Brine Inclusions Research Articles

The controls of post-entrapment diffusion on the solubility of chalcopyrite daughter crystals in natural quartz-hosted fluid inclusions

The presence of chalcopyrite daughter crystals in natural quartz-hosted fluid inclusions that do not dissolve when heated to trapping conditions suggests that inclusions are subject to post-entrapment modifications that affect chalcopyrite solubility. Previous double capsule experiments conducted by Mavrogenes and Bodnar (1994) concluded that the post-entrapment outward diffusion of H2 is responsible for the presence of non-dissolvable chalcopyrite crystals in natural, quartz-hosted brine inclusions. However, recent studies have shown that quartz-hosted inclusions can also be modified by diffusional H+ loss and Cu+ gain. This means that multiple factors may influence chalcopyrite solubility in different fluid inclusion types. In this study, the experimental procedure of Mavrogenes and Bodnar (1994) was recreated in order to rehydrogenate quartz-hosted, chalcopyrite-bearing fluid inclusions from the El Teniente Cu–Mo porphyry deposit, Chile. These inclusions had a range of salinities and densities. Results show that the experimental technique is successful for fluid inclusions that contain relatively small chalcopyrite daughter crystals and have moderate salinities (>5wt.% NaCleq). In contrast, chalcopyrite crystals do not dissolve in low density vapor inclusions even after rehydrogenation. The failure of chalcopyrite crystals to dissolve in these inclusions is attributed to their lower initial pH and higher sulfide concentrations, which led to greater post-entrapment H+ loss and Cu+ gain. This considered, Cu concentrations in moderate to high salinity inclusions are likely to reflect those present at trapping, suggesting that H2 loss is the primary control on the failed dissolution of chalcopyrite. By contrast, Cu concentrations in S-rich vapor inclusions can increase considerably via inward Cu+ diffusion in the presence of an external Cu-bearing fluid and a pH gradient between the inclusion and this fluid (Lerchbaumer and Audétat, 2012; Seo and Heinrich, 2013). In accordance with these studies, the post-entrapment modification of Cu concentrations in vapor inclusions may undermine the apparent importance of phase separated vapors as a key agent of Cu transport and deposition in porphyry systems.

A newly isolated Haloalkaliphilic bacterium from middle–late Eocene halite formed in salt lakes in China

Ancient living halotolerant bacteria and ancient DNA have been reported from bedded marine halite, but seldom from lacustrine halite of the geological age. A halotolerant bacterium (Haloalkaliphilic bacterium, designated as 3-4) was isolated from primary halite with abundant fluid inclusions. Primary halite crystallized in lacustrine Yunying Depression located in the northeastern Jianghan Basin of central China. Yunying Depression is an inland salt paleolake residing in a faulted basin formed during late Cretaceous/early Tertiary. Brine inclusions from the same layer of the salt that housed Haloalkaliphilic bacterium 3-4 are the middle–late Eocene primary halite crystals and have homogenization temperatures between 5.8 and 43.3 °C. The estimated age is between 33.9 and 48.6 Ma years old for these fluid inclusions, and this represents the long-term survivability of this microorganism Haloalkaliphilic bacterium 3-4. Sequence analysis of the partial fragment of 16S ribosomal DNA showed that the organism is similar to the lineage of Haloalkaliphilic bacterium and Oceanobacillus sp. The isolation of the microbe reinforces the long-term preservation possibility of life in extreme environment such as the fluid inclusions in halite.

Imaged brine inclusions in young sea ice—Shape, distribution and formation timing

Liquid inclusions in sea ice are variable and dependent on the myriad of physical conditions of the atmosphere–sea ice environment in which the sea ice was grown, and whether or not melting processes affected the sea ice. In that light, there exist relatively few observations and resultant quantification of the morphology and vertical distribution of brine inclusions in sea ice. Using a magnetic (3.0T) resonance (MR) imager using constructive interference steady state gradient echo sequence, we show that it is possible to image brine channels and pockets in an 18.5cm young sea ice core in three-dimensions in only four and a half minutes following core storage at −20°C. We present a three-dimensional image of a brine drainage channel feature in a young sea ice core, give the physical context for its formation by presenting the physical conditions of the atmosphere and water/sea ice prior to sea ice growth through the sampling date, and observe its physical characteristics. We illustrate that brine drainage channels may be established concurrently with ice growth, and indicate the amount and location of vertical and horizontal fluid connectivity in the young sea ice sample in the context of the environment in which it grew. Finally, we show that a vertical brine volume distribution profile can be calculated using MR image data, extending the (non-imaging) nuclear magnetic resonance work of others in this vein.

