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1.
New data on the geochemistry and isotopic composition of chloride brines of the Siberian Platform are presented. The distribution of stable isotopes (2H, 18O, and 37Cl) in brines of the Tunguska, Angara-Lena, western part of the Yakutian and Olenek artesian basins and 87Sr/86Sr in brines of the western part of the Olenek artesian basin was studied in the context of the problem of genesis of highly mineralized groundwaters. Results of the study and comparative analysis of the geochemical and isotopic peculiarities of the Siberian Platform brines conform to the theory of brine formation through the interaction of connate waters with enclosing rocks.  相似文献   

2.
In this study, compositions and δ13C and δ2H isotopic values of hydrocarbon gases from 5 mines in the Witwatersrand basin, South Africa, support the widespread occurrence of microbially produced methane in millions of years-old fissure waters. The presence of microbial methane is, to a large extent, controlled by the geologic formations in which the gases are found. Samples from the Witwatersand Supergroup have the largest microbial component based on δ13C and δ2H signatures and CH4/C2+ values. Based on mixing between a microbial CH4 component and a more 13C-enriched and 2H-depleted C2+-rich end member, conservative estimates of the % contribution of microbial CH4 to the gas samples range from >90% microbial CH4 at Beatrix, Masimong, and Merriespruit, to between 5 and 80% microbial CH4 at Evander, and <18% microbial CH4 at Kloof. The Witwatersrand basin’s history of thermal alteration of organic-rich ancient sedimentary units suggests a thermogenic origin for this 13C-enriched end member. Alternatively, the potential for an abiogenic origin similar to hydrocarbon gases produced by water-rock interaction at other Precambrian Shield mines is discussed. Microbial methane is predominantly found in paleo-meteoric fissure waters with δ18O and δ2H values that fall on the meteoric waterline, and have temperatures between 30 to 40°C. In contrast, fissure waters with a larger component of nonmicrobial hydrocarbon gases show a trend towards more enriched δ18O and δ2H values that fall well above the meteoric waterline, and temperatures of 45 to 60°C. The enrichment in 18O and 2H in these samples, and their high salinity, are similar to the isotopic and compositional characteristics of saline groundwaters and brines produced by water-rock interaction at Precambrian Shield sites elsewhere. The reported 100 Ma ages of fissure waters from the Witwatersrand and Ventersdorp formations suggest that these microbial hydrocarbon gases are the product of in situ methanogenic communities in the deep subsurface of the Witswaterand basin. Small subunit ribosomal RNA genes were amplified using archaeal-specific primer sets from DNA extracts derived from several of these waters. Fissure waters with a high proportion of microbial methane also contained sequences resembling those of known methanogens.  相似文献   

3.
The discovery of layered, SO4-rich sediments on the Meridiani Planum on Mars has focused attention on understanding the formation of acid–saline lakes. Many salt lakes have formed in southern Australia where regional groundwaters are characterized by acidity and high salinity and show features that might be expected in the Meridiani sediments. Many (but not all) of the acid–saline Australian groundwaters are found where underlying Tertiary sediments are sulfide-rich. When waters from the formations come to the surface or interact with oxidised meteoric water, acid groundwaters result. In this paper examples of such waters around Lake Tyrrell, Victoria, and Lake Dey-Dey, South Australia, are reviewed. The acid–saline groundwaters typically have dissolved solids of 30–60 g/L and pH commonly <4.5. Many contain high concentrations of Fe and other metals, leached from local sediments. The combination of acidity and salinity also releases Ra. Around salt-lakes, these acidic waters often emerge at the surface in marginal spring zones where the low density (ρ ∼ 1.04) regional water flows out over the denser (ρ ∼ 1.16) lake brines. In the spring zones examined, large amounts of Fe are commonly precipitated. In a few places minerals of the alunite-jarosite family are formed which can trap many other metals, including Ra. The studied groundwater systems were discovered by U exploration programs following up radiometric anomalies related to this Ra. Evaporation concentrates the lesser soluble salts (gypsum and some halite) on the surface of the lakes. The lake brines contain most of the more soluble salts and form a column within the porous sediments which is held in place by hydrostatic forces around the salt-lake. These brines are near-neutral in pH.  相似文献   

4.
One of the probable mechanisms that controls the composition of highly mineralized chloride groundwaters is studied using physicochemical numerical simulations of equilibria in water–rock systems. Concentrated brines in the Olenek cryoartesian basin in the northeastern Siberian Platform are determined to be undersaturated with respect of major rock-forming minerals, which suggests that the metamorphosed sedimentary brines should have been diluted by meteoric waters during a certain evolutionary episode of the permafrost zone of the basin in the Late Pleistocene and Holocene.  相似文献   

