Petrology and geochemistry of the Shilu Fe-polymetallic ore deposit in Hainan Province of

地球化学英文The study of Earth's chemistry, also known as geochemistry, involves the investigation of the chemical composition and processes of the Earth and its various systems. Geochemists examine the distribution and cyclingof elements and compounds within the Earth, as well astheir interactions with the atmosphere, hydrosphere, biosphere, and lithosphere.Geochemistry plays a crucial role in understanding the Earth's past, present, and future. By analyzing thechemical makeup of rocks, minerals, soils, water, and gases, geochemists can unravel the history of the Earth'sformation and evolution. They also study the impact of human activities on the environment, such as the release of pollutants into the air and water.One of the key areas of focus in geochemistry is the study of elemental abundances and the distribution of elements within the Earth's crust, mantle, and core. This involves investigating the processes of element formation, transport, and differentiation that have occurred over billions of years. Geochemists also explore the behavior ofelements under different environmental conditions, such as high pressures and temperatures, to understand their geochemical behavior.Geochemistry also plays a vital role in the exploration and extraction of natural resources, such as minerals, ores, and fossil fuels. By studying the geochemical signatures associated with these resources, geochemists can identify potential deposits and assess their economic viability. Additionally, geochemical techniques are used to monitorand mitigate environmental impacts associated with mining and resource extraction.Furthermore, geochemistry has important applications in environmental and climate studies. By analyzing thechemical composition of air, water, and soil, geochemists can assess the impact of human activities on the environment, such as pollution and climate change. Theyalso study natural processes, such as the carbon andnitrogen cycles, to understand their role in regulating the Earth's climate.In conclusion, geochemistry is a multidisciplinary field that integrates principles of chemistry, physics, biology,and geology to study the Earth and its processes. It has wide-ranging applications, from understanding the Earth's history to addressing contemporary environmental challenges and resource management.地球化学是研究地球及其各个系统的化学成分和过程的科学，也被称为地球化学。

环境地质学英语Environmental Geology（环境地质学）Geology（地质学）:1.Mineralogy（矿物学）2.Petrology（岩石学）3.Structural Geology（构造地质学）4.Sedimentology（沉积学）5.Stratigraphy（地层学）6.Geochemistry（地球化学）7.Geophysics（地球物理学）8.Paleontology（古生物学）Environmental Geology（环境地质学）:1.Environmental Geology Overview（环境地质学概述）2.Environmental Mineralogy（环境矿物学）3.Environmental Geochemistry（环境地球化学）4.Environmental Geophysics（环境地球物理学）5.Hydrogeology（水文地质学）6.Engineering Geology（工程地质学）7.Coastal Geology（海岸地质学）8.Geohazards（地质灾害）nd Use Planning（土地利用规划）10.W aste Disposal（废物处理）11.G roundwater Contamination（地下水污染）12.E nvironmental Risk Assessment（环境风险评估）13.E nvironmental Monitoring（环境监测）14.N atural Resource Management（自然资源管理）15.E nvironmental Remediation（环境修复）16.C limate Change and Environmental Geology（气候变化与环境地质学）17.S ustainable Development and Environmental Geology（可持续发展与环境地质学）18.E nvironmental Law and Policy（环境法律与政策）1.Groundwater Remediation（地下水修复）2.Geologic Hazards（地质灾害）3.Soil Mechanics（土力学）4.Soil Erosion（土壤侵蚀）5.Soil Contamination（土壤污染）6.Geologic Mapping（地质制图）7.Geologic Time Scale（地质时间尺度）8.Earthquake Hazard Assessment（地震危险评估）9.Ecological Footprint（生态足迹）10.Environmental Impact Assessment（环境影响评价）11.Geologic Disposal of Radioactive Waste（放射性废物地质处置）12.Coastal Zone Management（海岸带管理）13.Acid Mine Drainage（酸性矿山排放）14.Geologic Carbon Sequestration（地质碳封存）15.Soil Conservation（土壤保护）16.Ground Penetrating Radar（地质雷达）17.Geomorphology（地貌学）18.Geologic Remote Sensing（地质遥感）19.Environmental Geotechnics（环境岩土工程）20.Environmental Isotope Geochemistry（环境同位素地球化学）这些术语都是环境地质学中非常重要的概念，涉及到环境保护、资源利用、地质灾害等多个方面。

2019职称英语综合类阅读精选：PetroleumGeology and Other SciencPetroleum Geology and Other Sciences 石油地质学与其它科学1. Petroleum geology is the application of geology (thestudy of rocks) to the exploration for and production of oil and gas. Geology itself is firmly based onchemistry,physics,and biology,involving the application of essentially abstract concepts to observed data. In the past these data were basically observation and subjective,but they are now increasingly physical and chemical,and therefore more objective. Geology,in general,and petroleum geology,in particular,still rely on value judgements based on experience and an assessment of validity among the data presented.1、石油地质学是地质学(岩石研究)在油气勘探开发和生产中的应用。

