Clarkes of concentrations of trace elements in the Riphean fine-grained terrigenous rocks of the Uchur-Maya region and the Yenisei Range

The clarkes of concentrations (K_c) of a wide range of trace elements (Li, Be, B, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, In, Sb, Cs, Ba, REE, Hf, Ta, Hg, Tl, Pb, Bi, Th, and U) were analyzed for fine-gained terrigenous rocks (mudstones, metapelites) from the reference Riphean sections of the Uchur-Maya region and the Yenisei Range. It was established that the shales and mudstones of the Uchur and Aimchan groups in the Riphean hypostratotype section are characterized by moderate (2.5 < K_c < 5) and intense (K_c > 5) geochemical specialization for Li, B, and Zn. At the same time, the similar rocks of the Lakhanda and Ui groups do not exhibit any distinct geochemical specialization, although they are notably enriched in HREE. The metapelites from the basal formations of the Riphean sedimentary successions in the Yenisei Range are distinctly specialized for B and slightly for Li, Rb, Be, Nb, Ta, Th, Ge, and Cd. In addition, moderate specialization for Cu is characteristic of the metapelites from the Korda and Lopatino formations; for Bi, Sb, Hg, and V, for their analogs from the Potoskui Formation; and, for Hg and Cs, for the similar rocks from the Lopatino Formation. The metapelites of the Lower Riphean Korda Formation from the central zone of the Yenisei Range have elevated contents of significantly more elements (Li, Be, Sc, V, Cr, Co, Ni, Zn, As, Rb, Y, Zr, Nb, Sb, Ag, In, Hf, Hg, and others) than their counterparts from its eastern near-platform part. The mudstones of the ore-bearing (Pb, Zn) Gorevo Formation are characterized by elevated concentrations of several ore elements such as Pb, Cd, As, Sb, and Bi. The elevated K_c values of the rare lithophile and of several ore elements in the metapelites of the Yenisei Range are determined by the high geochemical differentiation of the Early Precambrian blocks constituting the western margin of the Siberian Craton, which were eroded in the Riphean, and the syn-sedimentary riftogenic and intraplate magmatism. On the contrary, the fine-grained and terrigenous rocks from the basal part of the Riphean section in the Uchur-Maya region are compositionally closer to the immature Late Archean substrates or their Early Proterozoic analogs.     

An Assessment of Performance in the Routine Analysis of Silicate Rocks Based on an Analysis of Data Submitted to the GeoPT Proficiency Testing Programme for Geochemical Laboratories (2001–2011)

Data reported by laboratories contributing to the GeoPT proficiency testing programme for geochemical laboratories over the period from 2001 to 2011 have been assessed to identify the elements and concentration ranges over which analytical performance can be considered satisfactory. Criteria developed in the paper indicated that performance in the content determination of the elements/constituents SiO₂, Al₂O₃, MnO, Cs, Dy, Er, Eu, Ga, Hf, Ho, Lu, Nd, Pr, Sm, Sr, Tb, Tl, Tm, U, Y, Yb and Zn was satisfactory over the full concentration range assessed. The elements/constituents TiO₂, Fe₂O₃(T), MgO, CaO, Na₂O, K₂O, P₂O₅, Ba, Be, Cd, Ce, Co, Gd, La, Li, Nb, Rb, Sb, Sc, Sn, Ta, Th, V and Zr showed some degradation in performance at lower concentration levels (approaching the detection limit of some techniques). Performance in determining LOI, As, Bi, Cr, Cu, Ge, Mo, Ni, Pb and W was in general unsatisfactory over the full concentration range assessed. Other elements (especially Fe(II)O, H₂O⁺, CO₂, Ag, Au, B, Br, Cl, F, Hg, I, In, Ir, N, Os, Pd, Pt, Re, Rh, S, Se, Te) could not be evaluated as they were not routinely reported by laboratories participating in the GeoPT programme, often because they are present in silicate rocks at sufficiently low concentrations to require a pre‐concentration stage. Some suggestions are made for the causes of unsatisfactory performance, but further progress will require a detailed assessment of the methods used by participating laboratories, which will form the subject of a further paper.     

