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1.
Thermal waters of northern (18°–27°S) and southern (37°–45°S) Chile occur in two very different climatic, geologic and hydrologic environments: arid closed basins with abundant evaporites in the north; humid climate and well drained valleys in the south. The origin and behavior of the main components of the two groups of waters are examined and compared to each other. The modeling of the alteration of volcanic rocks leads to water compositions very different from those observed both in the north and south. In addition to hydrothermal alteration and deep emanations, the Cl/Br ratio reveals a major contribution of saline waters to the two groups: infiltrating brines from salt lakes in the north; seawater in the south.In the north, concentrations of Cl, Br, Na, K, Ca, SO4, Li, B, Si result from the mixing of alteration waters with recycled brines. Hydrothermal alteration is obscured by this massive saline input, except for Mg. δ34S values are consistent with an origin of sulfate from salar brines, which are themselves derived from deep Tertiary gypsum. In the south, two processes account for the composition of thermal waters: mixing of alteration waters with seawater and deep magmatic contribution. The mixing process controls the concentration of Cl, Br, Na, Alk, Si, K, Ca, Mg. Magmatic inputs are detectable for SO4, Li and B. δ34S suggests that sulfate stems from the mixing of alteration waters with either marine SO4 in coastal waters or with deep SO2 in inland waters. In both the north and south, the Mg concentration is drastically lowered (<1 μmol/L) by the probable formation of a chlorite-type mineral. In the south, very small amounts of seawater (<1% in volume) are sufficient to imprint a clear signature on thermal waters. Not only coastal springs are affected by seawater mixing, but also remote inland springs, as far as 150 km from the sea. Subduction of marine sediments in the accretive margin could be the source of the marine imprint in thermal waters of southern Chile. Seawater may be expelled from the subducted lithosphere and incorporated into the mantle source.  相似文献   

2.
During Li recovery from salar brines, Li concentration is typically increased to about 60,000 mg L?1 by evaporation. We investigated the concentration changes of Li, Na, K, Mg, Cl, SO4, and B during evaporation of both natural Uyuni and artificial Atacama brines. The Uyuni brine exhibited a maximum Li concentration of 6810 mg L?1 at 31 days of evaporation, at which point the majority of the Na and K in the brine was removed. The Li concentration decreased with further evaporation due to precipitation as Li2SO4, such that the level at the 56 day mark was approximately 4130 mg L?1. In contrast, the artificial Atacama brine showed no pronounced Li precipitation, even after 54 days, at which point the Li concentration was 21,800 mg L?1. The initial concentrations of Na and K in the Atacama brine were higher than those in the Uyuni brine, and the Atacama solution still retained K after 54 days of evaporation. The order of precipitation of cation species during the evaporation of both brines was: Na, followed by K, Mg, and Li. Thus, Li precipitation in the Atacama brine might be prevented due to the more favored precipitations of Na and K, such that significant Li removal did not occur in this brine.  相似文献   

3.
《Applied Geochemistry》2001,16(1):35-55
Formation waters within Upper Carboniferous sandstones in the sub-sea Prince and Phalen coal mines, Nova Scotia, originated as residual evaporative fluids, probably during the precipitation of Windsor Group (Lower Carboniferous) salts which underlie the coal measures. Salinity varies from 7800 to 176,000 mg/l, and the waters are Na–Ca–Cl brines enriched in Ca, Sr and Br and depleted in Na, K, Mg and SO4 relative to the seawater evaporation curve. Br:Cl and Na:Cl ratios suggest that the brine composition corresponds to an evaporation ratio of as much as 30. The brines lie close to the meteoric line on H/O isotopic plots but with a compositional range of δ18O from −4.18 to −6.99 and of δD from −42.4 to −23.5, distant from modern meteoric or ocean water. Mine water composition contrasts with that of nearby salt-spring brines, which are inferred to have originated through dissolution of Windsor Group evaporites by modern meteoric waters. However, a contribution to the mine waters from halite dissolution and from Br in organic matter cannot be ruled out. Present concentrations of several elements in the brines can be explained by water–rock interaction. The original Windsor brines probably moved up into the overlying coal-measure sandstones along faults, prior to the Late Triassic. The high salinity and irregular salinity distribution in the Phalen sandstones suggests that the brines have undergone only modest dilution and are virtually immobile. In contrast, Prince waters show a progressive increase in salinity with depth and are inferred to have mixed with surface waters. Basinal brines from which these modern formation fluids were derived may have been important agents in base-metal and Ba mineralisation from the mid-Carboniferous onwards, as saline fluid inclusions are common in Zn–Pb sulphide deposits in the region.  相似文献   

4.
The Canning Basin contains several Mississippi Valley‐type Zn‐Pb sulphide prospects and deposits in Devonian carbonate reef complexes on the northern edge of the Fitzroy Trough, and in Ordovician and Silurian marine sequences on the northern margin of the Willara Sub‐basin. This study uses the ionic composition and 5D, δ18O, δ34S, 87Sr/86Sr isotopic data on present‐day deep formation waters to determine their origin and possible relationship to the Zn‐Pb mineralizing palaeofluids.