Examination of the formation phases of coalbed methane reservoirs in the Lu'an mining area (China) based on a fluid inclusion analysis and Ro method

In this article, we employed two paleothermometric scales, fluid inclusions and vitrinite reflectance (Ro), to analyze the geohistorical restoration data of coal-bearing strata in several mine fields of the Lu'an mining area and comprehensively investigate the major hydrocarbon accumulation phases in the coal reservoirs. Our analyses revealed that the area accommodated a rich development of inclusions, with a dominance of liquid-gaseous hydrocarbons inclusions and hydrocarbon-bearing brine inclusions. A Raman spectroscopy examination revealed a carbonaceous pitch association that originated from secondary transformations of the inclusions during a late stage of high-temperature events; based on the homogenization temperatures and salinity data, the inclusions resulted from two intermittent injection events. We concluded that the coal strata of the Lu'an mining area experienced two thermal maturation stages that corresponded to two major hydrocarbon phases. During the first major phase of the Late Permian to Late Triassic, the coal-bearing strata underwent slow subsidence, temperature elevation and increased coal maturity. During the second major phase of the Late Jurassic to Early Cretaceous, the coal-bearing strata exhibited soaring temperatures and hydrocarbon generation as a result of abnormal heat influences caused by Yanshanian volcanic activities and deep intrusive rocks.

Fluid Inclusions and Their Application in Hydrocarbon History and Genesis

The fluid inclusions characteristics and pore fluid salinity of 56 samples from clastic reservoir of the Lower Cretaceous were analyzed in the Tanzhuang Sag. The authors also discuss the hydrocarbon charge history and the genesis of secondary pores in the Lower Cretaceous. The multipeak distribution of homogenous temperature of the brine inclusions showed that the inclusions captured should be multiperiod fluids at various depths. Comparison of the homogeneous temperature of brine inclusions with the temperature on the burial history curve suggested that the source rocks had entered the stage of large-scale hydrocarbon generation. However, only individual brine inclusions containing methane were found, and no oil-bearing inclusions were seen. The absence of oil-bearing inclusions indicated that no large-scale oil charges and limited favorable mature source rocks were present in the study area. The paleosalinity varied with depth and was divided into three zones, namely two low-value zones in the shallow and deep burial and one high-value zone in the medium burial. The secondary pores were relatively developed in the high-salinity fluid zone. Secondary pores are chiefly related to the inorganic acid associated with dehydration and mutual transformation of clay materials, and to the organic acid released from limited mature organic matter.

Deformation conditions for fracturing in the Middle Devonian sequence of the central Appalachians during the Late Paleozoic Alleghenian orogeny

In the central Appalachians, fluid inclusion microthermometry and oxygen and carbon stable isotope analysis vein minerals from the Middle Devonian shale section show that fluid conditions (pressure, temperature, and composition) are constantly changing during deformation and vary spatially across the fold-thrust belt. The earliest fractures in the region formed prior to folding, early during the Alleghenian orogeny as the rocks were buried into the oil generation window. They contain minerals that contain degraded hydrocarbon inclusions and basinal brine inclusions. During multiple vein reopening events, later mineral stages contain increasingly more mature hydrocarbon fluids. Late quartz mineralization is pervasive and typically contains the high-temperature brine inclusions. The vein opening history is related to changes in fluid connectivity associated with (1) burial by over-thrusting and/or syntectonic depositional loading and/or (2) folding during uplift and erosion. Initial fracture formation and fluid-trapping depths range from 3.5 km (2.2 mi) in the Plateau province and along the Appalachian structural front to 4.5 to 5.0 km (2.8 to 3.1 mi) in the Valley and Ridge province. Late-stage fracturing and fracture reopening is related to the maximum syntectonic burial, which varies from about 4 km (2.5 mi) in the Plateau to over 11 km (6.8 mi) in the Valley and Ridge. Fractures in the Valley and Ridge and western Pennsylvania Plateau provinces cannot be categorized into the simple and classification model. Burial history modeling indicates that fractures forming within and near the end of the oil window were NNW- and NW-striking, not ENE-striking, fractures.

