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1.
On the south-eastern edge of Russia, the chemical composition of rainwater is controlled by sea salts, terrestrial material, as well as volcanic (Kuril islands volcanic area) and anthropogenic emissions, mostly in the southern part of the area. The predominant major ions of the Primorye, Sakhalin and the Kuril Islands rainwaters were respectively HCO3−–SO42−, Ca–Na, and of Cl–Na. Concentration of trace elements changes within 1–2 orders of magnitude but some difference in the distribution of the elements between continental and island rainwater is found. The concentration of the chemical elements in the particulate fraction varies from < 10% to 90% of the total concentration (dissolved + particulate) with the following distribution: Tl, Na, Ca, Sr, Zn, Cd (< 10%)–Be, Th, Bi, Rb, U, K, Sc (10–20%)–Cu, Mn, Mg, Mo, Se, Ba, Ni, As, Ag, Cs, Co, Y, Ga, V (20–50%)–Sb, Pb, Ge, Cr, Fe, Al (50–90%).The concentration of elements of the particulate fraction of the rainwater usually is significantly different from concentrations in the crust, including both higher and lower concentrations. The terrestrial contribution to dissolved elements was evaluated and follows the decreasing order: Fe > K, Mg, Ca > Ba, Sr > Na (65–1%). Close order was found for total (dissolved and solid) concentrations. Sea salt contribution to dissolved element concentration in the rainwater decrease in the following order: Cl, Mg > K, SO4 > Ca > HCO3−, Ba, Fe (78–0.1%). Calculation of anthropogenic and volcanic inputs for two ions (Cl− and SO42−) shows that anthropogenic inputs for the Vladivostok and Yuzno-Sakhalinsk cities can be evaluated as 15–20% of Cl− and up to 80–90% of SO42−. Volcanic components in the Kuril Islands, where anthropogenic inputs are absent, can reach up to 76% of SO42− and 36% of Cl−.  相似文献   

2.
For a period of 2 a, pore water composition in a heavily contaminated river floodplain soil was monitored in situ. Pore water samples were collected 12 times over all seasons in a profile ranging from aerobic to sulphidic redox conditions, and As, Cd, Cr, Cu, Pb, Zn, Mn, Fe, Ca, Cl, SO4, DOC, IOC and pH were determined. The variability of pH, IOC, DOC and Ca was found to be rather small during the year and within the profile (rsd < 0.04, 0.16, 0.24 and 0.22, respectively). The temporal variability of the metal and As concentrations was small, too, whereas changes with depth were distinct. Under sulphidic conditions, concentrations were below 1 μg L−1 (Cd, Cu, Pb) or 10 μg L−1 (Zn, As). The data set was compared with results from a geochemical model that was fully parameterised from literature data and included equilibrium speciation, sorption and mineral dissolution. The general pattern of the solid–solution partitioning of Cd, Cu, Zn and As in the profile was predicted well by mechanistic geochemical modelling on the basis of solid phase composition. Metals strongly bound to organic matter such as Cd and Cu were predicted better than metals mainly present within a mineral. Detailed information regarding the presence of colloidal Fe and Mn in pore water might improve the prediction of the solid–solution partitioning of a number of metals. The study also indicates that the chemical behaviour of Pb is still not understood sufficiently.  相似文献   

