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1.
Yang Changming 《地球科学》1986,(1)
本区原岩建造是-套基性—酸性火山凝灰岩（主要）+铁硅质岩+沉积岩组合。整个层序反映了一个较完整的火山喷发沉积旋回。含铁建造与沉积旋回在时空和物源上存在着密切的成因联系。铁矿的形成及分布并非受控于某一种岩石,而是受控于火山喷发沉积旋回。本文从岩浆分异、火山活动、沉积作用及构造运动等的发生、发展、演化的角度较全面地分析了火山喷发沉积旋回的控矿作用。 相似文献
2.
Beukes NJ Klein C Kaufman AJ Hayes JM 《Economic geology and the bulletin of the Society of Economic Geologists》1990,85(4):663-690
The transition zone comprises Campbellrand microbialaminated (replacing "cryptalgalaminate") limestone and shale, with minor dolomite, conformably overlain by the Kuruman Iron Formation of which the basal part is characterized by siderite-rich microbanded iron-formation with minor magnetite and some hematite-containing units. The iron-formation contains subordinate intraclastic and microbialaminated siderite mesobands and was deposited in deeper water than the limestones. The sequence is virtually unaltered with diagenetic mineral assemblages reflecting a temperature interval of about 110 degrees to 170 degrees C and pressures of 2 kbars. Carbonate minerals in the different rock types are represented by primary micritic precipitates (now recrystallized to microsparite), early precompactional sparry cements and concretions, deep burial limpid euhedral sparites, and spar cements precipitated from metamorphic fluids in close contact with diabase sills. Paragenetic pathways of the carbonate minerals are broadly similar in all lithofacies with kerogen intimately associated with them. Kerogen occurs as pigmentation in carbonate crystals, as reworked organic detritus in clastic-textured carbonate units, and as segregations of kerogen pigment around late diagenetic carbonate crystals. Locally kerogen may also be replaced by carbonate spar. Carbon isotope compositions of the carbonate minerals and kerogen are dependent on their mode of occurrence and on the composition of the dominant carbonate species in a specific lithofacies. Integration of sedimentary, petrographic, geochemical, and isotopic results makes it possible to distinguish between depositional, early diagenetic, deep burial, and metamorphic effects on the isotopic compositions of the carbonate minerals and the kerogen in the sequence. Major conclusions are that deep burial thermal decarboxylation led to 13C depletion in euhedral ferroan sparites and 13C enrichment in kerogen (organic carbon). Metamorphic sparites are most depleted in 13C. Carbonates in oxide-rich iron-formations are more depleted in 13C than those in siderite-rich iron-formation whereas the kerogens in oxide banded iron-formations (BIF) are more enriched. This implies that the siderite-rich iron-formations were not derived from oxide-rich iron-formation through reduction of ferric iron by organic matter. Organic matter oxidation by ferric iron did, however, decrease the abundance of kerogen in oxide-rich iron-formation and led to the formation of isotopically very light sparry carbonates. Siderite and calcmicrosparite both represent recrystallized primary micritic precipitates but differ in their 13C composition, with the siderites depleted in 13C by 4.6 per mil on average relative to calcmicrosparite. This means that the siderites were precipitated from water with dissolved inorganic carbon depleted in 13C by about 9 per mil relative to that from which the limestones precipitated. This implies an ocean system stratified with regard to total carbonate, with the deeper water, from which siderite-rich iron-formation formed, depleted in 13C. Iron-formations were deposited in areas of very low organic matter supply. Depletion of 13C may, therefore, derive not from degradation of organic matter but from hydrothermal activity, a conclusion which is supported by 18O composition of the carbonate minerals and trace element and rare earth element (REE) compositions of the iron-formations. 相似文献
3.
4.
天然沸石是岩石圈上部分布最广的硅酸盐矿物之一,它普遍地见于各种火山岩和火山-沉积岩中。沸石不仅在岩浆期后热液阶段生成,而且在沉积-成岩作用阶段、表生作用(风化)阶段、低级变质阶段都可以生成。由于沸石对周围的物理化学条件和热、动力变质作用反应灵敏,因此,它是了解地质体形成时的地质环境及其变化的良好的指示矿物。本文概述了我国东部中生代火山岩中沸石岩的分布、时代、产出的地层岩性剖面、原岩类型、矿物组合及其生成顺序,并探讨了它的形成条件和成因类型,其中主要涉及具有工业意义的斜发沸石岩和丝光沸石岩。 相似文献
5.
