大学专业英语课件.ppt

Mineralogy and geochemistry of trace elements in bauxites: the Devonian Schugorsk deposit, Russia lL. E. MORDBERG1,2,3, C. J. STANLEY2 , AND K. GERMANN3 l1. Russian Research Geological Institute (VSEGEI), Sredny pr 74, St. Petersburg, Russia l2. The NaturalHistory Museum, Cromwell Road, London SW7 5BD, UK l3. Technische Universitat Berlin, Lagerstattenforschung, Sekr. BH4, Ernst-Reuter-Platz 1, 10587 Berlin, Germany Abstract: l Processes of mineral alteration involving the mobilization and deposition of more than 30 chemical elements during bauxite formation and epigenesis have been studied on specimens from the Devonian Schugorsk bauxite deposit, Timan, Russia. Chemical analyses of the minerals were obtained by electron microprobe and element distribution in the minerals was studied by element mapping. Interpretation of these data also utilized high-resolution BSE and SE images. Specialized Vocabulary:Specialized Vocabulary: Mobilization mubilaizei-n n. 动员; 调动 Formation f:mein n. 构造, 编队, 形成 Epigenesis epidenisisepidenisis n. n. 渐成说渐成说; ; 地地 外力变质外力变质; ;后成后成 specimen spesimn n. 样本, 标本 electron microprobe 电子微探 针; 电子显微探针; 电子探针 l The main rock-forming minerals of the Vendian parent rock are calcite, dolomite, feldspar, aegirine, riebeckite, mica, chlorite and quartz; accessory minerals are pyrite, galena, apatite, ilmenite, monazite, xenotime, zircon, columbite, pyrochlore, chromite, bastnaesite and some others. Typically, the grainsize of the accessory minerals in both parent rock and bauxite is from 1 to 40 mm. However, even within these rather small grains, the processes of crystal growth and alteration during weathering can be determined from the zonal distribution of the elements. The most widespread processes observed are: Specialized Vocabulary:Specialized Vocabulary: parent rock parent rock 母岩母岩 Calcite Calcite klsaitklsait n. n. 矿矿 方解石方解石 Dolomite Dolomite dlmaitdlmait n. n. 白云石白云石 Feldspar Feldspar feldspfeldsp: n. : n. 长石长石 AegirineAegirine ei,ri:nei,ri:n n. n. 矿矿 霓石霓石 riebeckiteri:bekaitriebeckiteri:bekait n. n. 钠闪石钠闪石 mica mica maikmaik n. n. 云母云母 chlorite chlorite kl:raitkl:rait n. n. 绿泥石绿泥石 quartz quartz kw:tskw:ts n. n. 石英石英 accessory minerals accessory minerals 副矿物副矿物 pyrite pyrite pairaitpairait n. n. 矿矿 黄铁矿黄铁矿 galena galena li:nli:n n. n. 矿矿 方铅矿方铅矿 apatite apatite ptaitptait n. n. 磷灰石磷灰石 ilmeniteilmenite ilmnaitnilmnaitn. .矿矿 钛铁矿钛铁矿 Please follow the next page for Please follow the next page for the other Specialized Vocabulary the other Specialized Vocabulary of this pageof this page (1) Decomposition of Ti-bearing minerals such as ilmenite, aegirine and riebeckite with the formation of leucoxene, which is the main concentrator of Nb, Cr, V and W. Crystal growth can be traced from the zonal distribution of Nb (up to 16 wt.%). Vein-like leucoxene is also observed in association with organics. (2) Weathering of columbite and pyrochlore: the source of Nb in leucoxene is now strongly weathered columbite, while the alteration of pyrochlore is expressed in the growth of plumbopyrochlore rims around Ca- rich cores. Specialized Vocabulary:Specialized Vocabulary: Monazite mnzait n. 独居石 xenotime zentaim n. 磷钇矿 zircon z:kn n. 锆石 columbite klmbait n. 钶铁矿；铌 铁矿 pyrochlore pairkl:n. 矿烧绿石 chromite krumait n. 亚铬酸盐；铬 铁矿 bastnaesite n. 氟碳铈矿 grainsize n. 