3.
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   

4.
Chemical and isotope studies of natural CO2 accumulations aid in assessing the chemical effects of CO2 on rock and thus provide a potential for understanding the long-term geochemical processes involved in CO2 geological storage. Several natural CO2 accumulations were discovered during gas and oil exploration in France’s carbogaseous peri-Alpine province (south-eastern France) in the 1960s. One of these, the Montmiral accumulation at a depth of more than 2400 m, is currently being exploited. The chemical composition of the water collected at the wellhead has changed in time and the final salinity exceeds 75 g/L. These changes in time can be explained by assuming that the fraction of the reservoir brine in the recovered brine–CO2–H2O mixture varies, resulting in variable proportions of H2O and brine in the sampled water. The proportions can be estimated in selected samples due to the availability of gas and water flowrate data. These data enabled the reconstruction of the chemical and isotope composition of the brine. The proportions of H2O and brine can also be estimated from isotope (δ2H, δ18O) composition of collected water and δ18O of the sulfates or CO2. The reconstituted brine has a salinity of more than 85 g/L and, according to its Br− content and isotope (δ2H, δ18O, δ34S) composition, originates from an evaporated Triassic seawater that underwent dilution by meteoric water. The reconstitution of the brine’s chemical composition enabled an evaluation of the CO2–water–rock interactions based on: (1) mineral saturation indices; and (2) comparison with initial evaporated Triassic seawater. Dissolution of K- and SO4-containing minerals such as K-feldspar and anhydrite, and precipitation of Ca and Mg containing minerals that are able to trap CO2 (carbonates) are highlighted. The changes in concentration of these elements in the brine, which are attributed to CO2 interactions, illustrate the relevance of monitoring the water quality at future industrial CO2 storage sites.  相似文献   

5.
87Sr/86Sr ratios of brine from samples from the Michigan and Appalachian Basins, in Ontario and Michigan, covering the stratigraphic interval from the Cambrian to Mississippian, vary from 0.708 to 0.711. With the exception of the salt units of the Salina Formation (Silurian), most values are greater than seawater for the time in question, indicating water-rock interaction. The sources of the radiogenic Sr has not been identified. All samples plot below the GMWL in δ18O−δ2H space, with the Cambrian and Ordovician samples closest to the line. Mixing of brines meteoric and glacial (Pleistocene) water is indicated in some cases. The more concentrated brines from each stratigraphic unit show a very narrow spread in values. All the Ordovician brines show a narrow range over a 200 km area for Sr, O and H isotopes, indicating extensive lateral migration of the fluids.Strontium in the brine has not equilibrated isotopically with its host rock. In some cases the late-stage minerals saddle dolomite, calcite and anhydrite have the same 87Sr/86Sr ratios as the brine, indicating that they precipitated from the brine in isotopic equilibrium.  相似文献   

6.
Lead-and zinc-rich oil field brines from lowermost Cretaceous formations in central Mississippi locally contain geochemically significant levels of trace metals that are found in several types of sediment-hosted metallic mineral deposits, providing additional support for the genetic link between sedimentary formation waters and these deposits. Copper content of brine samples from Lower Cretaceous formations ranges from < 0.02 mg 1−1 to 0.37 mg 1−1, and silver was detected in 2 samples with a maximum value of 0.021 mg 1−1. Cobalt values range from <0.04 mg 1−1 to 0.22 mg 1−1, and molybdenum is present in the range of <0.03 mg 1−1 to 0.05 mg 1−1. Gold, platinum, and palladium were not found at levels above their respective lower detection limits of 0.0001 mg 1−1, 0.003 mg 1−1, and 0.002 mg 1−1 for the graphite furnace AA procedure used. Comparison of the results from this study to recent published studies of trace-metal solubilities in chloride-rich hydrothermal solutions suggests that the brines are approximately saturated with respect to Pb, Zn and Fe, and apparently are undersaturated with respect to Au, Pt, Pd, Sb, Co and probably Ag. The composite effects of the reduced sulfur content and physicochemical characteristics of the brines (i.e., salinity, temperature, redox state and pH), along with formation metal sources and brine migration history, apparently control the observed present-day concentrations of trace metals in Mississippi oil field brines.  相似文献   

7.
The geochemistry of 5 salt springs in the southwestern Mamfe Basin was investigated in order to infer the mineral content of their source and to relate the genesis of the springs to the local geology. Field observations revealed that, they are cold springs (23–28 °C), and are composed of secondary brines that are neutral to alkaline with pH values ranging from 7 to 8.7. Results of chemical analysis show that the springs contain major ions that form evaporite minerals, as well as chalcophile elements. The dominant cation is Na+ (>96%), and the dominant anion is Cl− (>99%). Based on correlation coefficients between ions that form evaporites and field occurrence of efflorescences of halite, it is suggested that the ancient evaporites in the Mamfe Basin are composed entirely of carbonate and chloride salts. Meteoric and convective fluid flow processes are responsible for the dissolution of ancient evaporites and subsequent migration of brines to the surface from underground. The brines migrate through permeable strata with migration pathways resulting from a combination of fracture porosity created by post––Cretaceous tectonism and intergranular porosity enhanced by the chemically aggressive migrating brines.  相似文献   

