It should take the long-term stable production of shale gas well and the effect of fracturing fluids transmission on gas multi-scale transport into consideration when determining the timing and pressure difference of fracturing fluids flowback from shale gas reservoirs.

Petrogenesis, Ore Mineralogy, and Fluid Inclusion Studies of the Tagu Sn–W Deposit, Myeik, Southern Myanmar

Most of the granite-related Sn–W deposits in Myanmar are located in the Western Granitoid Province (WGP) of Southeast Asia. The Tagu deposit in the southern part of the WGP is a granite related Sn–W deposit. The biotite granite is composed of quartz, feldspars (plagioclase, orthoclase, and microcline), and micas (muscovite and biotite) and belongs to S-type peraluminous granite. Abundances of large-ion lithophile elements (LILEs), such as Rb, K, and Pb, coupled with the deficiency of high-field-strength elements (HFSEs), such as Nb, P, and Ti, indicate that the parental magma for the Tagu granite was derived from the lower continental crust at syn-collisional setting. Mineralized veins consist of early-formed oxide ore minerals, such as cassiterite and wolframite, which were followed by the formation of sulfide minerals. Three main types of fluid inclusions were distinguished from the mineralized quartz veins hosted by granite and metasedimentary rocks: Type-A—two phases, liquid (L) + vapor (V) aqueous inclusions; Type-B—two phases, vapor (V) + liquid (L) vapor-rich inclusions; And type-C—three phases, liquid + CO2-liquid + CO2-vapor inclusions. Quartz in the veins hosted in granite corresponding with earlier deposition contains type-A, type-B, and type-C fluid inclusions, whereas that in the veins hosted in metasedimentary rocks corresponding with later deposition contains only type-A fluid inclusions. The homogenization temperatures of type-A inclusions range from 140 °C to 330 °C (mode at 230 °C), with corresponding salinities from 1.1 wt.% to 8.9 wt.% NaCl equivalent for quartz veins hosted in metasedimentary rocks, and from 230 °C to 370 °C (mode at 280 °C), with corresponding salinities from 2.9 wt.% to 10.6 wt.% NaCl equivalents for quartz veins hosted in granite. The homogenization temperatures of type-B vapor-rich inclusions in quartz veins in granite range from 310 °C to 390 °C (mode at 350 °C), with corresponding salinities from 6.7 wt.% to 12.2 wt.% NaCl equivalent. The homogenization temperatures of type-C H2O–CO2–NaCl inclusions vary from 270 °C to 405 °C (mode at 330 °C), with corresponding salinities from 1.8 wt.% to 5.6 wt.% NaCl equivalent. The original ascending ore fluid was probably CO2-bearing fluid which evolved into two phase fluid by immiscibility due to pressure drop in the mineralization channels. Furthermore, the temperature and salinities of two-phase aqueous fluids were later most likely decreased by the mixing with meteoric water. The salinities of the type-B vapor-rich inclusions are higher than those of the type-C CO2-rich inclusions, which may have resulted from CO2 separation from the fluids. The escape of gases can lead to an increase in the salinity of the residual fluids. Therefore, the main ore-forming mechanisms of the Tagu Sn–W deposit are characterized by fluid immiscibility during an early stage, and fluid mixing with meteoric water in the late stage at a lower temperature.

The tsavorite (gem quality green vanadium grossular) minerogenetic system in East Africa: a case of metamorphic partial melting and lateral secretion

When supercontinent Rodinia began to break up at ~ 800 Ma, wide rifts formed evolving into a passive margin of the Mozambique Ocean. At one stage, organic-rich pelites with gypsum/anhydrite (the later host rock of tsavorites) were interbedded with siliciclastics, carbonates, and bimodal volcanic rocks. Later, ocean closure, subduction, collision, and welding of various microcontinents and volcanic arcs formed the Mozambique Belt and at ~ 550 Ma, ended with the assembly of supercontinent Gondwana. In East Africa, deformation and metamorphism climaxed at 615–600 Ma. At peak metamorphic conditions, anatexis of siliciclastic metasediments produced abundant metamorphic mobilizates such as pegmatites and quartz veins. In the graphite schist hosting tsavorites, however, partial melting only produced small fractions of a supercritical hydrous liquid, the peculiar corrosive nature of which was due to the reduction of Ca-sulfate by reaction with organic C. Most of this melt/fluid phase remained within the host but migrated over short distances into structural traps of different origin; turbid green grossular crystallized from the melt and transparent tsavorite from residual fluids.