粒度；粒径 decomposition ,di:kmpzin n. 分解,腐败,变质 Ti-bearing mineral; leucoxene lju:kksi:n n. 白钛石；金红石；白榍石 plumbopyrochloreplumbopyrochlore 烧绿石烧绿石 rim rim n. rim rim n. 边边, ,轮缘轮缘, ,框框 Please follow the next page for the Please follow the next page for the other Specialized Vocabulary of this other Specialized Vocabulary of this pagepage (3) Dissolution of sulphide minerals and apatite and the formation of crandallite group minerals: crandallite crystals of up to 40 mm size show a very clear zonation. From the core to the rim of a crystal, the following sequence of elements is observed: Ca ? Ba ? Ce ? Pb ? Sr ? Nd. Sulphur also shows a zoned but more complicated distribution, while the distribution of Fe is rather variable. A possible source of REE is bastnaesite from the parent rock. More than twelve crandallite type cells can be identified in a single crandallite grain. Specialized Vocabulary:Specialized Vocabulary: sulphidesulphide slfaidslfaid n. n. 硫化物硫化物 apatite apatite ptaitptait n. n. 磷灰石磷灰石 crandallitecrandallite krndlaitkrndlait n. n. 纤磷钙铝纤磷钙铝 石石 zonationzonation zuneinzunein n. n. 成带；动植物的生物地理学的地成带；动植物的生物地理学的地 带分布；带状配列带分布；带状配列 Nb：Niobium naiubim n. 化 铌（41号元素，汉语发言n ） Cr：chromium krumjm n. 化 铬（24号元素，汉语发音g ) V：vanadium vneidim n. 化 钒（23号元素，汉语发音fn ) W：tungsten tstn n. 化 钨 （ 74号元素，汉语发音w） Ca：calcium klsim n. 化 钙（20号元素，汉语发音gi ) Ba：barium brim n. 化 钡（56号元素，汉语发音bi） Ce：cerium sirim n. 化 铈（58号元素，汉语发音sh） (4) Alteration of stoichiometric zircon and xenotime with the formation of metamict solid solution of zircon and xenotime: altered zircon rims also bear large amounts of Sc (up to 3.5 wt.%), Fe, Ca and Al in the form of as yet unidentified inclusions of 12 mm. Monazite seems to be the least altered mineral of the profile. In the parent rock, an unknown mineral of the composition (wt.%): ThO2 54.8; FeO 14.6; Y2O5 2.3; CaO 2.0; REE 1.8; SiO2 12.2; P2O5 2.8; total 94.2 (average from ten analyses) was determined. In bauxite, another mineral was found, which has the composition (wt.%): Specialized Vocabulary:Specialized Vocabulary: stoichiometricstoichiometric , ,stikimetrikstikimetrik adj. adj. 化学计算的；化学计量的化学计算的；化学计量的 metamict metmikt n. 蜕晶质 Pb：lead li:d n. 化 铅（82号元素，汉语发音qin） Sr：strontium strnim n. 化 锶（38号元素，汉语发音s） Sc：scandium skndim n. 化 钪（21号元素，汉语发音kng） Fe：iron ain n. 化 铁（26号元素，汉语发音ti ） Ca ：calcium klsim n. 化 钙（20号元素，汉语发音gi ) 铝（13号元素，汉语发音l） Th ：thorium :rim, n. 化 钍（90号元素，汉语发音t） Cu：copper kp n. 化 铜（29号元素，汉语发音tng） Cd：cadmium kdmim n. 化 镉（48号元素，汉语发音g） Bi：bismuth bizm n. 化 铋（83号元素，汉语发音b） ThO2 24.9; FeO 20.5; Y2O5 6.7; CaO 2.0; ZrO 17.6; SiO2 8.8; P2O5 5.4; total 89.3 (F was not analysed; average from nine analyses). Presumably, the second mineral is the result of weathering of the first one. Although the Th content is very high, the mineral is almost free of Pb. However,intergrowths of galena and pyrite are observed around the partially decomposed crystals of the mineral. Another generation of galena is enriched in chalcophile elements such as Cu, Cd, Bi etc., and is related to epigenetic alteration of the profile, as are secondary apatite and muscovite. Specialized Vocabulary:Specialized Vocabulary: weathering weri n. 风化 intergrowth intru n. 共生，交互生长 pyrite pairait n. 矿黄铁矿 galena li:n n. 矿方铅矿 Decomposed a. 已分解的, 已腐烂的 chalcophile klk,fail adj. 【地球 化学】亲铜的，亲硫的 epigenetic ,epidinetik adj. 