8.
We studied the mobility of silver, heavy metals and europium in waste from the Las Herrerías mine in Almería (SE Spain). The most abundant primary mineral phases in the mine wastes are hematite, hydrohematite, barite, quartz, muscovite, anorthite, calcite and phillipsite. The minor phase consisted of primary minerals including ankerite, cinnabar, digenite, magnesite, stannite, siderite and jamesonite, and secondary minerals such as glauberite, szomolnokite, thenardite and uklonscovite. The soils show high concentrations of Ag (mean 21.6 mg kg–1), Ba (mean 2.5%), Fe (mean 114,000 mg kg–1), Sb (mean 342.5 mg kg–1), Pb (mean 1,229.8 mg kg–1), Zn (mean 493 mg kg–1), Mn (mean 4,321.1 mg kg–1), Cd (mean 1.2 mg kg–1) and Eu (mean 4.0 mg kg–1). The column experiments showed mobilization of Ag, Al, Ba, Cu, Cd, Eu, Fe, Mn, Ni, Sb, Pb and Zn, and the inverse modelling showed that the dissolution of hematite, hausmannite, pyrolusite and anglesite can largely account for the mobilization of Fe, Mn and Pb in the leaching experiment. The mobility of silver may be caused by the presence of kongsbergite and chlorargyrite in the waste, while the mobility of Eu seems to be determined by Eu(OH)3, which controls the solubility of Eu in the pH–Eh conditions of the experiments. The mineralogy, pH, Eh and geochemical composition of the mine wastes may explain the possible mobilization of heavy metals and metalloids. However, the absence of contaminants in the groundwater may be caused by the carbonate-rich environment of “host-rocks” that limits their mobility.  相似文献   

9.
The methodology for green mining operation, one that extracts minerals from waste brine water for eco-friendly products, is appealing. Little Rann of Kutch (LRK) and the sites near Bhavnagar associated with producing sub soil brine water which contain strontium up to 215 mg/L. This value is significant considering its value in sea water (~8 mg/L). The high-strontium brines also contain elevated lithium (up to 2.98 mg/L) and uranium (up to 0.1 mg/L). The occurrence of strontium in the India’s brine water is poorly understood and inadequately represented in the literature. The objectives of this report, therefore, are to illustrate where strontium-rich brine waters occur in Gujarat (India). The investigation of strontium, lithium and uranium in sub-soil brine was accomplished by the ICP-OES instrument. We have checked the pH, density, specific gravity and Degree Bowme (DB’) of the all samples. Alkali and alkaline earth metals like Na, K, Mg, Ca and Ba; metalloid B; transition element like Zn, Cr and Fe; heavy metals like Cd, Pb and Ni were also analysed for toxicity evaluation and anion Cl– and SO4 –2 were analysed by classical methods. Field wise, there is considerable variation in strontium, lithium and uranium in sub-soil brine water.  相似文献   

