Mutual effects of fluoride and phosphate on their adsorption and desorption in fluoride-contaminated softs

Phosphate is one of the important nutrients for plant growth. In acidic and highly weathered soils, phosphate is ready to adsorb on Al and Fe oxides and transform into sparsely soluble Fe-P and Al-P solid phases, greatly reducing phosphate bioavailability. Aluminum and iron oxides in soils are important sinks for both phosphate and fluoride. In acidic soils, fluoride adsorption can dramatically facilitate dissolution of Al- and Fe-containing phases, which may influence the distribution and migration of both pollutants and nutrients including phosphate. To date, little information is available on mutual effects of fluoride and phosphate in fluoride-contaminated acidic soils. The objective of this study is to evaluate mutual effects of fluoride and phosphate on their adsorption/desorption in red soil, collected fi＇om Yingtan, Jiangxi Province, China, using a batch equilibrium method. The following results and conclusions were obtained. In heavily fluoride-contaminated soils, the adsorption of both fluoride and phosphate decreases with an increase in solution pH. Phosphate adsorption decreases progressively with increasing concentration of fluoride, suggesting that fluoride competes with phosphate for adsorption sites.     

THM Coupled Modeling in Near Field of an Assumed HLW Deep Geological Disposal Repository

One of the most suitable ways under study for the disposal of high-level radioactive waste (HLW) is isolation in deep geological repositories. It is very important to research the thermo-hydromechanical (THM) coupled processes associated with an HLW disposal repository. Non-linear coupled equations, which are used to describe the THM coupled process and are suited to saturated-unsaturated porous media, are presented in this paper. A numerical method to solve these equations is put forward, and a finite element code is developed. This code is suited to the plane strain or axis-symmetry problem. Then this code is used to simulate the THM coupled process in the near field of an ideal disposal repository. The temperature vs. time, hydraulic head vs. time and stress vs. time results show that, in this assumed condition, the impact of temperature is very long (over 10 000 a) and the impact of the water head is short (about 90 d). Since the stress is induced by temperature and hydraulic head in this condition, the impact time of stress is the same as that of temperature. The results show that THM coupled processes are very important in the safety analysis of an HLW deep geological disposal repository.     

Analysis of nanomolar concentrations of phosphate in seawater with Liquid Waveguide after Mg (OH)_2 coprecipitation

Phosphorous is an essential nutrient used by plants and animals for growth and energy transport. Phosphate cycling studies are important in understanding biological processes, and phosphate analyses are a standard part of the biogeochemists’ toolbox. How…     

Prediction of Overpressure Contributed Mainly by Structural Compression Using Impedance Inversion in Kuqa Depression, Tarim Basin

The origin and distribution of formation overpressure have effect not only on hydrocarbon migration and accumulation, but also on technique of drilling well. The study and prediction of overpressure are very important in basin analysis. At present, overpressure is mostly predicted by stack velocity.The process in calculating inter-velocity from stack velocity is very complex and inevitably leads to errors. Especially, this method is not available in the case that structural compression contribution to overpressure occurred. This paper introduces a new method, impedance inversion, to predict overpressure,and the principle is discussed. This method is used to predict the overpressure in Kuqa depression, Tarim basin and as a result, the absolute errors are less than 0.1, and relative errors are less than 5％ for predicted fluid pressure coefficients to the drill stem test (DST) measurements. It suggests that this method can be widely used to predict overpressure in foreland basins.     

