Mineralization of pegmatites in parts of the Oban Massif, Southeastern Nigeria： A preliminary analysis

The Oban Basement Massif of southeastern Nigeria is composed of metamorphosed rocks including phyllites, schists, gneisses and amphibolites cut by pegmatitic dykes of varying length and thickness, which intruded the metamorphic rocks. Preliminary geochemical study and analysis of these pegmatites from western Oban Massif at Uyanga, Akwa Ibami, Iwuru I, Iwuru Ⅱ and Igbofia showed that the pegmatites are highly albitized. This is incon-sistent with earlier postulations that the pegmatites in this part of Nige...     

青藏高原东北缘茶卡北山印支期(含绿柱石)锂辉石伟晶岩脉群的发现及Li-Be成矿意义

青藏高原东北缘茶卡北山地区首次发现锂辉石伟晶岩脉群。这些伟晶岩脉沿宗务隆山南缘断裂北侧密集出露,并呈狭窄带状北西向展布。到目前为止,已发现9条含绿柱石锂辉石伟晶岩脉(Li2O平均品位为1.11%~3.13%,BeO平均品位为0.06%)和13条含绿柱石伟晶岩(BeO平均品位为0.044%~0.056%)。伟晶岩锆石U-Pb测年确定其成岩成矿年龄为217 Ma,含绿柱石伟晶岩具有高SiO2(71.62%~77.34%)、Al2O3(15.57%~17.55%)和富K2O(1.99%~2.02%)、Na2O(6.09%~6.24%),稀土元素总量非常低(ΣREE=5.2~9.1μg/g),轻稀土元素略微富集((La/Yb)N=6.8~10.1),Eu具负异常(δEu=0.25~0.92),具有Cs、Rb、Ta、P和Pb富集,以及Ba、Th、La、Ce、Sr、Nd和Ti的强烈亏损特征。含绿柱石锂辉石伟晶岩具有高SiO2(75.73%~77.34%)、Al2O3(15.58%~17.52%)和富Na2O(3.0%~3.16%)、贫K2O(0.36%~0.79%),稀土元素总量也很低(ΣREE=5.3~6.0μg/g),轻稀土元素略微富集((La/Yb)N=3.1~4.6),Eu具强烈负异常(δEu=0.17~0.23)。相对于含绿柱石伟晶岩,含绿柱石锂辉石伟晶岩更加富集Cs、U、Nb、Ta、Th、Sn和B,更亏损K和P。含绿柱石伟晶岩和含绿柱石锂辉石伟晶岩锆石具有相似的Hf同位素组成,εHf(t)值分布范围在–15.1~–12.9之间,对应的Hf同位素地壳模式年龄tDM2为1.99~2.22 Ga,表明伟晶岩源于全吉地块古元古代地壳物质的重熔再造。茶卡北山(含绿柱石)含绿柱石锂辉石伟晶岩的发现可推断宗务隆山构造带东段是青藏高原北部一条新的、重要的锂铍成矿带,除Li和Be外,Nb、Ta、Cs和Sn可能也是有潜力的成矿元素。     

Zur Geochemie einiger Pegmatite der Ostalpen

Zusammenfassung 139 Proben von Gesteinen und Mineralen des Villacher Granites und von Pegmatitvorkommen im Kärntner Altkristallin (Kärnten/Österreich) sowie vergleichsweise 13 Proben von anderen Pegmatiten der Ostalpen und solchen der Böhmischen Masse wurden mit Hilfe flammenphotometrischer, emissionsspektrographischer, röntgenfluoreszenzspektrometrischer und teilweise auch gammaspektrometrischer Methoden auf die Elemente Li, Na, K, Rb, Be, Ca, Sr, Ba, B, Sc, Y, Yb, (Th, U), Ti, Zr, Ni und Ga analysiert.Es konnte gezeigt werden, daß zwischen dem voralpidischen Villacher Granit und dem pegmatitischen und aplitischen Ganggefolge im Kärntner Altkristallin zwischen Ossiacher See und Drautal Blutsverwandtschaft bestehen sollte.Mit zunehmender Größe des Pegmatitvorkommens und offenbar auch mit Annäherung an den Granit nimmt der Gehalt an Li, Rb, Be, B, Ga und Pb zu, der Gehalt an Ca, Sr, Ba, Ti, Sc u. a. hingegen ab. Das K/Rb-Verhältnis ist ebenso ein verläßlicher Indikator. In kleineren Pegmatitkörpern nähert sich der Gehalt der pegmatophilen Spurenelemente dem des Nebengesteins.Es werden Abhängigkeiten zwischen Mindestkonzentrationen und Mineralisationen gefunden: Granite der Ostalpen mit Berylliumgehalten über 5 ppm Be lassen Beryllmineralisationen in ihren Pegmatiten erwarten. In Pegmatit-Proben mit über 50 ppm Be sind unter dem Mikroskop Beryllnädelchen nachweisbar.Zinnstein tritt auf, wenn das Pegmatitgestein mehr als 20 ppm Sn enthält, Spodumen bei>0,1% Li und Xenotim bei>20 ppm Y.