The present‐day Canning Basin formation waters have salinity ranging from typically less than 5000 mg/L up to 250 000 mg/L locally. The brines are mixtures of highly saline water, formed by seawater which evaporated beyond halite saturation (bittern water), with meteoric water ranging in salinity from low (<5000 mg/L) to hypersaline water (up to about 50 000 mg/L) formed by re‐solution of halite and calcium sulphate minerals. The original marine chemical composition of the bittern‐dominated brines was changed to that of a Na‐Ca‐Cl water by addition of Ca and removal of Mg and SO4, initially by bacterial sulphate reduction and later by dolomitization of carbonate. Other reactions with terrigenous components of the sediment have provided additional Ca and Sr, including a small proportion of 87Sr‐rich material. The δ34S values of the bittern‐containing waters are within the range over which marine sulphate has fluctuated from the Ordovician to the Holocene, although one of the hypersaline waters has a value of +6.8%, indicating SO4 of non‐marine origin. The pH of the bittern‐containing waters is low (about 5) and they contain significant concentrations of dissolved Fe (up to 120 mg/L).

The Canning Basin bitterns appear similar in origin and chemical composition to highly saline marine brines in the Mississippi Salt Dome Basin, USA, which are known to be either metal or sulphide‐rich depending on the organic content of the host rock. In the Canning Basin, mixing of the bittern water with the various types of meteoric water has resulted in decreases in salinity, Na, Ca, Mg, K, Sr, Li and Fe, and increases in HCO3, SO4 and pH.

Mixing of the bitterns with other types of metalliferous fluids and/or with sulphate‐containing hypersaline meteoric waters formed from the same marine evaporite sequence should produce ore‐precipitating fluids which are relatively hot and saline, and the resulting ore deposit should be of high grade and contain abundant sulphate minerals. In the southern Canning Basin, this type of mixing and the corresponding style of ore deposit is evident in the evaporite‐associated areas of Zn‐Pb mineralization near the Admiral Bay Fault. If the bitterns mix with low salinity HCO3‐waters in near‐surface environments, then the ore‐precipitating fluids should have relatively low salinities and carbonate minerals would precipitate during later stages of mixing. In the Lennard Shelf, the present‐day formation waters, the style of the Zn‐Pb deposits, and range of salinity and temperature of the ore‐forming palaeofluids are consistent with this type of mixing.  相似文献   

5.
The formation of natural cryogenic brines   总被引：1，自引：0，他引：1  
The source of salts in the Ca-chloridic, hypersaline brines (up to 190 g Cl L−1) occurring in crystalline basement rocks in the Canadian, Fennoscandian and Bohemian Shields and their evolution have been investigated and reported. The Cl-Br-Na relationship indicates that these waters have been concentrated from seawater, by freezing during glacial times. The Na/Cl ratio (0.25 to 0.35) in the more saline fluids is compatible with cooling down to −30°C, where the most saline waters have been concentrated by a factor of 25 to 30 relative to the parent seawater.The brines formed from seawater within cryogenic troughs, along the subarctic continental margins, around ice sheets. The depressions within which the brines formed are the cryogenic analogues of the classic, evaporitic lagoon. One million years suffice to saturate with brine a 2000km-radius by 1km-depth rock volume at an H2O removal rate of only 2.8 mm/yr. Density-induced brine migration on a continental scale takes place via fissures below the ice.Our calculations, that were performed on a hypothetical ice sheet with dimensions compatible with the Laurentide ice sheet, demonstrate that during 1m.y., a 60m thick cryogenic sediment section could have formed. However, the precipitated minerals (mirabilite and hydrohalite) are repeatedly dispersed by the advance and retreat of the ice sheet, dissolved by melt water-seawater mixtures, and eroded during postglacial uplift, leaving almost no trace in the geological record.The cryogenic brines formed intermittently during and between glacial periods. The repeating advance and retreat of the ice sheets exerted a major control on the direction and intensity of brine flow. The cryogenic concentration of seawater and the migration of brine towards the center of the glaciostatic depression occurred mainly during the build up of the ice sheet, while reversal of the water flow from the center of the cryogenic basin outwards happened upon deglaciation. The flow of the waters in the subsurface was, inevitably, accompanied by significant dilution with melt water from the ice sheets.Using a “granitic” U concentration of 4 ppm and a (Ca-Mg mass balance based) rock/water ratio anywhere between 3.4 and 6.8 kg L−1, a few hundred thousand years of brine-rock interaction are sufficient for the growth of 129I in the most saline Canadian Shield brine to its present concentration (3.4×108 atoms 129I L−1). Hence, both the formation of the saline fluids and their emplacement in their present sites occurred most likely within the Pleistocene.The young age calculated for cryogenic brines in crystalline shields and the dynamic water flow therein should raise concern about the planning and construction of high-grade nuclear waste repositories in such rocks, which are already under way.  相似文献   