Iron and magnesium isotopic compositions of subduction-zone fluids and implications for arc volcanism

High-pressure (HP) metamorphic veins in eclogites provide insights into the composition and evolution of fluids in subduction zones. We here present the first Fe-Mg isotope data for three types of HP veins, eclogites and their mineral separates from the Dabie Orogen to constrain the Fe-Mg isotopic compositions of subduction-zone fluids and the Fe-Mg isotope behaviors during fluid-rock interaction and fluid evolution. The HP veins include omphacite-epidote (Omp-Ep), epidote-quartz (Ep-Qtz), and kyanite-epidote-quartz (Ky-Ep-Qtz) veins. The Omp-Ep veins first crystallized from eclogite-derived, solute-rich vein-forming fluids with the Ep-Qtz and Ky-Ep-Qtz veins successively crystallizing from the residual fluids after the formation of the Omp-Ep veins. The early Omp-Ep veins have much heavier Fe-Mg isotopic compositions compared to the host eclogites, indicating Fe-Mg isotope fractionation during fluid-rock interaction due to preferential dissolution of isotopically heavy Omp and Ep from the eclogites into the vein-forming fluids. The δ56Fe and δ26Mg values of the Omp-Ep, Ep-Qtz, and Ky-Ep-Qtz veins gradually decrease and positively correlate with the Eu/Eu* values of whole rock and epidote. This indicates that Fe-Mg isotope fractionation during fluid evolution results from continuous crystallization of isotopically heavy Omp and Ep from the vein-forming fluids. Our results thus demonstrate that Fe-Mg isotopes can significantly fractionate during the dissolution-precipitation processes of minerals in subduction zones.The high δ56Fe (0.04–0.21‰) and δ26Mg (−0.08 to 0.15‰) values of fluid-related HP veins within mafic eclogites indicate that fluids derived from subducted altered oceanic crust (AOC) probably have Fe-Mg isotopic compositions similar to or higher than those of mid-ocean ridge basalts (MORBs). Thus, contribution from AOC-derived fluids is unlikely to explain the light Fe and heavy Mg isotopic compositions of arc lavas. We propose that the light Fe and heavy Mg isotopic compositions of arc lavas may result from a combination of prior melt depletion and addition of serpentinite-derived 54Fe-26Mg-rich fluids into the overlying mantle wedge.

Footprints of element mobility during metasomatism linked to a late Miocene peraluminous granite intruding a carbonate host (Campiglia Marittima, Tuscany)

The Campiglia Marittima magmatic-hydrothermal system includes a peraluminous granite, its carbonatic host, and skarn. The system evolved generating a time-transgressive exchange of major and trace elements between granite, metasomatic fluids, and host rock. The process resulted in partial metasomatic replacement of the granite and severe replacement of the carbonate host rocks. The fluid activity started during a late-magmatic stage, followed by a potassic–calcic metasomatism, ending with a lower temperature acidic metasomatism. During the late-magmatic stage, B-rich residual fluids led to the formation of disseminated tourmaline–quartz orbicules. High-temperature metasomatic fluids generated a pervasive potassic–calcic metasomatism of the granite, with replacement of plagioclase, biotite, ilmenite, and apatite by K-feldspar, phlogopite–chlorite–titanite, titanite–rutile, and significant mobilization of Fe, Na, P, Ti, and minor HFSE/REE. The metasomatized granite is enriched in Mg, K, Rb, Ba, and Sr, and depleted in Fe and Na. Ca metasomatism is characterized by crystallization of a variety of calc-silicates, focusing along joints into the granite (endoskarn) and at the marble/pluton contact (exoskarn), and exchange of HFSE and LREE with hydrothermal fluids. Upon cooling, fluids became more acidic and fluorine activity increased, with widespread crystallization of fluorite from disequilibrium of former calc-silicates. At the pluton-host boundary, fluids were accumulated, and pH buffered to low values as temperature decreased, leading to the formation of a metasomatic front triggering the increasing mobilization of REE and HFSE and the late crystallization of REE–HFSE minerals.