10.
A total of 108 samples of meta-tonalites, metagranodiorites, granites and meta-tholeiites representing groups of Early to Late Archean age and different metamorphic history from SW and SE Greenland have been analyzed for Ca, K and 28 trace elements. There is no systematic change of the chemical composition with age observable. The results support petrologic experiments which suggest that tonalites and granodiorites (the most abundant rocks of the Archean crust) are partial melting products of a mafic lower crust. Modelling suggest that this crust consisted of garnet amphibolite derived from a source with a bulk composition resembling a slightly enriched rather than depleted mantle. The CeN/YbN ratio is above 10 in the majority of tonalites. Most samples have no Eu anomaly because of a balanced contribution from the minerals of a mafic rock (or a plagioclase-free source). The positive Eu anomaly of some granodiorites and of a minor proportion of tonalites can be explained as being caused by plagioclase accumulation during differentiation or by partial melting of plagioclase-rich fractions. Modelling with Zn excludes an origin of tonalitic melts by differentiation of basaltic to dioritic magmas. The Archean meta-diorites, meta-tonalites and meta-granodiorites from Greenland have generally lost some K and S relative to their suggested magmatic protoliths. Loss of Rb, Tl, Pb and K and relative gain of Ca, Sr, Ba and Sc connected with granulitization of meta-tonalites can be explained in the majority of cases by separation of about 25 percent granitic partial melt. High K/Rb, K/Pb, Zn/Cd and Nb/Th ratios of granulites plus low ratios of granites are almost in balance with intermediate ratios of amphibolite-facies tonalites. Retrogression of granulites into amphibolites was accompanied by introduction of Pb, Tl, Rb, Ba, Sr and K from Na-Cl-rich brines circulating on fractures. A comparison of the abundance of 24 elements (characterized by different compatibility) in the Archean crust of Greenland with the present bulk crust reflects only minor changes (Th, Nb) if at-all in the chemical composition of the continental crust since the Archean.  相似文献   

11.
Sabkhas are ubiquitous geomorphic features in eastern Saudi Arabia. Seven brine samples were taken from Sabkha Jayb Uwayyid in eastern Saudi Arabia. Brine chemistry, saturation state with respect to carbonate and evaporate minerals, and evaporation-driven geochemical reaction paths were investigated to delineate the origin of brines and the evolution of both brine chemistry and sabkha mineralogy. The average total dissolved solids in the sabkha brines is 243 g/l. The order of cation dominance is Na+   >>  Mg2+ >>  Ca2+>K+, while anion dominance is Cl− >> SO4 2− >> HCO3 −. Based on the chemical divide principle and observed ion ratios, it was concluded that sabkha brines have evolved from deep groundwater rather than from direct rainfall, runoff from the surroundings, or inflow of shallow groundwater. Aqueous speciation simulations show that: (1) all seven brines are supersaturated with respect to calcite, dolomite, and magnesite and undersaturated with respect to halite; (2) three brines are undersaturated with respect to both gypsum and anhydrite, while three brines are supersaturated with respect to both minerals; (3) anhydrite is a more stable solid phase than gypsum in four brines. Evaporation factors required to bring the brines to the halite phase boundary ranged from 1.016 to 4.53. All reaction paths to the halite phase boundary follow the neutral path as CO2 is degassed and dolomite precipitates from the brines. On average, a sabkha brine containing 1 kg of H2O precipitates 7.6 g of minerals along the reaction path to the halite phase boundary, of which 52% is anhydrite, 35.3% is gypsum, and 12.7% is dolomite. Bicarbonate is the limiting factor of dolomite precipitation, and sulfate is the limiting factor of gypsum and anhydrite precipitation from sabkha brines.  相似文献   