生外成的；后生的 Muscovite ,mskvait 白云母 Al：aluminum ,ljuminim, n. 化 铝（13号元素，汉语发音l） Y：yttrium itrim n. 化 钇（39号元素，汉语发音y） Si：silicon silikn n. 化 硅（14号元素，汉语发音gu） P：phosphorus fsfrs n. 化 磷（15号元素，汉语发音ln） Zr：zirconium z:kunim n. 化 锆（40号元素，汉语发音go） KEYWORDS: bauxite, laterite, weathering, geochemistry, mineralogy, trace elements, leucoxene, crandallite, zircon, xenotime, pyrochlore, galena. Specialized Vocabulary:Specialized Vocabulary: leucoxene lju:kksi:n n. 白钛石；金红石；白榍石 Introduction The problem of trace elements in bauxite profi les is important for a number of reasons. Firstly, deep chemical weathering is a geochemical process which is as important as magmatism, metamorphism or sedimentation. In addition, principles of concentration and/or differentiation of chemical elements during bauxite formation differ from those typical for magmatic, metamorphic and sedimentary processes. Specialized Vocabulary: Bauxite b:ksait n. 矾土, 铁 铝氧石, 化铝土矿 Magmatism：岩浆作用 Metamorphism metm:fi zm n. 变质作用 Chemical weathering 化学 风 化,化学风化作用,化学气候 sedimentation sedimentein n. 沉淀,沉降 Geochemical ,di:kemikl adj. 地球化学的 Sedimentary sedimentri a. 沉淀性的 Secondly, only a few elements such as Ga and V are successfully extracted as by-products of Al production, although some other elements may show high concentrations within bauxite profiles. Thus, the nature of the minerals containing trace elements is an important key for the understanding of their behaviour during bauxite formation. l The problem of mobility of chemical elements during deep weathering has been discussed for many years. However, the very small grain-size of bauxite (a few microns or even smaller) has hindered detailed investigations. Specialized Vocabulary:Specialized Vocabulary: extracted ikstrktid 萃取的 by-product bai,prdkt n. 副产品；附带产生的结果；意外 收获 mobility mobility mubilitimubiliti n. n. 可动性可动性, ,变动性变动性, ,情感不定情感不定 Ga：gallium lim n. 化镓 镓（23号元素，汉语发音ji） V：vanadium vneidim n. 化 钒（23号元素，汉语发音fn ) Al：aluminum ,ljuminim, n. 化 铝（13号元素，汉语发音l） The most widespread method used to determine element mobility was a comparison of its bulk content in the parent rock and in the weathering profile, frequently using isovolumetric calculations. Bardossy and Aleva (1990) compared data on six bauxite districts and concluded that there exist a number of elements for which their chemical properties unequivocally determine enrichment or depletion in all lateritic-bauxite districts (p. 145). This conclusion needs explanation. Specialized Vocabulary:Specialized Vocabulary: isovolumetricisovolumetric adj. adj. 等容的，定容的等容的，定容的 depletion depletion dipli:ndipli:n n. n. 消耗消耗, ,罄尽罄尽, ,放血放血 lateriticlateritic , ,ltritikltritik adj. adj. 含有红土的；红壤的含有红土的；红壤的 lateritic-bauxite：红土型铝土矿 l This study on the mineralogy and geochemistry of trace elements in bauxite was carried out on samples from the Schugorsk bauxite deposit from the Middle Timan, Russia. Material from this deposit contains higher levels of certain elements than normal(Mordberg, 1996, 1997) and is hence suitable for a detailed mineralogical investigation. Specialized Vocabulary:Specialized Vocabulary: mineralogy ,mineralogy ,minrldiminrldi 矿物学矿物学 Geology l Bauxite deposits of the Middle Timan are located in the North of European Russia, between the NE edge of the Russian Plate and the Pechorsk Depression (Fig. 1). Specialized Vocabulary:Specialized Vocabulary: Plate pleit n. 