地质学本身是以化学、物理和生物学为基础，应用其基本的抽象理论概念来解释观察到的资料。

在过去，这些资料主要凭主观观察获取。

现在借助物理和化学手段，因而更具客观性。

从根本上讲，地质学和石油地质学，仍然特别依赖于基于经验的数值判断和对现有资料的有效性评估。

第38卷第2期 吉林地质 Vol.38 No.2 2019年06月 JILIN GEOLOGY Jun. 2019 文章编号：1001—2427（2019）02 - 19 -吉林大石头河子地区新生代橄榄玄武岩岩石学和地球化学研究张 辉1，李翱鹏1，王福亮1，刘正阳21. 吉林省地质调查院，吉林 长春 130102；2.吉林省地质矿产勘查开发研究院，吉林 长春 130061摘要：吉林大石头河子地区新生代橄榄玄武岩为裂隙式喷发火山活动所产出的溢流相橄榄玄武岩，属于钙碱性玄武岩，岩浆来源于软流圈地幔，上升过程中经历了不同程度的橄榄石、单斜辉石的分离结晶作用，但基本未受到地壳物质混染作用影响，形成与滨太平洋板块俯冲引起的松花江断裂再次复活，诱发区域性张裂作用关系密切，构造背景为板内拉张环境。

关键词：橄榄玄武岩；岩石地球化学；岩石成因；大石头河子地区中图分类号：P618.13文献标识码：APetrology and geochemistry of Cenozoic olivine basalt inthe Dashitouhezi area of Jilin ProvinceZHANG Hui1, LI Ao-peng1, WANG Fu-liang1, LIU Zheng-yang21. Geological Survey of Jilin Province, Changchun 130102, Jilin,China;2.Research Institute of Geology and Mineral ResourcesExploration and Development of Jilin Province, Changchun 130061, Jilin, China Abstract: Cenozoic olivine basalts in Dashitouhezi area, Jilin Province, are overflow facies olivine basalts produced by fissure eruption volcanic activity, belonging to calc-alkaline basalts, whose magma comes from asthenospheric mantle. The magma has undergone the separation and crystallization of olivine and clinopyroxene to varying degrees, but it has not been affected by the contamination of crustal materials. Its formation is closely related to the revival of the Songhuajiang fault caused by the subduction of the littoral Pacific plate and the regional tension. The tectonic setting is the intraplate tension environment.Key words: Olivine basalts; geochemistry; petrogenesis; Dashitouhezi area0 引言 研究区处于敦化—密山断裂以西，伊通—依兰断裂以东以及索伦—西拉木伦—长春缝合带以北的区域范围内，是张广才岭造山带的重要组成部分(图1b)。

拉脊山口蛇绿混杂岩中辉绿岩的地球化学特征及SHＲIMP锆石U-Pb年龄*付长垒1闫臻1＊＊郭现轻2牛漫兰3夏文静3王宗起2李继亮4FU ChangLei1，YAN Zhen1＊＊，GUO XianQing2，NIU ManLan3，XIA WenJing3，WANG ZongQi2and LI JiLiang41.中国地质科学院地质研究所，大陆构造与动力学国家重点实验室，北京1000372.中国地质科学院矿产资源研究所，北京1000373.合肥工业大学资源与环境工程学院，合肥2300094.中国科学院地质与地球物理研究所，北京1000291.State Key Laboratory of Continental Tectonics and Dynamics，Institute of Geology，Chinese Academy of Geological Sciences，Beijing100037，China2.Institute of MineralＲesources，Chinese Academy of Geological Sciences，Beijing100037，China3.Department ofＲesources and Environment，Hefei University of Technology，Hefei230009，China4.Institute of Geology and Geophysics，Chinese Academy of Sciences，Beijing100029，China2013-01-30收稿，2013-06-24改回.Fu CL，Yan Z，Guo XQ，Niu ML，Xia WJ，Wang ZQ and Li JL.2014.Geochemistry and SHＲIMP zircon U-Pb age of diabases in the Lajishankou ophiolitic mélange，South Qilian terrane.Acta Petrologica Sinica，30（6）：1695－1706Abstract The Lajishankou ophiolitic mélange，which is an important ingredient of the ophiolitic mélange between the Central and the South Qilian terranes，contains varities of lithological units showing tectonic relationship between them.Diabases in this mélange occur as blocks and dykes respectively.The formers have SiO2contents of49.80% 50.13%，MgO contents of5.43% 5.64%，FeO T contents of10.96% 11.52%and relatively higher TiO2contents of2.38% 2.62%；the laters have SiO2contents of43.41%45.74%，MgO contents of9.04% 10.64%，FeO T contents of8.39% 9.96%and low TiO2contents of0.89% 1.02%.Theybelong to tholeiitic rocks.The diabase blocks have high totalＲEE contents（135.4ˑ10－6 150.9ˑ10－6）and（La/Yb）Nratios （3.51 4.03）with right-inclinedＲEE patterns and enrichment in large ion lithophile elements（includingＲb，Ba，K，Sr）and high field strength elements（including Th，Nb，Ta，Zr，Hf，Ti），showing typical features of OIB.However，the diabase dykes have lowtotalＲEE contents（36.10ˑ10－6 43.72ˑ10－6）and（La/Yb）Nratios（1.12 1.20）and flatＲEE patterns，indicating similar character of MOＲB.In addition，diabase blocks and dykes are lack of negative Nb，Ta and Ti anomalies.SHＲIMP zircon U-Pb dating of diabase block yields a weighted mean206Pb/238U age of491.0ʃ5.1Ma，representing the age of crystallization.These characters suggest that the mafic diabases in the Lajishankou ophiolitic mélange were probably formed in ocean island/seamount and mid-ocean ridge environments，which were mixed with other lithological units during the northward subduction-accretion of the Proto-Tethys Ocean.Key words Diabase；Ocean island/Seamount；Mid-ocean ridge；Ophiolitic mélange；Lajishan Mountain摘要拉脊山口蛇绿混杂岩是分布于中祁连和南祁连构造带之间蛇绿混杂带的重要组成部分。