6.
Twenty-four brine samples from the Heletz-Kokhav oilfield, Israel, have been analyzed for chemical composition and Li isotope ratios. The chemical composition of the brines, together with geological evidence, suggests derivation from (Messinian) seawater by evaporation that proceeded well into the gypsum stability field but failed to reach the stage of halite crystallization. The present salinity of the samples (18-47 g Cl/L) was achieved by dilution of the original evaporitic brine by local fresh waters. Like brines from other sedimentary basins, the Li/Cl ratios in the Heletz-Kokhav samples show a prominent Li enrichment (five-fold to eight-fold) relative to modern seawater. The isotopic ratios of Li, expressed in the δ 6Li notation, vary from −26.3 to −17.9‰, all values being significantly higher than that of modern seawater (−32‰) irrespective of their corresponding Li concentration (1.0-2.3 mg/L). The isotopic composition of Li and the Li/Cl ratio in the oilfield brines were acquired in two stages: (a) The original evaporated seawater gained isotopically light Li during the diagenetic interaction between the interstitial Messinian brine and the basin sediments. A parent brine with an elevated Li/Cl ratio was formed. The brine was later diluted in the oilfields. (b) The δ 6Li values of the final brines were determined during epigenetic interaction with the Heletz-Kokhav aquifer rocks. At the same time, the Li/Cl ratio inherited from stage (a) remained largely unchanged. This work represents the first use of lithium isotopic composition to elucidate the origin and evolution of formation waters in sedimentary basins.  相似文献   

7.
《Applied Geochemistry》1988,3(3):317-332
The chemistry and stable isotopes (18O, D) of highly concentrated chloride brines and minerals from the Asse salt mine in the north of the Federal Republic of Germany were studied. Chemical data indicate the occurrence of three types of brines: (a) Mg-Cl type, of carnallitite origin with Li < 30 mg/kg; (b) Na-Cl type brines, of rock salt origin, with Li > 100 mg/kg; and (c) almost pure MgCl2-type brines with Li > 100 mg/kg. The first group may be subdivided into brines with Li < 4.0 mg/kg and brines with Li between 18 and 30 mg/kg. Lithium is shown to be an efficient complementary tool in tracing the origin of the brines. The complex evolution of carnallitite-type brines is discussed in detail. Isotopic data of brines that were sampled directly from seepages (presumably unaltered) indicate that these brines are not a mixture with relatively fresh ground water from the overburden sediments. The stable isotope composition (18O and D) of hydration water in carnallite, kieserite and polyhalite sampled from the Asse mine were also studied. It is shown that water extracted from the so-called primary carnallite is isotopically different from water extracted from secondary carnallite. The isotopic fractionation factors for 18O and D between carnallite hydration water and mother solution were studied in the laboratory. Assuming that crystallization water of the so-called primary carnallite samples is not altered, the isotopic composition of the mother solution is evaluated.  相似文献   

8.
The salt waters from the Emilia-Romagna sector of the Northern Apennine Foredeep have been investigated using major and trace element and stable isotope (δ2H, δ18O, δ37Cl, δ81Br and 87Sr/86Sr ratio). Ca, Mg, Na, K, Sr, Li, B, I, Br and SO4 vs. Cl diagrams suggest the subaerial evaporation of seawater beyond gypsum and before halite precipitation as primary process to explain the brine’s salinity, whereas saline to brackish waters were formed by mixing of evaporated seawater and water of meteoric origin. A diagenetic end-member may be a third component for mud volcanoes and some brackish waters. Salinization by dissolution of (Triassic) evaporites has been detected only in samples from the Tuscan side of the Apennines and/or interacting with the Tuscan Nappe. In comparison with the seawater evaporation path, Ca–Sr enrichment and Na–K–Mg depletion of the foredeep waters reveal the presence of secondary processes such as dolomitization–chloritization, zeolitization–albitization and illitization. Sulfate concentration, formerly buffered by gypsum-anhydrite deposition, is heavily lowered by bacterial and locally by thermochemical reduction during burial diagenesis. From an isotopic point of view, data of the water molecule confirm mixing between seawater and meteoric end-members. Local 18O-shift up to +11‰ at Salsomaggiore is related to water–rock interaction at high temperature (≈150°C) as confirmed by chemical (Mg, Li, Ca distribution) and isotopic (SO4–H2O) geothermometers. 37Cl/35Cl and 81Br/79Br ratios corroborate the marine origin of the brines and evidence the diffusion of halogens from the deepest and most saline aquifers toward the surface. The 87Sr/86Sr ratio suggests a Miocene origin of Sr and rule out the hypothesis of a Triassic provenance of the dissolved components for the analyzed waters issuing from the Emilia-Romagna sector of the foredeep. Waters issuing from the Tuscan side of the Apennines and from the Marche sector of the foredeep show higher 87Sr/86Sr ratios because of the interaction with siliciclastic rocks.  相似文献   

