花山寨英碱正长岩地球化学特征及岩石成因探讨

花山寨英碱正长岩位于随州洪山镇与三里岗镇之间,侵入于震旦系随县群,Rb—Sr等时线年龄为215Ma。本文对该岩体的岩石学、矿物学和地球化学进行了详细研究,并探讨了岩石成因。岩石主要由条纹长石、石英和钠闪石组成,其次有少量霓石、钠长石及黑云母等。重要的付矿物有锆石、独居石、褐帘石和褐钇铌矿等。岩体以中粒英碱正长岩为主,东南边缘有细粒相出露。从中粒相至细粒相,Q、Or+Ab,REE、Nb、Zr、Th有明显增高趋势。REE模式大体相同,但δEu有所区别,中粒相>0.5,细粒相<0.4。岩石化学特征是Na_2O+K_2O高,δ>4,属碱性岩范畴。 Sf~(87)/Sr~(86)(I)=0.70917,δO~(18)smow=13.47‰,206Pb/204Pb、207Pb/204Pb、208Pb/204Pb分别为18.33、15.57和38.42。其成岩物质来源与下地壳有关。据矿物包体均一温度测定和据钠闪石中Na_(M4)和Al~(Iv)值估算,岩石形成温度为1000—1120℃,压力约6—7Kb。     

Streambed Sediment as a Barrier to Groundwater Pollution: Insights from Fieldwork and Modelling in the River Thames Basin

Integrated fieldwork and modelling has been undertaken to assess the vulnerability of riverside wells to pollution when river water is contaminated. Results highlight the importance of streambed sediments as a barrier to groundwater pollution by river water. The bed of the River Thames is lined with brown and grey organic-rich silts of low hydraulic conductivity (about 0.002 m/d). A 3-D model for solute transport in stream-aquifer systems was developed and applied to two riverside sites in the middle Thames valley. Model results indicate that well-water quality would only breach EC limits if the river was heavily polluted for a week or even a month (clearly an unlikely scenario). Sensitivity analyses showed the models to be far more sensitive to streambed parameters than to aquifer parameters. Thus it would be more sensible to focus fieldwork on the measurement of streambed properties than on the more usually measured aquifer parameters.     

Modeling metal bioaccumulation in a deposit-feeding polychaete from labile sediment fractions and from pore water

Estuarine sediments are often highly enriched in particle-reactive metal contaminants and because aquatic animals have often been shown to acquire metals predominantly from their diet, benthic animals feeding on deposited or resuspended sediments may also accumulate metals through this uptake pathway. Laboratory experiments were performed in which the surface deposit-feeding polychaete, Nereis succinea, was exposed to As(+ 5), Cd, and Cr(+ 3) in pore water or in estuarine sediments with and without enrichment with algal debris. These experiments generated metal uptake parameters (assimilation efficiency of ingested metal [AE], uptake rate constant of dissolved metal, efflux rate constants following dietary or aqueous metal exposures) used in a kinetic model of metal bioaccumulation. The model showed that > 97% of the body burden of these metals is accumulated through ingested sediment. The kinetic model was further modified to consider the geochemical fractionation of the metals in the sediments because metals bound to some fractions were shown to be unavailable to these polychaetes. The modified model substituted the AE term for each metal by the percentage of metal extracted in neutral and weak acid exchangeable fractions (termed “carbonex” fraction) multiplied by the slope of the regression between the metal AE and its fractionation in carbonex. The modified model generated predictions of As, Cd, and Cr body burdens in polychaetes at three different estuarine sites that matched independent field observations at these sites (r² = 0.84 for sediments without organic enrichment, r² = 0.87 with organic enrichment). Model predictions that relied on total metal concentrations showed weaker relationships (r² = 0.11-0.50). This study adds to the evidence for the dominance of dietary uptake of metals in aquatic animals and identifies a key sedimentary fraction of metals that can account for bioavailability of sediment-bound metals.     

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??Dolomite is the most important rock type for the development of the Ordovician effective reservoirs in the Ordos Basin. Its genesis remains controversial due to its complex and variable rock texture and occurrence. In this paper, through analysis of macroscopic regional geological background, microscopic rock texture, mineralogy, and geochemistry, the Ordovician dolomites in this area are divided into three types, i.e. micritic–fine powder crystal, coarse powder crystal, and fine (medium) crystal. It is pointed out that they were formed in three different dolomitization diagenetic environments, namely, penecontemporaneous dolomization by evaporative pumping, mixture dolomitization of freshwater and magnesium-rich brine, and seepage-reflux dolomitization, respectively. In terms of horizon and spatial distribution, they represent the features of "strata-controlled" and "region-specific". The analysis of genesis provides the following findings. First, the three types of dolomitization are correlated to certain extent in terms of temporal–spatial evolution. In other words, they were all originated along with the deposition of gypsum mineral under evaporation background. Second, the main pore types, i.e. dissolved pores, intercrystalline pores, and organic framework, were respectively formed in three types of dolomites. They generally distribute in "specific" type of dolomite, which indicates that the pore genesis is closely related to dolomitization diagenesis environment. Third, the development and distribution of effective dolomite reservoirs is mainly subject to three types of elements, such as primary sedimentary faices belts, diagenetic environment controlling regional dolomitization, and sequence boundary caused by variation of relative sea level.     