板块 The geology of the bauxite region has been given in detail by Likhachev (1993) and Mordberg (1996, 1997). Devonian bauxite deposits located within the Chetlass orogenic structure occur on folded, mostly carbonate strata of the Riphean. Deposits of both lateritic and karstic origin are found. The overlying rocks are Upper Devonian volcanogenic and sedimentary sequences; in some instances the bauxite profile is covered directly by Late Devonian trap basalt. l The Schugorsk bauxite deposit, the largest in the region, was formed over a Precambrian carbonate sequence which had been altered by alkali metasomatic processes. Specialized Vocabulary:Specialized Vocabulary: Orogenic: adj. 造山的；造山运 动的 carbonate k:bneit n. 碳酸盐 strata streit: n. 层(地层,岩歧, 阶层,薄片) lateritic ,ltritik adj. 含有红土的；红壤的 karstic adj.喀斯特的 Upper Devonian:(地质学)晚泥 盆世 volcanogenic ,volcanogenic ,vlkndenikvlkndenik adj. adj. 源于火山的；火山生成的源于火山的；火山生成的 sedimentary sequence:sedimentary sequence:沉积层序沉积层序 Precambrian Precambrian pri:kmbrinpri:kmbrin n. n. 前寒武纪前寒武纪, ,前塞武层前塞武层 carbonate carbonate k:bneitk:bneit n. n. 碳酸盐碳酸盐 Alkali n. Alkali n. 碱碱 Metasomatic ,metsumtik adj. 地交代的 Rock-forming minerals of the metasomatite are dolomite, calcite and K-feldspars. Plagioclase, aegerine, riebeckite, biotite and sericite are also present in various amounts. The weathered profile attains a total depth here of 100-120 m, and the main ore- forming minerals are boehmite, kaolinite and hematite with nearly monomineralic white boehmitic bauxites being widespread within the deposit. The ratio of carbonate and silicate minerals in the parent rock varies broadly with an average of 1:1. Due to this heterogeneity, the deposit cannot be treated as either the lateritic or the karstic type. Specialized Vocabulary:Specialized Vocabulary: Metasomatite: n. 交代岩，换质岩 dolomite dlmait n. 白云石 K-feldspars 钾长石 plagioclase pleidikleis, -kleiz n. 矿斜长石 riebeckite ri:bekait n. 矿钠闪石 biotite baitait n. 矿黑云母 sericite serisait n. 矿丝（绢） 云母 boehmite b:mait n. 矿勃姆石（一种水软铝石） hematite hemtait, n. 矿赤铁矿 monomineralic mnu,mainrlik adj. 单矿物的 silicate silicate silikitsilikit n. n. 硅酸盐硅酸盐 heterogeneity ,heterogeneity ,hetrudini:itihetrudini:iti n. n. 多相性多相性, ,异质性异质性 lateritic ,ltritik adj. 含有红土的；红壤的 Material and methods l Samples for the investigation were taken from drill cores. A part of each sample was powdered, and the levels present of 60 elements (including the major ones) were determined by XRF following standard methods at the Technical University of Berlin. A full description of the methods is given by Krumb (1998). The contents of elements in minerals were determined in polished sections using a wavlength-dispersive (WD) electron probe microanalyser (Cameca SX50) at the Natural History Museum, London. Specialized Vocabulary:Specialized Vocabulary: drill cores：岩心 polished polished plitplit a. a. 擦亮的擦亮的, ,精练的精练的, ,优美的优美的 MicroanalysermaikrunlaizMicroanalysermaikrunlaiz n. n. 微量分析仪微量分析仪 International standards were used for calibration of each element. The analytical conditions used were 15 kV and 20 nA with counting times of 20 s for Zr, Ca, Ti, Nb, P, Sc, Pb, Mn, Fe, Hf, Na, Mg, Al and Si; of 30 s for La, Ce, Th, U, Pb and W; and of 50 s for Y, Pr, Nd, Sm and Dy. Elemental X-ray maps were obtained using the following conditions: 15 kV, 100 nA and 200 mS per point. Specialized Vocabulary:Specialized Vocabulary: calibration ,klibrein n. 