Kimberlite and carbonatite dykes within the Premier diatreme root (Cullinan Diamond Mine, South Africa): New insights to mineralogical-genetic classifications and magma CO2 degassing

The ca. 1153 Ma Premier kimberlite pipe on the Kaapvaal craton has been intruded by late-stage kimberlite and carbonatite magmas forming discrete 0.5 to 5 m wide dykes within the lower diatreme. On the basis of petrography and geochemistry, the fresh kimberlite dykes represent archetypal monticellite phlogopite kimberlite of Group-1 affinity. Their mineral compositions, however, show marked deviations from trends that are typically considered as diagnostic for Group-1 kimberlite in mineralogical-genetic classification schemes for volatile-rich ultramafic rocks. Groundmass spinel compositions are transitional between magnesian ulvöspinel (a Group-1 kimberlite hallmark feature) and titanomagnetite trends, the latter being more diagnostic for lamproite, orangeite (formerly Group-2 kimberlite), and aillikite. The Premier kimberlite dykes contain groundmass phlogopite that evolves by Al- and Ba-depletion to tetraferriphlogopite, a compositional trend that is more typical for orangeite and aillikite. Although high-pressure cognate and groundmass ilmenites from the Premier hypabyssal kimberlites are characteristically Mg-rich (up to 15 wt% MgO), they contain up to 5 wt% MnO, which is more typical for carbonate-rich magmatic systems such as aillikite and carbonatite. Manganese-rich groundmass ilmenite also occurs in the Premier carbonatite dykes, which are largely devoid of mantle-derived crystal cargo, suggesting a link to the kimberlite dykes by fractionation processes involving development of residual carbonate-rich melts and fluids. Although mineralogical-genetic classification schemes for kimberlites and related rocks may provide an elegant approach to circumvent common issues such as mantle debris entrainment, many of the key mineral compositional trends are not as robust for magma type identification as previously thought.Utilizing an experimentally constrained CO2-degassing model, it is suggested that the Premier kimberlite dykes have lost between 10 and 20 wt% CO2 during magma ascent through the cratonic lithosphere, prior to emplacement near the Earth's surface. Comparatively low fO2 values down to −5.6 ∆NNO are obtained for the kimberlite dykes when applying monticellite and perovskite oxybarometry, which probably reflects significant CO2 degassing during magma ascent rather than the original magma redox conditions and those of the deep upper mantle source. Thus, groundmass mineral oxybarometry may have little value for the prediction of the diamond preservation potential of ascending kimberlite magmas.After correction for olivine fractionation and CO2-loss, there remains a wide gap between the primitive kimberlite and carbonatite melt compositions at Premier, which suggests that these magma types cannot be linked by variably low degrees of partial melting of the same carbonated peridotite source in the deep upper mantle. Instead, fractionation processes produced carbonate-rich residual melts/fluids from ascending kimberlite magma, which led to the carbonatite dykes within Premier pipe.