9.
《Applied Geochemistry》2004,19(4):519-560
The hydrogeochemistry of the Lac du Bonnet granitic batholith has been determined for the region of the Whiteshell Research Area (WRA) in southeastern Manitoba, Canada. This work forms part of the geosciences studies performed for the Canadian Nuclear Fuel Waste Management Program over the period 1980–1995 by Atomic Energy of Canada Limited (AECL). Knowledge of the variation of groundwater chemistry and its causes is useful in assessing the performance and safety of a nuclear fuel waste vault located at depths of up to 1000 m in a crystalline rock formation of the Canadian Shield. Groundwaters and matrix pore fluids have been obtained by standard sampling methods from shallow piezometers in clay-rich overburden, from packer-isolated borehole zones intersecting fractures or fault zones in the bedrock, and from boreholes in unfractured rock in AECL's Underground Research Laboratory (URL). Eighty-six individual fracture groundwaters have been sampled and analysed from permeable zones in 53 boreholes drilled to depths of up to 1000 m in the Lac du Bonnet batholith. In addition, 28 groundwaters from piezometers in a large wetland area near the URL have been sampled and analysed to determine the influence of clay-rich overburden on the bedrock hydrogeochemistry. Analyses have been made for major and minor ions, pH, Eh, trace metals, and stable and radioactive isotopes, to characterise these groundwaters and relate them to their hydrogeologic regimes. Shallow groundwaters in the fractured bedrock are generally dilute (TDS <0.3 g/l), Ca–Na–HCO3 waters and show little indication of mixing with Ca–Mg–HCO3–SO4 groundwater from overburden sediments. The near-modern levels of 3H and 14C, and a warm-climate 2H/18O signature in these groundwaters, indicates that the upper ∼200 m of fractured bedrock contains an active groundwater circulation system with a residence time of tens to hundreds of years. Deeper fracture groundwaters (200–400 m depth) in recharge areas, are more alkaline, Na–Ca–HCO3 waters and evolve to Na–Ca–HCO3–Cl–SO4 waters with increasing distance along the flow path. Isotopic data indicate the presence of a glacial melt-water component suggesting that the residence times of these waters are 103–105 a. These waters form a transition zone between the upper, advective flow regime and a deeper regime in sparsely fractured rock where groundwater in fractures and fracture zones is largely stagnant. At these depths (> 500 m), Na–Ca–Cl–SO4 waters of increasing salinity (up to 50 g/l) with depth are found and in some fractures the waters have evolved to a Ca–Na–Cl composition. Isotopic data indicate that these waters are warm-climate and pre-glacial in origin, with residence times of over 1 Ma. Pore fluids observed to drain from the unfractured rock matrix in the URL facility are almost pure Ca–Cl in composition, ∼90 g/l salinity, and have a 2H/18O composition displaced well to the left of the global meteoric water line, about which all other WRA groundwaters lie. This information indicates that these pore fluids have undergone prolonged water-rock interaction and have residence times of 101–103 Ma. Most of the deeper fracture groundwaters and pore fluids have low Br/Cl ratios and moderate to high δ34S values of dissolved SO4 which indicates that their salinity could be derived from a marine source such as the basinal sedimentary brines and evaporites to the west of the batholith. These fluids may have entered the batholith during early Paleozoic times when sedimentary rocks were deposited over the granite and were driven by a hydraulic gradient resulting from higher ground in western Canada. The hydrogeochemical data and interpretations show that below ∼500 m in the WRA, fracture-hosted groundwaters are very saline, reducing and old, and are, therefore, indicative of stagnant conditions over the period of concern for nuclear waste disposal (1 Ma). The intact rock matrix at these depths is extremely impermeable as indicated by the presence of pore fluids with unusual geochemical and isotopic characteristics. The pore fluids may represent basinal brines that have evolved geochemically and isotopically to their current composition over periods as long as 103 Ma.  相似文献   