5.
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   

6.
《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   

7.
Deuterium and O18 analyses were made on 25 formation-water samples from Miocene (Temblor Formation) and Eocene (McAdams Formation) reservoir rocks at Kettleman North Dome oil field, California, and on three surface water samples from Reef Ridge located about three miles to the west of the field. The δO18 values obtained generally increase with depth and most probably are due to temperature controlled exchange reactions with carbonate cement and dissolved carbonate species. The δD values obtained seem to be controlled primarily by the membrane behavior of shales modifying the assumed original values. The contribution of isotopic exchange between water and clays cannot be evaluated at present.The isotopic data support the conclusions based on a detailed study of geology, hydrodynamics, and formation water geochemistry (Kharaka, 1971) which indicate that:1. The Temblor Formation waters are probably meteoric in origin concentrated chemically and isotopically by shale membranes, and 2. The McAdams Formation waters were most probably obtained by squeezing the original interstitial marine connate waters of deposition from the underlying Mesozoic sediments.  相似文献   

8.
《Applied Geochemistry》1988,3(5):455-474
Formation waters in the Palo Duro Basin, Texas, U.S.A. fall into four major groups based on integrated chemical and isotopic characteristics: (1) interbed brines within the major Permian evaporite aquitard; these are the most chemically concentrated and18O-rich fluids in the basin, and are interpreted as evaporatively concentrated sea water which has been hydrologically isolated since the Permian; (2) brines below the salt on the eastern side of the basin have ClBr, divalent cation, and isotopic systematics indicating a mixture of evaporatively concentrated sea water and meteoric water of δD= −20‰; (3) brines below the salt on the western side of the basin have chemical and isotopic systematics suggesting a mixture of two pulses of meteoric water, one with δD= −20‰ and the other with δD= −55‰; and (4) waters above the salt have the isotopic composition of meteoric waters. Diagenetic alteration of the cation chemistry has occurred for brines within and below the salt. Aquifers below the salt on the eastern side are interpreted as having been charged with dense Permian evaporite brines which subsequently mixed in various amounts with a basin-wide pulse of Triassic meteoric water. On the western side the descending Triassic meteoric waters became saline by dissolution of halite and are currently mixing with a Tertiary pulse of meteoric water initiated by the Laramide uplift to the west. The hydrochemistry suggests flow on the western side of the basin and static conditions on the eastern side. An unrecognized, approximately N-S permeability restriction, or discontinuity in the potentiometric flow surface, is inferred for major aquifers in the central area of the basin.  相似文献   

9.
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10.
The Black Warrior Basin of the southeastern United States hosts one of the world’s most prolific and long-lived coalbed methane plays, and the wealth of experience in this basin provides insight into the relationships among basin hydrology, production performance, and environmental issues. Along the southeast margin of the basin, meteoric recharge of reservoir coal beds exposed in an upturned fold limb exerts a strong control on water chemistry, reservoir pressure, and production performance. Fresh-water plumes containing Na–HCO3 waters with low TDS content extend from the structurally upturned basin margin into the interior of the basin. Northwest of the plumes, coal beds contain Na–Cl waters with moderate to high-TDS content. Carbon isotope data from produced gas and mineral cements suggest that the fresh-water plumes have been the site of significant bacterial activity and that the coalbed methane reservoirs contain a mixture of thermogenic and late-stage biogenic gases.  相似文献   

11.
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12.
In the Niagara Peninsula of Southern Ontario, Canada, subeconomic occurrences of Mississippi Valley-type base metal assemblages are found in the petroliferous carbonate units of the Middle Silurian sedimentary succession. These units, which were deposited on the northwestern margin of the Appalachian Basin, were buried by about 2.4 km of Paleozoic sediments up to the time of the Appalachian orogeny. The sulphide minerals form 13 different assemblages and occur in veins, veinlets, vugs and stylolite seams. Distribution of the gangue minerals is irregular but the sulphide minerals display an overlapping vertical zonation. Although dolomite is more abundant in the Lockport Formation, the amount of dolomitization is not directly related to the degree of lead-zinc mineralization. The origin of the assemblages can be explained by a model that relates mineralization to the evolution of the Appalachian Basin. Minor quantities of sphalerite (in chert nodules) and pyrite (as framboids) precipitated during the early diagenetic stage. During later diagenesis, “hot” petroleum-bearing connate waters were expelled from sediments by compaction, and possibly later by the compressive forces of the Appalachian orogeny. As these waters moved outward and upward to zones of lower pressure, they became more saline and separated into liquid petroleum and connate brine phases. Petroleum, due to its lower density, preceded the general outward and upward movement of the connate brines to the basin margins. Here, the Middle Silurian carbonates of the Niagara Peninsula impeded the previous, relatively rapid flow, through the underlying clastics, and were locally enriched in petroleum as it moved into the immediately overlying Upper Silurian reservoirs. This petroleum provided source of reduced sulphur. During their passage, the connate brines probably leached metals from a variety of sediments of differing provenance. These metals precipitated as sulphides on reaching the zone of reduced sulphure. After uplift of the basin, the late Paleozoic strata were eroded and downward-moving meteoric groundwater leached metals, sulphates and carbonates from the host rocks. On reaching the reducing conditions of the water table, sulphides precipitated where the concentration of reduced sulphur was sufficiently high. This process, which is still continuing enables us to propose that many carbonate-hosted Pb-Zn deposits may have been enriched during periods of uplift.  相似文献   

