Rare earth element and stable isotope (O, S) geochemistry of barite from the Bijgan deposit, Markazi Province, Iran

The Bijgan barite deposit, which is located northeast of Delijan in Markazi Province of Iran, occurs as a small lenticular body at the uppermost part of an Eocene volcano-sedimentary rock unit. The presence of fossiliferous and carbonaceous strata suggests that the host rocks were deposited in a quiet marine sedimentary environment. Barite, calcite, iron oxides and carbonaceous clay materials are found as massive patches as well as thin layers in the deposit. Barite is marked by very low concentrations of Sr (1–2%) and total amounts of rare earth elements (REEs) (6.25–17.39?ppm). Chondrite-normalized REE patterns of barite indicate a fractionation of light REEs (LREEs) from La to Sm, similar to those for barite of different origins from elsewhere. The La_CN/Lu_CN ratios and chondrite-normalized REE patterns reveal that barite in the Bijgan deposit is enriched in LREE relative to heavy rare earth elements (HREEs). The similarity between the Ce/La ratios in the barite samples and those found in deep-sea barite supports a marine origin for barite. Lanthanum and Gd exhibit positive anomalies, which are common features of marine chemical sediments. Cerium shows a negative anomaly in most samples that was inherited from the negative Ce anomaly of hydrothermal fluid that mixed with seawater at the time of barite precipitation. The δ¹⁸O values of barites show a narrow range of 9.1–11.4‰, which is close to or slightly lower than that of contemporaneous seawater at the end of the Eocene. This suggests a contribution of oxygen from seawater in the barite-forming solution. The δ³⁴S values of barites (9.5–15.3‰) are lower than that of contemporaneous seawater, which suggests a contribution of magmatic sulfur to the ore-forming solution. The oxygen and sulfur isotope ratios indicate that submarine hydrothermal vent fluids are a good analog for solutions that precipitated barite, due to similarities in the isotopic composition of the sulfates. The available data including tectonic setting, host rock characteristics, REE geochemistry, and oxygen and sulfur isotopic compositions support a submarine hydrothermal origin for the Bijgan barite deposit. At the seafloor, barite deposition occurred where ascending Ba-bearing hydrothermal fluids encountered seawater. Sulfate was derived from the sulfate-bearing marine waters, and, to a lesser extent, by oxidized H₂S, which was derived from magmatic hydrothermal fluids.     

NUMERICAL SIMULATION OF SEDIMENT TRANSPORT IN DYNAMIC FLOW CONDITIONS

1 INTRODUCTION Rivers as a source of life can at the same time impose devastating conditions on the environment. It is , therefore, imperative to analyse and predict river behaviour for different given conditions and engineering activities. Therefore, the use of simulation tools in this field has become a necessity. Many computational tools for simulation of sediment transport in rivers are now available that can be used for prediction and design under different flow conditions. However, …     

Emarat carbonate-hosted Zn–Pb deposit, Markazi Province, Iran: A geological, mineralogical and isotopic (S, Pb) study

The Emarat deposit, with a total proved reserve of 10 Mt ore grading 6% Zn and 2.26% Pb, is one of the largest Zn–Pb deposits in the Malayer–Esfahan belt. The mineralization is stratabound and restricted to Early Cretaceous limestones and dolomites. The ore consists mainly of sphalerite and galena with small amounts of pyrite, chalcopyrite, calcite, quartz, and dolomite. Textural evidence shows that the ore has replaced the host rocks and thus is epigenetic.Sulfur isotopes indicate that the sulfur in sphalerite and galena has been derived from Cretaceous seawater through thermochemical sulfate reduction. Sulfur isotope compositions of four apparently coprecipitated sphalerite–galena pairs suggest their precipitation was under equilibrium conditions. The sulfur isotopic fractionation observed for the sphalerite–galena pairs corresponds to formation temperatures between 77 °C and 168 °C, which agree with homogenization temperatures of fluid inclusions.Lead-isotope studies indicate that the lead in galena has been derived from heterogeneous sources including orogenic and crustal reservoirs with high ²³⁸U/²⁰⁴Pb and ²³²Th/²⁰⁴Pb ratios. Ages derived from the Pb-isotope model give meaningless ages, ranging from Early Carboniferous to future. It is probable that the Pb-isotope model ages that point to an earlier origin than the Early Cretaceous host rocks are derived from older reservoirs in the underlying Carboniferous or Jurassic units, either from the host rocks or from earlier-formed ore deposits within these units.This research and other available data show that the Emarat Zn–Pb deposit has many important features of Mississippi Valley-type (MVT) lead–zinc deposits and thus we argue that it is an MVT-type ore deposit.     

Plates on saturated porous elastic foundations

The problem of plates on consolidating soil is considered. Biot's three-dimensional consolidation theory, the generalization of Terzaghi's model, is employed to account for the consolidation process. A mathematical model is developed and the differential equations governing the system together with the proper boundary conditions are derived. A variational formulation of the problem and a convenient approximate method of solution are also presented. For numerical analysis, the problem of a rectangular plate on consolidating soil under various loading conditions is numerically solved and the effects of various physical factors on the settlements and the pore pressures are studied.     