10.
Interstitial brines from the Temblor and the McAdams sandstones at Kettleman are essentially NaCaCl solutions with subsidiary SO4 and the total salinities are roughly 30,000 and 10,000 ppm, respectively. Activities of H+ and all other aqueous species have been calculated for 100°C (the in situ temperatures of the brines) from chemical analyses of the brines and 100-degree dissociation constants alone. The brine alkalinities measured at surface temperature appear to be too low when comparing them against alkalinities calculated from the measured pHs of the brines. Consequently, alkalinities calculated for 25°C were substituted for the measured ones in the calculation of the distribution of aqueous species at 100°C.Although the brines are nearly neutral (pH 6·3–d7·9) at surface temperature, their pHs calculated for 100°C range from 8·1 to 8·7 (± 0·35). These pHs and the 100-degree activities of the other aqueous species permit graphic representation of the brines on activity diagrams. Most brines fall at or near the boundaries between the stability fields of quartz, albite, microcline, mica, montmorillonite and anhydrite. Because these minerals are present as authigenic phases in the sandstones, the calculations suggest that the minerals are in stable equilibrium with the brines. By contrast, the calculations suggest that the brines are supersaturated by about three orders of magnitude with respect to calcite, also present in the sandstones. One possible explanation for this is kinetic inhibition of calcite crystallization by Mg2+ and SO42? ions in the brines. Phosphatic pellets, glauconite and probably dolomite, pyrite and some kaolinite are early authigenic minerals preserved in the sandstones and they are not now in equilibrium with the brines, which are supersaturated with respect to dolomite and pyrite. The chemical relationship between the brines and the diagenetic minerals laumontite and sphene, also present in the Temblor Formation, cannot be assessed reliably until the thermodynamic properties of laumontite and of aqueous titanium complexes are well known.  相似文献   

11.
《Applied Geochemistry》2003,18(9):1297-1312
The concentrations of As in surface- and up to 90 °C ground waters in a tholeiite flood basalt area in N-Iceland lie in the range <0.03–10 μg/kg. With few exceptions surface waters contain <0.5 μg/kg As whereas ground waters generally contain >0.5 μg/kg As. The As content of ground waters increases on the whole with rising temperature. Arsenic is highly mobile in the basalt-water environment of the study area. An insignificant fraction of the As dissolved from the rock is taken up into secondary minerals. Arsenic is less mobile than B but considerably more mobile than Na which has the highest mobility among the major aqueous components. A significant fraction of the As in the basalt occurs in an easily soluble form. The As hosted in the primary minerals is expected to be concentrated in the titano-magnetite. This mineral is stable in contact with both surface- and ground waters and does not, therefore, supply As to the water, explaining the difference in mobility between As and B. Aqueous As concentrations are a reflection of water/rock ratios, i.e. how much rock a given quantity of water has dissolved. This ratio increases with increasing temperature and increasing residence time of the water in contact with the rock. The distribution of As species has been calculated on the assumption of equilibrium at the redox potential retrieved from measurement of aqueous Fe(II) and Fe(III) concentrations. These calculations indicate that pentavalent As is stable in surface waters and in ground waters with an in situ pH of <10 and would occur mostly as H2AsO4− and HAsO4−2. In higher pH ground waters the concentrations of the arsenite species H2AsO3− is significant at equilibrium, up to 65% of the total dissolved As.  相似文献   

12.
Saline groundwaters were recovered from undisturbed (Restigouche deposit) and active (Brunswick #12 mine) Zn-Pb volcanogenic massive sulfide deposits in the Bathurst Mining Camp (BMC), northern New Brunswick, Canada. These groundwaters, along with fresh to brackish meteoric ground and surface waters from the BMC, have been analyzed to determine their major, trace element and stable isotopic (O, H, C, and B) compositions. Saline groundwaters (total dissolved solids = 22-45 g/L) are characterized by relatively high Na/Ca ratios compared to brines from the Canadian Shield and low Na/Clmolar and δ11B isotopic compositions (−2.5‰ to 11.1‰) compared to seawater. Although saline waters from the Canadian Shield commonly have oxygen and hydrogen isotopic compositions that plot to the left of the global meteoric water line, those from the BMC fall close to the water line. Fracture and vein carbonate minerals at the Restigouche deposit have restricted carbon isotopic compositions of around −5‰ to −6‰. The carbon isotopic compositions of the saline waters at the Restigouche deposit (+12‰ δ13CDIC) are the result of fractionation of dissolved inorganic carbon by methanogenesis. We suggest that, unlike previous models for shield brines, the composition of saline waters in the BMC is best explained by prolonged water-rock reaction, with no requirement of precursor seawater. We suggest that elevated Br/Cl ratios of saline waters compared to seawater may be explained by differential uptake of Br and Cl during groundwater evolution through water-rock reaction.  相似文献   