Hydrothermal sulfur geochemistry on molybdenite deposition of the Questa Mo-deposit, New Mexico, USA

We conducted combined microthermometry and LA-ICP-MS microanalysis in the several brine inclusion assemblages of the Questa porphyry Mo deposits, USA and the nearby cogenetic Rito del Medio granitoid to study the hydrothermal geochemistry responsible for a molybdenite deposition in the Climax-type Mo deposit. We analyzed S concentrations in the fluid inclusions by using a recent technique on S quantification in the singly-targeted fluid inclusions. We found plenty of S in the fluid inclusions adequate to precipitate molybdenite, and the molybdenite might be precipitated in the tight temperature range of 350–450 °C in the Questa. A fractional crystallization in the causative magma would enrich Mo in the evolving magmatic-hydrothermal fluids from the early-stage hydrothermal breccias (MHBX) to the postdating stockwork veinlets (STW), while maintaining S to precipitate molybdenite in the Questa.

Copper partitioning between felsic melt and H2O–CO2 bearing saline fluids

Analysis of fluid inclusions from porphyry copper deposits reveals that magmatic vapor and brine are vital for the removal of copper from arc magmas and its transport to the site of ore deposition. Experiments in melt–vapor–brine systems allow for investigation of the partitioning of copper between silicate melts and volatile phases at magmatic conditions. The presence of CO2 affects both the pressure at which a melt saturates with respect to volatile phases. Therefore, the partitioning of copper among felsic (rhyolitic) melt, vapor and brine in CO2-bearing experiments was examined to provide insights into copper partitioning and the generation of porphyry copper and related deposits.We present results from experiments performed at 800°C and 100MPa in CO2-bearing melt–vapor–brine systems with XCO2v+b=0.10 and 0.38. The compositions of vapor and brine inclusions, and run-product glasses, were determined during the course of this investigation. Microthermometric measurements of fluid inclusions show an increase in the salinity of the magmatic brine (∼65 to ∼70wt% NaCleq) and decrease in the salinity of the vapor (∼3.5 to ∼1wt% NaCleq) as XCO2 is increased from 0.10 to 0.38. The partitioning of copper between brine and vapor (DCub/v±2σ) increases from 25 (±6) at XCO2=0.10, to 100 (±30) at XCO2=0.38. The partitioning of copper between vapor and melt (DCuv/m±2σ) decreases from 9.6 (±3.3) at XCO2=0.10, to 2 (±0.8) at XCO2=0.38. These data demonstrate that copper partitioning in sulfur-free, CO2-bearing systems is controlled by the changes in the salinity of the vapor and brine that, in turn, are functions of XCO2. No change in the apparent equilibrium constants for Cu–Na exchange was observed in Fe-bearing experiments which supports a salinity-dependent model for copper partitioning.An existing model (MVPart) for ore metal partitioning between melt and volatile phases was modified to incorporate partitioning data from CO2-bearing experiments. The model can be used to predict trends in efficiency of removal of copper from melts into exsolving CO2-bearing magmatic volatile phases at a fixed pressure and temperature. The CO2-MVPart model predicts that CO2-rich (XCO2=0.38) magmatic vapor will remove half of the available copper from the melt, without a contribution from the brine, compared to low CO2 (XCO2≤0.10) systems. Thus, periods of CO2-rich vapor exsolution are not expected to be associated with efficient removal of copper from shallow felsic melts.

Fluids and H2O activity at the onset of granulite facies metamorphism

Evidence is accumulating from experimental petrology and thermodynamic calculations based on detailed descriptions of key natural occurrences that H2O activity at the regional amphibolite facies-granulite boundaries in high-grade Precambrian gneiss terranes (coincident with the orthopyroxene isograd) is considerably higher (0.3–0.6) than previously thought (0.15–0.3). This revision provides insight into the significance of fluid inclusions in minerals of the incipient charnockites characteristic of the granulite facies transitions in several Precambrian gneiss terranes. Observations on NaCl-dominated brine inclusions in minerals, including some new data in this paper, in rocks from such places as the Kabbal–Satnur–Halagur area of the Archean Shield of South India have salt concentrations consonant with the stabilization of orthopyroxene relative to calcic amphibole and biotite; closely associated CO2-dominated fluid inclusions can have substantial H2O contents at typical incipient granulite facies conditions (700–750°C and 0.5–0.7GPa) and can thus have been in equilibrium with the associated brines as immiscible metamorphic fluids. Observed densities of the best-preserved CO2-rich fluid inclusions in quartz are consistent with those expected from the equation of state of CO2 at incipient granulite facies pressure-temperature conditions.It seems likely that the role of fluids in granulite facies metamorphism of the deep crust has been considerably underemphasized in discussions, still prevalent, which concentrate on the role of fluid-deficient partial melting as the primary agent, to the exclusion of a possible role of metamorphic fluids and metasomatism.