Tectonic systems and the deposition of iron-formation 总被引：8，自引：0，他引：8
Gordon A. Gross 《Precambrian Research》1983,20(2-4)
The iron-formation group of chemically precipitated cherty iron-rich sediments ranges in age from Early Precambrian to Recent and is composed of a variety of lithological facies. Iron-formations are classified as Lake Superior and Algoma types to emphasize the contrasting conditions in the spectrum of sedimentary-tectonic environments in which they formed. Thick stratigraphic units of Lake Superior type iron-formation, which form the most extensive iron ranges of the world, are part of sedimentary-tectonic systems that developed along the margins of cratons or continental platforms and were deposited over extended periods of time under relatively stable tectonic conditions. The Algoma type iron-formations were deposited with volcanic rocks and greywacke in various tectonic-volcanic systems, formed under more dynamic tectonic conditions, but are otherwise comparable to present day spreading ridges on the ocean floor. The thick sequences of Lake Superior type iron-formation deposited between 2.7 and 2.0 Ga form part of major sedimentary-tectonic systems that extended along the margins of continents. Direct biogenic factors and the composition of the atmosphere probably had only limited influence on the precipitation of these chemical sediments. 相似文献
6.
H. N. Bhattacharya Indranil Chakraborty Kaushik K. Ghosh 《Journal of Earth System Science》2007,116(3):245-259
Banded iron-formations (BIF) form an important part of the Archean supracrustal belts of the Jharkhand-Orissa region, India.
Major, trace and REE chemistry of the banded iron-formation of the Gandhamardan, Deo Nala, Gorumahisani and Noamundi sections
of the Jharkhand-Orissa region are utilized to explore the source of metals and to address the thermal regime of the basin
floor and the redox conditions of the archean sea. Hydrothermal fluids of variable temperatures might have contributed the
major part of the Fe and other trace elements to the studied banded iron-formations. Diagenetic fluids from the sea floor
sediments and river water might have played a subdued role in supplying the Fe and other elements for the banded iron-formations. 相似文献
7.
The Early Palaeoproterozoic Brockman Supersequence comprises banded iron formation (BIF), bedded chert, limestone, mudrock, sandstone, breccia, tuffaceous mudstone, ashfall tuff and, in sections not reported here, basalt and rhyolite. Density current rhythms are preserved in sandstones, mudrocks, tuffaceous mudstones and limestones. Relics of similar rhythms in BIF imply that its precursor sediments were also deposited by density currents. Hemipelagic deposits are siliciclastic or mixed siliciclastic–volcaniclastic mudstones. Bedded chert, chert nodules and the chert matrix of BIF preserve evidence for formation by diagenetic replacement. For bedded chert (and chert nodules), silica replacement occurred before compaction close to or at the sediment–water interface, indicating that it is siliceous hardground. The chert matrix of BIF formed during compaction but before burial metamorphism. Original sediments were resedimented from two sources: (1) limestone, mudrock, sandstone, breccia and tuffaceous mudstone from a shelf; and (2) BIF from within the basin realm. Shelf sediments were resedimented to basin-floor fans during third-order lowstands. The precursor sediments to BIF are interpreted to have been granular hydrothermal muds, composed of iron-rich smectite and particles of iron oxyhydroxide and siderite that were deposited on the flanks of submarine volcanoes and resedimented by density currents. Resedimentation occurred by either bottom currents or gravity-driven turbidity currents, and the resulting sediment bodies may have been contourite drifts. The concept that BIF records high-frequency alternating precipitation from ambient sea water of iron minerals and silica is negated by this study. Instead, it is postulated that the precursor sediments to BIF originated in much the same way as modern Red Sea hydrothermal iron oxide deposits, implying that at least the particles of iron oxyhydroxide originated from the oxidation of vent fluids by sea water. Several orders of cyclicity in basin filling establish a relationship between rising to high sea levels, episodic sea-floor hydrothermal activity and BIF that is reminiscent of the link between eustacy and spreading-ridge pulses. 相似文献
8.