13.
《Applied Geochemistry》2001,16(6):633-649
Water inflows in the Gotthard Highway Tunnel and in the Gotthard Exploration Tunnel are meteoric waters infiltrating at different elevations, on both sides of an important orographic divide. Limited interaction of meteoric waters with gneissic rocks produces Ca–HCO3 and Na–Ca–HCO3 waters, whereas prolonged interaction of meteoric waters with the same rocks generates Na–HCO3 to Na–SO4 waters. Waters circulating in Triassic carbonate-evaporite rocks have a Ca–SO4 composition. Calcium-Na–SO4 waters are also present. They can be produced through interaction of either Na–HCO3 waters with anhydrite or Ca–SO4 waters with a local gneissic rock, as suggested by reaction path modeling. An analogous simulation indicates that Na–HCO3 waters are generated through interaction of Ca–HCO3 waters with a local gneissic rock. The two main SO4-sources present in the Alps are leaching of upper Triassic sulfate minerals and oxidative dissolution of sulfide minerals of crystalline rocks. Values of δ34SSO4 < ∼+9‰ are due to oxidative dissolution of sulfide minerals, whereas δ34SSO4 >∼+9‰ are controlled either by bacterial SO4 reduction or leaching of upper Triassic sulfate minerals. Most waters have temperatures similar to the expected values for a geothermal gradient of 22°C/km and are close to thermal equilibrium with rocks. However relatively large, descending flows of cold waters and ascending flows of warm waters are present in both tunnels and determine substantial cooling and heating, respectively, of the interacting rocks. The most import upflow zone of warm, Na-rich waters is below Guspisbach, in the Gotthard Highway Tunnel, at 6.2–9.0 km from the southern portal. These warm waters have equilibrium temperatures of 65–75°C and therefore constitute an important low-enthalpy geothermal resource.  相似文献   

14.
Highly mineralized waters of different chemical types and origin occur in the flysch formations and their bedrocks in the western part of the Polish Carpathians. The marine sedimentation water of the flysch formations is not preserved, as the most mineralized and the heaviest isotopic values of flysch waters are characterized by δ18O and δ2H values in the ranges of 5–7‰ and −(20–30)‰, respectively. Their origin is related to the dehydration of clay minerals during burial diagenesis, with molecules of marine water completely removed by molecules of released bound water. They are relatively enriched in Na+ in respect to the marine water, supposedly due to the release of Na+ during the illitization of smectites and preferable incorporation of other cations from the primary brine into newly formed minerals. In some parts of younger formations, i.e. in the Badenian sediments, brines occur with isotopic composition close to SMOW and Cl− contents greatly exceeding the typical marine value of about 19.6 g/L, supposedly due to ultrafiltration. Most probably, the marine water of the flysch formations was similarly enriched chemically in its initial burial stages. Final Cl− contents in diagenetic waters depend on different Cl− contents in the primary brines and on relationships between diagenetic and further ultrafiltration processes. In some areas, diagenetic waters migrate to the surface along fault zones and mix with young local meteoric waters becoming diluted, with the isotope composition scattering along typical mixing lines. In areas with independent CO2 flow from great depths, they form chloride CO2-rich waters. Common CO2-rich waters are formed in areas without near-surface occurrences of diagenetic waters. They change from the HCO3–Ca type for modern waters to HCO3–Mg–Ca, HCO3–Na–Ca and other types with elevated TDS, Mg2+ and/or Na− contents for old waters reaching even those of glacial age. Bedrocks of the flysch are represented by Mesozoic and Paleozoic mudstones, sandstones and carbonates, and in some areas by Badenian sediments. Brines of the Mesozoic and Paleozoic bedrocks are usually significantly enriched in Ca2+ and Mg2+ in comparison with the Badenian brines. By analogy to the deepest brines in the adjacent Upper Silesian Coal Basin, they are supposed to originate from paleometeoric waters of a hot climate.  相似文献   