12.
The carbonate-hosted Kabwe Pb–Zn deposit, Central Zambia, has produced at least 2.6 Mt of Zn and Pb metal as well as minor amounts of V, Cd, Ag and Cu. The deposit consists of four main epigenetic, pipe-like orebodies, structurally controlled along NE–SW faults. Sphalerite, galena, pyrite, minor chalcopyrite, and accessory Ge-sulphides of briartite and renierite constitute the primary ore mineral assemblage. Cores of massive sulphide orebodies are surrounded by oxide zones of silicate ore (willemite) and mineralized jasperoid that consists largely of quartz, willemite, cerussite, smithsonite, goethite and hematite, as well as numerous other secondary minerals, including vanadates, phosphates and carbonates of Zn, Pb, V and Cu.Galena, sphalerite and pyrite from the Pb–Zn rich massive orebodies have homogeneous, negative sulphur isotope ratios with mean δ34SCDT permil (‰) values of − 17.75 ± 0.28 (1σ), − 16.54 ± 0.0.27 and − 15.82 ± 0.25, respectively. The Zn-rich and Pb-poor No. 2 orebody shows slightly heavier ratios of − 11.70 ± 0.5‰ δ34S for sphalerite and of − 11.91 ± 0.71‰ δ34S for pyrite. The negative sulphur isotope ratios are considered to be typical of sedimentary sulphides produced through bacterial reduction of seawater sulphate and suggest a sedimentary source for the sulphur.Carbon and oxygen isotope ratios of the host dolomite have mean δ13CPDB and δ18OSMOW values of 2.89‰ and 27.68‰, respectively, which are typical of marine carbonates. The oxygen isotope ratios of dolomite correlate negatively to the SiO2 content introduced during silicification of the host dolomite. The depletion in 18O in dolomite indicates high temperature fluid/rock interaction, involving a silica- and 18O-rich hydrothermal solution.Two types of secondary fluid inclusions in dolomite, both of which are thought to be related to ore deposition, indicate temperatures of ore deposition in the range of 257 to 385 and 98 to 178 °C, respectively. The high temperature fluid inclusions contain liquid + vapour + solid phases and have salinities of 15 to 31 eq. wt.% NaCl, whereas the low temperature inclusions consist of liquid + vapour with a salinity of 11.5 eq. wt.% NaCl.Fluid transport may have been caused by tectonic movements associated with the early stages of the Pan-African Lufilian orogeny, whereas ore deposition within favourable structures occurred due to changes in pressure, temperature and pH in the ore solution during metasomatic replacement of the host dolomite. The termination of the Kabwe orebodies at the Mine Club fault zone and observed deformation textures of the ore sulphides as well as analysis of joint structures in the host dolomite, indicate that ore emplacement occurred prior to the latest deformation phase of the Neoproterozoic Lufilian orogeny.  相似文献   

13.
A cluster of minor Mississippi Valley-type deposits occurs in northwestern Ohio. The district, which forms a northeasterly trending belt that cuts across the Findlay Arch, extends from the Indiana border to the Lake Erie Islands. The minerals of the deposits — chiefly celestite, fluorite and sphalerite with lesser amounts of barite and galena — show variation in both geographic and stratigraphic distribution. Dolomites of Middle Silurian to Middle Devonian age, which are the host rocks, also form an important aquifer system. The deposits are of interest because they might be indicators of economic mineralization at depth.Through a reconnaissance study, one-hundred ground-water samples from shallow wells (less than 50 m deep) were collected across an area of approximately 19 000 km2. Recharge takes place in the southern part of the area while ground-water flow is northward towards Lake Erie. The majority of the samples are high in sulfate with the source being evaporites within the carbonate sequence. The remainder of the water samples are rich in bicarbonate. Trend surface maps for the major constituents indicate that the ground-water chemistry for the region is established chiefly by the lithology and the flow system. Trend surface maps for F−, Sr and Ba reflect the geographic distribution of the minerals in the deposits. Correlations are weakened, however, due to the influence of geochemical barriers such as SO42− on Ba and Sr, and Ca on F−. The map for Pb follows the trends of the major constituents instead of the mineralization.In a detailed study across northwestern Sandusky County, which lies near the center of the district, 46 samples were collected in an area of 78 km2. Trend surface maps for Ca, Mg, SO42− and total dissolved solids reflect the chemistry of the bedrock and display concentrations that increase along the local flow path. Maps for F−, Sr and Ba correlate with mineralization in the vicinity, the first of these displaying a local trend and the last two correlating with regional trends.  相似文献   

