Integration of In Situ Experiments and Numerical Simulations to Reveal the Physicochemical Circumstances of Organic and Inorganic Precipitation at a Thermal Spring

Organic and inorganic precipitates are both characteristic in the active hypogenic karst area of Buda Thermal Karst in Hungary. As an active system, it is a good natural laboratory to study ongoing precipitation processes. Because of anthropogenic influence and the complexity of spring environments, it is challenging to reveal all the governing factors in the process of precipitation. In situ experiments, i.e. artificially controlled natural systems simplify the complexity by adding, excluding or stabilizing influencing parameters during the experiment. CO₂ degassing drives changes in the physicochemical parameters of spring waters from the discharge along their flow path. The rate and spatial extension of these changes depend on local hydrogeological, geological, climatic, topographical etc. factors, affecting precipitation processes. In this study, two one-day-long in situ experiments were executed to examine the physicochemical parameter changes of thermal water in a tunnel. The integration of the results with reactive transport models revealed the physicochemical processes of ingassing and degassing and predicted CaCO₃ precipitation along the flow path. Small-scale roughness of the channel surface seemed to further influence pH and concentration of HCO₃^?. After 6 weeks of thermal water flowing, organic precipitate (biofilm) formed close to the discharge and then, with a sharp change, inorganic precipitate (calcite) dominates a bit further from the discharge. In situ experiments and connected numerical simulations revealed the role of CO₂ degassing and calcite precipitation in the changes of physicochemical parameters, but organic precipitates also have to be considered near the discharge.     

Thermodynamic model of the formation of ore bodies at the Akchatau wolframite greisen-vein deposit

The Akchatau wolframite deposit in central Kazakhstan is a typical greisen deposit. Extensive geological and geochemical data, including those on numerous geochemical signatures (isotopic composition of O, H, C, noble gases, data on fluid inclusions, REE, and others) allowed us to decipher the physicochemical conditions and main factors that caused metasomatism and ore formation. Physicochemical modeling by the HCh program package (designed by Yu.B. Shvarov) was applied to reconstruct the composition of the greisenizing solution, cooling, boiling, interaction with granites; condensation of the gas phase; and fluid mixing. The predominant species of W transfer, (NaHWO _{4 aq} ⁰ ), and precipitation factors were determined. In small ore bodies, precipitation was caused by a temperature decrease. The precipitation of wolframite in near-vein greisens is related to the interaction of boiling highly mineralized solutions with host granites. Boiling does not affect wolframite precipitation but increases the content and ore potential of the greisenizing fluids, facilitating the formation of high-grade wolframite ores. In the filling veins of these bodies, ore precipitation is related to the dilution of solutions by weakly mineralized exogenic waters and the condensate of the gas phase. Tungsten mineralization of the Akchatau deposit was formed in an oxidizing environment, which is controlled by granite minerals during mobilization of ore components.     

Bacterially mediated mineralization of vaterite

Myxococcus xanthus, a common soil bacterium, plays an active role in the formation of spheroidal vaterite. Bacterial production of CO₂ and NH₃ and the transformation of the NH₃ to and OH⁻, thus increasing solution pH and carbonate alkalinity, set the physicochemical conditions (high supersaturation) leading to vaterite precipitation in the microenvironment around cells, and directly onto the surface of bacterial cells. In the latter case, fossilization of bacteria occurs. Vaterite crystals formed by aggregation of oriented nanocrystals with c-axis normal to the bacterial cell-wall, or to the core of the spherulite when bacteria were not encapsulated. While preferred orientation of vaterite c-axis appears to be determined by electrostatic affinity (ionotropic effect) between vaterite crystal (0001) planes and the negatively charged functional groups of organic molecules on the bacterium cell-wall or on extracellular polymeric substances (EPS), analysis of the changes in the culture medium chemistry as well as high resolution transmission electron microscopy (HRTEM) observations point to polymorph selection by physicochemical (kinetic) factors (high supersaturation) and stabilization by organics, both connected with bacterial activity. The latter is in agreement with inorganic precipitation of vaterite induced by NH₃ and CO₂ addition in the protein-rich sterile culture medium. Our results as well as recent studies on vaterite precipitation in the presence of different types of bacteria suggest that bacterially mediated vaterite precipitation is not strain-specific, and could be more common than previously thought.     