Chapter 13: Reactions at the Earth’s Surface: Weathering, Soils, and Stream ChemistryIntroductionThe geochemistry of the Earth's surface is dominated by aqueous solutions and their interactions with rock. We saw in the last chapter that the upper continental crust has the approximate average composition of granodiorite, and that the oceanic crust consists of basalt. But a random sample of rock from the crust is unlikely to be either; indeed it many not be an igneous rock at all. At the very surface of the Earth, sediments and soils predominate. Both are ultimately produced by the interaction of water with Òcrystalline rockÓ (by which we mean igneous and metamorphic rocks). Clearly, to fully understand the evolution of the Earth, we need to understand the role of geochemi-cal processes involving water.Beyond that, water is essential to life and central to human activity. We use water for drinking, cooking, agriculture, heating, cooling, resource recovery, industrial processing, waste disposal, trans-portation, fisheries, etc. Water chemistry, i.e., the nature of solutes dissolved in it, is the primary factor in the suitability of water for human use. ÒPollutedÓ water is unsuitable for drinking and cook-ing; saline water is unsuitable for these uses as well as agriculture and many industrial uses, etc. W e have been particularly concerned with water pollution in the past few decades; that is with the im-pact of human activity on water chemistry. Both our advancing technology and our exponentially in-creasing numbers have made pollution problems progressively worse, particularly over the past cen-tury. However, we have also become more aware of the adverse impact of poor water quality on hu-man health and the quality of life, and perhaps less tolerant of it as well.Understanding and addressing problems of water pollution requires an understanding of the behav-ior of natural aqueous systems for at least two reasons. First, to identify pollution, we need to know the characteristics of natural systems. For example, Pb can be highly toxic, and high concentrations of Pb in the blood have been associated with learning disabilities and other serious problems. How-ever, essentially all waters have some finite concentration of Pb; we should be concerned only when Pb concentrations exceed natural levels. Second, natural processes affect pollutants in the same way they affect their natural counterparts. For example, cadmium leached from landfills will be subject to the same adsorption/desorption reactions as natural Cd. To predict the fate of pollutants, we need to understand those processes.In this chapter, we focus on water and its interaction with solids at the EarthÕs surface. We can broadly distinguish two kinds of aqueous solutions: continental waters and seawater. Continental wa-ters by this definition include ground water, fresh surface waters (river, stream and lake waters), and saline lake waters. The compositions of these fluids are obviously quite diverse. Seawater, on the other hand, is reasonably uniform, and it is by far the dominant fluid on the earth's surface. Hy-drothermal fluids are third class of water produced when water is heated and undergoes accelerated interactions with rock and often carry a much higher concentration of dissolved constituents than fresh water. Our focus in this chapter will be on the chemistry of continental waters and how they interact with rock. We we consider seawater in Chapter 15.Redox in Natural WatersThe surface of the Earth represents a boundary between regions of very different redox state. The atmosphere contains free oxygen and therefore is highly oxidizing. In the EarthÕs interior, however, there is no free oxygen, Fe is almost entirely in the 2+ valance state, reduced species such as CH4, CO, and S2 exist, and conditions are quite reducing. Natural waters exist in this boundary region and their redox state, perhaps not surprisingly, is highly variable. Biological activity is the principal cause of this variability. Plants (autotrophs) use solar energy to drive thermodynamically unfavorablephotosynthetic reactions that produce free O 2, the ultimate oxidant, on the one hand and organicmatter, the ultimate reductant, on the other. Indeed it is photosynthesis that is responsible for theoxidizing nature of the atmosphere and the redox imbalance between the EarthÕs exterior and inte-rior. Both plants and animals (heterotrophs) liberate stored chemical energy by catalyzing the oxi-dation of organic matter in a process called respiration . The redox state of solutions and solids at theEarthÕs surface is largely governed by the balance between photosynthesis and respiration. By thiswe mean that most waters are in a fairly oxidized state because of photosynthesis and exchange withthe atmosphere. When they become reducing, it is most often because respiration exceeds photosyn-thesis and they have been isolated from the atmosphere. Water may also become reducing as a resultof reaction with sediments deposited in ancient reduced environments, but the reducing nature of thoseancient environments resulted from biological activity. Weathering of reduced primary igneous rocksalso consumes oxygen, and this process governs the redox state of some systems, mid-ocean ridge hy-drothermal solutions for example. On a global scale, however, these processes are of secondary im-portance for the redox state of natural waters.The predominant participants in redox cycles are C, O, N, S, Fe, and Mn. There are a number ofother elements, for example, Cr, V, As, and Ce, that have variable redox states; these elements,however, are always present in trace quantities and their valance states reflect, rather than control,the redox state of the system. Although phosphorus has only one