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1.
《Applied Geochemistry》1998,13(4):463-475
Strontium isotope ratios were measured on 13 rock, 18 leachate and 28 pore-water samples from the Milk River aquifer, the confining argillaceous formations, and the glacial till mantling the recharge area. Strontium isotope ratios (87Sr/86Sr) of pore waters from the aquifer, confining units, and the glacial till ranged from 0.7069 to 0.7082. The 87Sr/86Sr ratios in aquifer pore waters decrease with increasing distance from the aquifer recharge area, and this is interpreted to be the result of mixing and water–rock interaction within the aquifer.The solute composition of the recharging groundwater is modified by the local lithology, causing distinct geochemical patterns along different flow paths within the aquifer. Whole-rock 87Sr/86Sr ratios indicate that the shales and till are generally more radiogenic than the aquifer sandstone. The authigenic carbonate cements and rock-forming minerals comprising the major lithologic units had little apparent influence on the pore-water Sr chemistry. Carbonate cement leachates from the till and the aquifer sandstone are more radiogenic than those from the confining shale formations. Feldspar separates from the aquifer sandstone have relatively radiogenic Sr isotope ratios, whereas bentonites from the Milk River and Colorado Shale Formations have whole-rock and leachate Sr isotope ratios that are relatively unradiogenic. Ratios of most Milk River aquifer pore waters are lower than those of any leachates or whole rocks analyzed, except the bentonites.The 87Sr/86Sr ratios of exchangeable Sr in the bentonites are similar to ratios found in the more evolved pore waters. Simple rock–water interaction models calculated for the whole-rock, leachate, and exchangeable-ion/pore-water pairs indicate that ion exchange with bentonite clays within the Milk River and Colorado Shale Formations appears to influence the isotopic evolution of the pore-water Sr in each of these units. 相似文献
2.
《Quaternary Science Reviews》2007,26(11-12):1547-1556
A new method of permafrost dating with the cosmogenic radionuclide 36Cl is presented. In the first application, syngenetic ice wedges are dated using the ratio of 36Cl and Cl concentrations in ice as the signal. 36Cl is produced in the atmosphere by nuclear reactions of cosmic rays on argon. Stable chlorine enters the atmosphere from the oceans. Their ratio does not depend on chloride concentration in precipitations and on sublimation of snow. In situ production of 36Cl in permafrost ice via cosmic ray-induced reactions and neutron capture are calculated and the dating age limit is estimated as 3 million years. 36Cl/Cl ratios in permafrost samples from cape Svyatoy Nos (Laptev Sea coast), North-Eastern Siberia, are measured by accelerator mass spectrometry. Analysis of the first results and the calculated dates support the feasibility of the 36Cl permafrost dating method 相似文献
3.
Robert L Cullers Sambhudas Chaudhuri Bill Arnold Moon Lee Carlton W Wolf 《Geochimica et cosmochimica acta》1975,39(12):1691-1703
The REE (rare earth element) content of a wide variety of clay mineral groups have been analyzed using radiochemical neutron activation and have been found to be quite variable in absolute REE content (range of ∑REE = 5.4–1732) and less variable in relative REE content (range of chondritenormalized La/Lu = 0.9–16.5). The variable REE content of the clay mineral groups is probably determined by the REE content of the source rock from which the clay mineral was derived and not from the separate minerals in the rock.The clay-sized fractions of the Havensville and Eskridge shales of Kansas and Oklahoma have similar relative REE distributions and identical negative Eu anomaly size as the composite of NAS (N. American shales), but an absolute REE content (range of ∑REE = 46–348) that may differ significantly from the composite of NAS. The clay-sized fraction of samples from any given outcrop did not vary much in absolute or relative REE content, but samples from northern Oklahoma, probably composed of continental to near-shore marine sediments, have higher absolute REE contents and higher La/Lu ratios than samples of marine deposits in Kansas (e.g. mean ∑REE in Oklahoma = 248; mean ∑REE in Kansas = 69–116). The differencess in the REE content between samples in Oklahoma and Kansas may be caused by chemical weathering processes in the source area, exchange reactions in the environment of deposition, or diagenesis and do not appear to be a result of the different clay minerals.Most samples have Eu anomalies relative to chondrites (range of Eu/Sm ratios of samples = 0.035–1.17; chondrites = 0.35). Some montmorillonites and kaolinites are anomalous in Eu relative to the NAS (range of Eu/Sm ratios of samples = 0.056–0.21; NAS = 0.22). These anomalies may be inherited from source rocks with Eu anomalies originally produced by igneous processes, or they may be produced by chemical weathering processes in the source area. 相似文献
4.