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Contribution to the geochemistry of some pegmatites in the Eastern Alps

Summary 139 samples of rocks and minerals from the granite of Villach and from pegmatites of the Carinthian Old Cristalline Complex (Austria) and additional 13 samples for comparison purposes from other pegmatites in the Eastern Alps and the Bohemian Mass were analyzed for the elements Li, Na, K, Rb, Be, Ca, Sr, Ba, B, Sc, Y, Yb, (Th, U), Ti, Zr, Mn, Co, Ni, and Ga using flamephotometric, emission-spectrographic, x-ray-fluorescence spectrometric and partially gamma-spectrometric methods.It could be shown that the prealpidic granite of Villach and the pegmatites of the Carinthian Old Cristalline Complex lying between the Lake of Ossiach and the Drau Valley are probably consanquineous. The contents of Li, Rb, Be, B, Ga, and Pb increase with the size of the pegmatite and with increasing proximity to the granite. Other elements, like Ca, Sr, Ba, Ti, Sc, show the reverse relation.Also the K/Rb-ratio is a good indicator. The trace-element content of small pegmatite bodies approaches that of the wall rocks.Relationships between the concentration of some elements and the mineralization have been found: One may expect beryllium minerals in pegmatites of granites of the Eastern Alps if the granite contains more than 5 ppm Be. Pegmatites samples containing more than 50 ppm Be show needles of beryll under the microscope. Cassiterite appeares, if the content of the pegmatitic rock reaches 20 ppm Sn, spodumen, if it exceeds 0,1% Li, and Xenotim, if it exceeds 20 ppm Y.

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Mit 7 Abbildungen     

Geochemistry of the Pegmatitic Rocks and Minerals in the Kenticha Belt, Southern Ethiopia: Implication to Geological Setting

Trace element distribution patterns are reported for whole rocks (granites, aplites, greisens, pegmatites, alaskites) and minerals from the Kenticha pegmatite field. The data shed light on the evolution, regional and local zonal pattern of the granitepegmatites and associated mineralization in the Kenticha belt. The complex mineralization of commercial concentrations of Ta, Nb, Hf, Zr, REE, U and Th is related to Be, Li, Cs, Rbbearing zones of pegmatites and is structurally controlled. Whole rock chemical signatures of the suite of felsic rocks of the Kenticha belt are predominantly similar to those generated by subduction in modern magmatic arcs and indicate a mantle derivation. Columbotantalite concentrates extracted from the pegmatitic ores represent the basic raw materials from which a number of possible byproducts can be recovered.     

THE GEOCHEMISTRY OF TANTALUM AND NIOBIUM

Ta and Nb are associated in nature. Both are oxyphile and are related geochemically to Fe, Mn, Ti, rare earths U, Th, Zr, W, Sn, Bi, and Sb. Both accompany the alkali metals,especially Na and Li. Their close relationship explains their isomorphism in mineral-forming processes. Zr, W, and Sn entrain Ta and Nb in the crystal lattices of their minerals in limited amounts. The concentration of Ta and Nb increases in the course of magma evolution from ultrabasic to alkalic. Nb predominates over Ta in the main kinds of rocks by from 5:1 to 17:1. Only in granite pegmatites is Ta dominant. In granitic rocks Ta and Nb are associated with Fe, Mn, Bi, Sb, W, and Sn. In granosyenitic complexes they form complex minerals with Ti, rare earths of the Y subgroup, U, and Th. Concentrations of Ta and Nb in granitic and granosyenitic complexes increase toward the end of the magmatic and pegmatitic processes, and afterward diminish toward the end of the pneumatolytic-hydrothermal processes. In alkalic complexes Ta and Nb are associated with Ti, rare earths of the Ce group, and Th. Concentrations of Ta and Ni in alkalic massifs are caused by magmatic differentiation. In alkalic ultrabasic complexes, in magmatic and pegmatitic processes, Ta and Nb do not form independent minerals but enter into minerals of Ti and Fe, i. e. perovskite, titanomagnitite, and pyroxenes. --M. Russell.     