Ashima Saikia Bibhuti Gogoi Mansoor Ahmad Talat Ahmad 《Journal of Earth System Science》2014,123(5):959-987
The Bathani volcanic and volcano-sedimentary (BVS) sequence is a volcanic and volcano-sedimentary sequence, best exposed near Bathani village in Gaya district of Bihar. It is located in the northern fringe of the Chotanagpur Granite Gneiss Complex (CGGC). The volcano-sedimentary unit comprises of garnet-mica schist, rhyolite, tuff, banded iron formation (BIF) and chert bands with carbonate rocks as enclaves within the rhyolite and the differentiated volcanic sequence comprises of rhyolite, andesite, pillow basalt, massive basalt, tuff and mafic pyroclasts. Emplacement of diverse felsic and mafic rocks together testifies for a multi-stage and multi-source magmatism for the area. The presence of pillow basalt marks the eruption of these rocks in a subaqueous environment. Intermittent eruption of mafic and felsic magmas resulted in the formation of rhyolite, mafic pyroclasts, and tuff. Mixing and mingling of the felsic and mafic magmas resulted in the hybrid rock andesite. Granites are emplaced later, cross-cutting the volcanic sequence and are probably products of fractional crystallization of basaltic magma. The present work characterizes the geochemical characteristics of the magmatic rocks comprising of basalt, andesite, rhyolite, tuff, and granite of the area. Tholeiitic trend for basalt and calc-alkaline affinities of andesite, rhyolite and granite is consistent with their generation in an island arc, subduction related setting. The rocks of the BVS sequence probably mark the collision of the northern and southern Indian blocks during Proterozoic period. The explosive submarine volcanism may be related to culmination of the collision of the aforementioned blocks during the Neoproterozoic (1.0 Ga) as the Grenvillian metamorphism is well established in various parts of CGGC. 相似文献
9.
The Nkout deposit is part of an emerging iron ore province in West and Central Africa. The deposit is an oxide facies iron formation comprising fresh magnetite banded iron formation (BIF) at depth, which weathers and oxidises towards the surface forming caps of high grade hematite/martite–goethite ores. The mineral species, compositions, mineral associations, and liberation have been studied using automated mineralogy (QEMSCAN®) combined with whole rock geochemistry, mineral chemistry and mineralogical techniques. Drill cores (saprolitic, lateritic, BIF), grab and outcrop samples were studied and divided into 4 main groups based on whole rock Fe content and a weathering index. The groups are; enriched material (EM), weathered magnetite itabirite (WMI), transitional magnetite itabirite (TMI) and magnetite itabirite (MI). The main iron minerals are the iron oxides (magnetite, hematite, and goethite) and chamosite. The iron oxides are closely associated in the high grade cap and liberation of them individually is poor. Liberation increases when they are grouped together as iron oxides. Chamosite significantly lowers the liberation of the iron oxides. Automated mineralogy by QEMSCAN® (or other similar techniques) can distinguish between Fe oxides if set up and calibrated carefully using the backscattered electron signal. Electron beam techniques have the advantage over other quantitative mineralogy techniques of being able to determine mineral chemical variants of ore and gangue minerals, although reflected light optical microscopy remains the most sensitive method of distinguishing closely related iron oxide minerals. Both optical and electron beam automated mineralogical methods have distinct advantages over quantitative XRD in that they can determine mineral associations, liberation, amorphous phases and trace phases. 相似文献
10.
Minor elements in sphalerite and galena from Binnatal 总被引：1，自引：0，他引：1
Stefan Graeser 《Contributions to Mineralogy and Petrology》1969,24(2):156-163
The trace element contents of 23 sphalerites and galenas from Binnatal, Switzerland, have been determined. Most of these samples have been previously studied in respect to lead and sulphur isotope abundances. Coloration of sphalerites — varying from yellow to black for nearly identical iron contents — seems to be strongly influenced by the manganese content. A linear relationship between sulphur isotope composition and copper content in sphalerites was found. Trace elements in galenas show a significant inverse relationship between silver and copper. With the determination of the bismuth content, it is possible to distinguish several galena types; a similar grouping has been found by lead isotope determinations. The results of the trace analyses are discussed in connection with the occurrence of a large number of very rare and special Pb-As-sulphosalt minerals in the Binnatal dolomites. 相似文献
11.