13.
δD and δ18O values have been determined for fluid inclusions in 45 samples of Permian halite. The inclusions are enriched in 18O relative to the meteoric water line but are depleted in D relative to ocean water. Inclusions with the more positive δ-values coincide with the isotopic composition expected for evaporating sea water which follows a hooked trajectory on a δD-δ18O diagram. Inclusions with more negative δ-values may represent more highly evaporated sea water but probably reflect synsedimentary or diagenetic mixing of meteoric water with evaporite brines. The isotope systematics in these inclusions are sufficiently similar to those of a modern evaporite pan to indicate that Permian sea water was isotopically similar to modern sea water.Connate evaporite brines can have negative δ-values because of the probable hooked isotope trajectory of evaporating sea water and/or synsedimentary mixing of evaporite brines with meteoric waters. Subsurface formation waters composed of mixtures of remnant primary evaporite brines and later meteoric waters may be more common than previous isotopic evidence has suggested.  相似文献   

14.
Conjoint consideration of distribution of major, rare earth elements (REE) and Y (combined to REY) and of H, O, C, S, Sr isotopes reveals that four types of groundwater are distinguishable by their chemical composition presented by spider patterns. REY patterns indicate thermo-saline deep water and two types of shallow saline groundwaters. Presence of connate waters is not detectable. Sr isotope ratios distinguish three sources of Sr: fast and slow weathering of biotite and K-feldspar in Pleistocene sediments, respectively, and dissolution of limestones. δ13C(DIC) indicate dissolution of limestone under closed and open system conditions. Numerous samples show δ13C(DIC) > 13‰ which is probably caused by incongruent dissolution of calcite and dolomite. The brines from below 1,000 m represent mixtures of pre-Pleistocene seawater or its evaporation brines and infiltrated post-Pleistocene precipitation. The shallow waters represent mixtures of Pleistocene and Recent precipitation salinized by dissolution of evaporites or by mixing with ascending brines. The distribution of water types is independent on geologic units and lithologies. Even the Tertiary Rupelian aquiclude does not prevent salinization of the upper aquifer.  相似文献   

15.
The long-lived halogen radioisotopes 129I and 36Cl provide valuable information regarding the source of fluids in hydrocarbon systems and in localized areas where infiltration of younger meteoric water has occurred. Despite the utility of these two isotopes in providing time-signatures for fluid end-members, considerable uncertainty remains regarding the interpretation of “intermediate-age” waters in hydrologic systems. These waters are likely the result of the combination of two or more halogen sources at some time in the past, each with its own characteristic concentration and isotopic composition. In order to unravel the evolution of these “intermediate-age” waters, the effect that infiltration of meteoric water has on the isotopic composition of older formation waters is modeled. Also evaluated is the effect that the timing of dilution has on 129I and 36Cl signatures observed in the present, specifically, the hypothesis that halogen isotopic signatures imparted by the mixing of brine and meteoric waters early in the development of a sedimentary basin are quantitatively different from those imparted by the mixing of old brines with recent meteoric waters.  相似文献   

16.
The epigenetic Pb-Zn deposits of the southern Benue Valley (Nigeria) are localized within Cretaceous sediments of an intracontinental rift basin. Fluid inclusion studies of vein minerals from the Abakaliki and Ishiagu orebodies show that sphalerite and quartz were deposited at relatively low temperatures (102–175 °C), with ore-fluid salinity mostly in the range of 17–25 equiv. wt% NaCl. Trace-element contents of sphalerite and galena are also consistent with the low temperature of formation and epigenetic origin. On the basis of the geotectonic setting, the mode of occurrence and fluid-inclusion characteristics, mineralization is attributed to connate brines set into motion by a high geothermal gradient accompanying continental rifting. Mineral deposition was caused principally by rapid cooling due either to reaction with wall rocks or mixing with meteoric or descending water of low salinity.  相似文献   