valance state (+V) under naturalconditions, its concentration in solution is closely linked to redox state because the biological reactionsthat control redox state also control phosphorus concentration, and because it is so readily adsorbed o nFe oxide surfaces.Water in equilibrium with atmospheric oxygen has a p ε of +13.6 (at pH = 7). At this p ε, thermody-namics tells us that all carbon should be present as CO 2 (or related carbonate species), all nitrogen as NO 3±, all S as SO 42±, all Fe as Fe 3+, and all Mnas Mn 4+. This is clearly not the case and this dise-quilibrium reflects the kinetic sluggishness of many, though not all, redox reactions £. Given the dise-quilibrium we observe, the applicability of thermody-namics to redox systemswould appear to be limited.Thermodynamics may never-theless be used to develop partial equilibrium models.In such models, we can make use of redox couples t h a t might reasonably be at equi-librium to describe the redox state of the system. In Chap-ter 3, we introduced the tools needed to deal with redox reactions: E H , the hydrogen scale potential (the poten-tial developed in a standard hydrogen electrode cell) and p ε, or electron activity. W e found that both may in turn be related to the Gibbs Free Energy of reaction through£ While this may make life difficult for geochemists, it is also what makes it possible in the firstplace. We, like all other organisms, consist of a collection of reduced organic species that manage topersist in an oxidizing environment!Table 13.1. pe Values of Principle Aquatic Redox Couples Reaction p ε¡p εW 1 14O 2(g) + H + + e Ð ® 12H 2O +20.75+13.752 15NO 3± + 65H + + e Ð ® 110N 2(g) + 35H 2O +21.05+12.653 12MnO 2(s) + 2H + + e Ð ® 12Mn 2+ + H 2O +20.8+9.84 54NO 3± + 65H + + e Ð ® 18NH 4+ + 38H 2O +14.9+6.155Fe(OH)3(s) + 3H + + e Ð ® Fe 2+ + 3H 2O +16.0+1.06 12CH 2O* + H + + e Ð ® 12CH 3OH +4.01-3.017 18SO 42- + 54H + + e Ð ® 18H 2S + 12H 2O +5.25-3.58 18SO 42- + 98H + + e Ð ® 18HS Ð + 12H 2O +4.25-3.69 18CO 2(g) + H + + e Ð ® 18CH 4(g) + 14H 2O +2.9-4.11016N 2(g) + 43H + + e Ð ® 13NH 4++4.65-4.711 14CO 2(g) + H + + e Ð ® 14CH 2O* + 14H 2O -0.2-7.2 The concentration of Mn 2+ and Fe 2+ are set to 1 µM.* We are using ÒCH 2OÓ, which is formally formaldahyde, as an abbreviation for organic matter generally (for example, glucose is C 6H 12O 6).the Nernst Equation (equ. 3.121). These are all the tools we need; in this section, we will see how we can apply them to understanding redox in aqueous systems.Table 13.1 lists the pε¡ of the most important redox half reactions in aqueous systems. Also listed are pεW values. pεW is the pε¡ when the concentration of H+ is set to 10-7 (pH = 7). The relation be-tween pε¡ and pεW is simply:pεW= pε° + log [H+]ν = pε° – ν × 7Reactions are ordered by decreasing pεW from strong oxidants at the top to strong reductants at the bot-tom. In this order, each reactant can oxidize any product below it in the list, but not above it. Thus sulfate can oxidize methane to CO2, but not ferrous iron to ferric iron. Redox reactions in aqueous sys-tems are often biologically mediated. In the following section, we briefly explore the role of the bi-ota in controlling the redox state of aqueous systems.Biogeochemical Redox ReactionsAs we noted above, photosynthesis and atmospheric exchange maintains a high pε in surface wa-ters. Water does not transmit light well, so there is an exponential decrease in light intensity with depth. As a result, photosynthesis is not possible below depths of 200 m even in the clearest waters. In murky waters, photosynthesis can be restricted to the upper few meters or less. Below this Òphotic zoneÓ, biologic activity and respiration continue, sustained by falling organic matter from the photic zone. In the deep waters of lakes and seas where the rate of respiration exceeds downward advection of oxygenated surface water, respiration will consume all available oxygen. Once oxygen is consumed, a variety of specialized bacteria continue to consume organic matter and respire utilizing oxidants other than oxygen. Thus pε will continue to decrease.Since bateria exploit first the most energetically favorable reactions, Table 13.1 provides a guide the sequence in which oxidants are consumed as pε decreases. From it, we can infer that once all mo-lecular oxygen is consumed, reduction of nitrate to molecular nitrogen will occur (reaction 2). This processes, known as denitrification, is carried outby bacteria, which use the oxygen liberated to oxidize organic matter and the net energy liber-ated to sustain themselves. At lower levels of pε, other bacteria reduce nitrate to ammonia (reaction 4), a process called nitrate reduction, again using the oxygen liberated to oxidize or-ganic matter. At about this pε level, Mn4+ will be reduced to Mn2+. At lower pε, ferric iron is reduced to ferrous iron. The reduction of both Mn and Fe may also be biologically mediated in whole or in part.From Table 13.1, we can expect that fermenta-tion (reaction 6 in Table 13.1) will follow reduc-tion of Fe. Fermentation can involve any of a number of reactions, only one of which, reduction of organic matter (carbohydrate) to methanol, is represented in Table 13.1. In fermentation reac-tions, further reduction of some of the organic car-bon provides a sink of electrons, allowing oxida-tion of the remaining organic carbon; for example in glucose, which has 6 carbons, some are oxidized to CO2 while others are reduced to alcohol or ace-tic acid. While these kinds of reactions can be carried out by many organisms, it is bacterial-me-pH-8-4481218peFigure 13.1. Important biogeochemical redox couples in natural waters.diated fermenation that is of geochemical interest.At lower pε, sulfate is used as the oxidant by sulfate-reducing