α谱法测定低微量铀、钍含量的研究

Alpha-spectrometric technique is described as an independent method of determining micro-content of U^233 and Th^233. This method is based on the comparison of U^234 and Th^233 alpha spectral activity in geological samples with U^232 and Th^233 spectral activity contributed by the spike of known concentration. The experiment procedure consists in dissolving fine powdered sample with acid and adding a given amount of U^232-Th^223 spike. The uranium and thorium are then separated by ion exchange. After purification each fraction is mounted on a separate stainless steel disk for measurement by alpha spectrometer which consist essentially of a surface barrier deterctor and a low noise amplification system connected to a multichannel analyser. After correcting for background, tail and other factors, the desired U^232 and Th^232 concentrations can be calculated. The data obtained by the alpha-spectrometric method using U^232-Th^223 spike are compared with colorimetric determination. Excellent agreement is obtained between the two sets of results. The coefficient of correlation is about 0.98 for U^234 and 0.97 for Th^232. The accuracy of uranium and thorium analyses by this method depends primarily upon the counting statistics of U^233, U^232, Th^233 and Th^223 and, to a lesser extent, upon the calibration of U^233-Th^238 spike. Errors of uranium and thorium concentration by this method are generally 2 to 5 per cent.     

Rare Earth Elements and Yttrium (REY) Geochemistry of Reefal Limestones in the Ordovician,Tarim Basin,NW China and their Paleoenvironment Implications

This study examines the rare earth elements and yttrium (REY) concentrations of twenty-five samples from the reef outcrop exposed along the Lianglitage Mountain in the Ordovician, Tarim Basin in China. The concentration analysis provides constraints on the paleoenvironment during reef deposition. Based on the detailed sedimentology and petrographic work, we divide the reef facies into four sub-facies: the base facies, reef-core facies, reef-flank facies, and sealing facies. The geochemical data (such as major and trace elements, carbon and oxygen isotopes, and REYs) are further used to study the coeval seawater characteristics as well as potential diagenesis overprints. The result indicated that the diagenesis has little effect on the REY patterns of the reefal limestones. The REY concentrations of the reefal limestones are overall low (ranging from 3.69 to 19.60 ppm, arithmetic mean=10.22 ppm, SD=5.4). The PAAS-normalized REY patterns are consistently flat compared to the typical well-oxidized, shallow marine water patterns. However, the light REE (LREE) depletions, positive La anomalies, negative Ce anomalies and positive Y anomalies, suggest that these reefal limestones are likely an indicative of contemporaneous seawater REY signals. The seawater-like Y/Ho ratios (average at 37.51) further support that REY signals in these limestones are likely a reflection of seawater with little diagenetic modifications. The low Y/Ho ratios presented only in the reef-flank facies and sealing facies are likely a suggestion of detrital contamination. Hence, this study confirms that REY patterns of the limestones at the base facies and reef-core facies can record ancient seawater information, and reefs can be used as a potential geochemical proxy for paleoenvironment studies throughout the Earth’s history.     

Separation of nano-colloids in soils

The study of the physicochemical behaviour of colloids and particles in nature has emerged as a scientific problem of critical importance because of the widespread acknowledgement of their significance in controlling the speciation and fate of essential nutrients and contaminants in the aquatic and soil environments （Ledin et al., 1995; Lead et al., 1999, Doucet et al., 200 l; McCarthy et al., 1989; Koterba et al., 1993; Kretzschmar et al., 1999）. Se＇quaris and Lewandowski （2003） developed a method based on sedimentation and centrifugation steps to fractionate agricultural top soils after suspension in water. However, progress in the field has been limited by the lack of appropriate techniques for the isolation and characterization of colloids and particles in their native form （Lead et al., 1997）. The primary difficulties in separation and analysis are colloidal instability and their small size and low concentration. As a result, reliable, unbiased and minimally perturbing methods for sampling and fractionation are primary requirements for the study of colloids and particles if valuable information is to be obtained. In recent years, cross-flow ultra-filtration （CFUF） has become one of the most commonly used techniques for collecting and separating freshwater and marine colloids and particles （Petrus evski et al., 1995; Gustafsson et al., 1999; Benoit et al., 1999; Sigg et al., 2000; Gue＇guen et al., 2002; Benedetti et al., 2003）. CFUF has hitherto been used for studies of the biogeochemical cycling of a variety of elements, such as carbon （Benner et al., 1992; Santschi et al., 1998）, radionuclides （Moran et al., 1992）, trace metals （Reitmeyer et al., 1996） and nutrients （Bauer et al., 1996）. The purpose of this study was to develop a protocol to fractionate particles in soil, to measure particle size distributions and to quantify chemical characteristics within different particle size fractions.     