17.
《Applied Geochemistry》1995,10(4):447-460
Brines in the Miocene formations of the Upper Silesian Coal Basin have isotopic composition close to SMOW, which identifies them as the connate marine water. However, controversies exist on the origin of brines in the Carboniferous formations. Isotopic and hydrochemical data exclude any relationship to marine water and enrichment by evaporation. The most common brine which occurs at great depths can be identified as the oldest infiltration in a very hot climate (δ18O ⋟ −2‰, δD ⋟ −20‰, Cl− content 34 to 140 g/L). This brine is free of SO42− and U, and rich in Ba2+ and226Ra. Its salinity is probably related to the leaching of evaporites and intensive weathering of rocks during the Rotliegendes.Other brines are difficult to identify because their isotopic contents are within the range of mixing between the oldest brine and the Quaternary waters (δ18O ⋟ 10‰, δD ⋟ 70‰). Isotopic and hydrochemical data allow identification of several occurrences of brine formed by meteoric water of a warm Tertiary climate, after the last marine transgression in the Tortonian. That brine is rich in SO42− and contains moderate contents of226Ra and U. Its salinity is thought to result from leaching of Miocene evaporites. Two other identified types of brines can be related to some infiltration periods before the last marine transgression. The sources in salinity of these 2 types remain unknown. Mining activity results in a common occurrence of mixed brines. When the Quaternary component dominates, its identification is easy from the isotopic composition, whereas the end brine component can ususally be identified by chosen ion ratios and the presence or lack of sulphates.  相似文献   

18.
Atacamite, a copper hydroxychloride, is an important constituent of supergene oxide zones of copper deposits in northern Chile, whereas in similar deposits elsewhere, it is rare. In Chile, it has generally been assumed to be a primary constituent of the supergene zones. There are two difficulties with this supposition. The first is that atacamite requires saline water for its formation, whereas supergene oxidation was caused by percolating, oxygenated meteoric water, mainly rainwater. The second is that atacamite dissolves rapidly or undergoes phase change when exposed to fresh water. Supergene enrichment of copper deposits in northern Chile extended over a long period, 44 to 9 Ma, being terminated by the onset of hyperaridity. During this period, there was at least intermittent rainfall, exposing previously formed atacamite to dissolution or phase change. Furthermore, atacamite-bearing oxide zones in several deposits are directly overlain by thick Miocene alluvial gravels; the stream waters that transported these gravels would have permeated the oxide zones. In some deposits, atacamite-bearing assemblages occur both in the oxide zones and in contiguous gravels. We suggest that atacamite-bearing oxide assemblages are more likely to have been a replacement of preexisting oxide phases after the onset of hyperaridity at about 9 Ma. A hyperarid climate made possible evaporation and concentration of chloride in meteoric waters. In this paper, we discuss another source of saline waters to modify oxide zones. Dewatering of the Domeyko Basin expelled brines along faults, some of which had earlier guided the location of porphyry deposits. At the Spence porphyry copper deposit, saline waters, which δD vs δ 18O isotope analyses identify as basinal brines, are presently rising through the deposit, then flowing away along the base of the covering gravels. Compositions of these waters lie within the stability fields of atacamite and brochantite, the two minerals that comprise the oxide zone. Evidence is presented for other porphyry deposits, Radomiro Tomic and Gaby Sur, that basinal brines may have been involved in the late formation of atacamite.  相似文献   

19.
《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   

20.
Thermal mineral waters and extractable geothermal energy are an important and still underestimated natural wealth of Bulgaria. Their diversity is due to the complex geological structure, intense neotectonic activity, and the resulting complex character of meteoric water circulation. Reproductive hydrogeothermal systems with low-mineralized thermal waters of meteoric origin and resrvoir temperatures ranging between 30 and 100 (maximum 120) °C occur in the southern and north-eastern part of the country. Their total reproductive potential is estimated at 14–15 m3s–1. In the northern part (Moesian platform), regional hydrogeothermal reservoir with connate (marine) and mixed (marine and meteoric) mineral waters and brines are identified, the temperatures varying from 40 to 140 (maximum 150) °C. Huge resources of geothermal energy with commercial importance are accumulated in them. The hydrogeothermal wealth of Bulgaria provides as important basis for the development of balneological and multi-seasonal tourism, bottling industries, geothermal heating of buildings and greenhouses, aquaculture and other related activities.  相似文献   

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