Modelling argon dynamics in first-year sea ice

Focusing on physical processes, we aim at constraining the dynamics of argon (Ar), a biogeochemically inert gas, within first year sea ice, using observation data and a one-dimensional halo-thermodynamic sea ice model, including parameterization of gas physics. The incorporation and transport of dissolved Ar within sea ice and its rejection via gas-enriched brine drainage to the ocean, are modeled following fluid transport equations through sea ice. Gas bubbles nucleate within sea ice when Ar is above saturation and when the total partial pressure of all three major atmospheric gases (N2, O2 and Ar) is above the brine hydrostatic pressure. The uplift of gas bubbles due to buoyancy is allowed when the brine network is connected with a brine volume above a given threshold. Ice-atmosphere Ar fluxes are formulated as a diffusive process proportional to the differential partial pressure of Ar between brine inclusions and the atmosphere. Two simulations corresponding to two case studies that took place at Point Barrow (Alaska, 2009) and during an ice-tank experiment (INTERICE IV, Hamburg, Germany, 2009) are presented. Basal entrapment and vertical transport due to brine motion enable a qualitatively sound representation of the vertical profile of the total Ar (i.e. the Ar dissolved in brine inclusions and contained in gas bubbles; TAr). Sensitivity analyses suggest that gas bubble nucleation and rise are of most importance to describe gas dynamics within sea ice. Ice-atmosphere Ar fluxes and the associated parameters do not drastically change the simulated TAr. Ar dynamics are dominated by uptake, transport by brine dynamics and bubble nucleation in winter and early spring; and by an intense and rapid release of gas bubbles to the atmosphere in spring. Important physical processes driving gas dynamics in sea ice are identified, pointing to the need for further field and experimental studies.

Identification of Carotenoids in Ancient Salt from Death Valley, Saline Valley, and Searles Lake, California, Using Laser Raman Spectroscopy

Carotenoids are common components of many photosynthetic organisms and are well known from the red waters of hypersaline ecosystems where they are produced by halophilic algae and prokaryotes. They are also of great interest as biomarkers in extraterrestrial samples. Few laser Raman spectroscopy studies have examined ancient field samples, where pigments and microscopic life are less defined. Here, we have identified carotenoids in ancient halite brine inclusions, 9 ka to 1.44 Ma in age, from borehole cores taken from Death Valley, Saline Valley, and Searles Lake, California, for the first time with laser Raman spectroscopy. Carotenoids occurred in fluid inclusions as colorless to red-brown amorphous and crystalline masses associated with spheroidal algal cells similar in appearance to the common halophilic alga Dunaliella. Spectra from carotenoid standards, including β-carotene, lycopene, and lutein, were compared to microscopically targeted carotenoids in fluid inclusions. Carotenoids produced characteristic bands in the Raman spectrum, 1000-1020 cm⁻¹ (v₃), 1150-1170 cm⁻¹ (v₂), and 1500-1550 cm⁻¹ (v₁), when exposed to visible laser excitation. Laser Raman analyses confirmed the presence of carotenoids with these characteristic peaks in ancient halite. A number of band sets were repeated at various depths (ages), which suggests the stability of this class of organic molecules. Carotenoids appear well preserved in ancient salt, which supports other observations, for example, preserved DNA and live cells, that fluid inclusions in buried halite deposits preserve intact halophilic microbial ecosystems. This work demonstrates the value of laser Raman spectroscopy and carotenoids in extraterrestrial exploration for remnants of microbial life.

Fluid Inclusion Study of the Higher Himalayan Quartzitic Pelites, Garhwal Himalaya, India: Implications for Recrystallization History of Metasediments