Measurement of the total nitrogen in lake sediments： Comparison and its environmental significance

Nitrogen cycle is an important bio-geochemical process in the environment. Measurement of the total nitrogen （TN） is a routine experiment in agriculture, biology and environmental sciences. The Kjeldahl method （KM） and elemental analyzer method （EA） are both commonly used to determine TN. Total nitrogen by EA is the sum of nitrate （NO3）, nitrite （NO2）, organic nitrogen and ammonia. Total nitrogen by KM （TKN） is made up of both organic nitrogen and ammonia. A comparative study focused on the two methods is conducted by analysis of TN in 97 samples from the sediment sequence of Gouchi, a salt lake in North China. KM presents a higher degree of accuracy than EA with a standard deviation of 0.007 vs. 0.024. With the presence of nitrate and/or nitrite nitrogen, however, measurement by KM is considerably lower than that by EA. Therefore, for samples from lake sediment sequences or soils in North China, KM is inapplicable to determining TN because of usually high contents of nitrous salt. Despite the inconsistency, use of both methods to the same samples makes sense in reconstructions of climatic and environmental changes from lake sediments. In Lake Gouchi, the contents of nitrate and nitrite nitrogen vary from 1.40% in the lower part of the sequence to 14.77% in the uppermost part, suggesting a gradual evolution process from a fresh water lake to the present-day salt lake.     

An Effective Method for Free Vibration of Plate on Elastic Half Space

The vibration analysis of a plate on an elastic foundation is an important problem in engineering. It is the interaction of a plate with the three-dimensional half space and the plate is usually loaded from both the upper and lower surfaces. The contact pressure from the soil can not be predefined. According to Lambs solution for a single oscillating force acting on a point on the surface of an elastic half space, and the relevant approximation formulae, a relation between the local pressure and the deflection of the plate has been proposed. Based on this analysis, the reaction of the soil can be represented as the deformation of the plate. Therefore, the plate can be separated from the soil and only needs to be divided by a number of elements in the analysis. The following procedure is the same as the standard finite element method. This is a semi-analytical and semi-numerical method. It has been applied to the dynamic analysis of circular or rectangular plates on the elastic half space, at low or high frequency vibration, and on rigid, soft or flexible foundations. The results show that this method is versatile and highly accurate.     

Molar‐Tooth Structure from the Mesoproterozoic Wumishan Formation in Lingyuan,Yanshan Region,North China,and Geological Implications

Although its origin has not yet reached a consensus so far, MTS (Molar-Tooth Structure) has been documented for more than 100 years. Current study reports a discovery of MTS from the Mesoproterozoic Wumishan Formation, Lingyuan, Yanshan Region, North China, and the features and geological implications of MTS are further discussed. Here, straitigraphic horizons of MTS’s occurrences show that it was mainly located within the top part of the Wumishan Formation, i.e., limestone unit. Four kinds of morphology of MTS, i.e., fine fusiform, debris, ribbon, ptigmatic and nodular (irregular), were recognized and thought to be highly related to the sedimentary environments and facies. Geochemistry of MTS including oxides, trace elements and C, O and Sr isotopes indicates that the horizons of MTS-bearing is of higher Sr/Ba and Ca/Mg ratios, lower positive δ13C and highly negative δ18O values than the adjacent stratigraphic levels of rare MTS. Lithology, morphology and geochemistry of MTS in the Wumishan Formation suggest that MTS occurs mainly in shallow subtidal near the storm wave base, which is typically characterized by warm temperature, oversaturated calcium carbonate seawater and high organic productivity. Furthermore, occasional enrichment of algae bacteria here is more favorable for the calcification of calcium oozes and catalytic for MTS. C isotope composition of the Wumishan Formation and MTS of this study is well correlated with that of the Mesoproterozoic Belt Supergroup, North America and Riphean, Siberia, suggesting that MTS acts as a sedimentary record responding to global changes and is a perfect indicator in Precambrian stratigraphic correlation worldwide.     