锡矿山超大型锑矿床流体成矿作用及矿床成因

本文对锡矿山流体包裹体,稳定同位素,活动性微量元素,硅化作用及元素存在相态和淋滤率进行了详细研究。揭示了其成矿流体来源于深循环大气降水,是一种中低温,低盐度的弱碱性流体,成矿物质来自于前泥盆系地层,主要是震旦,寒武系地层,区域地层可能经受过大规模的流体运移作用。得出了锡矿山锑矿是由深循环大气降水林滤基底地层的成矿物质后形成含矿流体沿主断裂向上运移至浅部,由于物理化学条件的改变导致锑沉淀成矿的结论。     

Study of groundwaters using the environmental tritium and hydrochemical data in the Belgrade region

A study of tritium content and some physicochemical parameters has been performed in order to investigate interconnection between surface and atmospheric waters and underground waters in Belgrade area. Samples of the precipitation at Zeleno Brdo-Belgrade meteorological station, the Danube and the Sava river water, and underground water (Ranney wells and piezometers) have been analyzed. The³H content, the content of dissolved ions, total hardness, and electrical conductivity have been measured. The tritium data show existence of two water strata in the aquifer. The upper stratum (about 16 m thick) contains older water (mean monthly³H concentration of 17 TU) and has weak interaction with the river and the precipitation. Below this stratum lies the principal water bearing stratum, strongly connected with the river with the³H concentration similar to that of surface water (mean monthly³H concentration of 50 TU) and spreading out through the entire aquifer. The contribution of the Sava river water and the two water layers at the Ranney well are calculated starting with the hydrological aquifer model, which supposes that three water components are mixed in the pumped Ranney well water. According to calculation results using the³H concentration and physicochemical characteristics as parameters, more than 70 percent of the water pumped by the Ranney well (in 1983) comes from the Sava with a time delay of less that 15 days.Properties of tritium distribution in precipitation, river waters, and underground water in the Belgrade region are established from the results of measurements of³H concentrations in the period 1976–1983.     

安徽铜陵狮子山矿田铜、金共生与分离的热力学研究

狮子山矿田是安徽铜陵矿集区内最具代表性的大型铜金多金属矿田.矿田内铜、金矿床或矿体既各自独立产出,义相互共生或伴生,铜矿化和金矿化在时间上和空间上存在既共生又分离的现象.本文选择矿田内代表性铜矿床和金矿床开展系统的流体包裹体地球化学研究,并进行成矿流体中铜、金溶解度的热力学理论计算和1分析,探索铜、金共生与分离的机制和...     

Was Phanerozoic reef history controlled by the distribution of non-enzymatically secreted reef carbonates (microbial carbonate and biologically induced cement)?