The Geochemistry of Scapolite: Part II. Trace Elements, Petrology, and General Geochemistry

Fifty scapolites have been analysed spectrographically for numerouselements. Average concentrations (p.p.m.) were as follows: B25, Be 9–3, Ga 33, Ti 82, Li 56, Cu 4–4, Zr 59,Mn 57, Sr 1,800, Pb 45, Ba 120, Rb 20. The following were seldomor never detected: Cr, Ni, Co, Mo, Sn, V, Sc, Ag, Y, La. Themajor elements Ca, Na, K were also determined. The distributionof the trace elements can be explained by isomorphous substitution,but no detailed correlation of trace elements with each otheror with major elements was found. Refractive indices were determined and the relation betweenaverage index and per cent Me was examined: correlation waspoor, which may in part be attributed to analytical error. Examination of scapolite parageneses shows that scapolite characteristicallyoccurs in the upper amphibolite facies or the pyroxene hornfelsfacies: it is not restricted to these and may occur in any faciesfrom zeolitic to granulitic and in any hornfels facies. Theelements generally concentrated in scapolite include Ca, Na,C, Cl, S, H, B, Be, Li, Sr, Pb. The presence of C, Cl, S, Htestify to genesis in the presence of high partial pressureof CO₂, Cl₂, SO₃, H₂O (or related compounds), that is in pneumatolytic,pegmatitic, or hydrothermal environments. The concentrationof B, Be, Li can also be attributed to these conditions. The source of the elements concentrated in scapolite must inpart be common rocks. In a limited contact zone, the nearbymagma supplied some elements, but where regional scapolitizationhas taken place the presence of magma is less clear. Many commonrocks or rock series contain all the necessary constituents,but some particular conjunction of conditions is necessary forscapolite to form, or it would be more common.     

Rare-metal pegmatites of Wamba,central Nigeria - their formation in relationship to late Pan-African granites

he Sn-(Nb, Ta) mineralization of the Wamba field (central Nigeria) occurs in muscovite-quartz-microcline pegmatites, which are related to the late-orogenic Pan-African (f 550 Ma) "Older Granites". The emplacement of granites and pegmatites was controlled by late Pan-African shear tectonics. The granitoid magmatism was multiphase and has produced peraluminous biotite granite, biotite-muscovite granite, and muscovite granite plutons. Sodic metasomatism has altered highly evolved granite cupolas and many of the pegmatite dikes. The pegmatitic mineralization of predominantly cassiterite is closely associated with albitization. Chemical data of granites and granitic and pegmatitic muscovites show that Rb, Cs, Sn, Nb, and Ta are enriched during both magmatic and postmagmatic evolution, with highest contents of these elements in early muscovites of the albitized and mineralized pegmatites. Trace-element chemistry of the pegmatitic muscovites reveals a chemical zonation of the pegmatite field related to the late-orogenic shear system.     

The Geochemistry of Scapolite Part II. Trace Elements, Petrology, and General Geochemistry

Fifty scapolites have been analysed spectrographically for numerouselements. Average concentrations (p.p.m.) were as follows: B25, Be 9-3, Ga 33, Ti 82, Li 56, Cu 4-4, Zr 59, Mn 57, Sr 1,800,Pb 45, Ba 120, Rb 20. The following were seldom or never detected:Cr, Ni, Co, Mo, Sn, V, Sc, Ag, Y, La. The major elements Ca,Na, K were also determined. The distribution of the trace elementscan be explained by isomorphous substitution, but no detailedcorrelation of trace elements with each other or with majorelements was found. Refractive indices were determined and the relation betweenaverage index and per cent Me was examined: correlation waspoor, which may in part be attributed to analytical error. Examination of scapolite parageneses shows that scapolite characteristicallyoccurs in the upper amphibolite facies or the pyroxene hornfelsfacies: it is not restricted to these and may occur in any faciesfrom zeolitic to granulitic and in any hornfels facies. Theelements generally concentrated in scapolite include Ca, Na,C, Cl, S, H, B, Be, Li, Sr, Pb. The presence of C, Cl, S, Htestify to genesis in the presence of high partial pressureof CO₂, Cl₂, SO₃, H₂O (or related compounds), that is in pneumatolytic,pegmatitic, or hydrothermal environments. The concentrationof B, Be, Li can also be attributed to these conditions. The source of the elements concentrated in scapolite must inpart be common rocks. In a limited contact zone, the nearbymagma supplied some elements, but where regional scapolitizationhas taken place the presence of magma is less clear. Many commonrocks or rock series contain all the necessary constituents,but some particular conjunction of conditions is necessary forscapolite to form, or it would be more common.     