14.
The Niujiaotang zinc deposit in southeastern Guizhou, China, is a Mississippi Valley-type Zn deposit within Early Cambrian carbonate rocks. Sphalerite is enriched in cadmium (average 1.4 wt.% Cd), which occurs mostly as isomorphous impurities in the sphalerite lattice. Discrete cadmium minerals (greenockite and otavite) are rare and are found almost exclusively in the oxidation zone of the deposit, probably formed as secondary minerals during weathering–leaching processes. Geochemical data show that the sulfides are enriched in heavy sulfur, with δ34S ranging from +10.0‰ to +32.8‰ (mean +22.5‰). The consistent Pb isotopic compositions in different sulfide minerals are similar to that of Cambrian strata. The ore lead probably came from U- and Th-rich upper crustal rocks, such as the Lower Cambrian Wuxun Formation. The ore fluid is of low-temperature (101°C to 142°C) type, with a Na–Ca–Mg–Cl-dominant composition, and is interpreted as oil-field brine. The data indicate that the metals were mainly derived from the Early Cambrian strata (Qingxudong and Wuxun Formations), whereas sulfur is sourced from sulfate in Cambrian strata or oil-field brines of the Majiang petroleum paleoreservoir. The genetic model for the deposit invokes an Early Cambrian shallow-sea environment on the Yangtze Platform. Zinc and Cd in seawater were concentrated in abundant algae via unknown biological mechanisms, resulting in large amounts of Zn- and Cd-rich algal ooliths. During the Ordovician, concurrent with destruction of the Majiang petroleum paleoreservoir, oil-field brines migrated from the center of the basin to the margin leaching metals from the Cambrian strata. In the Niujiaotang area, preexisting Zn and Cd, particularly in the Qingxudong and Wuxun Formation, were further mobilized by hot brines rising along the Zaolou fault system, forming stratiform and generally conformable Zn–Cd orebodies in reactive carbonate lithologies.  相似文献   

15.
The Okchon black shale in Korea provides a typical example of natural geological materials enriched with potentially toxic elements. The Chung-Joo, Duk-Pyung, Geum-Kwan, I-Won, Bo-Eun and Chu-Bu areas are underlain by these black shales and slates of the Guryongsan Formation or the Changri Formation, which are parts of the Okchon Group in the central part of the southern Korean Peninsula. In order to investigate the enrichment levels and dispersion patterns of potentially toxic elements in the rock–soil–plant system, environmental geochemical surveys were undertaken in the above six study areas in the Okchon Zone. After appropriate preparation, rock and soil samples were analyzed for potentially toxic elements by instrumental neutron activation analysis (INAA) and inductively coupled plasma atomic emission spectrometry (ICP-AES), and plant samples by atomic absorption spectrometry (AAS). In particular, Ba, Cd, Mo, V and U in Okchon black shales are highly enriched, and their mean concentrations are significantly higher than those in black slates. These elements are geochemically associated, and might be enriched simultaneously. The highest mean concentrations of 42.0 μg g−1 As, 2100 μg g−1 Ba, 10.9 μg g−1 Cd, 213 μg g−1 Mo, 83 μg g−1 U, 938 μg g−1 V and 394 μg g−1 Zn are found in black shales from the Duk-Pyung area. Mean concentrations of As, Mo and U in soils overlying black shales occurring in the Duk-Pyung area (30 μg g−1 As, 24 μg g−1 Mo and 50 μg g−1 U) and Chu-Bu area (39 μg g−1 As, 15 μg g−1 Mo and 27 μg g−1 U) are higher than the permissible level. Enrichment index values of the six study areas decrease in the order of Duk-Pyung > Chu-Bu > Bo-Eun > Chung-Joo > Geum-Kwan = I-Won areas. Relationships between trace element concentrations in soils and plants are significantly correlated, and the biological absorption coefficients (BAC) in plants are in the order of Cd > Zn = Cu > Pb, which suggests that Cd is more bioavailable to plants than the other elements. Cadmium concentrations in plant species decrease in the order of chinese cabbage > red pepper > soybean = sesame > rice stalk > corn > rice grain. From the result of sequential extraction analysis of soils, relatively high proportions of Cu, Pb and Zn are present as residual fractions, and that of Cd as non-residual fractions. Cadmium occurs predominantly as exchangeable/water-acid soluble phase in soils, and this is in agreement with the findings of high Cd concentrations in plants.  相似文献   