《Applied Geochemistry》1991,6(4):447-464
Analytical data are presented for Cl, Br and I on a regional scale for the Milk River aquifer. The three halides show strikingly similar spatial distributions and are highly correlated. Concentrations are low in the freshwater portions of the aquifer but increase by as much as two orders of magnitude along the margins. However, halide ratios reach nearly constant values moving down-gradient, suggesting the dominance of a common subsurface source for these ions. Ratios of Cl/I and Cl/Br are less than those of seawater and fit an origin derived from the diagenesis of organic matter in the sediments. Halide ratios rule out leakage and/or diffusion from the underlying Colorado Group as a major influence on the chemistry; the favored hypothesis is altered connate seawater diffusing from low-permeability units within the Milk River Formation as the primary source of salts. This hypothesis of an internal source has important implications for solute sources in other aquifers affected by saline waters because it does not require the importation of a distant fluid.The129I/I ratio has a meteoric value in groundwater collected near the recharge area, but ratios for downflow waters are only 8–70% of this value. Due to the 16 Ma half-life of129I, these data indicate that most of the increase in dissolved I cannot derive from concentration of a meteoric source by ion filtration, but must have a subsurface origin. Concentrations of129I producedin situ by spontaneous fission of238U attain measurable levels only in the oldest waters sampled (ages≥ 105a), in which it may account for nearly 90% of the total dissolved129I concentration.Water ages based upon36Cl/Cl data range up to 2 Ma if uncorrected for any dilution by subsurface sources of dead Cl. If one assumes that the subsurface contributions of Cl contribute at least 90% of total Cl in the distal portion, then the36Cl-based ages are reduced to ∼ 1Ma, somewhat greater than those estimated by hydrodynamic modeling. 相似文献
5.
The isotopic composition of Sr has been measured in 73 formation-water samples from Paleozoic strata in the Illinois basin; 87Sr/86Sr ratios range from 0.7079 to 0.7108. With the exception of four samples, the waters are more radiogenic than corresponding Paleozoic sea-water values. The relatively narrow range of slightly elevated 87Sr/86Sr rations is uniformly distributed in waters throughout the stratigraphic column and in Silurian waters across the basin. Isotopic analyses of core samples from reservoir rocks show an absence of water-rock Sr isotopic equilibration. Basin lithology and analyses of detrital rock units indicate that clay minerals in shales and in quartz sandstone matrices represent the only significant source of radiogenic Sr for the waters. Silurian and Devonian water show a two-component mixing relation which suggests that they comprise a single hydrogeological system that evolved when radiogenic water from New Albany shales entered Silurian-Devonian carbonate rocks and mixed with marine interstitial water. Regional migration of the waters and associated petroleum within the Silurian-Devonian strata, proposed in other studies, is consistent with the Sr isotopic data. Under favorable circumstances subsurface waters are capable of retaining a Sr isotopic recor of their evolution. 相似文献
6.