bacteria to oxidize organic matter, and at even lower pε, nitrogen is reduced to ammonia (reaction 9), a process known as nitrogen fixa-tion, with the nitrogen serving an the electron acceptor for the oxidization of organic matter. This re-action is of great biological importance, as nitrogen is an essential ingredient of key biological com-pounds such as proteins and DNA (see Chapter 14), and hence is essential to life; all plants must therefore take up inorganic nitrogen. While a few plants, blue-green algae (cyanobacteria) and leg-umes, can utilize N2, most require ÒfixedÓ nitrogen (ammonium, nitrate, or nitrite). Hence nitrogen-fixing bacteria play an essential role in sustaining life on the planet.To summarize, in a water, soil, or sediment column where downward flux of oxygen is less than the downward flux of organic matter, we would expect to see oxygen consumed first, followed by reduction of nitrate, manganese, iron, sulfur, and finally nitrogen. This sequence is illustrated on a pε-pH dia-gram in Figure 13.1. We would expect to see a similar sequence with depth in a column of sediment where the supply of organic matter exceeds the supply of oxygen and other oxidants. EutrophicationThe extent to which the redox sequence described above proceeds in a body of water depends on a several factors. The first of these is temperature structure, because this governs the advection of oxy-gen to deep waters. As mentioned above, light (and other forms of electromagnetic energy) is not transmitted well by water. Thus only surface waters are heated by the Sun. As the temperature of surface water rises, its density decreases (fresh water reaches it greatest density at 4¡ C). These warmer surface waters, known in lakes as the epilimnion, generally overlie a zone where temperature decreases rapidly, known as the thermocline or metalimnion, and a deeper zone of cooler water, known as the hypolimnion. This temperature stratification produces a stable density stratification which prohibits vertical advection of water and dissolved constitutents, including oxygen and nutri-ents. In tropical lakes and seas, this stratification is permanent. In temperate regions, however, there is an annual cycle in which stratification develops in the spring and summer. As the surface water cools in the fall and winter, its density decreases below that of the deep water and vertical mixing occurs. The second important factor governing the extent to which reduction in deep water oc-curs is nutrient levels. Nutrient levels limit the amount of production of organic carbon by photosyn-thesizers (in lakes, phosphorus concentrations are usually limiting; in the oceans, nitrate and micro-nutrients such as iron appear to be limiting). The availability of organic carbon in turn controls bio-logical oxygen demand (BOD) In water with high nutrient levels there is a high flux of organic car-bon to deep waters and hence higher BOD.In lakes with high nutrient levels, the temperature stratification described above can lead to a situation where dissolved oxygen is present in the epilimnion and absent in the hypolimnion. Regions where dissolved oxygen is present are termed oxic, those where sulfide or methane are present are called anoxic. Regions of intermediate pε are called suboxic. Lakes are where suboxic or anoxic condi-tions exist as a result of high biological producitivy are said to be eutrophic. This occurs naturally in many bodies of water, particularly in the tropics where stratification is permanent. It can also occur, however, as a direct result addition of pollutants such as sewage to the water, and an indirect result of pollutants such as phosphate and nitrate. Addition of the latter enhances productivity and availability of organic carbon, and ultimately BOD. When all oxygen is consumed conditions become anaerobic and the body of water becomes eutrophic. Where this occurs naturally, ecosystems have adapted to this circumstance and only anaerobic bacteria are found in the hyperlimnion. When it re-sults from pollution, it can be catastrophic for macrofauna such as fish that cannot tolerate anaerobic conditions.Redox and Biological Primary ProductionThe biota is capable of oxidations as well as reductions. The most familiar of these reactions isphotosynthesis. Most organisms capable of photosynthesis, which includes both higher plants and avariety of single-celled organisms, produce oxygen as a biproduct of photosynthesis:CO 2 + H 2O ® CH 2O + O 213.1However, there are also photosynthesis pathways that do not produce O 2. Green and purple sulfurbacteria are phototrophs that oxidize sulfide to sulfur in the course of photosynthesis:CO 2 + 2H 2S ® CH 2O + 14S 8 + H 2O 13.2This reaction requires considerably less light energy (77.6 vs. 476 kJ/mol) than oxygenic photosynthe-sis, enabling these bacteria survive at lower light levels than green plants.While photosynthesisis is far and away the primary way in which organic carbon is produced orÒfixedÓ, chemical energy rather than light energy may also be used to fix organic carbon in processescollectively known as chemosynthesis . In chemosynthesis, the energy liberated in oxidizing reducedinorganic species is used to reduce CO 2 to organic carbon. For example, nitrifying bacteria oxidizeammonium to nitrite in a process known as nitrification :CO 2 + 23NH 4 + 13H 2O ® CH 2O + 23NO 2– + 43H +13.3Colorless sulfur bacteria oxidize sulfide to sulfate in fixing organic carbon:CO 2 + H 2S + O 2 + H 2O ® CH 2O + SO 42− + 2H+13.4Redox Buffers and Transition Metal ChemistryThe behavior of transition metals in aqueous solutions and solids in equilibrium with them is par-ticularly dependent on redox state. Many transition metals have more than one valence state withinthe range of p ε of