16.
An integrated mineralogical-geochemical study of unconformity-related Au-Pd occurrences within and around the Permo–Triassic basins of southwest England, UK, has confirmed the importance of low temperature (86±13°C), hydrothermal carbonate veins as hosts for the mineralisation. Fluid inclusion data for the carbonate gangue, supported by stable isotope (13C and 18O) and radiogenic (87Sr/86Sr) data, have identified three principal fluids: (1) a reducing calcic brine [>25 wt% salinity, <0.5 NaCl/(NaCl+CaCl2)] originating in the sub-unconformity basement and an expression of advanced mineral–fluid interaction; (2) an oxidising sodic brine [~16 wt% salinity, >0.9 NaCl/(NaCl+CaCl2)] originating in the post-unconformity red beds under evaporitic conditions, and (3) an oxygenated, low salinity groundwater (<3 wt% salinity). The sodic brine is reasoned to be the parent metalliferous fluid and to have acquired its enrichment in Au and Pd by the leaching of immature sediments and intra-rift volcanic rocks within the local Permo–Triassic basins. Metal precipitation is linked to the destabilisation of Au and Pd chloride complexes by either mixing with calcic brines, dilution by groundwaters or interaction with reduced lithologies. This explains the diversity of mineralised settings below and above the unconformity and their affinity with red bed brines. The paucity of sulphide minerals, the development of selenides (as ore minerals and as mineral inclusion in gold grains), the presence of rhodochrosite and manganoan calcites (up to 2.5 wt% Mn in calcite) and the co-precipitation of hematite and manganese oxides are consistent with the overall high oxidation state of the ore fluids. A genetic model is proposed linking Permo–Triassic red beds, the mixing of oxidising and reducing brines, and the development of unconformity-related precious metal mineralisation. Comparison with other European Permo–Triassic basins reveals striking similarities in geological setting, mineralogy and geochemistry with Au, Au-Pd and selenide occurrences in Germany (Tilkerode, Korbach-Goldhausen), Poland (Lubin) and the Czech Republic (Svoboda nad Úpou and Stupná). Though the known Au-Pd occurrences are sub-economic, several predictive criteria are proposed for further exploration.Editorial handling: B. Lehmann  相似文献   

17.
《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   

18.
The dissolution kinetics of carbonate rocks sampled from the Keg River Formation in Northeast British Columbia were measured at 50 bar pCO2 and 105 °C, in both natural and synthetic brines of 0.4 M ionic strength. Natural brines yielded reaction rates of −12.16 ± 0.11 mol cm−2 s−1 for Log RCa, and −12.64 ± 0.05 for Log RMg. Synthetic brine yielded faster rates of reaction than natural brines. Experiments performed on synthetic brines, spiked with 10 mmol of either Sr or Zn, suggest that enhanced reaction rates observed in synthetic brines are due to a lack of trace ion interaction with mineral surfaces. Results were interpreted within the surface complexation model framework, allowing for the discrimination of reactive surface sites, most importantly the hydration of the >MgOH surface site. Dissolution rates extrapolated from experiments predict that CO2 injected into the Keg River Formation will dissolve a very minor portion of rock in contact with affected formation waters.  相似文献   

19.
The mineralogy and geochemistry of the massive pyrite-pyrrhotite mineralization, which contains minor magnetite, sphalerite and galena, the weathered profile and surface gossan at Mugga Mugga in Western Australia have been examined. Reactions between amphibolite wall rocks and acid waters from the oxidation of the iron sulfides have resulted in distinct mineralogical zonation of the weathered profile which is further modified near the surface by lateritization. At the base of the weathered zone an opaline chert (Opal-CT) has been precipitated from fluctuations of the water table. A gossanous zone from 25.14–68.80 m with boxworks after massive pyrite is modified by abundant kaolinite, dickite and an alunite-type mineral derived from amphibolite wall rocks, while above 25.14 m both plinthite and mottled clay zones of a laterite profile are evident. Some characteristics of a mature gossan profile – sulfate-phosphate-arsenate near the base, a carbonate zone higher in the profile, and an oxide zone near the surface – overprint the gross zonation.At the interface between sulfide and weathered rock Mg, Ca, K, S, Zn, Cd, Hg, Ba are depleted, As, Sb, Mo, Cr and V contents increase and in the weathered zone, SiO2, TiO2, P2O5, SO3, Pb, Zn, Hg, Sb, Co, Ni, W, Ba, Sr and Zr decrease up the profile whilst Al2O3, Fe2O3, CO2, Cu and As increase. Of the elements associated with the massive pyrite (Pb, Zn, Cu, Ag, As, Cd, Hg, Sb, Co, Ni) anomalous concentrations of Pb, Cu, Ag, As and Sb occur in the surface gossan despite the possibility of complete leaching by highly acidic solutions. These anomalies are similar to those found in gossans over pyrite mineralization elsewhere in the Yilgarn Block.  相似文献   