Throughout most of the Phanerozoic, reef rigidity resulted as much, or more, from early lithification by microbial carbonates and biologically induced cements (non-enzymatic carbonates) than from biological encrustation of, or by, large, enzymatically secreted metazoan skeletons. Reef framework is divided into four categories: (1) skeletal metazoan; (2) non-skeletal microbialite (stromatolite and thrombolite); (3) calcimicrobe; and (4) biocementstone, in which small or delicate organisms serve as scaffolds for rigid cement crusts. The last three categories are dominated by non-enzymatic carbonates. Skeletal framework and non-skeletal microbialite framework were the most abundant framework types through the Phanerozoic. The composition and abundance of skeletal framework was controlled largely by mass extinction events, but most reefs consisted of both microbialite and skeletal organisms in a mutually beneficial relationship. Microbialite framework was abundant throughout the Palaeozoic and early Mesozoic, but declined after the Jurassic. Calcimicrobe framework was important during the Cambrian-Early Ordovician and Devonian and biocementstone framework was important from the late Mississippian to the Late Triassic. The Phanerozoic history of reefs does not correlate well with the stratigraphic distribution of large, skeletal ‘reef builders’, or with a variety of physicochemical parameters, including sea-level history, Wilson Cycle or global climate cycles. Because non-enzymatic carbonates result from induction by non-obligate calcifiers, and not enzymatic precipitation by obligate calcifiers, the distribution of these carbonates was controlled to a larger extent by temporal changes in physicochemical parameters affecting the saturation state of sea water with respect to carbonate minerals. Changes in pCO₂, Ca/Mg ratios, cation concentrations and temperature may have affected the abundance of non-enzymatic carbonates and, hence, reefs, independently from the effects of these same parameters and mass extinction events on skeletal reef biota. The decline in abundance of reefal microbialite and absence of calcimicrobe and biocementstone reef framework after the Jurassic may be a result of relatively low saturation states of sea water owing to increased removal and sequestration of finite marine carbonate resources by calcareous plankton since the Jurassic. Reef history is difficult to correlate with temporal changes in specific global parameters because these parameters affect skeletal biota and biologically induced carbonate precipitation independently. Hence, reef history was regulated not just by skeletal reef biota, but by parameters governing non-enzymatic carbonates.     

Geochemical mobility of Au and Ag during hydrothermal transfer and precipitation: Thermodynamic simulation

The thermodynamic simulation of the geochemical mobility of Au and Ag during their hydrothermal transfer and precipitation was conducted with regard for the formation of continuous nonideal Au-Ag solid solutions (or Au_XAg_1?X) alloys) and with the analysis of the effects of principal physicochemical parameters (temperature, pH, redox potential, and the concentrations of sulfide sulfur and chloride ions) on the solubility of Au-Ag alloys of various composition. Predominant Au and Ag complexes and the types of solutions were identified, which are characterized by different extractive ability with respect to these metals. A tendency in the variations in the Au/Ag ratio in the solid phase during the evolution of the hydrothermal process was revealed with regard for various conditions under which Ag sulfides can occur. The possible effect of the Au_XAg_1?X/solution ratio on the composition of the Au-Ag mineralization was demonstrated, and tendencies in the variations in the composition (fineness) of the alloys during their redeposition were identified.     

Silicification of Riphean Carbonate Sediments (Yurubcha-Tokhomo Zone,Siberian Craton)

Types and lateral and vertical distribution of silicification in Riphean (largely dolomitic) rocks of the Yurubcha-Tokhomo zone of the Siberian Craton are discussed. It is shown that quartz and pyroclastic material in sediments were subjected to intense dissolution in a highly alkaline Riphean basin with the release of silica. Rapid and abrupt decrease in alkalinity during hiatus and desiccation periods resulted in the precipitation of dissolved silica and silicification of near-surface sediments. Lateral distribution of silicification was controlled by the redistribution of silica during the pre-Vendian hiatus, when surface waters were filtered through a carbonate massif with the simultaneous karst formation and silica dissolution. In the water discharge area, secondary silica was precipitated owing to changes in pH values and other physicochemical conditions.     

Simulating experiment on the hydrothermal superimposing metallogenesis of the Dongguashan strata-bound copper deposit

Series of sedimentary hydrothermal-diplogenetic copper deposits have been found scattering in the region along the middle-lower reaches of the Yangtze River, and their metallogenetic mechanism is still in hot debate. In order to reveal the ore-forming kinetics of sedimentary process and hydrothermal superimposition, and evaluate the role of sedimentary pyrite in the enrichment and precipitation of copper, a set of simulating experiments on the reaction between pyrite and CuCl2 solution were conducted. According to the physicochemical characteristics of the ore-forming fluid of the Dongguashan copper deposit, Anhui Province, 100 MPa was selected as the experimental pressure, and the experimental temperatures were set at 450, 350, 250 and 150°C, respectively. The reactions between pyrite grains isolated from the Shimenkou strata-bound pyrite deposit and the solution with 0.2 mol/L CuCl2 and 1.0 mol/L NaCl were experimentally simulated. Then, variations in surface topography and surface chemistry of the experimental pyrite grains were documented using scanning electronic microscopy (SEM), atomic force microscopy (AFM), Auger electron spectrometry (AES) and X-ray photoelectron spectroscopy (XPS), and the solution and newly formed minerals were analyzed using inductively coupled plasma (ICP-AES) and X-ray diffraction (XRD) techniques. Desulphurization of pyrite surface was observed and new copper minerals were detected. It is proposed that pyrite can act as a geochemical barrier for the enrichment and precipitation of copper from the solution under the experimental conditions. Furthermore, the ore-forming mechanism of sedimentary hydrothermal-diplogenetic copper deposits was discussed.     