Geochemistry of sedimentary rocks and its relation to crustal evolution and mineralization in Southwest Yangtze Massif, China

Through a systematic study on trace elements and REE geochemistry of mudstone deposited in the basin and lower slope environments during Upper Proterozoic to Triassic in the Southwest Yangtze Mssif,three geochemical abnormal horizons of which the geochemical characteristics are quite different from those of other horizons have been established for the first time.They are the Lower Cambrian,the Upper Devonian and the Upper Permian,As compared with the crustal evolution in this area.these three geochemical abnormal horizons are corresponding to the pulling-apart periods of geotectonic cycles.which illustrates that uncommon depositional sources puring into the basin from the earth‘s interior may be one of the most important causes to originate the geochemical anomalies in these lhrizons.Thus it can be realized that the geochemistry of post-Archean sedimentary rocks has a great deal to do with the crustal evolution and it can be used as a tracer to analyze the crustal evolution.The elements in this area are mainly concentrated in these geochemical abnormal horizons,and the degree of enrichment and deficiency of trace elements in other horizons is very limited.A series of research on mineralization indicates that the main strata-bound ore deposits discovered in the Southwest Yangtze Massif occur in the Cambrian,Devonian and Permian-Trassic strata.The results of isotope tracer resarch have also proved that most of the metallogenic elements in these ore deposits came from the host strata.which illustrates that the geochemical abnormal horizons may have made great contributions to these ore-forming processes.Thus it can be concluded that it is only the particular horizons corresponding to the particular periode of earth‘s evolution that can they be the significant source beds because only in these uncommon horizons there can be highly enriched metallogeinc elements.which may be one of the most important reasons for explaining the time-bound nature of mineralization.     

一种新的分层冻胀量观测方法及其在季节冻土区的应用

Observation of delamination frost-heave is of significance in the study of foundation frost damage. The three main methods of observing delamination frost-heave, which are mono-frost-heave-ruler method, multi-frost-heave-ruler method and magnetic-loop method, are briefly introduced in this paper at first. Their respective advantages and disadvantages are analyzed. And then, according to the mechanism of frost-heave and the law of water migration and ice-forming in the freezing soil, a new approximate indirect method of observing the delamination frost-heave, which is antitheses, is brought forward by comparing surface frost-heave and frost-depth. On the basis of observation result in Chengyu Expressway and Daqing, its applicability is analyzed from three aspects under different groundwater level and soil property in seasonal frozen area. The result shows that this method is applicable for these two areas.     

Separation and Precise Measurement of Lithium Isotopes in Three Reference Materials Using Multi Collector‐Inductively Coupled Plasma Mass Spectrometry

Lithium separation technique for three reference materials has been established together with precise determination of lithium isotope using a Neptune multi collector-inductively coupled plasma mass spectrometry (MC-ICP-MS). The solutions of lithium element standard reference materials, potassium, calcium, sodium, magnesium and iron single element, were used to evaluate analytical methods applied. Three separate stages of ion-exchange chromatography were carried out using organic cation-exchange resin (AG 50W-X8). Lithium was enriched for the three stages using different eluants, which are 2.8 M HCl, 0.15 M HCl and 0.5 M HCl in 30% ethanol, respectively. The columns for the first and second stages are made of polypropylene, and those for the third stage are made of quartz. Total reagent volume for the entire chemical process was 35 mL for three reference materials. The recovery yielded for the three stages is 98.9–101.2% with an average of 100.0%, 97.6–101.9% with an average of 99.9%, and 99.8–103.3% with an average of 100.6%, respectively. The precision of this technique is conservatively estimated to be ±0.72–1.04‰ (2σ population), which is similar to the precision obtained by different authors in different laboratories with MC-ICP-MS. The δ7Li values (7Li/6Li relative to the IRMM-016 standard) determined for andesite (AGV-2) and basalt (BHVO-2) are 5.68‰ (n=18), 4.33‰ (n=18), respectively. The δ7Li value (7Li/6Li relative to the L-SVEC standard) determined for IRMM-016 is –0.01‰ (n=15). All these analytical results are in good agreement with those previously reported. In addition, the results for the same kinds of samples analyzed at the MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, are consistent with those obtained at the Plasma Laboratory, University of Maryland, within analytical uncertainty. According to these experiment results, it is concluded that this proposed procedure is a suitable method for determining the lithium isotopic composition of natural samples.     