Abstract Quartzitic pelites forms a part of Higher Himalayan Crystalline of higher geotectonic zone in Garhwal Himalaya. Quartzitic pelites (locally known as Pandukeshwar Quartzite) in Garhwal Himalaya is sandwiched between high grade metamorphic rocks of Central Crystallines and Badrinath Formation. Fluid inclusion studies are carried out on the detrital, and recrystallized quartz grains of quartzitic pelites to know about the fluid phases present during recrystallization processes at the time of maximum depth of burial. The quartzitic pelite (Pandukeshwar Quartzite) essentially consists of recrystallised quartz with accessory minerals like mica and feldspar. Fluid microthermometry study reveals the presence of three types of fluids: (i) high-salinity brine, (ii) CO2- H2O and (iii) H2O-NaCl. These fluids were trapped during the development of grain and recrystallization processes. The high saline brine inclusions and CO2- H2O fluid with the density of 0.90 to 0.97 gm/cm3 are remnants of provenance area. CO2 density in detrital quartz grains characterise the protolith of the sandstone as granite or metamorphic rock. The H2O–NaCl fluids involved in the recrystallization processes at temperature-pressure of 430-350°C; 4.8 to 0.5 Kbars as constrained by fluid isochores of CO2- H2O and H2O–NaCl inclusions and bulging and sub- grain development during recrystallization processes. The re-equilibration of the primary fluid due to elevated internal and confining pressure is evident from features like ‘C’ shaped cavities, stretching of the inclusions, their migration and decrepitation clusters. The observed inclusion morphology revealed that the rocks were exhumed along an isothermal decompression path.

The major-ion composition of Cenozoic seawater: The past 36 million years from fluid inclusions in marine halite

Fluid inclusions from ten Cenozoic (Eocene-Miocene) marine halites are used to quantify the major-ion composition (Mg^2+^, Ca^2+^, K^+^, Na^+^, SO~4~^2−^, and Cl^−^) of seawater over the past 36 My. Criteria used to determine a seawater origin of the halites include: (1) stratigraphic, sedimentologic, and paleontologic observations; (2) Br^−^ in halite; (3) δ^34^S of sulfate minerals; (4) ^87^Sr/^86^Sr of carbonates and sulfates; and (5) fluid inclusion brine compositions and evaporation paths, which must overlap from geographically separated basins of the same age to confirm a "global" seawater chemical signal. Changes in the major-ion chemistry of Cenozoic seawater record the end of a systematic, long term (\>150 My) shift from the Ca^2+^-rich, Mg^2+^- and SO~4~^2−^-poor seawater of the Mesozoic ("CaCl~2~ seas") to the "MgSO~4~ seas" (with higher Mg^2+^ and SO~4~^2−^\>Ca^2+^) of the Cenozoic. The major ion composition of Cenozoic seawater is calculated for the Eocene-Oligocene (36-34 Ma), Serravallian-Tortonian (13.5-11.8 Ma) and the Messinian (6-5 Ma), assuming chlorinity (565 mmolal), salinity, and the K^+^ concentration (11 mmolal) are constant and the same as in modern seawater. Fluid inclusions from Cenozoic marine halites show that the concentrations of Mg^2+^and SO~4~^2−^ have increased in seawater over the past 36 My and the concentration of Ca^2+^ has decreased. Mg^2+^ concentrations increased from 36 mmolal in Eocene-Oligocene seawater (36-34 Ma) to 55 mmolal in modern seawater. The Mg^2+^/Ca^2+^ ratio of seawater has risen from ∼2.3 at the end of the Eocene, to 3.4 and 4.0, respectively, at 13.5 to 11.8 Ma and 6 to 5 Ma, and to 5 in modern seawater. Eocene-Oligocene seawater (36-34 Ma) has estimated ranges of SO~4~^2−^ = 14--23 mmolal and Ca^2+^ = 11--20 mmolal. If the (Ca^2+^)(SO~4~^2−^) product is assumed to be the same as in modern seawater (∼300 mmolal^2^), Eocene-Oligocene seawater had Ca^2+^ ∼16 mmolal and SO~4~^2−^ ∼19 mmolal. The same estimates of Ca^2+^ and SO~4~^2−^ for Serravallian-Tortonian seawater (13.5-11.8 Ma) are SO~4~^2−^ = 19--27 mmolal and Ca^2+^ = 8--16 mmolal and SO~4~^2−^ ∼24 mmolal and Ca^2+^ ∼ 13 mmolal if the (Ca^2+^)(SO~4~^2−^) product is equal to that in modern seawater. Messinian seawater has an estimated range of SO~4~^2−^ ∼21--29 mmolal and Ca^2+^ ∼7--15 mmolal with SO~4~^2−^ ∼26 mmolal and Ca^2+^ ∼12 mmolal assuming the (Ca^2+^)(SO~4~^2−^) product is equal to that in modern seawater. Regardless of the estimation procedure, SO~4~^2−^ shows progressively increasing concentrations from 36 Ma to the present values, which are the highest of the Cenozoic.