G.J. Wasserburg J. Aléon A.N. Krot K. Nagashima 《Geochimica et cosmochimica acta》2011,75(17):4752-4770
We report on a study of Al3509, a large Na- and Cl-rich, radially-zoned object from the oxidized CV carbonaceous chondrite Allende. Al3509 consists of fine-grained ferroan olivine, ferroan Al-diopside, nepheline, sodalite, and andradite, and is crosscut by numerous veins of nepheline, sodalite, and ferroan Al-diopside. Some poorly-characterized phases of fine-grained material are also present; these phases contain no significant H2O. The minerals listed above are commonly found in Allende CAIs and chondrules and are attributed to late-stage iron-alkali-halogen metasomatic alteration of primary high-temperature minerals. Textural observations indicate that Al3509 is an igneous object. However, no residual crystals that might be relicts of pre-existing CAI or chondrule minerals were identified. To establish the levels of 26Al and 36Cl originally present, 26Al-26Mg and 36Cl-36S isotopic systematics in sodalite were investigated. Al3509 shows no evidence of radiogenic 26Mg∗, establishing an upper limit of the initial 26Al/27Al ratio of 3 × 10−6. All sodalite grains measured show large but variable excesses of 36S, which, however, do not correlate with 35Cl/34S ratio. If these excesses are due to decay of 36Cl, local redistribution of radiogenic 36S∗ after 36Cl had decayed is required. The oxygen-isotope pattern in Al3509 is the same as found in secondary minerals resulting from iron-alkali-halogen metasomatic alteration of Allende CAIs and chondrules and in melilite and anorthite of most CAIs in Allende. The oxygen-isotope data suggest that the secondary minerals precipitated from or equilibrated with a fluid of similar oxygen-isotope composition. These observations suggest that the formation of Al3509 and alteration products in CAIs and chondrules in Allende requires a very similar fluid phase, greatly enriched in volatiles (e.g., Na and Cl) and with Δ17O ∼ −3‰. We infer that internal heating of planetesimals by 26Al would efficiently transfer volatiles to their outer portions and enhance the formation of volatile-enriched minerals there. We conclude that the site for the production of Na- and Cl-rich fluids responsible for the formation of Al3509 and the alteration of the Allende CAIs and chondrules must have been on a protoplanetary body prior to incorporation into the Allende meteorite. Galactic cosmic rays cannot be the source of the inferred initial 36Cl in Allende. The problem of 36Cl production by solar energetic particle (SEP) bombardment and the possibility that 36Cl and 41Ca might be the product of neutron capture resulting from SEP bombardment of protoplanetary surfaces are discussed. This hypothesis can be tested comparing inferred “initial” 36Cl with neutron fluencies measured on the same samples and on phases showing 36S∗ by Sm and Gd isotopic measurements. 相似文献
7.
《Applied Geochemistry》2005,20(3):599-609
36Cl produced by thermonuclear bomb testing has been proposed as an additional tool to date or at least to identify recent groundwater components. In order to investigate the behaviour of 36Cl in shallow groundwater a multi-tracer approach (3H/3He, SF6, CFC-12 and 85Kr) was used to characterise and date the groundwater of a quaternary sands aquifer which is located on the Island of Funen near the city of Odense, Denmark. Recharge to the semi-confined shallow aquifer occurs through permeable sand windows and fractured tills at the surface. Locally, however, mixing with older pre-bomb water from the underlying limestone aquifer may occur. The integrated analyses of the available tracer data allowed a well constrained age structure determination of the investigated water system.The 36Cl/Cl ratios measured in groundwater were used to reconstruct the fallout rates for radioactive 36Cl at Odense. The calculated fallout values exceeded the fallout estimated based on data from the Dye-3 ice core in Greenland. Recycling of the bomb peak fallout seems to be the most probable reason of the high values measured. The local extent of this process is difficult to quantify, which impedes the use of 36Cl for dating. 相似文献
8.
《Applied Geochemistry》1991,6(4):435-445
The36Cl/Cl ratios of 12 groundwater samples from the Milk River aquifer were determined by accelerator mass spectrometry. Using known Cl concentrations,36Cl concentrations were deduced. Approximately linear relations were observed between the logarithm of the36Cl concentration, the Cl concentration, and the distance from the recharge area along two flow paths. The results are discussed in two approaches:
- (1)in an interpretation of the linear relation between logarithm of the36Cl concentration and Cl concentration excluding and includingin situ production of36Cl;
- (2)in a diffusion model. The increase of the Cl concentration with the distance from the recharge area is considered to be due to diffusion of Cl from the underlying confining Colorado shale to the aquifer.