Spatial trends and losses of major and trace elements in agricultural acid sulphate soils distributed in the artificially drained Rintala area,W. Finland

Acid sulphate soils, common in the coastal areas of Finland, contribute strongly to high acid, S and metal loadings on adjacent surface waters. This, in turn, is causing significant harm to the aquatic ecology. There is, however, limited knowledge on the total amounts of acidity and chemical elements leached from these soils. The overall objective of this study was to determine geochemical patterns in acid sulphate soils and their parent sediments and, based on the identified patterns assess the extent, mechanisms and present state of leaching of major and trace elements from these soils. The distribution of pH, aqua regia extractable concentrations of P and metals (Al, Ba, Ca, Co, Cr, Cu, Fe, K, La, Mg, Mn, Na, Ni, Sr, Th, Ti, V, Zn) and total concentrations of S and C were determined in 30 vertical profiles collected in the 23 km² large Rintala agricultural area (mid-western Finland) underlain largely with S-rich sediments. It was found that approximately 70% of the area consists of acid sulphate soils with a minimum pH<4.0, an average depth of 1.8 m, and S concentrations in the parent sediments varying from 0.24 to 1.04%. Acid sulphate soils have not developed where the S concentrations in the sediments are ⩽0.10% or where the concentrations of organic C in the soil zones are >4%. Four different methods were used to estimate the losses of chemical elements from the acid sulphate soils: (1) the concentrations in the soil were compared with those in the parent sediments, (2) due to indicated heterogeneities in several profiles, the vertical changes of the immobile Ti was used to re-calculate element losses, (3) element depletions in the acid sulphate soils (as compared to those in the parent sediments) were compared to the corresponding depletions in the non acid sulphate soils, (4) element concentrations in drainage waters were compared with those in the parent sediments. Based on these calculations, it was assessed that the percentual leaching of the aqua regia extractable fraction (total for S) has been as follows: S (40–50%), Na (30–50%), Mn (25–35%), Sr (15–20%), Ca–Ni–Co (approximately 10%), Mg–K–Zn (5–10%), Th–La–Cu–Al–P–Ti–Fe (<5%), and Ba–Cr–V (<1%). While it was possible to quite accurately estimate the percentages and thus the amounts of elements lost, it was not possible to estimate the rate of leaching as there is no available detailed information on dates when ditching activities and thus oxidation-acidification processes started. Other calculations indicated that the mobile S reservoir is still some 15 ton/hectare, which is huge but still smaller than the losses that have occurred since the area was drained (23–28 ton/hectare).     

Geochemistry of K‐feldspar and Muscovite in Rare‐element Pegmatites and Granites from the Totoral Pegmatite Field,San Luis,Argentina

The geochemistry of K‐feldspar for K, P, Sr, Ba, Rb, Cs, Ga, and of muscovite for the same elements plus Nb and Ta, was used for proving the parental relationships of S‐type granites and LCT (Li, Cs, Ta) rare‐element pegmatites in the southernmost pegmatitic field of the Pampean pegmatite province in Argentina. The variation of K/Rb‐Cs, K/Cs‐Rb, K/Rb‐Rb/Sr, K/Rb‐Ba in K‐feldspar from the granites and pegmatites show that they form an association with the evolutional sequence: granites → barren‐ to transitional pegmatites → beryl type, beryl‐columbite‐phosphate pegmatites → complex type of spodumene subtype pegmatites → albite‐spodumene type → albite type pegmatites. This sequence reflects the regional distribution of the different magmatic units. The Ta‐Cs diagram for muscovite reveals that none of the studied pegmatites exceed the threshold established in previous studies for being considered with important tantalum oxide mineralization. The granites and pegmatites constitute a rare‐element pegmatitic field in which different magmatic units form a continuous fractionation trend, extended from the less evolved granitic facies to the most geochemically specialized pegmatites     