Role of sea ice in global biogeochemical cycles: emerging views and challenges

Observations from the last decade suggest an important role of sea ice in the global biogeochemical cycles, promoted by (i) active biological and chemical processes within the sea ice; (ii) fluid and gas exchanges at the sea ice interface through an often permeable sea ice cover; and (iii) tight physical, biological and chemical interactions between the sea ice, the ocean and the atmosphere. Photosynthetic micro-organisms in sea ice thrive in liquid brine inclusions encased in a pure ice matrix, where they find suitable light and nutrient levels. They extend the production season, provide a winter and early spring food source, and contribute to organic carbon export to depth. Under-ice and ice edge phytoplankton blooms occur when ice retreats, favoured by increasing light, stratification, and by the release of material into the water column. In particular, the release of iron – highly concentrated in sea ice – could have large effects in the iron-limited Southern Ocean. The export of inorganic carbon transport by brine sinking below the mixed layer, calcium carbonate precipitation in sea ice, as well as active ice-atmosphere carbon dioxide (CO2) fluxes, could play a central role in the marine carbon cycle. Sea ice processes could also significantly contribute to the sulphur cycle through the large production by ice algae of dimethylsulfoniopropionate (DMSP), the precursor of sulphate aerosols, which as cloud condensation nuclei have a potential cooling effect on the planet. Finally, the sea ice zone supports significant ocean–atmosphere methane (CH4) fluxes, while saline ice surfaces activate springtime atmospheric bromine chemistry, setting ground for tropospheric ozone depletion events observed near both poles. All these mechanisms are generally known, but neither precisely understood nor quantified at large scales. As polar regions are rapidly changing, understanding the large-scale polar marine biogeochemical processes and their future evolution is of high priority. Earth system models should in this context prove essential, but they currently represent sea ice as biologically and chemically inert. Palaeoclimatic proxies are also relevant, in particular the sea ice proxies, inferring past sea ice conditions from glacial and marine sediment core records and providing analogues for future changes. Being highly constrained by marine biogeochemistry, sea ice proxies would not only contribute to but also benefit from a better understanding of polar marine biogeochemical cycles.

Ore Genesis and Hydrothermal Evolution of the Baiyinnuo'er Zinc-Lead Skarn Deposit, Northeast China: Evidence from Isotopes (S, Pb) and Fluid Inclusions

The Baiyinnuo’er zinc-lead deposit (32.74 Mt at 5.44% Zn, 2.02% Pb, and 31.36 g/t Ag), located in the south segment of the Great Xing’an Range, is the largest Zn-Pb deposit in northern China. Skarn and orebodies mainly occur between the different units of the Huanggangliang Formation, or within the contact zone between the intrusions and Permian marble. Several phases of igneous rocks exposed within the mining areas, and among them the Yanshanian plutonic rocks, which intruded into limestone of the early Permian Huanggangliang Formation, are interpreted to be the source of ore, since their Pb isotope compositions (206Pb/204Pb = 18.25–18.35, 207Pb/204Pb = 15.50–15.56, and 208Pb/204Pb = 38.14–38.32) are highly consistent with the sulfides, including sphalerite, galena, and chalcopyrite (206Pb/204Pb = 18.23–18.37, 207Pb/204Pb = 15.47–15.62, and 208Pb/204Pb = 37.93–38.44). Sulfur isotope values of the sulfides give a narrow δ 34S interval of −6.1 to −4.6‰ (mean = −5.4‰, n = 15), suggesting the ore-forming fluid is of magmatic origin. Three main paragenetic stages of skarn formation and ore deposition have been recognized based on petrographic observation, which are the preore stage (garnet-clinpyroxene-wollastonite-magnetite ± sulfides), the synore stage (sulfides-epidote-quartz-calcite ± garnet), and the postore stage (calcite-chlorite-quartz-fluorite). Several fluid evolution episodes can be inferred from microthermometric results at the Baiyinnuo’er Zn-Pb deposit: 1. Immiscibility: Preore-stage coexistence of halite-bearing brine inclusions (S1-type, ~44 wt % NaCl equiv) and vapor-rich fluid inclusions (V-type) sharing the same homogenization temperatures (~470°C) confirms that fluid unmixing occurred under lithostatic pressures of ~400 bars (~1.5 km), and the brine is considered to account for most prograde skarn minerals (e.g., clinopyroxene). 2. Overpressure trapping: Preore-stage brine inclusions homogenized by halite dissolution (S2-type) postdated the immiscible assemblages. This type of inclusions is characterized by high but variable (minimum) trapping pressures (150–3,000 bars) relative to S1-type inclusions and can be explained as a result of entrapment under overpressuring condition. 3. Boiling: The presence of both vapor and liquid inclusions (i.e., V- and L-type) in the same assemblages within synore-stage quartz, calcite, and sphalerite indicates the occurrence of fluid boiling (~350°C), at hydrostatic pressures of ~150 bars, and depth of ~1.5 km), which resulted in large-scale mineralization in the Baiyinnuo’er Zn-Pb deposit. 4. Mixing with external fluids: Fluid inclusions scattered within postore-stage calcite or secondary trails in synore-stage minerals show low homogenization temperatures (<260°C) and both decreasing (for L-type) and increasing (for CaCl2-bearing inclusions, i.e., Lc-type) trends for salinities as homogenization temperatures decrease, implying addition of both meteoric water (low-temperature, low-salinity) and basinal brines (low-temperature, Ca-rich), respectively. Systematic fluid inclusion studies also indicate that the mineralization-related fluid is of magmatic origin. Prograde minerals formed during the preore-stage fluid immiscibility while sulfides deposition occurred during the synore-stage fluid boiling. Mixing with external fluids began as the hydrothermal system cooled to <300°C, when the main metal precipitation process had ended.