9.
The South Alligator uranium deposits are located in the Northern Territory, Australia, south-west from the recent discoveries of Nabarlek, Ranger, Koongarra and Jabiluka. All five deposits occur in intensely folded Early Proterozoic rocks around the perimeter of the Kombolgie Formation, a flatlying Middle Proterozoic sandstone unit. It is proposed that during reconstitution (weathering or diagenesis) of acid volcanic rocks, groundwaters leached uranium and percolated down into the groundwater system of the permeable sandstone and conglomerate unit at the base of the sequence. Uranium as uranyl ion was stable in relatively high Eh groundwater conditions and was carried in solution until active reducing conditions were met with which resulted in reduction of uranyl ion to insoluble UO2. Reduction occurred where faulting had brought underlying carbonaceous shales up against the sandstone aquifer, or where groundwater could percolate down permeable fault zones into the carbonaceous shales. These structural, chemical traps were sites of uranium accumulation. 相似文献
10.
Usama A. Abu Risha 《Hydrogeology Journal》2016,24(4):987-1000
The use of 14C (half-life?=?5,730 years) in modeling the evolution of the 36Cl/Cl ratios in groundwater is reported for the first time. The complexity of the Cl–36Cl system due to the occurrence of different Cl and 36Cl sources and the difficulty of the determination of the initial groundwater 36Cl/Cl ratios have raised concerns about the reliability of using 36Cl (half-life?=?301 thousand years, a) as a groundwater-dating tool. This work uses groundwater 14C age as a calibrating parameter of the Cl–36Cl/Cl decay-mixing models of three wells from the southwestern Great Artesian Basin (GAB), Australia. It aims to allow for the different sources of Cl and 36Cl in the southwestern GAB aquifer. The results show that the initial Cl concentrations range from 245 to 320 mg/l and stable Cl is added to groundwater along flowpaths at rates ranging from 1.4 to 3.5 mg/l/ka. The 36Cl content of the groundwater is assumed to be completely of atmospheric origin. The samples have different Cl–36Cl/Cl mixing-decay models reflecting recharge under different conditions as well as the heterogeneity of the aquifer. 相似文献
11.
In the Pine Creek Geosyncline, fast moving, annually recharged, low-salinity ground waters dissolve uranium- and magnesium-enriched gangue minerals from mineralized aquifer rocks. The level of dissolved uranium depends on prevailing pH, Eh, salinity and degree of adsorption, which limits its effectiveness as an exploration indicator. Near each known deposit, leaching of magnesium-enriched gangue minerals produces ground waters with very similar major-element concentration plots, the shape of which constitutes a mineralized aquifer “signature”. Gangue minerals also supply high levels of Mg2+ (expressed as NMg = [Mg2+]/[Ca2+ + Mg2+ + Na+ + K+] in milliequivalents per litre) to contained ground waters, NMg > 0.8 being common in ground waters from mineralized aquifers at each Pine Creek Geosyncline deposit. Data from Ranger One No. 3 ore body illustrates how progressive mixing of waters from mineralized and unmineralized aquifers causes graded reductions in NMg, which, when plotted onto a ground plan, delineate a hydrogeochemical aureole.High NMg (> 0.8) coincides with high uranium concentration (> 20 μg/l of U) in ground waters near Nabarlek and Ranger. Because pH-Eh conditions in aquifers at Jabiluka depress uranium solution, < 10 μg/l of U is present, although NMg values are generally > 0.8. To date NMg has always been < 0.8 in nonmineralized aquifer waters, whereas uranium may be > 50 μg/l in ground waters from felsic igneous aquifers, which can be identified as uneconomic by low (< 0.4) NMg, and by a fixed relationship between uranium and co-leached species such as F- and soluble salts.Measurements of pH, Eh, salinity, Fe(II), Ca, Mg, Na, K, Cl, SO4, total carbonate, phosphate, F-, Cu, Pb, Zn and U in waters from 48 percussion holes in and near the Koongarra ore bodies have been related to mineralogy recorded in drill logs. The composition of waters from 20 holes near and along strike from known mineralization, fitted the mineralized aquifer “signature”, had NMg > 0.8 and uranium up to 4100 μ/l. These data confirm the use in this region of NMg as a hydrogeochemical indicator of uranium mineralization; they also indicate additional zones of possible mineralization. 相似文献
12.