water. In a number of cases, the metal is much more soluble in one valence state thanin others. The best examples of this behavior are provided by iron and manganese, both of which aremuch more soluble in their reduced (Fe 2+, Mn 2+) than in oxidized (Fe 3+, Mn 4+) forms. Redox conditionsthus influence a strong control on the concentrations of these elements in natural waters.Because of the low solubility of theiroxidized formes, the concentrations of Fe,Mn, and similar metals are quite low under ÒnormalÓ conditions, i.e., high p ε and near-neutral pH. There two common circum-stances where higher Fe and Mn concentra-tions in water occur. The first is when sul-fide ores are exposed by mining and oxi-dized to sulfate, e.g.:2FeS 2(s) + 2H 2O + 7O 2 ® 4H + + 4SO42−+ 2Fe 2+This can dramatically lower the pH ofstreams draining such areas. The lower pHin turn allows higher concentrations of dis-solved metals (e.g., Figure 13.2), even underoxidizing conditions. The second circum-stance where higher Fe and Mn concentra-tions occur is under suboxic or anoxic condi-tions that may occur in deep waters of lakesand seas as well as sediment pore waters.Under these circumstances Fe and Mn arepH -12-8-4048121820p e Figure 13.2. Contours of dissolved Fe activity as afunction of p ε and pH.reduced to their soluble forms, allowing much higher concentrations.In cases where precipitation or solution involves a change in valence or oxidation state, the solubil-ity product must include p ε or some other redox couple, e.g.:Fe 2O 3 +6H ++2e – ® 2Fe 2+ +3H 2O K =a Fe 2+2a H +6a e –218SO 42− + 54H + + e - ® 18H 2S + 12H 2O 13.6in which case p ε is given by:p p H S SO pH εε=°−−1845242ln [][]–13.7Under the assumption that this reaction controls the redox state of the solution, electrons may beeliminated from other redox reactions by substituting the above expression. For example, iron redoxequilibrium may be written as: 18SO 42−+ 54H + + Fe 2+ ® 18H 2S + 12H 2O + Fe 3+ 13.8In this sense, the p ε of most natural waters will be controlled by a redox buffer , a concept we consid-ered in Chapter 3. Example 13.1 illustrates this approach.Figure 6.1, we can see that at pH below 6.4, H2CO3 will be the dominant carbonate species, so we chose this as the carbonate species. Our components are therefore H+, SO4, H2CO3, Fe2+, and H2S. The spe-cies of interest will include H+, OHÐ, SO42–, H2S, HSÐ, H2CO3, HCO3−, as well as the various species of Fe (Fe2+, Fe3+, Fe(OH)2+, Fe(OH)2+, Fe(OH)3 (we assume that the concentrations of CO32−, HSO4–and S2- are neglible at this pH; we shall neglect them throughout).Our next step is to determine pH. For TOT H we have:TOT H=[H+]–[OH–]–[HCO3–]–[HS–]+54ΣFe3+13.10 The presence of the Fe3+ term may at first be confusing. To understand why it occurs, we can use equa-tion 13.7 to express Fe3+ as the algebraic sum of our components:Fe3+=18SO42–+54++Fe2+–18H2S+12H2O13.11 The first 4 terms on the right hand side of equation 13.10 are simply alkalinity plus additional CO2 produced by oxidation of organic matter, so 13.10 may be rewritten as:TOT H=54ΣFe3+–Alk–[CH2O]13.12 Inspecting equation 13.10, we see that HCO3−is by far the largest term. Furthermore, the Fe term in equation 13.12 is neglible, so we have:TOT H∼–[HCO3–]∼6×10–413.13 The conservation equation for carbonate is:ΣH2CO3=[H2CO3]+[HCO3–]=ΣCO2+Σ[CH2O]=1.3×10–3Hence: H2CO3 = ΣΗ2CO3 – HCO3− = (1.3 – 0.6) × 10-3We can use this to calculate pH since:K=[HCO3–][H+][H2CO3]=10–6.35Solving for [H+] and substitutiong values, we find that pH = 6.28.For the conservation equation for sulfate, we will have to include terms for both Fe3+ (equation 13.11) and organic matter. Writing organic matter as the algebraic sum of our components we have:CH2O=12H2S+H2O+CO2–12SO42––H+The amount of sulfate present will be that originally present less that used to oxidize organic matter. The only other oxidant present in the system is ferric iron, so the amount of sulfide used to oxidize or-ganic matter will be the total organic matter less the amount of ferric iron initially present. The sul-fate conservation equation is then:ΣSO4=[SO42–]–12ΣCH2O+18ΣFe3+∼1.0×10–4M(the Fe term is again neglible). The amount of sulfide present will be the amount created by oxidation of organic matter, less the amount of organic matter oxidized by iron, so the sulfide conservation equa-tion is:ΣH2S=H2S+HS–=+12ΣCH2O–18ΣFe3+=1×10–4M13.14 We now want to calculate the speciation of sulfide. We haveΣH2S=H2S+HS–=1×10–4M and K1H2S=[H+][HS–][H2S]=10–7Solving these two equations, we have:[HS–]=10–410710–6.23=1.92×10–5The development of anoxic conditions leads to an interesting cycling of iron and manganese withinthe water column. Below the oxic-anoxic boundary, Mn and Fe in particulates are reduced and dis-solved. The metals then diffuse upward to the oxic-anoxic boundary where they again are oxidizedand precipitate. The particulates then migrate downward, are reduced, and the cycle begins again.A related phenomena can occur within sediments. Even where anoxic conditions are not achievedwithin the water column, they can be achieved within the underlying sediment. Indeed, this will oc-cur where burial rate of organic matter is high enough to exceed the supply of oxygen. Figure 13.3shows an example, namely a sediment core from southern Lake Michigan studied by Robbins and Cal-lender (1975). The sediment contains about 2% organic carbon in the upper few centimeters, which de-creases by a factor of 3 down core. The concentration of acid-extractable Mn in the solid phase (Figure13.3a), presumably surface-bound Mn and Mn oxides, is constant at about 540 ppm in the upper 6 cm, butdecreases rapidly to about 400 ppm by 12 cm. The concentration of dissolved Mn in the pore water in-creases from about 0.5 ppm to