Sulfide and silicate anatexis in the Balmat zinc deposit (New York, USA) and its implications for ore remobilization

The Cross-Cutting zone of the Fowler ore body is one of the many ore bodies of the Balmat, NY massive sulfide zinc deposit that underwent remobilization during upper amphibolite metamorphism and associated deformation. The kilometer-scale remobilization is difficult to reconcile with purely solid-state processes. Given that other polymetallic ores of similar metamorphic grade have been shown to have undergone varying degrees of anatexis, SEM-EDS micro-petrographic analysis of ores was undertaken to determine if melts were present in Balmat ores during metamorphism and deformation. Low melting temperature micro-inclusions of sulfosalt and sulfide assemblages occur predominantly in Qtz-Py and Kfs-Py domains that cross-cut peak metamorphic assemblages. These results indicate that localized anatexis occurred on the prograde path, producing low volumes of melts of varying composition. Polymetallic sulfide melts were initiated by the prograde breakdown of minor phases containing low melting temperature chalcophile elements including As, Sb, Pb, and Cu. Alkaline silicate ± carbonate ± sulfide melts were fluxed by halogens, sulfur and other volatile components, released during metamorphism of evaporitic and organic-rich horizons in the marble-dominated host sequence. These low-volume melts and residual fluids would have wetted grain boundaries, affecting the rheology of the bulk ore, and facilitating remobilization of the ores through a combination of solid- and liquid-state processes.

A refined model for lithosphere evolution beneath the decratonized northeastern North China Craton

The eastern North China Craton (NCC), where an initially diamondiferous deep cratonic mantle root was lost during Paleozoic and Mesozoic time, represents a prime natural laboratory to study the processes and mechanisms of continental lithospheric mantle destruction and replacement, which remain, however, controversial. In this study, detailed petrography, whole-rock and mineral compositions of spinel-facies peridotite xenoliths from Cenozoic basalts in the Huinan area, northeastern NCC, are presented to provide new constraints on the transformation of the subcontinental lithospheric mantle (SCLM). These xenoliths define two groups based on textural observation and mineral modes: Group 1 peridotites show protogranular textures and consist of harzburgites and dunites. They have low Al2O3 contents in whole-rock and orthopyroxene (0.53–1.06 wt.% and 2.10–3.21 wt.%, respectively), high olivine modes (79–96%), whole-rock MgO (44.8–47.9 wt.%) and Mg# (100 Mg/(Mg + FeT) molar: 90.1–90.7), suggesting that they were derived from moderately refractory SCLM. In contrast, Group 2 xenoliths display porphyroclastic to protogranular textures and consist of lherzolites and harzburgites with rare spinel-pyroxene intergrowths. They have overall higher Al2O3 (1.48–3.23 wt.% and 3.02–4.65 wt.%, respectively) in whole-rock and orthopyroxene, lower olivine modes (64–83%), MgO (38.6–44.5 wt.%) and whole-rock Mg# values 87.6–90.1, and they may represent fertile SCLM. Peridotites of both groups have similar equilibration temperatures (i.e., 923–977 °C and 881–1110 °C, respectively), which are not correlated with Mg# in olivines, suggesting that they coexist over a range of depths. However, clinopyroxenes in the Group 1 xenoliths display LREE-enriched and convex-upward REE patterns, whereas those in Group 2 mainly show LREE-depleted and spoon-shaped REE patterns, with minor LREE-enriched and convex-upward ones. In addition, spinel-pyroxene intergrowths indicative of garnet destabilization are ubiquitous in Group 1, consistent with variable Al2O3 over a narrow range of Mg# in some opx and low HREE in some cpx, but rare in Group 2 peridotites. Interaction of the fertile mantle with melts similar to the Cenozoic basalts at high melt–rock ratios eradicated most signatures of their origin in the garnet stability field, whereas the refractory peridotites, which reacted with residual melts or fluids at low melt/fluid-rock ratios, retained evidence for the former presence of garnet. We suggest that, combined, these observations are best reconciled if portions of ancient refractory lithosphere, which were partly delaminated during multiple subduction episodes affecting the eastern NCC, were re-accreted together with fertile mantle during asthenospheric upwelling driven by extension.