The Effect of Air Bubbles and Headspace on the Aqueous Concentrations of Volatile Organic Compounds in Sampling Vials

The presence of headspace and air bubbles in volatile organic analysis sampling vials lowers the actual aqueous concentration of these compounds due to the partitioning of solutes into the gaseous phase. This could make the sample invalid for analysis.
In this work, the effects of air bubbles and headspace on the aqueous concentration of 60 volatile organic compounds listed in U.S.Environmental Protection Agency (U.S. EPA) Method 8260 were evaluated experimentally and theoretically. The results showed that for air to water ratios of 1 to 20 and less, there was no significant effect on the aqueous concentrations of target organic solutes in the sampling vials. When the air to water ratio was increased to 1 to 10, the recovery rates of four organic compounds were lower than the control. Laboratory experiments on sampling vials showed that the presence of air bubbles or headspace with the volumetric air to water ratios of 1 to 20 and less do not produce any significant effect on the original concentrations for most targeted volatile organic compounds.
The experimental results also indicated that in 40 mL sampling vials with headspace range of 2 to 8 mL, the recovery rates of most volatile organic compounds with high values of Henry's law constant (> 0.01 Atm m³/mol. at 25°C) were larger than the calculated rates.     

Weathering and soils formation on different parent materials in Golestan Province,Northern Iran

Geochemical, mineralogical, and micromorphological characteristics of soils and their relevant parent rocks including loess, ignimbrite, sandstone and limestone were investigated to identify the soil-parent material uniformity and the weathering degree of soils in Golestan Province, northern Iran. Highly developed Calcixerolls and moderately developed Haploxerepts were formed on loess and limestone, respectively. In contrast, the soils formed on ignimbrite and sandstone were non-developed Entisols. Illite was the dominant clay mineral found in ignimbrite and sandstone in both the A horizon and parent material. In loess derived soils however, smectite was dominant especially in the Bt horizon compared to its parent material indicating partly to its pedogenic formation. In limestone, illite and vermiculite were dominant both in the A and C horizons. Ti/Zr ratio proved that the studied soils were closely related to their underlying parent materials geochemically. Chemical index of alteration (CIA), micromorphological index of soil development (MISECA), smectite/illite+chlorite ratio and magnetic susceptibility were applied to investigate the degree of soil development. Results showed that the most and the least developed soils were those formed on loess deposits and limestone, respectively. Application of the different geochemical and pedogenetic approaches was proved to be useful in identifying the relevance of soils to their underlying parent materials and also their degree of development.     

Reliability and sensitivity analysis of wedge stability in the abutments of an arch dam using artificial neural network

In this study, the seismic stability of arch dam abutments is investigated within the framework of the probabilistic method. A large concrete arch dam is considered with six wedges for each abutment. The seismic safety of the dam abutments is studied with quasi-static analysis for different hazard levels. The Londe limit equilibrium method is utilized to calculate the stability of the wedges in the abutments. Since the finite element method is time-consuming, the neural network is used as an alternative for calculating the wedge safety factor. For training the neural network, 1000 random samples are generated and the dam response is calculated. The direction of applied acceleration is changed within 5-degree intervals to reveal the critical direction corresponding to the minimum safety factor. The Latin hypercube sampling (LHS) is employed for sample generation, and the safety level is determined with reliability analysis. Three sample numbers of 1000, 2000 and 4000 are used to examine the average and standard deviation of the results. The global sensitivity analysis is used to identify the effects of random variables on the abutment stability. It is shown that friction, cohesion and uplift pressure have the most significant effects on the wedge stability variance.

     

Prediction of River Stage-Discharge Process Based on a Conceptual Model Using EEMD-WT-LSSVM Approach

Water Resources - This study proposed a hybrid pre-processing approach along with a conceptual model to enhance the accuracy of river discharge prediction. In order to achieve this goal, Ensemble...     

Effects of environmental factors on classification of loessderived soils and clay minerals variations,northern Iran

Land-use type under different topographic conditions and human activities affects soil development. We investigated the effects of land-use, topography and human activity on soil classification changes in the Toshan watershed in northern Iran. Seven representative pedons derived from loess parent materials were studied on different land-uses and topographic positions. The studied pedons in forest (FO) on backslopes and footslope were classified as Calcic Haploxeralfs and Typic Haploxeralfs, respectively. The soils in abandoned lands (AB) and orchards (OR), where formerly under natural forests, located on the shoulder and backslopes positions were classified as Calcic Haploxeralfs and Vertic Haploxeralfs, respectively. Well-developed argillic horizons as indicators for higher degrees of soil evolution were observed in more-stable areas under the natural forest or less disturbed areas. Clay lessivage through these soil profiles have led to formation of Typic or Calcic Haploxeralfs, while under croplands (CP) were classified as Typic Calcixerepts. Conversion of sloping deforested areas to CP along with inappropriate management have accelerated soil erosion, resulting in unstable conditions in which decalcification and formation of developed soils cannot occur. Paddy cultivation in flat areas has caused to reduced conditions and formation of Typic Haplaquepts. Because of unfavorable conditions for chemical weathering (e.g. lower water retention compared to more-stable areas) no vermiculite was detected in the CP. The results showed that evolution and classification of the studied soils were strongly affected by land-use type, topography and management.