amaximum of 1.35 ppm at 5 cm and then subsuquently decreases (Figure 13.3) to a constant value of about 0.6 ppm in the bottom half of the core.Because the Lake Michigan re-gion is heavily populated, it is tempting to interpret the data in Figure 13.3, particularly the in-crease in acid-extractable M n near the core top, as being a result of recent pollution. However,Robbins and Callender (1975)demonstrated that the data could be explained with a simple steady-state diagentic model in-volving Mn reduction, diffusion,and reprecipitation (as MnCO 3).In Chapter 5, we derived the Di-=+R i Σ(5.171)The first term on the right is thechange in total vertical flux withdepth, the second is the sum ofrates of all reactions occuring.There are two potential flux dC/dt (µg/cm 3/yr)0369Dissolution Rate 00.5 1.0 1.5Mn (ppm)Pore Water J J J J J J J J J J J J J J J J J 400450500550Mn (ppm)0510152025303540D e p t h (c m )Solid phase J J J J J J J J J J J JJ J J J JJ a b c Figure 13.3. (a) Concentration of acid-leachable Mn in Lake Michigan sediment as a function of depth. (b) (b) Dissolved M n in pore water from the same sediment core. Solid line shows the dissolution-diffusion-reprecipitation model of Robbins andCalender (1975) constrained to pass through 0 concentration at 0depth. Dashed line shows the model when this constraint is removed. (c) Dissolution rate of solid Mn calculated from rate of change of concentration of acid-leachable Mn and used to produce the model in (b). From Robbins and Calender (1975).terms in this case, pore water advection (due ot compaction) and diffusion. There are also several re-action occurring: dissolution or desorption associated with reduction and a precipitation reaction. I f the system is at steady state, then ¶c/¶x = 0. Assuming steady-state, Robbins and Callender (1975) derived the following verision of the diagenetic equation:φD d 2cdx2–v dcdx–φk1(c–c f)+φk0(z)=013.16where φ is porosity (assumed to be 0.8), D is the diffusion coefficient, v is the advective velocity (-0.2 cm/yr), and k1 is the rate constant for reprecipitation reactions, and k0 is the dissolution rate (expressed as a function of depth). The first term is the diffusive term, the second the advective, the third the rate of reprecipitation, and the fourth is the dissolution rate. The dissolution rate must be related to the change in concentration of acid-extractable Mn. Thus the last term may be written as:φk0(z)=φRφ∂c s ∂xwhere R is the sedimentation rate (g/cm2/yr) and c s is the concentration in the solid. Using least squares, Robbins and Callender found that the parameters that best fit the data were D = 9 × 10-7 cm2/sec (30 cm2/yr) k1 = 1 yr-1 and c f = 0.5 ppm. The solid line in Figure 12.44b represents the prediction of equation 13.16 using this values and assuming c0 (porewater concentration at the surface) is 0. The dashed line in Figure 13.3b assumes c0 = 0.6 ppm. The latter is too high, as c0 should be the same con-centration as lake water. Robbins and Callender (1975) speculated that the top cm or so of the core had been lost, resulting in an artifically high c0.Redox cycling, both in water and sediment can effect the concentrations of other a number of other elements. For example, Cu and Ni form highly insoluble sulfides. Once pε decreases to levels where sulfate is reduced to sulfide, dissolved concentrations of Cu and Ni decrease dramatically due to sul-fide precipitation. The dissolved concentrations of elements that are strongly absorbed onto particu-late Mn and Fe oxihydroxide surfaces, such as the rare earths and P, often show significant increases when these particulates dissolved as Mn and Fe are reduced. The effect of Fe redox cycling on P is particularly significant because P is most often the nutrient whose availability limites biological productivity in freshwater ecosystems. Under oxic conditions, a fraction of the P released by decom-position of organic matter in deep water or sediment will be adsorbed by particles (particularly Fe) and hence lost from the ecosystem to sediment. If conditions become anoxic, iron dissolves and ad-sorbed P is released into solution, where it can again become available to the biota. As a result, lakes that become eutrophic due to P pollution can remain so long after the the pollution ceases because P is simply internally recycled under the prevailing anoxic conditions. Worse yet, once conditions become anoxic, nonanthropogenic P can be released from the sediment, leading to higher biological production and more severe anoxia.Weathering, Soils, and Biogeochemical CyclingWeathering is the process by which rock is physically and chemically broken down into relatively fine solids (soil or sediment particles) and dissolved components. The chemical component of weath-ering, which will be our focus, could be more precisely described as the process by which rocks origi-nally formed at higher temperatures come to equilibrium with water at temperatures prevailing a t the the surface of the Earth.Weathering plays a key role in the exogenic geochemical cycle (i.e., the cycle operating at the sur-face of the Earth). Chemical weathering supplies both dissolved and suspended matter to rivers and seas. It is the prinicipal reason that the ocean is salty. Weathering also supplies nutrients to the bi-ota in form of dissolved components in the soil solution; without weathering terrestrial life would be far different and far more limited. Weathering can be an important source of ores. The Al ore bauxite is the product of extreme weathering that leaves a soil residue containing very high concentrations of aluminum oxides and hydroxides. Weathering, together with erosion, transforms the surface of the Earth, smoothing out the roughness created by volcanism and tectonism.。