Late Accumulation of Kunbei Area in Qaidam Basin

This paper is aimed to find out the main reason of late accumulation of Kunbei area in Qaidam Basin using geochemistry and seismic data and to provide scientific evidence to the potential petroleum exploration in this area. Reservoirs in Kunbei fault terrace zone originate from petreoleum generated by source rocks of E32 in Zhahaquan depression after N23(about 5.2Ma), which means a charcteristic of hysteretic hydrocarbon generation. Brine inclusions shows two hydrocarbon charging periods.The first charging most likely happens at N1 and the second begins at N21,continuing to Q.Two deformaton stages exist in the study area due to the Tibet Plateau uplifting. The accumulations of first stage have been damaged after Middle N1. The reservoirs of Kunbei zone at present are almost orignated from E32 in depression. Above all,the primary cause of late accumulation is due to long-distance effects of the Tibet Plateau uplifting.

Pore-scale modeling of multiphase reactive transport with phase transitions and dissolution-precipitation processes in closed systems

A pore-scale model based on the lattice Boltzmann (LB) method is developed for multiphase reactive transport with phase transitions and dissolution-precipitation processes. The model combines the single-component multiphase Shan-Chen LB model [X. Shan and H. Chen, Phys. Rev. E 47, 1815 (1993)], the mass transport LB model [S. P. Sullivan et al., Chem. Eng. Sci. 60, 3405 (2005)], and the dissolution-precipitation model [Q. Kang et al., J. Geophys. Res. 111, B05203 (2006)]. Care is taken to handle information on computational nodes undergoing solid-liquid or liquid-vapor phase changes to guarantee mass and momentum conservation. A general LB concentration boundary condition is proposed that can handle various concentration boundaries including reactive and moving boundaries with complex geometries. The pore-scale model can capture coupled nonlinear multiple physicochemical processes including multiphase flow with phase separations, mass transport, chemical reactions, dissolution-precipitation processes, and dynamic evolution of the pore geometries. The model is validated using several multiphase flow and reactive transport problems and then used to study the thermal migration of a brine inclusion in a salt crystal. Multiphase reactive transport phenomena with phase transitions between liquid-vapor phases and dissolution-precipitation processes of the salt in the closed inclusion are simulated and the effects of the initial inclusion size and temperature gradient on the thermal migration are investigated.

Selective copper diffusion into quartz-hosted vapor inclusions: Evidence from other host minerals, driving forces, and consequences for Cu–Au ore formation