Phosphate stromatolites from condensed cephalopod limestones, Upper Jurassic, Southern Spain

Upper Jurassic phosphate stromatolites of the Almola Sierra (Southern Spain) encrust macrofossils and hardgrounds, and form oncoids included within pelagic, condensed fossiliferous limestones. Their accretion was determined by bacterially mediated precipitation of phosphate, by the trapping and binding of fine siliciclastics and pelagic biomicrite and by the encrustation of benthonic foraminifera. Phosphorous, trace elements and rare-earth elements were concentrated from degraded organic matter and seawater by stromatolite-building communities, which mediated the formation of phosphate-rich and Fe-Al-Si-rich organic gels under oxic conditions, favouring the precipitation of amorphous mineral precursors (ACP and Fe-Al-Si oxyhydroxides). The observed Ce-enrichment for some stromatolites is explained by oxidative scavenging of Ce⁴⁺ from seawater by Fe—Mn oxyhydroxides. The bacterially mediated gels were able to migrate and fill the voids of the stromatolite structure, and later changed to carbonate-fluorapatite, haematite and poorly crystalline Fe-rich clays under postoxic conditions. Phosphatization of trapped carbonate particles also occurred. The phosphate stromatolites formed on a sediment-starved pelagic swell, during periods of no carbonate sedimentation and hardground development. Stromatolite lamination provides evidence for rhythmic alternation between bacterially mediated phosphogenesis, sedimentation and erosion, suggesting episodic changes in the sedimentary environment. Although some of the parameters that controlled phosphate precipitation associated with the stromatolites (local high organic productivity, sediment starvation, moderate depth of deposition and physicochemical conditions) were similar to those found in modern and ancient phosphogenic settings, the palaeogeographical framework and the intensity of sedimentary processes were different to those of the World's major phosphorite deposits.     

还原体（体系）与富铀矿的形成

铀是变价元素,还原体(体系)在铀富集过程中起着相当重要的作用。还原体(体系)可分两类:一类为自还原体(体系),这是指还原体(剂)是热液本身的还原体系,还原剂和铀在同一热液体系中搬运、迁移,然后在变化了的物理化学条件下,铀依靠热液本身的还原性能而被还原沉淀。另一类为外部还原体系,这是指铀的沉淀的还原作用是依靠围岩中的还原剂或地球化学场。两类还原体(体系)对铀的富集成矿具有不同方式,从而有不同的地质环境要求。     

Coordination nature of aluminum (oxy)hydroxides formed under the influence of low molecular weight organic acids and a soil humic acid studied by X-ray absorption spectroscopy