西天山查岗诺尔和智博铁矿区火山岩地球化学特征、锆石U-Pb年龄及地质意义 总被引：18，自引：4，他引：14
西天山东段的查岗诺尔铁矿和智博铁矿赋存于以玄武岩、玄武安山岩、粗面岩以及安山质凝灰岩为主的晚石炭世火山岩中, 对火山岩的形成时代以及构造地质背景的研究是重建成矿过程的关键。本文通过对两个矿区的火山岩进行岩石地球化学和LA-ICP-MS锆石U-Pb测年分析来探讨火山岩形成的构造环境与时代。地球化学分析表明大多数火山岩化学成分从钙碱性、高钾钙碱性变化到钾玄岩系列,富集轻稀土元素(LREE)和大离子亲石元素(LILE; 如Rb、Th、K),重稀土元素(HREE)配分平坦,同时具有Nb、Ta、Ti的强烈亏损,类似于岛弧火山岩的地球化学特征。大多数玄武质火山岩在构造环境判别图中位于火山弧环境。LA-ICP-MS锆石U-Pb测年显示流纹岩和英安岩的206Pb/238U加权平均年龄分别为301.8±0.9Ma和300.3±1.1Ma。此外,对两件闪长岩样品测年获得206Pb/238U加权平均年龄介于303.8～305Ma之间。火山岩与闪长岩样品具有类似的地球化学特征以及形成时代,表明它们可能来源于同一母岩浆,形成于相同的构造背景下。结合区域地质资料,本文认为矿区内出露的高钾钙碱性到钾玄岩系列火山岩可能属于俯冲过程末期阶段大陆岛弧岩浆作用的产物。 相似文献
12.
赞坎铁矿床是塔什库尔干地区一个典型的沉积变质型铁矿,具有多阶段成矿的特征,是塔什库尔干地区铁矿成矿作用演化的典型代表。文章将赞坎铁矿床主要矿石矿物磁铁矿的形成划分为3个世代,分别为条带状磁铁矿、浸染状磁铁矿和粗晶脉状或块状磁铁矿,分别代表3个成矿阶段的产物。电子探针和LAICP-MS原位分析表明,赞坎铁矿从条带状磁铁矿到粗晶块状磁铁矿随着磁铁矿的成矿演化主量元素中Al元素有减少的趋势,而Ti、Mn、Mg、V元素均具有增加的趋势;微量元素中Co、Nb、Hf、Ta等具有减少的趋势,Sc、Ga、Zr、Sn等元素具有增加的趋势。根据以上各成矿阶段中磁铁矿成分变化,并结合前人的研究成果发现,赞坎铁矿早期条带状磁铁矿与火山沉积作用有关,成矿后期特别是在粗晶块状和脉状磁铁矿阶段受岩浆热液影响明显,富铁矿有岩浆热液的参与。 相似文献
13.
The Marda complex is a sequence of andesitic to dacitic to rhyolitic volcanic rocks filling a synformal structure in submarine basalt, banded iron-formation and siliceous sediments in the Archaean Yilgarn Block of Western Australia. The Marda volcanic rocks are in part subaerial and exhibit calc-alkaline chemistry. Their Rb/Sr age is 2635 ± 80 m.y. with an initial ratio of 0.7029 ± 0.0015. The Marda lavas represent products of a differentiated late to syn-tectonic, anatectic magma derived from the base of the Archaean crust. Calc-alkaline volcanic complexes are uncommon in the Yilgarn Block. 相似文献
14.