刻度,校准， Zr：zirconium z:kunim n. 化 锆（40号元素，汉语发音go） Ca：calcium klsim n. 化 钙（20号元素，汉语发音gi ) Ti：titanium taiteinjm n. 化 钛（22号元素，汉语发音ti） Nb ：Niobium naiubim n. 化 铌（41号元素，汉语发言n ） P：phosphorus fsfrs n. 化 磷（15号元素，汉语发音ln） Sc：scandium skndim n. 化 钪（21号元素，汉语发音kng） Pb：lead li:d n. 化 铅（82号元素，汉语发音qin） Mn：manganese ,mgni:z n. 化 锰（25号元素，汉语发音mng Fe：iron ain n. 化 铁（26号元素，汉语发音ti ） Hf：hafnium hfnim n. 化 铪（72号元素，汉语发音h） Results Rock geochemistry l The distribution parameters of Ti, P, S and trace elements within the Schugorsk weathering profile are given in Table 1. Specialized Vocabulary:Specialized Vocabulary: parameter prmit n. 参数,参量 weathering profile (岩层) 风化剖面， 风化壳 Na：sodium sudjm, -dim n. 化 钠（11号元素，汉语发音n） Mg：magnesium mgni:zjm n. 化 镁（12号元素，汉语发音mi） Al：aluminum ,ljuminim, n. 化 铝（13号元素，汉语发音l） Si：silicon silikn n. 化 硅（14号元素，汉语发音gu） La ：lanthanum lnnm n. 化 镧（57号元素，汉语发音ln） Ce：cerium sirim n. 化 铈（ 58号元素，汉语发音sh ） Th：thorium :rim, n. 化 钍（90号元素，汉语发音t） U：uranium jureinim n. 化 铀（92号元素，汉语发音yu） W：tungsten tstn n. 化 钨 （ 74号元素，汉语发w） For comparison, data for the average composition of bauxite deposits of the world (Bronevoy et al., 1985) are also supplied. It can be seen that the studied profile is strongly enriched in lithophile elements such as Nb, Th, REE and Zr which are typical of alkali rocks. Chalcophile elements such as Pb, Sb, Bi and presumably Cd are also prominent, and the enrichment in W and Tl is of great interest also. The other elements which are found in amounts greater than average for bauxite are Ti, P, Ga, Ni, Sc, Sn, Sr and Zn. Some elements such as Ag, Co, U and V show concentrations close to average, while S, As, Cr, Cu and Hf occur in relatively small amounts. Specialized Vocabulary:Specialized Vocabulary: lithophile element 亲石元素 Chalcophile element亲铜元素 prominent prminnt adj. 突出的，显著的；杰出的 Tl：thallium lim n. 化 铊（22号元素，汉语发音t） Y：yttrium itrim n. 化 钇（39号元素，汉语发音y） Pr： praseodymium ,preiziudimim 镨（59号元素，汉语发音p） Nd：neodymium ni:udimimn. 化 钕（60号元素，汉语发音n） Sm：samarium smrim n. 化 钐（62号元素，汉语发音shn Dy：dysprosium disprusim n. 化 镝（66号元素，汉语发音d） Sb：stibium stibim n. 化 锑（66号元素，汉语发音t） Cd：cadmium kdmim n. 化 镉（48号元素，汉语发音g） Both Zr/Hf (47.2) and Th/U (17.5) are much higher than their average values for bauxite. l Correlation analysis of element contents (Table 2) allows at least three groups of elements to be distinguished with high positive links among elements within each group. Specialized Vocabulary:Specialized Vocabulary: Zn：zink zik n. 化 锌（30号元素，汉语发音xn） Ag：silver silv n. 化 银（47号元素，汉语发音yn） Co：cobalt kub:lt n. 化 钴（27号元素，汉语发音g） As：arsenic :snik n. 化 砷（33号元素，汉语发音shn） One group unites P, Ba, Sr, Bi and V; the other elements having a positive correlation with some of these are Ni and Pb. This group represents crandallite mineralization within the profile. The second group consists of REE (La, Sm, Nd, Pr and Ce) with adjusted Y and, to a lesser extent, U. It reflects the presence of P- minerals such as monazite and xenotime.From these two groups, only Pb and Ce correlate positively with each other, both correlating with Cr and Sc as well. Specialized Vocabulary:Specialized Vocabulary: positive correlation (化)正相关 crandallite krndlait n. 纤磷钙铝石 to a lesser extent 在较小程度上 monazite mnzait n. 独居石 xenotime zentaim, zi:- n. 矿磷钇矿 Ni：nickel n