15.
Chemistry of major and minor elements, 87Sr/86Sr, δD, δ18O and δ34S of brines were measured from Tertiary strata and Quaternary salt lakes in the western Qaidam Basin. The water chemistry data show that all oilfield brines are CaCl2 type. They were enriched in Ca2+, B3+, Li+, Sr2+, Br−, and were depleted in Mg2+, SO4 2−, which indicated that these brines had the characteristics of deeply circulated water. The relationship between δD and δ18O shows that all data of these brines decline towards the Global Meteoric Water Line (GWL) and Qaidam Meteoric Water Line (QWL), and that the intersection between oilfield brines and Meteoric Water Lines was close to the local spring and fresh water in the piedmont in the western Qaidam Basin. The results suggest that oilfield brines has initially originated from meteoric water, and then might be affected by water-rock metamorphose, because most oilfield brines distribute in the range of metamorphosing water. The 87Sr/86Sr values of most oilfield brines range from 0.71121 to 0.71194, and was less than that in salt lake water (>0.712), but close to that of halite in the study area. These imply that salt dissolution occurred in the process of migration. In addition, all oilfield brines have obviously much positive δ34S values (ranging from 26.46‰ to 54.57‰) than that of salt lake brines, which was caused by bacterial sulfate reduction resulting in positive shift of δ34S value and depleteed SO4 2− in oilfield brines. Combined with water chemical data and δD, δ18O, 87Sr/86Sr, δ34S values, we concluded that oilfield brines mainly originate from the deeply circulated meteoric waters, and then are affected by salt dissolution, water-rock metamorphose, sulfate reduction and dolomitization during the process of migration. These processes alter the chemical compositions of oilfield brines and accumulate rich elements (such as B, Li, Sr, Br, K and so on) for sustainable utilization of salt lake resources in the Qaidam Basin.  相似文献   

16.
The Suzhou granite suite is the anorogenic product, which is located on the inactive continental margin of east China. It was emplaced about 141 Ma ago, occurring as a stock with a polygonal outline on the surface, belonging to alkali potash-feldspar granites with K2O > Na2O, Reit’s alkali coefficient = 0.694, SiO2 = 74.95, and Al2O3/(K2O + Na2O)mol= 1. Besides K and Na, Li and Rb are also rather high. Highlycharged metals such as Zr, Nb, REE, Y, Sn, Th, Ga and Zn are 10, or even 50 times higher than those in the ordinary granites. Halogen elements such as F and Cl are high in abundance with F = 2700 ppm and Cl = 170 ppm on average. The abundances of deep-source elements such as Ti, Al, Ca, Mg and P are relatively low, with A12O3 = 12.65% and Ca + Mg < 1%. High Ga and low Al contents are typomorphically characteristic of A type granites. Biotite in the rocks is, for the most part, annite, usually filling in quartz and feldspar crystals, indicating that the crystallization of magma proceeded under relatively anhydrous condition. More than 40 kinds of accessory minerals have been identified, of which the mantle-derived mineral chrompicotite and moissanite is of great interest. Two different intrusions, the major and supplementary intrusions, can be distinguished in the granite suite. The rock-forming temperature is estimated to be 810°C, pressure 2.5 kbars, pH 8.1,18O/16O low(δ18OWR = 6.19‰), andfo2= 10−16. The abundances of REE are high and Eu depletion is remarkable (δEu = 0.24). A variety of mineral deposits related to the Suzhou granite suite have been recognized.  相似文献   

17.
《Applied Geochemistry》1988,3(2):185-203
Chemical and isotopic analyses of water from drill holes and mines throughout the Fennoscandian Shield show that distinct layers of groundwater are present. An upper layer of fresh groundwater is underlain by several sharply differentiated saline layers, which may differ in salinity, relative abundance of solutes, and O, H, Sr and S isotope signature. Saline groundwater can be classified into four major groups based on geochemistry and presumed origin. Brackish and saline waters from 50–200 m depth in coastal areas around the Baltic Sea exhibit distinct marine chemical and isotopic fingerprints, modified by reactions with host rocks. These waters represent relict Holocene seawater. Inland, three types of saline groundwater are observed: an uppermost layer of brackish and saline water from 300–900 m depth; saline water and brines from 1000–2000 m depth; and superdeep brines which have been observed to a depth of at least 11 km in the drill hole on the Kola Peninsula, U.S.S.R. Electrical and seismic studies in shield areas suggest that such brines are commonly present at even greater depths. The salinity of all inland groundwaters is attributed predominantly to water-rock interaction. The main solutes are Cl, Ca, Na and Mg in varying proportions, depending on the host rock lithology. The abundance of dissolved gases increases with depth but varies from site to site. The main gas components are N2, CH4 (up to 87 vol.%) and locally H2. The δ13C value for methane is highly variable (−25 to −46%), and it is suggested that hydrothermal or metamorphic gases trapped within the surrounding rocks are the most obvious source of CH4. The uppermost saline water has meteoric oxygen-hydrogen isotopic compositions, whereas values from deeper water plot above the meteoric water line, indicating considerably longer mean residence time and effective low temperature equilibration with host rocks. Geochemical and isotopic results from some localities demonstrate that the upper saline water cannot have been formed through simple mixing between fresh water and deep brines but rather is of independent origin. The source of water itself has not been satisfactorily verified although superdeep brines at least may contain a significant proportion of relict Precambrian hydrothermal or metamorphic fluids.  相似文献   