Organic ligands in the environment hinder the formation of crystalline Al precipitation products by perturbing the hydrolytic and polymeric reactions of Al resulting in the formation of short-range ordered (SRO) mineral colloids with varying degrees of crystallinity. However, the effect of these ligands on the mechanisms of their formation and nature of the transformation products of Al (oxy)hydroxides at the atomic and molecular levels is not well understood. In this study, the coordination structure of Al in Al (oxy)hydroxides formed under the influence of varying concentrations of low molecular weight (LMW) organic acids such as citric, malic, salicylic and acetic acids and a humic acid (HA) was investigated with X-ray absorption near edge structure (XANES) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction analysis. The Al K- and L-edge XANES spectra showed that with increasing LMW organic acid concentration the coordination number of Al changed from 6-fold to a mixture of 4- and 6-fold, except for acetate as acetate was unable to perturb the formation of Al (oxy)hydroxides at the acetate/Al molar ratio (MR) = 0.1. The proportion of 4-fold to 6-fold coordinated Al in the Al precipitation products depended on the structure and functionality of the LMW organic acids. The incorporation of the LMW organic acid into the network structure of Al (oxy)hydroxides prevented the formation of sheets/inter-layer H-bonding that was required for the formation of crystalline Al (oxy)hydroxides. The HA used in this study only slightly perturbed the crystallization of the Al (oxy)hydroxides at the concentrations used. The Al K-edge data showed that Al coordination number had not been altered in the presence of HA. The findings obtained in the present study are of fundamental significance in understanding the physicochemical behavior of soils and sediments, and their relation to the accumulation and transport of nutrients and pollutants in the environment.     

Fahlores of the Prasolovka Au-Ag volcanogenic deposit, Kunashir Island, Russian Far East

The chemical study shows that fahlores from the Prasolovka deposit are complex compounds with significant variations in their composition and the proportions of their constituent elements. Based on their major-element composition, they are subdivided into 3 species and 11 inter-and intra-species varieties. The chemical composition of the fahlores in different mineral assemblages from different ore types indicates that As fahlores subsequently replaced by Sb, Te-Sb, and Te fahlores during ore precipitation. The revealed evolution of the ore solutions from the early to late stages testifies that different ores at the Prasolovka deposit were formed under different physicochemical conditions.     

热液成矿分带的溶解－沉淀波结构

热液成矿分带是一种输运－反应问题。热液成矿分带基本属于渗滤交代分带性质，它是溶解－沉淀波在可渗透介质中形成和传播的结果。本文应用物理化学流体动力学中的渗滤与溶解－沉淀反应耦合过程理论研究溶解－沉淀波的结构特征，并进一步应用多组分耦合系统动力学中的用于原理揭示其形成的动力学机制，最后提出了一种热流成矿分带理论，对热液成矿分带问题的性质、热液成矿分带的本质和热液成矿分带的结构特征与形成机制提出了新认识。     

热液成矿作用地球化学:以金矿为例

文中以金矿为例总结了热液成矿地球化学特征,包括热液蚀变、金在成矿热液中的地球化学行为、富集-沉淀机制以及在硫化物中的存在形式。热液蚀变过程中形成的矿物组合反映了成矿流体的地球化学特征,蚀变模式具有重要的找矿勘探意义。在热液体系中,金主要以Au-Cl或者Au-S络合物的形式进行运移,体系温度、压力、氧逸度以及硫逸度等条件的变化是导致络合物分解、金沉淀的主要机制。在较高压力条件下,金趋向于在热液蒸汽相中富集。As和Sb是金矿热液体系中常见的伴生元素,在较低硫逸度条件下,形成自然砷/自然锑-自然金组合。金从热液中沉淀后主要以显微包裹体或者固溶体金的形式赋存于黄铜矿、毒砂、磁黄铁矿以及黄铁矿等硫化物中,而硫化物中固溶体金的量主要受热液H_2S活动性的控制。     

Source of salinity in the groundwater of Lenjanat Plain,Isfahan, Iran

The present study aimed at identifying the salinity source in the groundwater of Lenjanat Plain. To do so, non-isotopic geochemical methods were employed: groundwater samples were collected seasonally from 33 wells widespread in the area, and physicochemical parameters as well as major and minor elements were measured in the 132 samples. The data collected from the field and laboratory measurements were interpreted through statistical and hydrogeochemical graphs, mass ratios and saturation indexes obtained from modeling. The results revealed that hydrogeochemical properties of the study aquifer were controlled by rock/water interactions including ion exchange, dissolution of evaporation deposits (halite and gypsum) and precipitation/dissolution of carbonates. Based on the values of Cl/Br ratio in Lenjanat groundwater (329–4,492), dissolution of evaporation deposits in aquifer was the main cause for groundwater salinity. Considering the Lenjanat groundwater geochemical properties, the data confirm the reported Cl/Br ratios for groundwater affected by the dissolution of evaporation deposits (Cl/Br > 300) and overlaps with the range of Cl/Br ratios for domestic sewage effluent groundwater. Selecting the best chemical components and their ratios in non-isotopic geochemical methods provides an accurate distinction between sources of groundwater salinity.     