为探讨辽宁大台沟铁矿床的成矿物质来源及形成环境,选取典型铁矿石5块进行主量元素、微量元素和稀土元素分析测试。结果显示:大台沟铁矿床保存有明显的化学沉积特征,化学成分主要由Fe_2O_3,FeO和SiO_2组成(Fe_2O_3+FeO+SiO_2=87.33%～96%),其他组分(MnO,MgO,CaO,Na_2O,K_2O,TiO_2,P_2O_5,Al_2O_3)含量较低;页岩标准化后的稀土元素配分曲线显示为稀土总量低(ΣREE平均为19.65×10-6),轻稀土元素相对亏损,重稀土元素相对富集;且具有一定的Eu(Eu/Eu~*=1.52～2.72),Y(Y/Y~*=1.18～1.52),La(La/La~*=1.17～2.26)的正异常,弱的Ce(Ce/Ce~*=0.79～0.92)异常;Y/Ho值平均34.19接近于海水的分布范围;Sr/Ba值平均1.79,属于火山岩和海相沉积物;Ti/V值平均38.84,属于火山建造。这些特征表明:该矿床的形成可能与海相火山沉积物有关,属于火山沉积变质型铁矿范围;成矿物质来源于热水和海水的混合作用;矿床形成于相对于缺氧的环境。 相似文献
15.
Abstract. The Cikidang gold deposit, discovered in 1991, is located within the Bayah dome, a Tertiary-Quaternary volcanic zone at west end of Java, which is well known as a gold district (e.g., Pongkor and Cikotok mines). Typical low-sulfidation quartz-adularia-sericite(-calcite) vein deposits represent the gold deposit in the district.
The Cikidang vein system comprises four sub-parallel quartz-adularia-sericite(-calcite) veins that are rich in manganese oxide and limonite with very poor amount of sulfides. These vary from 0.5 to 2.7 m thick and extend for up to 1,000 m long. The vein trends roughly N-S and dip 60 to 86° toward west. The ore grades vary from trace to 74.9 g/t Au and 1.2 to 225.0 g/t Ag. A K/Ar age determination on adularia yielded 2.4 Ma for the Cikidang vein.
The ore minerals are represented by electrum, argentite, aguilarite and pyrite. Electrum shows the compositional ranges of Ag (50–65 atom %). The gangue minerals are dominated by quartz with variable amounts of calcite, sericite, adularia, clay minerals, manganese oxide and limonite. The vein textures are so variable as banded, colloform, comb, brecciated and massive. Host rocks, composed of Miocene lapilli tuff and breccia, suffered from pervasive hydrothermal alterations. Wall rocks adjacent to the vein are characterized by argillic and propylitic alteration.
The fluid inclusion study of the Cikidang vein shows homogenization temperatures ranging from 170 to 260°C. Salinities are low, generally below 3 wt% NaCl equivalent. Oxygen isotope results suggest meteoric water in origin for ore fluids responsible for the Cikidang deposit. 相似文献
The Cikidang vein system comprises four sub-parallel quartz-adularia-sericite(-calcite) veins that are rich in manganese oxide and limonite with very poor amount of sulfides. These vary from 0.5 to 2.7 m thick and extend for up to 1,000 m long. The vein trends roughly N-S and dip 60 to 86° toward west. The ore grades vary from trace to 74.9 g/t Au and 1.2 to 225.0 g/t Ag. A K/Ar age determination on adularia yielded 2.4 Ma for the Cikidang vein.
The ore minerals are represented by electrum, argentite, aguilarite and pyrite. Electrum shows the compositional ranges of Ag (50–65 atom %). The gangue minerals are dominated by quartz with variable amounts of calcite, sericite, adularia, clay minerals, manganese oxide and limonite. The vein textures are so variable as banded, colloform, comb, brecciated and massive. Host rocks, composed of Miocene lapilli tuff and breccia, suffered from pervasive hydrothermal alterations. Wall rocks adjacent to the vein are characterized by argillic and propylitic alteration.
The fluid inclusion study of the Cikidang vein shows homogenization temperatures ranging from 170 to 260°C. Salinities are low, generally below 3 wt% NaCl equivalent. Oxygen isotope results suggest meteoric water in origin for ore fluids responsible for the Cikidang deposit. 相似文献
16.