Chemical variations and significance of phosphates from the Fregeneda-Almendra pegmatite field, Central Iberian Zone (Spain and Portugal)

Granitic pegmatites are widespread within a schist-metagreywacke complex in the Fregeneda-Almendra area (Central Iberian Zone). They intrude pre-Ordovician metasedimentary rocks and show a zonal distribution relative to the Meda-Penedono-Lumbrales granitic complex, from barren bodies to those enriched in Li, F, Sn, Nb>Ta, P and Be. Based on mineralogical criteria, these pegmatites are classified into three main categories: barren, intermediate and rare-element pegmatites, with each type including various subtypes. Phosphates are present in many pegmatites that usually occur as fine-grained accessory minerals. The most complex association of such minerals includes numerous Fe–Mn phosphates that occur in intermediate pegmatites. Al-phosphates are characteristic of Li-rich pegmatites. Electron microprobe analyses of representative phosphates reflect compositional differences depending on the pegmatite type. The Fe/(Fe+Mn) ratio of phosphates tends to decrease as the evolution degree of the pegmatites increases.     

The Albera zoned pegmatite field,Eastern Pyrenees,France

Summary Four types of pegmatites comprise the zoned pegmatite field in the eastern sector of the Albera Massif. Type I is represented by barren pegmatites with graphic textures; type II comprises transitional varieties with Li-Fe-Mn phosphates, Be (chrysoberyl) and scarce Nb-Ta and U oxide minerals; type III consists of pegmatites with significant zones of replacement containing Li-Fe-Mn phosphates, beryl and more abundant Nb-Ta oxide minerals; and type IV, muscovite-quartz-albite pegmatites are highly mineralized with Be, Nb-Ta and HREE. REE mineralization is strongly related to abundance of graphite in the late pegmatite units and in the host-rock. The individual pegmatite types are distributed within four subparallel zones concentric around anatectic muscovite-biotite leucogranites, with type I within the granites or close to the contact, and type IV pegmatites in the outermost areas. The zoning from type I to type IV could relate to fractionation processes which generated the pegmatites and is characterized by an enrichment of Mn, Ta, Na, Li, P, Be and REE. According to the pegmatite distribution and their fractionation trends, we propose an origin by differentiation of a granitic melt.

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Résumé On a établi quatre types de pegmatites dans le champ pegmatitique zoné du secteur est du Massif des Albères (Pyrénées Orientales, France). Celles de type I sont des pegmatites non minéralisées avec des textures graphiques, celles de type II sont des variétés intermediaires avec des phosphates à Li-Fe-Mn, Be (chrysobéryl) et des rares oxides à Nb-Ta et U; celles de type Ill sont des pegmatites avec des zones de réplacement bien dévéloppées et qui contiennent des phosphates à Li-Fe-Mn, du béryl et des oxides à Nb-Ta plus abondants; celles de type IV sont des pegmatites bien minéralisées à Be, Nb-Ta et des T.R. La minéralisation à T.R. est liée à des phénomènes de graphitisation répandus dans les unités tardives de la pegmatite et dans l'encaissant. La distribution de chaque type de pegmatite correspond à quatre zones à peu près parallèles et concentriques autour des granites anatectiques à muscovite-biotite, avec le type I dans les granites ou prochain au contact, et les pegmatites à type IV dans la bande plus externe. La zonation serait due à des processus de fractionnement qui auraient généré les pegmatites et qui sont caracterisés par un enrichissement en Mn, Ta, Na, Li, P, Be et T.R. dès les pegmatites de type I vers celles de type IV. On propose un origine par différentiation des granites en vue de la distribution des pegmatites.