Corrected groundwater 14C ages from the carbonate aquifer in Yucca Flat at the former Nevada Test Site (now the Nevada National Security Site), USA, were evaluated by comparing temporal variations of groundwater 36Cl/Cl estimated with these 14C ages with published records of meteoric 36Cl/Cl variations preserved in packrat middens (piles of plant fragments, fecal matter and urine). Good agreement between these records indicates that the groundwater 14C ages are reasonable and that 14C is moving with chloride without sorbing to the carbonate rock matrix or fracture coatings, despite opposing evidence from laboratory experiments. The groundwater 14C ages are consistent with other hydrologic evidence that indicates significant basin infiltration ceased 8,000 to 10,000 years ago, and that recharge to the carbonate aquifer is from paleowater draining through overlying tuff confining units along major faults. This interpretation is supported by the relative age differences as well as hydraulic head differences between the alluvial and volcanic aquifers and the carbonate aquifer. The carbonate aquifer 14C ages suggest that groundwater velocities throughout much of Yucca Flat are about 2 m/yr, consistent with the long-held conceptual model that blocking ridges of low-permeability rock hydrologically isolate the carbonate aquifer in Yucca Flat from the outlying regional carbonate flow system. 相似文献
13.
14.
The 36Cl dating method is increasingly being used to determine the surface-exposure history of Quaternary landforms. Production rates for the 36Cl isotopic system, a critical component of the dating method, have now been refined using the well-constrained radiocarbon-based deglaciation history of Whidbey and Fidalgo Islands, Washington. The calculated total production rates due to calcium and potassium are 91±5 atoms 36Cl (g Ca)−1 yr−1 and are 228±18 atoms 36Cl (g K)−1 yr−1, respectively. The calculated ground-level secondary neutron production rate in air, Pf(0), inferred from thermal neutron absorption by 35Cl is 762±28 neutrons (g air)−1 yr−1 for samples with low water content (1–2 wt.%). Neutron absorption by serpentinized harzburgite samples of the same exposure age, having higher water content (8–12 wt.%), is 40% greater relative to that for dry samples. These data suggest that existing models do not adequately describe thermalization and capture of neutrons for hydrous rock samples. Calculated 36Cl ages of samples collected from the surfaces of a well-dated dacite flow (10,600–12,800 cal yr B.P.) and three disparate deglaciated localities are consistent with close limiting calibrated 14C ages, thereby supporting the validity of our 36Cl production rates integrated over the last 15,500 cal yr between latitudes of 46.5° and 51°N. Although our production rates are internally consistent and yield reasonable exposure ages for other localities, there nevertheless are significant differences between these production rates and those of other investigators. 相似文献
15.
《Applied Geochemistry》1993,8(6):643-647
Mazor (1992) has reinterpreted several previous 36Cl studies. The studies he revised used extensive physical hydrogeological data to aid in interpretation of the 36Cl measurements. Major ion chemistry and other isotope tracers were considered in order to evaluate the groundwater geochemistry. The studies then used simple geochemical models to account for Cl behavior in the subsurface. The result of these 36Cl dating studies was in reasonable agreement with both numerical models of the aquifer systems and with independent geochemical studies.Mazor (1992) has reinterpreted these studies based on the assumption that spatial variation in chemical and isotope data should be attributed to unspecified “discontinuities” in the flow regime. The conceptual models of aquifer hydrodynamics resulting from this approach differ radically not only from the previous 36Cl interpretations, but also from the findings of virtually all previous hydrogeological and geochemical investigations. Although Mazor's “reinterpretations” are provocative, he does not show how they explain the data of the numerous previous studies better than the conceptual models presented by the authors of those studies, nor has he demonstrated that his new models are consistent with the fundamental physical laws governing groundwater flow. Until this is satisfactorily accomplished I will continue to prefer the original 36Cl interpretations. 相似文献
16.