Study impact of sample treatment and insitu fluids on shale wettability measurement using NMR

Nuclear Magnetic Resonance (NMR) is a good alternative to conventional Amott-Harvey imbibition test or US Bureau of Mines (USBM) test, to measure wettability in shales. The conventional methods do not work primarily because of the long time it takes to flow through the nano pores in the shales. Contact angle measurements typically used in shales do not account for pore connectivity. Hence, NMR is becoming a standard reliable method to measure wettability in shales.This study focuses on two aspects of wettability measurement in shales. First, Looyestijn and Hofman (2006) proposed an equation to calculate wettability using NMR data based on their experiments on carbonate rocks. Sulucarnain et al. (2012) applied this method to shales. In their method, the residual fluids in the plugs are neglected because it is difficult to ascertain what proportion of residual fluids is hydrocarbon and what proportion is water. However, in liquid-rich shales like Eagle Ford, there could be significant amount of residual fluids which must be accounted in the wettability calculation. This study integrates Source Rock Analysis (SRA), NMR and helium porosity data to determine the nature of the residual fluids and account for them while doing wettability calculations. Thus, an improved equation for wettability is proposed by modifying the original equation.Second, in this study, wettability measurements on preserved, dried and cleaned sample states were carried out. The comparison of the three states suggest that drying and cleaning the samples, changes the original wettability of the system and make the rocks appear more oil wet. The effects of drying are more pronounced than cleaning. The above argument is supported both by SRA data and Scanning Electron Microscope (SEM) images. The SRA data shows an increase in S1 and a corresponding decrease in S2 peak which suggests that heating the sample at 100 °C may crack the heavy hydrocarbons in the sample. The SEM image analysis also show the possible movement and resolidification of bitumen and other heavy hydrocarbons. These mobile fractions are believed to flow into the water-wet pores and turn them oil-wet.

Monitoring gas hydrate formation with magnetic resonance imaging in a metallic core holder

Methane hydrate deposits world-wide are promising sources of natural gas. Magnetic Resonance Imaging (MRI) has proven useful in previous studies of hydrate formation. In the present work, methane hydrate formation in a water saturated sand pack was investigated employing an MRI-compatible metallic core holder at low magnetic field with a suite of advanced MRI methods developed at the UNB MRI Centre. The new MRI methods are intended to permit observation and quantification of residual fluids in the pore space as hydrate forms. Hydrate formation occurred in the water-saturated sand at 1500 psi and 4 °C. The core holder has a maximum working pressure of 4000 psi between -28 and 80 °C. The heat-exchange jacket enclosing the core holder enabled very precise control of the sample temperature. A pure phase encode MRI technique, SPRITE, and a bulk T1-T2 MR method provided high quality measurements of pore fluid saturation. Rapid 1D SPRITE MRI measurements time resolved the disappearance of pore water and hence the growth of hydrate in the sand pack. 3D π-EPI images confirmed that the residual water was inhomogeneously distributed along the sand pack. Bulk T1-T2 measurements discriminated residual water from the pore gas during the hydrate formation. A recently published local T1-T2 method helped discriminate bulk gas from the residual fluids in the sample. Hydrate formation commenced within two hours of gas supply. Hydrate formed throughout the sand pack, but maximum hydrate was observed at the interface between the gas pressure head and the sand pack. This irregular pattern of hydrate formation became more uniform over 24 hours. The rate of hydrate formation was greatest in the first two hours of reaction. An SE-SPI T2 map showed the T2 distribution changed considerably in space and time as hydrate formation continued. Changes in the T2 distribution are interpreted as pore level changes in residual water content and environment.

Two-tiered magmatic-hydrothermal and skarn origin of magnetite from Gol-Gohar iron ore deposit of SE Iran: In-situ LA–ICP-MS analyses