荷花山铅锌矿与铜陵地区其它矿床成矿控制因素的对比研究

为了探讨荷花山铅锌矿控矿因素上与铜陵地区其它矿床异同，运用宏、微观相结合，地质观察研究同位素地球化学以及流体包裹体分析相结合的方法，通过地层岩性、地质构造、特定地质体及成矿流体的来源和性质等几个方面与成矿关系的比较，揭示了这种新类型矿床的控矿因素的特点是与岩浆关系不密切的低温热液、角砾岩控矿。得出了这种新类型矿床既具有铜陵地区其它矿床的控矿因素，同时也具有自己独特的控矿因素的结论。     

Geochemical characteristics of the Permian marine mudstone and constraints on its provenance and paleoenvironment in the Fenghai area, Fujian Province, southeastern China

Permian marine strata have gradually become a research focus in the world. The marine strata of the Late Permian Dalong Formation (P₃d) in the Fenghai area, Fujian Province, have become more and more important as their geochemical characteristics record important geological information and are a good indicator for recovering and reconstructing the paleosedimentary environments and tectonic attributes. The major elements, trace elements and rare earth elements were analyzed by XRF and ICP-MS, respectively. Based on the results of detailed field geological surveys, profile measurements as well as typical sample collection, the tectonic setting and provenance of Permian marine mudstone were comprehensively discussed. The results showed that the Dalong Formation (P₃d) was deposited in an active continental margin tectonic environment as revealed by the relation between Fe₂O₃ + MgO and TiO₂ and Al₂O₃/SiO₂. The fingerprint characteristics of Mn, Fe, Co, Ni and REE and the ratio of U/Th, V/Cr, Sr/Ba, (La/Yb)_N and V/(V + Ni) indicated that the sedimentary provenance was mainly derived from potassium feldspar, followed by muscovite. Sedimentary water bodies showed a gradually decreasing depositional rate trend, water depth gradually shallowing and paleo-salinity and productivity gradually increasing. Moreover, since transient delamination occurred during sedimentary processes, sedimentary water bodies showed obvious neritic characteristics. It was consistent with the results revealed by lithological and geochemical characteristics. Calcareous mudstone and siltstone transitioned into fine sandstone from bottom to top, indicating paleo-water bodies became shallow. The research results provided good reference and guidance for understanding Permian paleo-sedimentary environments and tectonic attributes of the Yong’an area, Fujian Province, southeastern China.     

浙西开化桐村花岗斑岩地球化学特征及找矿潜力

通过对浙西开化桐村岩体野外剖面采样和地球化学研究,判断桐村岩体应属过铝质高钾钙碱系列花岗斑岩,通过稳定的稀土元素和微量元素来确定岩体的类型等特征。稀土配分模式与同熔型花岗斑岩（I型）一致,微量元素分布模式的特点是大离子亲石元素明显富集,具有明显Ta、Nb、P、Ti负异常,类似于“岛弧”环境的岩石特征,与斑岩型矿床母岩相比,不具有良好的找矿潜力。     

陕西金龙山金矿古楼山矿段元素地球化学特征

古楼山矿段位于金龙山金矿田的西北部,与丘岭矿段处于同一地球化学异常中,是另一异常浓集中心,目前在丘岭矿段已探明储量超过50 t,古楼山矿段由于工作程度较低,未取得大的突破.通过对古楼山矿段原生晕的分析,发现原生晕中As、Sb、Au元素相关性高且呈正相关关系,表明As、Sb、Au为该区金矿预测的主要元素组合,建立了地球化...     

柴达木盆地石炭系烃源岩评价

在野外地质调查基础上,系统分析了柴达木盆地石炭系烃源岩分布以及地球化学特征,并从有机质丰度、类型和成熟度方面对烃源岩进行了综合评价。研究认为:柴达木盆地石炭系烃源岩广泛分布在全盆地大部分地区。柴北缘烃源岩厚度大\,分布广,厚度中心主要位于欧龙布鲁克山一带,最大残余厚度达900 m;柴南缘厚度次之,沿盆地边缘呈带状展布,在格尔木-乌图美仁-甘森一带厚度在400~500 m之间,盆地西北及东南角厚度较小。石炭系主要发育暗色泥岩、碳酸盐岩和煤3种类型烃源岩。暗色泥岩有机质丰度均值为1.28%,有机质类型主要为Ⅲ型与Ⅱ₂型,处于成熟-高成熟阶段,为中等-好的烃源岩;碳酸盐岩有机质丰度较低,平均值为0.37%,有机质类型为Ⅱ₁-Ⅱ₂型,综合评价为差烃源岩;石炭系煤岩则为良好的气源岩。总体而言,柴达木盆地石炭系分布广泛,具有较好的油气勘探远景。      

西藏多龙矿集区玄武岩类化学组分特征及构造背景

选择多龙矿集区美日切错组地层中的玄武岩–玄武安山岩–安山岩样品进行常量元素、稀土元素和痕量元素测试。通过分析,认为多不杂铜矿床碱性玄武岩形成于板内洋岛环境,钙碱性玄武岩类形成于大陆弧环境;拿若铜矿床安山岩形成于大陆弧环境;尕尔勤铜矿床钙碱性玄武岩形成于后碰撞弧环境。初步揭示出多龙矿集区板块俯冲作用引发地幔流体作用的成矿机制,地幔交代作用及其产物是洋岛玄武岩富集的主要原因,板块俯冲作用及其产物是岛弧玄武岩富集的主要原因。