Recent experimental studies have raised concerns that Cu concentrations in quartz-hosted fluid inclusions from magmatic–hydrothermal ore deposits do not represent pristine concentrations in the trapped fluids, but are modified by post-entrapment diffusional exchange through the host quartz. New microanalyses of fluid inclusions hosted in topaz show significantly lower Cu concentrations in vapor inclusions, compared to otherwise identical inclusions hosted by coexisting quartz, whereas coeval brine (hypersaline liquid) inclusions are very similar independent of host mineral in one sample. Sulfur is present as a major component in all vapor inclusions, as in most porphyry-related vapor inclusions, and Cu never exceeds S, but commonly matches the S content at a molar ratio of Cu:S⩽2 in vapor inclusions hosted by quartz.Univalent ions with a radius smaller than ∼1Å are known to diffuse rapidly through the channels of the quartz structure, parallel to its crystallographic c axis. Since only Cu concentrations differ between topaz- and quartz-hosted inclusions, we hypothesize that Cu+ and H+ re-equilibrate by diffusional ion exchange through these channels, while all other element concentrations remain essentially unchanged. A thermodynamic model considering charge-balanced Cu+H+ exchange and diffusive H2 re-equilibration of an initially Cu-poor but S-rich vapor inclusion with a typical rock-buffered fluid environment outside the host crystal demonstrates a strong chemical driving force for Cu+ to migrate from the surrounding rock into the fluid inclusion during cooling of the system. The driving force for Cu diffusion, against the gradient in total Cu concentration, is the abundant H+ liberated inside the inclusion by dissociation of HCl and particularly by the precipitation of CuFeS2 by reaction with the initially trapped H2S and/or SO2. Gold is not only a much larger ion, but is subject to an opposing driving force, suggesting that high concentrations of this larger ion analyzed in vapor inclusions probably represent true gold concentrations in magmatic–hydrothermal vapor.These findings imply that brine–vapor separation in porphyry deposits does not cause selective Cu transfer to the vapor, but is more likely to destabilize Cu complexes and promote copper ore deposition during decompression and unmixing of the two fluid phases. By contrast, Au may be selectively transferred into the vapor phase, allowing its transport through the deeper porphyry copper deposits to form epithermal gold deposits closer to the earth’s surface.

Structural deformation and fluid flow from East Sichuan to the northwestern periphery of the Xuefeng Uplift, China

Hydrocarbon preservation conditions have restricted exploration in the Middle and Upper Yangtze, and structural deformation and fluid activity have played an important role in the origin and preservation of oil and gas. In order to study that how the deformation and fluid activity impact the hydrocarbon preservation, we did some field work and collected some calcite vein samples for analysis of deformation periods using acoustic emission and fluid inclusions. Combined with previous studies, the strata distribution, tectonic deformation and fluid characteristics show that there are three structural belts in the study area: East Sichuan, West Hunan and Hubei and the northwestern periphery of the Xuefeng Uplift, and that their tectonic deformation style, fluid inclusion characteristics and hydrocarbon preservation are different. The breakthrough thrusts were well developed in the anticline core, and a lot of hydrocarbon inclusions were found in calcite veins around the thrusts in East Sichuan. The breakthrough thrusts were only in the syncline core in West Hunan and Hubei, and the brine inclusions did not contain hydrocarbon in calcite veins around the thrusts. Many breakthrough thrusts were found in the northwestern periphery of the Xuefeng Uplift, where there were only rare calcite veins. The deformation and hydrocarbon inclusion indicated that when there was no fault breakthrough in East Sichuan, the Paleozoic covered by the Triassic regional cap was good for hydrocarbon preservation. The strata above the Lower Paleozoic were denuded, and lots of brine inclusions and deep infiltration of surface water were found in the West Hunan and Hubei, so only the part of the syncline area with a well developed Silurian regional cap had good preservation conditions. Intense tectonic movements and denudation were widely developed in the northwestern periphery of the Xuefeng Uplift, where there were only paleo-reservoirs, non-hydrocarbon fluid activity and poor preservation conditions.

Accurate and precise quantification of major and trace element compositions of calcic–sodic fluid inclusions by combined microthermometry and LA-ICPMS analysis

Determination of absolute trace-element concentrations in fluid inclusions using laser-ablation (LA) ICPMS requires an internal standard, i.e., the concentration of one element must be independently known from independent observation. Microthermometric determination of the last melting temperature of ice, hydrohalite or halite is routinely used to calculate apparent salinities in wt.% NaCl equivalent, using phase relations in the binary H2O–NaCl system to estimate Na concentration. Calculating the concentrations of all other elements requires an empirical correction, if additional salt concentrations are of similar magnitude as that of NaCl. If CaCl2 is the main additional salt component, as in many low-temperature basin and basement brines, absolute Na concentrations (wt.% NaCl abs.) can be obtained by observing two melting temperatures (hydrohalite and either ice or halite), uniquely defining the major element composition of the fluid in the ternary model system H2O–NaCl–CaCl2 and allowing Na to be used as internal standard for quantifying all minor and trace elements. Test results for a range of compositions show that calcium concentration can be determined more precisely by microthermometry than by LA-ICPMS analysis, but that both methods agree within error. The combined approach of microthermometry and LA-ICPMS analysis described here permits reliable quantification of major (Ca, Na) as well as trace element concentrations in sodic–calcic brine inclusions, even in Ca-rich host minerals such as fluorite or Ca-bearing carbonates.