M. -Z. Min X. -Z. Luo S. -L. Mao Z. -Q. Wang R. C. Wang L. -F. Qin X. -L. Tan 《Ore Geology Reviews》2001,17(4)
A fossil wood cell texture with pitchblende and coffinite found at a sandstone-hosted roll-type uranium deposit, Xinjiang, NW China, is first reported here for the country. In the mineralized sandstone, detrital grains consisting of quartz, feldspar, rock fragments, carbonaceous trashes, mica and accessory minerals were deposited in early Turassic time and were cemented by clays and minor authigenic calcite and quartz. Pitchblende and minor coffinite are principal ore minerals at the deposit, and selectively replaced carbonized fossil wood remnants or filled fossil wood cells. An excellent fossil wood cell texture with primary uranium minerals formed. Replacement of organic debris by primary uranium minerals may be due to a local reducing environment resulting from the production of CH4, H2S or H2SO3 in its decomposition, and a biochemical reaction indicated by the common presence of framboidal pyrite. 相似文献
17.
Mazor (1992) has reinterpreted several previous 36Cl studies. The studies he revised used extensive physical hydrogeological data to aid in interpretation of the 36Cl measurements. Major ion chemistry and other isotope tracers were considered in order to evaluate the groundwater geochemistry. The studies then used simple geochemical models to account for Cl behavior in the subsurface. The result of these 36Cl dating studies was in reasonable agreement with both numerical models of the aquifer systems and with independent geochemical studies.Mazor (1992) has reinterpreted these studies based on the assumption that spatial variation in chemical and isotope data should be attributed to unspecified “discontinuities” in the flow regime. The conceptual models of aquifer hydrodynamics resulting from this approach differ radically not only from the previous 36Cl interpretations, but also from the findings of virtually all previous hydrogeological and geochemical investigations. Although Mazor's “reinterpretations” are provocative, he does not show how they explain the data of the numerous previous studies better than the conceptual models presented by the authors of those studies, nor has he demonstrated that his new models are consistent with the fundamental physical laws governing groundwater flow. Until this is satisfactorily accomplished I will continue to prefer the original 36Cl interpretations. 相似文献
18.
贵州铜仁坝黄磷矿中铀赋存状态的逐级化学提取研究 总被引：1，自引：1，他引：0
贵州铜仁坝黄磷块岩矿床富集放射性元素铀,利用逐级化学提取分析方法对该地区黄磷矿中铀的赋存状态进行探究,有助于进一步探讨磷块岩型铀矿的分布规律、成矿机理及铀资源的综合开发。本文采用经修改的Tessier法流程,提取了水溶态、可交换离子态、碳酸盐结合态、铁锰氧化物结合态、有机质黄铁矿态、强酸提取态和残渣态等七种不同形态的铀。研究发现:黄磷矿中的铀主要以独立铀矿物和类质同象置换的形式存在,分别占37.83%、37.21%,少量铀(占24.96%)以分散吸附形式存在。分析表明:独立铀矿物在富磷、黄铁矿脉和镜面擦痕发育的岩层中含量较高,说明热液活动有利于独立矿物形式铀的富集;类质同象铀与黄磷矿中的磷含量呈正相关关系,铀元素可能是以离子置换的方式赋存于胶磷矿的晶格缺陷中;吸附形态铀的含量受到岩石中黏土矿物含量和黄铁矿脉的影响,有机质黄铁矿态是吸附形态铀存在的主要方式,少量铀通过扩散作用吸附于黏土矿物表面。除类质同象铀因其存在形式不易被提取利用外,独立铀矿物及吸附形态铀对于未来优化资源配置具有现实意义。 相似文献
19.