Genesis of magnetite from Gol-Gohar iron deposit (GGID) of southeastern Iran is studied with reference to elemental composition. More than 1.2 billion tonnes of magnetite ore at 58% total Fe is hosted by greenschist- to amphibolite-facies metapelites and magnesian marbles. The GGID occurs in the mainly-metamorphic terrain of Sanandaj-Sirjan geological province, with continental-margin tectonic setting. The magnetite-bearing ore is divided into two distinct types of massive and banded; the latter hosted mainly by magnesian marbles. Both subtypes of the ore bodies are associated with mineral assemblages consisting of calcite, dolomite, forsterite, tremolite-actinolite, talc, serpentine, and chlorite. The ore minerals in both subtypes are magnetite, hematite with minor amounts of pyrite, pyrrhotite, and chalcopyrite. Concentrations of temperature-dependent elements, Ti, Al, and Ga in the two subtypes would suggest that temperature of formation was higher for the massive magnetite (with Ti = 626 ppm, Al = 69 ppm and Ga = 56 ppm, on average) and relatively lower for the banded magnetite (with Ti = 60 ppm, Al = 62 ppm and Ga = 4 ppm, on average). The multi-element diagrams, for massive magnetite, show patterns closer to those of magmatic-hydrothermel iron deposits (Kiruna-type), whereas, patterns of the banded magnetite match better with those of skarn deposits, particularly the magnesian skarns. Average concentrations of V (>1000 ppm) and Cr (∼4 ppm) of the massive subtype fall within the range of those of Kiruna-type deposits, and the in average lower concentrations of V (∼10 ppm) and Cr (∼1 ppm) of the banded magnetite match the values of skarn deposits. The average V content of the massive magnetite (1342 ppm) is consistent with the global range of magmatic-hydrothermal magnetite (up to 3880 ppm), but different from global values of purely-magmatic magnetites (up to 6600 ppm). The banded magnetites contain 0.21–25 ppm V, which is only consistent with the lowest values of hydrothermal magnetites. We contend that the massive magnetite was formed by magmatic-hydrothermal processes (i.e., Kiruna type) and the banded magnetites were generated via metasomatic reactions between iron-rich residual magmatic fluids and the magnesian carbonate host rocks (i.e., skarn type).

The competition between rates of deformation and solidification in syn-kinematic granitic intrusions: Resolving the pegmatite paradox

While fully-crystallized granites, rich in feldspar, generally serve to strengthen the continental crust, their precursor melts are assumed to be important agents of crustal weakening. Many syn-tectonic granitic pegmatites are deformed within shear zones but ubiquitously preserve undeformed primary magmatic textures, implying that they were largely molten during shearing. Yet the shapes of pegmatite bodies indicate that they deformed with a greater competence than their surroundings. This co-located pair of material behaviours is paradoxical. We interpret field relationships in a typical pegmatite/shear zone association (Torrisdale, NW Scotland) and propose a mechanism by which syn-tectonic granitic melts may, in effect, act as competent bodies while not yet fully crystallized. Competence was rapidly increased by preferential crystallization on intrusion margins that served to encapsulate residual melt inside stiff rinds. Further crystallization may have been pulsed as the concentrations of crystallization-inhibitors (fluxes) increased in residual fluids. Postulating the existence of initial stiff rinds also consistent with modern estimates for rates of feldspar crystallization (cms/yr) from undercooled hydrous silicic magma to form pegmatites. These greatly outpace strain-rate estimates for shear zones. Thus, fully liquid granitic melts may only be present fleetingly and have little opportunity to weaken deforming crust before crystallization begins.

Pore Diameter of Mesoporous Silica Modulates Oxidation of H2O2-Sensing Chromophore in a Porous Matrix.

Hydrogen peroxide (H2O2) is an attractive chemical because of its bleaching properties in paper and pulp industry and as a disinfectant in the food, water, and medical industries. However, it is important to monitor the residual H2O2 level after its usage and prevent any unintended health problems or chemical reactions. Most H2O2 sensors often utilize fluorophores or electrical circuitry that requires an additional irradiation or a digital display. To this end, this study presents a 3,3',5,5'-tetramethylbenzidine (TMB)/horseradish peroxidase (HRP)-loaded patch that alerts the presence of high H2O2 levels by generating a visible blue color. We hypothesized that water-insoluble TMB immobilized within mesoporous silica particles of proper pore diameter and structure would act as a colorimetric indicator through the H2O2-mediated oxidation within a cross-linked patch. We examined this hypothesis by immobilizing TMB molecules in mesoporous silica particles with 2 and 7 nm diameter cylindrical pores as well as on nonporous silica particles. Then, we loaded these TMB-silica particles and HRP in a porous alginate patch via sequential in situ cross-linking reaction and lyophilization. In the presence of 25-5000 μM H2O2, which simulate H2O2 concentrations found in residual disinfecting fluids, the patch loaded with TMB-mesoporous silica particles with 7 nm diameter pores generated a distinct blue color with varying intensities depending on the H2O2 concentration. The design principles demonstrated in this study should be applicable to a broad array of sensors to be integrated into a moldable, three-dimensional matrix.