1965-2015年新疆夏季不同等级降水的空间分布特征

根据新疆51个台站1965-2015年夏季逐日降水资料,将降水划分为小雨、中雨及大雨3个等级,分析了新疆近51 a夏季不同等级降水量、降水日数及降水强度的空间分布特征,并讨论了各等级降水日、降水量及降水强度与总降水量的空间相似程度以及各等级降水对夏季总降水的贡献。结果表明：新疆降水主要集中在夏季,并以小雨为主。以天山山脉为界,南北两疆降水空间分布存在明显差异,北疆夏季降水量（日）占年降水量（日）的36%~45%（36%~39%）,南疆夏季降水量（日）占年降水量（日）的51%~63%（48%~60%）;新疆夏季不同等级降水量、降水日及降水强度的空间分布不均匀。新疆夏季总降水量与各等级降水量的空间相似系数最为密切,与各等级降水强度的空间相似系数相对较小;新疆夏季小雨贡献率最大,中雨其次,大雨最小,夏季降水量和降水日的变化主要受小雨的影响。     

富F熔体-溶液流体体系的地球化学性状及成矿效应研究进展

F既是重要的岩浆挥发分,又是重要的助熔剂和矿化剂,同时也是克拉克值较大的元素之一,并且在(铝)硅酸盐熔体中高度可溶。本文从F的常见工业矿物和主要赋存形式、分配行为的多样性、对其它元素分配行为的影响、矿化作用(即亲氟元素在热液体系中的氟化物络合形式、存在环境和沉淀机制等)、萤石和冰晶石的溶解及沉淀机制以及富F岩浆一热液体系的成矿专属性及特征6个方面探讨了F的地球化学成矿作用。结论认为:F必须有能力大量进入与花岗质或伟晶岩质熔体共存的含水流体相中才具有进一步的成矿学意义,云英岩化、钠长石化、含黄玉—萤石石英脉、具有较高F/CaO比值的残余熔体以及F在高度演化花岗质岩浆中的过饱和等因素均可能导致含矿富F热液的出溶;但总体上,富F岩浆—热液体系具有成矿专属性的原因之一仍在于:F首先通过对熔体物理化学性质的影响间接支配着高场强亲氟元素如W、Sn、Nb、Ta、REE、U等的热液成矿效应。     

云南东川铜矿床流体演化与成矿机制研究

东川铜矿床是我国重要的沉积岩容矿的层状铜矿床(SSC),具有显著的多层位成矿特征和典型的铜硫化物分带。本研究以不同层位铜矿体的流体包裹体为研究对象,通过岩相学观察、显微测温和激光拉曼成分分析,发现东川群多层位铜矿体存在浅色和深色包裹体2种类型:浅色包裹体成分以H₂O为主,含丰富的石盐子晶和少量钾盐、硬石膏子晶,代表了氧化型含矿卤水,具中低温(140~300 ℃)、中高盐度(12%~44%)的特征,属于Na ⁺、K ⁺、Ca ²⁺-Cl ^-(SO₄ ^2-)型盆地卤水,主要来源于海相蒸发岩的溶解和层间建造水;深色的含有机质包裹体代表了还原型流体,来源于黑山组碳质板岩和落雪组中的藻类生物分解。东川铜矿床以落雪组的含叠层石砂质白云岩作为主要沉淀系统,黑山组碳质板岩为隔挡层,形成一个流体封闭的物理化学圈闭,氧化含矿卤水通过供给系统运移到具还原性质的沉淀系统中,与还原型富硫流体和含有机质的地层发生混合反应,形成多层位的层状铜矿体和层控脉状铜矿体。