Isolation and characterization of phenanthrene-degrading strain Sphingomonas sp. GY2B

Polycyclic aromatic hydrocarbons （PAHs） are of great concern since most of them have been shown to be toxic, mutagenic, and carcinogenic. Bioremediation, based on certain species of microorganisms, is regarded as an alternative method to detoxify or remove PAHs from the contaminated sites. Phenanthrene has been often used as a model substance for microbial metabolism of ＂bay-region＂ and ＂K-region＂ containing carcinogenic PAH. The focus of the present study is to isolate and identify microorganisms which could use phenanthrene as the sole carbon and energy source. Such microorganisms are expected to be of interest as a source organism for the bioremediation of PAHs polluted soils. The bacterial consortia were enriched from PAH contaminated soils with water-silicon oil biphasic systems. An aerobic bacterial strain efficiently utilizing phenanthrene as the sole carbon and energy source was isolated from bacterial consortia GY2 and identified as Sphingomonas sp. strain GY2B. Strain GY2B was susceptible to some common used antibiotics such as cefuroxime, chloramphenicol, erythromycin and tetracycline and intermediate susceptible to amoxycillin. Moreover, no plasmids could be isolated from strain GY2B using the standard alkaline-SDS method. At pH 7.4 and 30℃ strain GY2B had an optimal growth condition and in this condition above 99.8% phenanthrene was degraded under initial concentration of 100 mg/L. The addition of low concentration of glucose （10-200 mg/L） in MSM containing 100 mg/L phenanthrene could enhance the growth of strain GY2B, while the high concentration of glucose （〉500 mg/L） could exert an inhibitive effect on cell growth. Besides phenanthrene, strain GY2B could also use naphthalene, phenol, 1-hydroxy-2-naphthoic acid, 2-naphthol, salicylic acid and catechol as the sole carbon and energy source. The growth of strain GY2B on salicylic acid and catechol showed that the degradation of phenanthrene might follow salicylate pathway.     

Geochemical characteristics and geological significance of the Neoproterozoic carbonates from northern Anhui Province,China

Petrographical and geochemical studies were carried out of the Neoproterozoic carbonates from northern Anhui Province, China. These carbonates can be subdivided into two types, including purified limestone (PL) and mixed limestone and siliclastic rocks (MLS). PLs are low in Si, Al, Zr and total REE but high in CaO compared with MLSs. Correlations between Zr, Fe2O3, P2O5 and total REE are also less remarkable, indicating that they were not obviously contaminated by continental materials but directly precipitated from seawater. So they can be used for the inversion of paleo-seawater REE patterns. The inversed results indicated that the REE pattern of Neoproterozoic seawater was similar to that of the modern seawater except for the lack of Ce depletion, which was probably affected by the reduced hydrothermal solution. In combination with previous studies, the geochemical trending of these carbonatic samples towards the continental arc in the La- Th-Sc and Th-Sc-Zr/10 diagrams is interpreted as the contamination of arc volcanism. The tectonic background of the southern margin of the North China Craton in the Neoproterozoic was probably related to the Grenville orogeny during the convergence of the Rodinia supercontinent, rather than an intra-plate environment.     