Halogenation Chemistry of Hydraulic Fracturing Additives under Highly Saline Simulated Subsurface Conditions.

Unconventional natural gas extraction via hydraulic fracturing coupled with horizontal drilling (HDHF) has generated disruptive growth in the domestic energy sector. Field analyses of residual HDHF fluids have detected halogenated species, potentially the product of unexplored reactions between authigenic halides and HDHF additives. Utilizing a custom high-pressure reactor system, we simultaneously screened 12 frequently disclosed, functionally diverse HDHF additives to uncover transformation chemistry. One emergent pathway, the halogenation of cinnamaldehyde in the presence of ammonium persulfate, demonstrated the potential for oxidative breakers to react with halides to yield reactive halogen species. Halogenated product formation, product distribution, and kinetics were evaluated with respect to shale well subsurface condition, linking transformation risk to measurable well-dependent characteristics (e.g., halide compositions, well temperatures, and pH). In a representative flowback brine, the brominated product dominated on a molar percent basis (6 ± 2%, as normalized by initial cinnamaldehyde loading) over chlorinated (1.4 ± 0.4%) and iodinated forms (2.5 ± 0.9%), reflecting relative halide abundance and propensity for oxidation. This work demonstrates that relevant subsurface reactions between natural brines and hydraulic fracturing additives can result in the unintended formation of halogenated products.

Ti-Nb Mineralization of Late Carbonatites and Role of Fluids in Its Formation: Petyayan-Vara Rare-Earth Carbonatites (Vuoriyarvi Massif, Russia)

This article is devoted to the geology of titanium-rich varieties of the Petyayan-Vara rare-earth dolomitic carbonatites in Vuoriyarvi, Northwest Russia. Analogues of these varieties are present in many carbonatite complexes. The aim of this study was to investigate the behavior of high field strength elements during the late stages of carbonatite formation. We conducted a multilateral study of titanium- and niobium-bearing minerals, including a petrographic study, Raman spectroscopy, microprobe determination of chemical composition, and electron backscatter diffraction. Three TiO2-polymorphs (anatase, brookite and rutile) and three pyrochlore group members (hydroxycalcio-, fluorcalcio-, and kenoplumbopyrochlore) were found to coexist in the studied rocks. The formation of these minerals occurred in several stages. First, Nb-poor Ti-oxides were formed in the fluid-permeable zones. The overprinting of this assemblage by residual fluids led to the generation of Nb-rich brookite (the main niobium concentrator in the Petyayan-Vara) and minerals of the pyrochlore group. This process also caused niobium enrichment with of early generations of Ti oxides. Our results indicate abrupt changes in the physicochemical parameters at the late hydro (carbo) thermal stage of the carbonatite formation and high migration capacity of Ti and Nb under these conditions. The metasomatism was accompanied by the separation of these elements.

Geochemistry of ore-forming fluids, Deh-Salm uneconomic porphyry Mo system, SW Nehbandan, Iran: a fluid inclusion investigation