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With 5 Figures     

华南幕阜山花岗伟晶岩的矿物化学特征及指示意义

华南晚中生代幕阜山花岗复式岩基内部及周缘广泛发育花岗伟晶岩脉,部分岩脉富含Li-Nb-Ta等元素,形成大型－超大型稀有金属矿床.本文以幕阜山北缘断峰山地区贫锂伟晶岩类和南缘仁里地区新发现的富锂伟晶岩为主要研究对象,通过详细的岩相学和主要及特征矿物（长石、云母、电气石、石榴子石、绿柱石、铌钽铁矿）的微区原位EPMA和LA-ICP-MS主微量元素地球化学的对比分析,深入探讨了伟晶岩的分类、成因演化及成矿潜力.按照特征矿物组合将伟晶岩划分为断峰山地区电气石伟晶岩、电气石－绿柱石伟晶岩、绿柱石伟晶岩、铌钽铁矿－绿柱石伟晶岩和仁里地区的锂电气石－锂云母伟晶岩5类.5类岩脉中的长石、云母、电气石和/或石榴子石的化学成分记录了不同程度花岗伟晶岩脉的演化阶段,按岩浆演化程度由低至高依次为电气石伟晶岩→电气石－绿柱石伟晶岩→绿柱石伟晶岩→铌钽铁矿－绿柱石伟晶岩→锂电气石－锂云母伟晶岩,并分别对应伟晶岩稀有金属富集程度分类中的无矿→（含Be）→富Be→富Be、Nb、Ta→富Li、Be、Nb、Ta阶段.这一结果表明仁里地区伟晶岩已演化至晚期富集多种稀有金属元素阶段,具有Li-Nb-Ta多金属成矿潜力,而断峰山地区的伟晶岩演化程度相对较低.断峰山电气石－绿柱石伟晶岩中的色带电气石晶体发育强烈成分环带,由内向外可明显分为5环,自核部至边部,Li、Zn、Ga、Ge、Nb、Ta、Sn、Pb等不相容元素和金属元素含量逐渐升高,清晰记录了正常岩浆演化序列及稀有金属富集过程.结合前人有关幕阜山花岗岩类的研究资料,本文认为幕阜山伟晶岩为该地区晚中生代巨量花岗质岩浆经历长期结晶分异作用晚期的分异产物.      

Assessing the control exerted by soil mineralogy in the fixation of potentially harmful elements in the urban soils of Lisbon,Portugal

The main purposes of this study are the textural, chemical and mineralogical characterization of the urban soils of Lisbon and the identification of probable relations between the several soil properties. The results are used to infer which soil properties control the superficial dispersion of potential harmful elements to human health. Soil sampling was carried out in 51 selected sites all through the city, under the criterion that such sites should be spaces usually frequented by children. The concentrations of 42 elements in the >2 mm soil size fraction were determined at a commercial laboratory in Canada (ActLabs, LTD), by ICP-MS/ICP-OES after an acid digestion with aqua regia. The soil mineralogy was determined by X-ray diffraction in the <2 and <62 μm size fractions. The results indicate that the urban soils have mainly a sandy texture and a main mineralogical assemblage of quartz, K-feldspar, plagioclase and calcite. In terms of clay minerals, smectite, illite and kaolinite are the main clays in the soil. Smectite and illite show a dichotomy in their distribution, with the smectites prevailing in the soils of the volcanic complex of Lisbon, which are classified as being residual, and illite prevailing in the remaining soils, which are considered mainly as man-made soils. Smectite seems to exert an important role in the fixation of Ni and Cr. The results of the geochemical study show that Ni and Cr have concentrations above the soil guideline value established to the UK and pose a probable risk to human health.     

山西平朔安太堡露天矿9号煤层中的微量元素

使用ＩＣＰ－ＡＥＳ方法对安太堡露天矿９号煤层中的微量元素进行了系统测定,检测出５３种微量元素,将研究煤样的平均微量元素质量分数与世界范围微量元素平均质量分数相比较,煤样中Ｌｉ,Ｇａ,Ｓｒ,Ｚｒ,Ｎｂ,Ｓｎ和Ｔａ具有较高的富集,而Ｃｒ,Ｃｏ,Ｎｉ,Ｇｅ,Ｒｂ,Ｙ,Ｃｓ和Ｂａ具有较低的富集,研究资料表明不同微量元素在垂向剖面上其质量分数具有不同的分布特征。经相关分析表明：（１）与镜质组含量相关的元素有     

Behaviour of the trace elements in a front of metasomatic-metamorphism in the Dalradian of Co. Donegal

The epidioritc and quartzite of the Malin Head district, (Ireland) are considered by Holmes and Reynolds [7] to be metasomatically transformed into skarn-rocks and mica-schist respectively. The trace element contents of these rocks were investigated using semi-quantitative methods in order to study the behaviour of the different trace elements during the metasomatic changes which have taken place. The elements which have been determined are Rb, Ba, Ag and Pb; Sr, Y and La; Li, Cr, Ni, Co, V, Cu, Sc, Sn and Mo; Ga; Zr, Be, Tl, Ge and In. The trace elements follow the major elements for which they can substitute in favourable crystal lattices, the substitution being in accord with Goldschmidts rules. Rb, Ba and probably Pb and Ag follow and substitute for K; Sr and Y for Ca and probably K; Li, Cr, Ni, Co, V, Cu, Sc, Sn and Mo for Mg, Fe² and Fe³; and Ga for Al.     