From Cycles to Sequences:Sequence Stratigraphy and Relative Sea Level Change for the Late Cambrian of the North China Platform

In the Late Cambrian, the North China Platform was a typical carbonate ramp platform. The Upper Cambrian of the northern part of the North China Platform is famous for the development of bioherm limestones and storm calcirudites and can be divided from bottom to top into the Gushan, Changshan and Fengshan formations. In this set of strata, the deep-ramp mudstone and marls and the shallow-ramp packstones and grainstones constitute many carbonate meter-scale cycles of subtidal type. More tidal-flat dolomites axe developed in the Upper Cambrian of the southern margin of the North China platform, in which limestone and dolomite beds also constitute many carbonate meter-scale cycles of the peritidal type. These cycles are marked by a variety of litho-facies successions. There are regularly vertical stacking patterns of meter-scale cycles in long-term third-order sequences, which is the key to discerning such sequences. Third-order sequence is marked by a particular sedimentary-facies succession that is the result of the environment-changing process of deepening and shoaling, which is genetically related to third-order sea level changes. Furthermore, four third-order sequences can be grouped in the Upper Cambrian of the North China Platform. The main features of these four third-order sequences in the northern part of the platform can be summarized as follows: firstly, sequence-boundaries are characterized by drowning unconformities; secondly, the sedimentary-facies succession is generally constituted by one from deep-ramp facies to shallow-ramp facies; thirdly, a succession of “CS (?) HST” (i.e., “condensed section and highstand system”) forms these four third-order sequences. The chief features for the third-order sequences in the southern part of the North China Platform comprises: more dolomites are developed in the HSTs of third-order sequences and also developed more carbonate meter-scale cycles of peritidal types; the sedimentary-facies succession of the third-order sequences is marked by “shallow ramp-tidal flat”; the sequence boundaries are characterized by exposure punctuated surfaces. According to the changes for the third-order sequences from the north to the south, a regular sequence-stratigraphic framework can be established. From cycles to sequences, the study of sequence stratigraphy from litho-facies successions to sedimentary-facies successions exposes that as follows: meter-scale cycles that are used as the basic working unit actually are litho-facies successions formed by the mechanism of a punctuated aggradational cycle, and third-order sequences that are constituted by regularly vertical stacking patterns of meter-scale cycles are marked by sedimentary-facies successions. On the basis of the changing curve of water depth at each section, the curve of the relative third-order sea level changes in the late Cambrian of the North China Platform can be integrated qualitatively from changing curve of water depth. The correlation of Late Cambrian long-term sea level changes between North China and North America demonstrates that there are not only similarities but also differences, reflecting control of long-term sea level changes both by global eustacy and by regional factors.     

Some High—P—Subtype and Low—P—Subtype F—Rich Granites in South China

The F-rich granites in South CHina could be distinguished as the high-P subtype and the low-P subtype according to their P2O5 contents.There are obvious differences in chemical composition of these two subtypes,The high-P subtype is strongly peraluminous and characterized by low silica and very low REE contents,while the low-P subtype is weakly peraluminous and characterized by high silica and very high REE contents.There are also some differences in chmical compositions of feldspars and micas for these two subtypes,The phosphorus of the high-P subtype mainly appears to be in the feldspar structure as PAlSi-2 substitution or subordinately in amblygonite as an accessory mineral,while the phosphorus of the low-P subtype is mainly in apatite and other phosphate minerals.     