Dr. A. E. Kelepertsis E. Chatsidimitriadis 《International Journal of Earth Sciences》1983,72(1):167-190
Detailed chemical and mineralogical data are presented for 37 samples of surface sediments collected from the Kalloni gulf, (eastern half), Lesvos island, northern Greece. The sediments are largely carbonate-rich muds, though near the eastern and northern coast of the gulf higher proportions of biogenic and lithogenic sands and gravels occur. The main minerals are quartz, feldspar (andesine), clay minerals (montmorillonite, illite, Kaolinite) and the carbonate minerals (calcite, Mg-calcite, aragonite). The mathematical method of factor analysis was applied in order to explain the mineralogical and geochemical variations. These variations can be interpreted in terms of variations in provenance and depositional environment. Six factors were produced accounting for 83.6 % of the total data variance: (a) a Si-Al-Na-K-Ti-Rb-Ba-Y-Zr factor controlled by clays and detrital minerals such as feldspars and zircon opposed by a CaCO2-Cu-Sc-Sr-La association (carbonate, minerals), (b) an organic carbon factor (C-Fe-Ce-Zn-Rb-Ni-Y-Nb), (c) a Fe-Mg-Cr-Ni factor representing control by peridotite, (d) a Ce-Nd-Fe-Ni-Zn-La factor controlled by silicate minerals, (e) a Al-Fe-Ti-P-V factor controlled by chlorite amphiboles or pyroxenes of volcanic or basaltic intrusions, (f) a Mn-Fe-Zn-factor controlled by iron-manganese oxides. Similarities in trace element composition among Kalloni gulf bottom sediments, and source lithologies indicate that the trace elements are derived from the adjacent landmasses. The AI/Ti ratio of the sediments is consistent with the terrigenous nature of sendimentation in the Kalloni gulf. 相似文献
17.
《地学前缘(英文版)》2016,7(6)
Banded iron formations(BIFs) are major rock units having hematite layers intermittent with silica rich layers and formed by sedimentary processes during late Archean to mid Proterozoic time. In terrestrial environment, hematite deposits are mainly found associated with banded iron formations. The BIFs in Lake Superior(Canada) and Carajas(Brazil) have been studied by planetary scientists to trace the evolution of hematite deposits on Mars. Hematite deposits are extensively identified in Meridiani region on Mars. Many hypotheses have been proposed to decipher the mechanism for the formation of these deposits. On the basis of geomorphological and mineralogical studies, aqueous environment of deposition is found to be the most supportive mechanism for its secondary iron rich deposits. In the present study, we examined the spectral characteristics of banded iron formations of Joda and Daitari located in Singhbhum craton in eastern India to check its potentiality as an analog to the aqueous/marine environment on Mars. The prominent banding feature of banded iron formations is in the range of few millimeters to few centimeters in thickness. Fe rich bands are darker(gray) in color compared to the light reddish jaspilitic chert bands. Thin quartz veins(4 mm) are occasionally observed in the handspecimens of banded iron formations. Spectral investigations have been conducted in VIS/NIR region of electromagnetic spectrum in the laboratory conditions. Optimum absorption bands identified include 0.65, 0.86, 1.4 and 1.9 mm, in which 0.56 and 0.86 mm absorption bands are due to ferric iron and 1.4 and1.9 mm bands are due to OH/H_2O. To validate the mineralogical results obtained from VIS/NIR spectral radiometry, laser Raman and Fourier transform infrared spectroscopic techniques were utilized and the results were found to be similar. Goethite-hematite association in banded iron formation in Singhbhum craton suggests dehydration activity, which has altered the primary iron oxide phases into the secondary iron oxide phases. The optimum bands identified for the minerals using various spectroscopic techniques can be used as reference for similar mineral deposits on any remote area on Earth or on other hydrated planetary surfaces like Mars. 相似文献
18.