Geochemical Exploration on the Stream Sediments of Gabal El Mueilha Area, Central Eastern Desert, Egypt: An Overview on the Rare Metals

Abstract: El Mueilha area consists of post-collision granitic rocks intruding Pan-African metasediments, metavolcanics and granodiorites. Tin mineralization in Gabal El Mueilha is either of vein type or disseminated in the greisenized and albitized parts of the granitic rocks. Cassiterite and wolframite-bearing quartz veins also characterize a small intrusion of muscovite granite at El Mueilha tin mine area. Detailed geochemical prospecting for the rare metals Sn, Nb, Be, Li, U, Th and some other trace elements was carried out at Gabal El Mueilha area using stream sediments survey. Sixty-seven stream sediment samples were collected from the main drainage patterns of the study area. Statistical parameters were calculated for the analyzed elements. The sought elements Sn, Nb, Be and Li have relatively high background values in the studied sediments. This may reflect the role of the pathfinder elements (Nb, Be and Li) during secondary dispersion survey for Sn mineralization.
Geochemical maps were constructed to delineate anomalous areas with abnormally high rare metal contents. The anomalous Sn, Nb and Be areas are mainly encountered in the main stream draining the mineralized zones of El Mueilha tin mine and near the SW albitized parts of the post-collision granite. Correlation coefficient matrices show significant positive relation between Sn and the rare metals group (Nb, Rb and Li) at 99 % significant level. R-mode factor analysis for the concerned elements yields five factor–model.     

ON CERTAIN RELATIONSHIPS IN THE DISTRIBUTION OF RARE METAL PEGMATITE FIELDS

Prospecting for rare metal (Li, Cs, Be) pegmatites, as well as those of other metals, is facilitated by a closer analysis of the structural control in the given pegmatitic field, and of the relationships between positions of pegmatitic outcrops and the erosion surface of their parent granitic intrusives. The latter relationships become progressively more difficult to analyze as the depth of the surface of erosion increases, and the intrusive control becomes the main determinant of the positions of the pegmatites.- -V. P. Sokoloff.     

Chemical Analysis of Iron Meteorites by Inductively Coupled Plasma-Mass Spectrometry

Iron meteorites were analysed for nineteen siderophile and chalcophile elements by conventional inductively coupled plasma-mass spectrometry with the specific aim of demonstrating that this technique is an effective alternative to the more routine, yet complex, methodologies adopted in this field such as instrumental or radiochemical neutron activation analysis. Two aliquots of each meteorite sample, in the form of small shavings, were dissolved, one in 6 mol l^-1 HNO₃ and the other in aqua regia , and diluted to a final concentration of 1 mg sample per 1 ml of solution, without pre-concentrating the analytes. Nitric acid solutions were used for the determination of the elements Cr, Co, Ni, Cu, Ga, Ge and As; aqua regia solutions were analysed for the elements Mo, Ru, Rh, Pd, In, Sn, Sb, W, Re, Ir, Pt and Au. Samples were analysed by external calibration, carried out using synthetic multi-elemental solutions, and internal standardisation (with Be, Rb and Bi selected as internal standards). The results obtained from the analyses of nine geochemically well-characterized iron meteorites (Canyon Diablo, Odessa, Toluca, Coahuila, Sikhote-Alin, Buenaventura, Tambo Quemado, Gibeon, NWA 859) with widely variable chemical compositions are in good agreement with literature values for most elements. Detection limits were generally below the lowest concentration observed in iron meteorites. The most notable exception is for Ge, which cannot be successfully determined in the low-Ge meteorites of groups IVA, IVB and IIIF and a number of ungrouped irons. A test of the overall reproducibility of the adopted method, undertaken by repeatedly analysing the same Odessa IAB meteorite specimen, yielded relative standard deviations (1 s ) of between 1 and 6% for all elements except Cr (40%).