20.
The Changkeng Au and Fuwang Ag deposits represent an economically significant and distinct member of the Au–Ag deposit association in China. The two deposits are immediately adjacent, but the Au and Ag orebodies separated from each other. Ores in the Au deposit, located at the upper stratigraphic section and in the southern parts of the orefield, contain low Ag contents (< 11 ppm); the Ag orebodies, in the lower stratigraphic section, are Au-poor (< 0.2 ppm). Changkeng is hosted in brecciated cherts and jasperoidal quartz and is characterized by disseminated ore minerals. Fuwang, hosted in the Lower Carboniferous Zimenqiao group bioclastic limestone, has vein and veinlet mineralization associated with alteration comprised of quartz, carbonate, sericite, and sulfides. Homogenization temperatures of fluid inclusions from quartz veinlets in the Changkeng and Fuwang deposits are in the range of 210 ± 80 °C and 230 ± 50 °C, respectively. Salinities of fluid inclusions from the two deposits range from 1.6 to 7.3 wt.% and 1.6 to 2.6 wt.% equiv. NaCl, respectively. The δDH2O, δ18OH2O, δ13CCO2 and 3He/4He values of the fluid inclusions from the Changkeng deposit range from − 80‰ to − 30‰, − 7.8‰ to − 3.0‰, − 16.6‰ to − 17.0‰ and 0.0100 to 0.0054 Ra, respectively. The δDH2O, δ18OH2O, δ13CCO2 and 3He/4He values of fluid inclusions from the Fuwang deposit range from − 59‰ to − 45‰, − 0.9‰ to 4.1‰, − 6.7‰ to − 0.6‰ and 0.5930 to 0.8357 Ra, respectively. The δDH2O, δ18OH2O, δ13CCO2 and 3He/4He values of the fluid inclusions suggest the ore fluids of the Changkeng Au-ore come from the meteoric water and the ore fluids of the Fuwang Ag-ore are derived from mixing of magmatic water and meteoric water. The two deposits also show different Pb-isotopic signatures. The Changkeng deposit has Pb isotope ratios (206Pb/204Pb: 18.580 to 19.251, 207Pb/204Pb: 15.672 to 15.801, 208Pb/204Pb: 38.700 to 39.104) similar to those (206Pb/204Pb: 18.578 to 19.433, 207Pb/204Pb: 15.640 to 15.775, 208Pb/204Pb: 38.925 to 39.920) of its host rocks and different from those (206Pb/204Pb: 18.820 to 18.891, 207Pb/204Pb: 15.848 to 15.914, 208Pb/204Pb: 39.579 to 39.786) of the Fuwang deposit. The different signatures indicate different sources of ore-forming material. Rb–Sr isochron age (68 ± 6 Ma) and 40Ar–39Ar age (64.3 ± 0.1 Ma) of the ore-related quartz veins from the Ag deposit indicate that the Fuwang deposit formed during the Cenozoic Himalayan tectonomagmatic event. Crosscutting relationships suggests that Au-ore predates Ag-ore. The adjacent Changkeng and Fuwang deposits could, however, represent a single evolved hydrothermal system. The ore fluids initially deposited Au in the brecciated siliceous rocks, and then mixing with the magmatic water resulted in Ag deposition within fracture zones in the limestone. The deposits are alternatively the product of the superposition of two different geological events. Age evidence for the Fuwang deposit, together with the Xiqiaoshan Tertiary volcanic-hosted Ag deposit in the same area, indicates that the Pacific Coastal Volcanic Belt in the South China Fold Belt has greater potential for Himalayan precious metal mineralization than previous realized.  相似文献   

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