ABSTRACTBased on the fluid inclusion and rock sample geochemistry in Deh-Salm hydrothermal system, it is shown that uneconomic molybdenite mineralization occurred in both stockwork- and limited skarn-type alterations. Homogenization temperatures and salinities based on microthermometry data are presented for fluid inclusions from hydrothermal quartz associated with pyrite, galena, sphalerite and rare molybdenite mineralization. The data indicate that ore mineral precipitation occurred within a temperature range of 250° to > 490°C from moderate to high-salinity (9 to > 42 wt% NaCl equivalent) aqueous fluid. Two stages of hydrothermal activity characterized by high-salinity fluids (> 30 wt% NaCl equivalent) are identified; 1) relatively high-temperatures (350° to > 490°C); 2) lower temperatures (170° to 250°C). The high-salinity, high-temperature stage is interpreted to be the evidence for resurgent boiling. Dilution of these fluids by convicting meteoric water resulted in low to moderate salinity fluids, which dominated the inclusion population in quartz hosted crystals. The high-salinity, low-temperature fluid inclusions identify the residual fluids derived from boiling which happened as a result of a change in the pressure regime from dominantly lithostatic to hydrostatic conditions. Condensation and infiltration of ground waters caused major chemical variations, increasing the hydrostatic pressure, and the acid-washed processes on the system. The intense acid-washed and the intrusive rock depth is suggested to be the main reasons caused an uneconomic metal deposition in Deh-Salm system.

Genetic relationship between granitic magmatism and W mineralization recorded in the Nanling Scientific Drilling (SP-NLSD-2) in the Pangushan W mining district, South China

The Nanling Region in South China hosts numerous W-dominated polymetallic deposits that are related to Mesozoic granites. Although considerable amounts of age data have been obtained, the genetic relationship between granitic magmatism and W mineralization remains unclear. The Nanling Scientific Drilling (SP-NLSD-2) in the Pangushan W deposit has penetrated Upper Devonian sedimentary rocks (4.1–721.9 m), Sinian sedimentary rocks (721.9–1287.9 m) and Mesozoic granite (1287.9–2012.1 m). The drill hole clearly reveals a zonation including exocontact W-bearing quartz veins, alkali autometasomatic zone and primary K-feldspar granite. The K-feldspar granite at the depth of 1880 m, and rocks of potassium autometasomatic zone at 1414 m and greisenized zone at 1288 m have magmatic zircon grains with U–Pb ages of 164.8 ± 1.4 Ma, 161.7 ± 1.6 Ma, and 153.8 ± 1.2 Ma, respectively. Molybdenite Re–Os ages of endocontact mineralization at the depths of 1302 m and 1291 m are 155.9 ± 3.1 Ma and 155.0 ± 2.3 Ma, respectively. Muscovite Ar–Ar ages of exocontact mineralization at the depths of 1050 and 885 m are 154.9 ± 1.5 Ma and 154.0 ± 3.0 Ma, respectively, and molybdenite Re–Os age of exocontact quartz-vein type mineralization at 860 m is 152.0 ± 2.6 Ma. These new ages indicate that the granite emplacement, potassium autometasomatism, greisenization, and W mineralization occurred at ∼164.8 Ma, ∼161.7 Ma, ∼153.8 Ma, and 155.9–152 Ma, respectively. The W mineralization was approximately 9–13 Myr younger than the hosting granite. The whole-rock and feldspar chemical compositions of K-feldspar granite, potassium autometasomatic zone, greisenized zone, and feldspar-quartz veins indicate the sequence of metal transportation and concentration to form the zonation. The granite crystallized from high-K calcalkaline, metaluminous to peraluminous, highly differentiated magmas that were enriched in W and Bi. During crystallization, the magmas underwent potassium autometasomatism caused by post-magmatic fluids which were rich in K, Fe, W, and rare-earth elements (REE) but poor in Na and Ca, and formed the potassium autometasomatic zone. The evolved post-magmatic fluids became rich in K, Si, Ca, REE, and W but poor in Na and Fe and initiated greisenization to generate the greisenized zone, which almost exhausted Ca, REE, Na, and Fe of the fluids. The later crystallization of feldspar quartz veins exhausted K and caused the residual post-magmatic fluids to be rich in Si and W. The fluids formed W-bearing quartz veins with decreasing temperature and pressure. The main reason for W enrichment in the hydrothermal fluids was due to the successive crystallization of minerals rather than autometasomatism.