Fluid inclusion microthermometry, Raman spectroscopy and noble gas plus halogen geochemistry, complemented by published stable
isotope data, have been used to assess the origin of gold-rich fluids in the Lachlan Fold Belt of central Victoria, south-eastern
Australia. Victorian gold deposits vary from large turbidite-hosted ‘orogenic’ lode and disseminated-stockwork gold-only deposits,
formed close to the metamorphic peak, to smaller polymetallic gold deposits, temporally associated with later post-orogenic
granite intrusions. Despite the differences in relative timing, metal association and the size of these deposits, fluid inclusion
microthermometry indicates that all deposits are genetically associated with similar low-salinity aqueous, CO2-bearing fluids. The majority of these fluid inclusions also have similar 40Ar/36Ar values of less than 1500 and 36Ar concentrations of 2.6–58 ppb (by mass) that are equal to or much greater than air-saturation levels (1.3–2.7 ppb). Limited
amounts of nitrogen-rich fluids are present at a local scale and have the highest measured 40Ar/36Ar values of up to 5,700, suggesting an external or distinct source compared to the aqueous fluids. The predominance of low-salinity
aqueous–carbonic fluids with low 40Ar/36Ar values, in both ‘orogenic’ and ‘intrusion-related’ gold deposits, is attributed to fluid production from common basement
volcano-sedimentary sequences and fluid interaction with sedimentary cover rocks (turbidites). Aqueous fluid inclusions in
the Stawell–Magdala deposit of western Victoria (including those associated with N2) preserve mantle-like Br/Cl and I/Cl values. In contrast, fluid inclusions in deposits in the eastern structural zones, which
contain more abundant shales, have elevated molar I/Cl ratios with maximum values of 5,170 × 10−6 in the Melbourne Zone. Br/I ratios in this zone range from 0.5 to 3.0 that are characteristic of fluid interaction with organic-rich
sediments. The maximum I/Cl and characteristic Br/I ratios provide evidence for organic Br and I released during metamorphism
of the shales. Therefore, the regional data provide strong evidence for the involvement of sedimentary components in gold
mineralisation, but are consistent with deeper metamorphic fluid sources from basement volcano-sedimentary rocks. The overlying
sediments are probably involved in gold mineralisation via fluid–rock interaction. 相似文献
20.
Hydrogeochemical processes affecting groundwater in an irrigated land in Central Tunisia 总被引：7，自引：4，他引：3
Intissar Farid Rim Trabelsi Kamel Zouari Kamel Abid Mohamed Ayachi 《Environmental Earth Sciences》2013,68(5):1215-1231
Detailed hydrogeochemical investigation has provided new information concerning the major factors and mechanisms controlling the groundwater chemistry of Chougafiya basin. The hydrogeochemical characteristics of groundwaters comprise three main types: Cl–SO4–Ca, Cl–SO4–Na and Cl–Na. Hydrochemical characteristics based on the bivariate diagrams of major (Cl?, SO4 2?, NO3 ?, HCO3 ?, Na+, Mg2+, K+ and Ca2+) and some trace (Br? and Sr2+) ions, mineral saturation indices and hierarchical cluster analysis indicate different origins of groundwater mineralization. The water–rock interaction (dissolution of evaporitic minerals), followed by cation exchange reactions with clay minerals, constitute the main processes that control groundwater salinization. However, the chemical composition of brackish groundwater in the central and southern parts of the study area is influenced by a mixing process with Sabkhas salt groundwater. The mixing proportions inferred from chloride mass balance prove that the contribution of Sabkhas groundwater to Quaternary aquifer ranges between 2.7 and 9.1 %. These intrusion rates reflect the progress of the saltwater–freshwater interface, which is mainly controlled by the piezometric level variation and the distance to the Sabkhas. 相似文献