18.
Large quantities of highly saline brine flow from gas wells in the Marcellus Formation after hydraulic stimulation (“fracking”). This study assesses the composition of these flowback waters from the Marcellus shale in Pennsylvania, USA. Concentrations of most inorganic components of flowback water (Cl, Br, Na, K, Ca, Mg, Sr, Ba, Ra, Fe, Mn, total dissolved solids, and others) increase with time from a well after hydraulic stimulation. Based on results in several datasets reported here, the greatest concentration of Cl− in flowback water is 151,000 mg/L. For total Ra (combined 226Ra and 228Ra) in flowback, the highest level reported is 6540 pCi/L. Flowback waters from hydraulic fracturing of Marcellus wells resemble brines produced from conventional gas wells that tap into other Paleozoic formations in the region. The Br/Cl ratio and other parameters indicate that both types of brine formed by the evaporation of seawater followed by dolomitization, sulfate reduction and subsurface mixing with seawater and/or freshwater. Trends and relationships in brine composition indicate that (1) increased salt concentration in flowback is not mainly caused by dissolution of salt or other minerals in rock units, (2) the flowback waters represent a mixture of injection waters with highly concentrated in situ brines similar to those in the other formations, and (3) these waters contain concentrations of Ra and Ba that are commonly hundreds of times the US drinking water standards.  相似文献   

19.
《Applied Geochemistry》1998,13(5):651-671
Highly saline fluids were encountered during the German Continental Deep Drilling Project (KTB) from depths ranging between 2 and 3 km to about 9 km. The most reliable data were obtained from samples extracted during a long-term pumping test in the 4000-m deep KTB pilot hole. Some 460 m3 Ca–Na–Cl brines with about 68 g l−1 total dissolved solids (TDS) and some 270 m3 associated gases, mainly N2 and CH4 were pumped to the surface from the main fracture system situated near the bottom of the pilot hole. Geochemical and isotopic data support the hydraulic tests which suggest the presence of an open and large fluid reservoir at depth. The pumped fluids from this main fracture system were released from a deep reservoir situated at more than 5500 m depth which is hydraulically connected with the 9101 m deep KTB main hole, drilled some 250 m to the northeast of the pilot hole.While Ca and Sr contents of the extracted brines may be the result of water–rock interaction, Cl is most likely of external origin. The Cl is hypothesized to derive from geotectonic processes rather than to descending infiltration of paleo-seawater (evaporitic brines). The sampled fluids have probably migrated from a deeper reservoir to their present position since the Cretaceous–Tertiary period due to tectonic activity. However, several isotopic studies have identified an admixture of descending paleowaters down to more than 4000 m depth. The high 36Cl/Cl ratio of the fluids sampled during the long-term pumping test point to a host rock highly enriched in U–Th, unlike the sampled KTB country rocks. The fluid reservoir is believed to be in contact with the Falkenberg granite massif situated about 2 km to the E of the KTB holes, capable of supplying sufficient neutron flux for considerable subsurface production of 36Cl. The Na–Cl–(K-, SO4) precursor fluids of the Ca–Na–Cl brines were produced in the course of extensive tectonic processes since the Late Caledonian within the Bohemian Massif.  相似文献   

20.
Partition coefficients for the rare earth elements (REE) Ce, Sm and Tm between coexisting garnets and hydrous liquids have been determined at high pressure and temperatures (30 kbar and 1300 and 1500°C). Two synthetic systems were studied, Mg3Al2Si3O12-H2O and Ca3Al2Si3O12-H2O, in addition to a natural pyrope-bearing system.Deviations from Henry's Law behaviour occur at geologically relevant REE concentrations. At concentrations < 3 ppm Ce, < 12 ppm Sm, < 80 ppm Tm in pyrope and < 100 ppm Ce, < 250 ppm Sm, < 1000 ppm Tm in grossular (at 30 kbar and 1300°C), Dgarnet liquidREE increases as the REE concentration in the garnet decreases. At higher concentrations, DREE is constant. Dgrossular liquidREE also constant when the garnet contains less than about 2 ppm Sm or Tm. The REE concentration at which DREE becomes constant increases with increasing temperature, decreasing REE ionic radius and increasing Ca content of the garnet.Partitioning behaviour of Ce, Sm and Tm between a natural pyrope-rich garnet and hydrous liquid is analogous to that in the synthetic systems and substantiates the substitution model proposed by Harrison and Wood (1980).Values of DREEgarnet/liquid for which Henry's Law is obeyed are systematically higher for grossular than for pyrope (Dpyrope/liquid = 0.067(Ce), 0.108(Sm), 0.155(Tm) and Dgrossular/Liquid = 0.65(Ce), 0.75(Sm), 4.55(Tm).The implications of non-Henry's Law partitioning of REE for models of basalt petrogenesis involving garnet are far-ranging. Deviations from Henry's Law permit refinements to be made to calculated REE abundances once basic model parameters have been defined.  相似文献   

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