Zhiyuan Sun WangJingbin Yuwang Wang Lingli Long Zhaohua Luo Xiaohua Deng Qitao Hu Menglong Wang 《地学前缘(英文版)》2020,(2):697-713
The volcanic rocks hosting the iron deposits in the Aqishan–Yamansu metallogenic belt are sodium-rich.The geochronology,petrography,and geochemistry of minerals and sodium-rich rocks as well as the relationship between these rocks and the iron deposits are studied.Geochemically,the ore-hosting volcanic rocks are sodiumrich(the averages of Na2O and Na2O/K2O are 4.31 wt.%and 8.56,respectively)and belong to the calc-alkaline series.They are enriched in LREEs and LILEs(Ba,U,K,and Sr),but depleted in HFSEs(Nb,Ta,and Ti).SHRIMP zircon U–Pb dating of the crystal tuff in the Aqishan Formation and the dacite in the Tugutu Bulak Formation yields ages of 337.52.3 Ma(n?15,MSWD?0.85)and 313.03.3 Ma(n?13,MSWD?0.74),respectively,indicating that the sodium-rich volcanic rocks formed from the early–late Carboniferous.Electron microprobe data from plagioclases demonstrate that albites and/or oligoclases were formed in the basic–intermediate–acid volcanic rocks.Two stages of albitization are identified,and the latter is likely attributed to the dissolution of iron in the Aqishan–Yamansu belt.The sodium-rich volcanic rocks probably formed by the interaction between volcanic lava and seawater after volcanoes erupted on the seafloor;meanwhile,the albites formed by element substitution in a low-metamorphic environment.The spatiotemporal coupling relationship between sodium-rich volcanic rocks and iron deposits in the Aqishan–Yamansu belt is favorable.Iron dissolved from the dark minerals of basic–intermediate volcanic rocks through sodium metasomatism is one of the material sources for the iron deposits. 相似文献
19.
The Al-Batin alluvial fan covers a broad area of southern Iraq. It was the main battlefield of two devastating wars in 1991 and 2003, during which huge amounts of depleted uranium (DU) were used. This study aims to assess the geochemistry of this fan sediment including the potential effects of the DU used. Sixty-three samples were collected from sediments including three samples from sediments under tanks attacked by DU ammunition. Major elements were measured by XRF (fusion bead method), whereas ICP-MS was used to measure the trace elements. The results suggest that the most dominant major minerals are in the order of: quartz?>?secondary gypsum?>?calcite?>?feldspar, clay minerals?>?iron oxide, and show abnormal concentrations of Sr, Cr, Ni, and V. This study also determined an area with high concentration of U in the north east part of the fan. Statistical analysis and spatial distribution of important elements suggests that two major factors affect mineral formation. The first factor reflects the influence of minerals in the source area of the sediments (Arabian Shield): quartz, carbonate, clay minerals, feldspars, as well as iron oxides and elevated concentrations of V, Ni, and Cr. The second factor points at authigenic formation of secondary gypsum and celestite and elevated U concentration under the control of a hot arid climate and the specific groundwater situation. However, the origin of the sediments is geogenic, while the anthropogenic impact seems to be minor. Spatial distribution of U and the 235/238U ratio did not show any peaks in the places where tanks have been destroyed. This is contrary to media speculations and some scientific reports about the permanent risks of DU in the area, which creates public concern about the potential risk of living in this area. 相似文献
20.
The major (Al, Ti, Ca, Mg, Fe, Mn, Si) and trace element (Cd, Cr, Cu, Hg, Li, Ni, Pb, V, Zn) concentrations in surficial
(<20 cm) sediments from fjords and open coastal waters around Greenland have been determined. Regionally, high concentrations
of Fe, Ti, Mg, Cr, Cu, Ni, and V occur in some west and east coast sediments, but they appear to be natural in origin, as
there is no indication of anthropogenic influence. Chemical partition indicates that most of the heavy metals are structurally
bound in various silicate, oxide, and sulfide minerals. These host minerals occur more or less equally in the coarse and fine
sediment fractions (material >63 μm and <63 μm) and have accumulated at the same rate as other detrital clastic material.
Provenance and glaciomarine deposition are the main factors controlling the abundance and distribution of the major and trace
elements. The chemical composition reflects the mineralogical differences in the provenance of glacial marine material deposited
by water and ice adjacent to Greenland. The main source of the sediments enriched in Ti, Fe, Mg, Cr, Cu, Ni, and V appears
to be material derived from the volcanic rocks of the Mesozoic-Tertiary Provinces of Greenland by glacial erosion.
Received: 26 June 1995 · Accepted: 11 August 1995 相似文献