·165·丹凤铀矿田位于丹凤三角区内，是我国花岗（伟晶）岩型铀矿床的重要产区，区内主要产出有光石沟铀矿床、陈家庄铀矿床和小花岔铀矿床等（图1）。

自1957年最早发现光石沟铀矿床至今，该区已经开展了较为详细地找矿勘查工作，许多专家学者也对丹凤铀矿田开展了较多的地学研究工作，如岩体及矿床地质特征、岩体及矿床物质来源、岩体成岩年龄、矿床成因等方面，取得了许多的重要认识。

1　区域地质概况丹凤铀矿田位于华北克拉通南缘的北秦岭加里东褶皱带东段，地理位置上处于陕南丹凤县与商洛县全部或部分行政区内，主要夹持在蔡川断裂和商丹断裂之间，因蔡川断裂与商丹断裂在西侧交汇构成三角形而又称丹凤三角区（图1）。

丹凤铀矿田归属于秦祁昆成矿域内秦岭-大别铀成矿省的北秦岭铀成矿带内，属于古商丹洋闭合区。

区内目前已勘查具有工业价值的花岗（伟晶）doi ：10.3969/j.issn.1004-275X.2018.06.071丹凤铀矿田地质特征研究进展宋　炎（东华理工大学　地球科学学院，江西　南昌　330013）摘　要：丹凤铀矿田位于北秦岭造山带东段的丹凤三角区内，是我国重要的花岗伟晶岩型铀矿床集中区。

通过收集前人对丹凤铀矿田的相关研究资料，主要对区内花岗岩的岩相学、岩石地球化学、年代学等特征进行了总结。

迄今为止，丹凤铀矿田研究程度尚浅，如矿物学、放射性蚀变特征、成矿时代、成矿流体等方面仍有待进一步研究。

关键词：丹凤铀矿田；花岗岩；铀矿床；地质特征中图分类号：P618.61 文献标识码：A 文章编号：1004-275X（2018）06-165-03Research Progress on geological characteristics of Danfeng uranium ore fieldSong Yan（East China University of Technology，Nanchang，Jiangxi 330013）Abstract ：Danfeng uranium ore field is located in the Danfeng triangle area of the eastern part of the North Qinling Mountains orogenic belt. It is an important granite pegmatite type uranium deposit concentration area in China. By collecting the previous research data on the Danfeng uranium ore field，this paper mainly summarizes the petrography，rock geochemistry and chronology of the granites in the region. So far，the degree of research in Danfeng uranium ore field is still shallow，such asmineralogy，characteristics of radioactive alteration，metallogenic age，ore-forming fluid and other aspects still need further study.Key words：Danfeng uranium ore field；granite；uranium deposit；geological characteristics1.古近系；2.下古生界云架山群；3.下古生界丹凤群；4.下元古界秦岭群；5.海西期片麻状花岗岩；6.加里东期二长花岗岩；7.加里东期白岗质花岗岩；8.伟晶岩脉；9.断层；10.多期活动构造断裂；11.铀矿床；12.地名；13.省界图1　丹凤地区地质简图岩型铀矿床主要有光石沟铀矿床与陈家庄铀矿床，二者各产出在丹凤三角区内最大的两个岩体东南缘的岩体内（黄龙庙岩体、灰池子岩体）。