Diffusion of Sm-Nd in Scheelite and its Significance to Isotopic Dating and Tracing

As the principal ore mineral in various tungsten (-gold) deposits, scheelite (CaWO4) plays an important role in directly dating the timing of ore formation, and in tracing associated material sources through the study of its Sm-Nd geochronology and Nd isotopic characteristics. Since the retention of Sm-Nd systematics within scheelite is presently unconstrained, equivocal interpretations for isotopic data resulting from this method have occurred quite often in previous studies that apply these isotopic data. In order to better elucidate the closure of Sm-Nd in scheelite, the kinetics of Sm and Nd within this mineral lattice were investigated through calculation of diffusion constants presented herein. The following Arrhenius relations were obtained: DNd = 4.00exp(?438 kJ·mol–1/RT) cm2/s DSm = 1.85exp(?427 kJ·mol–1/RT) cm2/s showing diffusion rate of Nd is near identical to Sm in scheelite when at the same temperature. However, compared to other rare earth elements (REEs), which have markedly different atomic radii to either Nd or Sm, these are shown to exhibit a great variation in diffusivities. The observed trends in our data are in excellent agreement with the diffusion characteristics of REEs in other tetragonal ABO4 minerals, indicating that ionic radius is a key constraint to the diffusivity of REEs in the various crystal lattices. With this in mind, the same substitution mechanism and a very slight discrepancy in radii will allow us to infer that significant Sm/Nd diffusional fractionation in scheelite is unlikely to occur during most geological processes. Based upon the diffusion data determined herein, Sm and Nd closure temperatures and retention times in scheelite are discussed in terms of diffusion dynamics. Those results suggest that closure temperatures for Sm-Nd within this mineral are relatively high in contrast to the temperature ranges of ore-formation responsible for scheelite-related deposits, and any later thermal environments. It is likely, therefore, that relevant isotopic information could be easily retained under most geological conditions, since initial crystallization of the scheelite. In addition, comparison of this mineral-element pair over a range of temperatures with some other common minerals used as geochronometers (e.g., zircon and apatite) indicates that Sm-Nd system has a slower diffusive rate in scheelite than for Sr in apatite or Ar in quartz, and only a little faster than for Pb in zircon. It should be noted, within most hydrothermal deposits where zircon has crystallized, its size is typically no more than 100 μm, whereas scheelite commonly occurs as macroscopic grains. For this reason, the larger dimensions of scheelite would provide a robust Sm-Nd system more able to resist perturbations, relating to any later thermal process. As such Sm-Nd investigations of scheelite are akin to U-Pb within zircon samples used in isotopic dating. These observations indicate that Sm-Nd age and isotopic information can provide reliable data in all but the most extreme case, especially when data are extracted from macroscopic grains of scheelite that are chosen to be “pristine” (i.e., free of surface alteration and/or fractures).     

A Multi–fluid Constrain for the Forming of Potash Deposits in the Savannakhet Basin: Geochemical Evidence from Halite

The Khorat Plateau on the Indochina Terrane is known to have formed during the closure of the Tethys Ocean, although the origin of its potash mineral deposits is a topic of current debate. Data from a borehole on Savannakhet Basin is used in this study to re-define the evaporation processes of the study area. Geochemical analyses of halite from various borehole-derived evaporite strata have elucidated the fluid sources from which these ores formed. Measured δ11 B indicated that ore deposits formed primarily due to evaporation of seawater, although non-marine fluids affected the later stages of the evaporation process. Fluctuations in B and Br concentrations in carnallite-and sylvite-rich strata indicate the influence of fresh water. Boron concentration in carnallite unit indicated the influence of hydrothermal fluids. From the relative timings of these various fluid influxes, the evolution of these evaporates can be divided into four stages:(1) an initial marine evaporation at the beginning of the deposit's formation, where seawater(and minor fresh water) trapped on the uplifted Khorat Plateau produced sediments and salts with Br contents lower than those of normal marine-derived evaporites;(2) a transgression stage, where seawater recharged the basin;(3) a hydrothermal infiltration stage, which was coeval with the late Yanshan movement; and(4) a stage of fresh water supply, as recorded by fluctuations in B and Br contents, inferring intermittent fresh water influx into the basin. Thus, although evaporites on the Savannakhet Basin primarily formed via marine evaporation, they were also influenced to a significant degree by the addition of non–marine fresh water and hydrothermal fluids.