Geochemical characteristics of crustal anatexis during the formation of migmatite at the Southern Sierra Nevada,California

We provide data on the geochemical and isotopic consequences of nonmodal partial melting of a thick Jurassic pelite unit at mid-crustal levels that produced a migmatite complex in conjunction with the intrusion of part of the southern Sierra Nevada batholith at ca. 100 Ma. Field relations suggest that this pelitic migmatite formed and then abruptly solidified prior to substantial mobilization and escape of its melt products. Hence, this area yields insights into potential mid-crustal level contributions of crustal components into Cordilleran-type batholiths. Major and trace-element analyses in addition to field and petrographic data demonstrate that leucosomes are products of partial melting of the pelitic protolith host. Compared with the metapelites, leucosomes have higher Sr and lower Sm concentrations and lower Rb/Sr ratios. The initial ⁸⁷Sr/⁸⁶Sr ratios of leucosomes range from 0.7124 to 0.7247, similar to those of the metapelite protoliths (0.7125–0.7221). However, the leucosomes have a much wider range of initial ε_Nd values, which range from −6.0 to −11.0, as compared to −8.7 to −11.3 for the metapelites. Sr and Nd isotopic compositions of the leucosomes, migmatites, and metapelites suggest disequilibrium partial melting of the metapelite protolith. Based on their Sr, Nd, and other trace-element characteristics, two groups of leucosomes have been identified. Group A leucosomes have relatively high Rb, Pb, Ba, and K₂O contents, Rb/Sr ratios (0.15<Rb/Sr<1.0), and initial ε_Nd values. Group B leucosomes have relatively low Rb, Pb, Ba, and K₂O contents, Rb/Sr ratios (<0.15), and initial ε_Nd values. The low Rb concentrations and Rb/Sr ratios of the group B leucosomes together suggest that partial melting was dominated by water-saturated or H₂O-fluxed melting of quartz + feldspar assemblage with minor involvement of muscovite. Breakdown of quartz and plagioclase with minor contributions from muscovite resulted in low Rb/Sr ratios characterizing both group A and group B leucosomes. In contrast, group A leucosomes have greater contributions from K-feldspar, which is suggested by: (1) their relatively high K concentrations, (2) positive or slightly negative Eu anomalies, and (3) correlation of their Pb and Ba concentrations with K₂O contents. It is also shown that accessory minerals have played a critical role in regulating the partitioning of key trace elements such as Sm, Nd, Nb, and V between melt products and residues during migmatization. The various degrees of parent/daughter fractionations in the Rb–Sr and Sm–Nd isotopic systems as a consequence of nonmodal crustal anatexis would render melt products with distinct isotopic signatures, which could profoundly influence the products of subsequent mixing events. This is not only important for geochemical patterns of intracrustal differentiation, but also a potentially important process in generating crustal-scale as well as individual pluton-scale isotopic heterogeneities.     

Abundances of chemical elements of the granitoids in different geotectonic units of China and their characteristics

On the basis of actual analytical data of 767 composited samples collected mainly from about 750 large to middle representative granitoid bodies all over China, the average chemical compositions and element abundances of about 70 chemical elements of SiO₂, Al₂O₃, Fe₂O₃, FeO, MgO, CaO, Na₂O, K₂O, H₂O⁺, CO₂, TFe₂O₃, Ag, As, Au, B, Ba, Be, Bi, Cd, Cl, Co, Cr, Cs, Cu, F, Ga, Ge, Hf, Hg, Li, Mn, Mo, Nb, Ni, P, Pb, Rb, S, Sb, Sc, Se, Sn, Sr, Ta, Th, Ti, Tl, U, V, W, Zn, Zr, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y in alkalifeldspar granite, syenogranite and adamellite in 7 geotectonic units in China such as Tianshan-Xing’an orogenic series, Sino-Korean metaplatform, Kunlun-Qilian-Qinling orogenic series, Yunnan-Tibet orogenic series, Yangtze metaplatform, South China-Youjiang orogenic zone and Himalayan orogenic belt, are calculated and presented in this paper. In addition, the characteristics of petrochemical parameters, trace element contents and rare earth element distributions of different rock types of the granitoids in different geotectonic units are also sufficiently discussed. Translated from Acta Geologica Sinica, 2007, 81(1): 47–59 [译自: 地质学报]     

Geochemistry and genesis of the Lengenbach Pb-Zn-As-Tl-Ba-mineralisation,Binn Valley,Switzerland

 The Lengenbach Pb-Zn-As-Tl-Ba mineralisation is located in Triassic dolostones of the Penninic zone in the Swiss Alps where Alpine metamorphism reached upper greenschist to lower amphibolite grade. Geochemical data are used to constrain the origin of this unique occurrence. Two metamorphic redox environments are present: the As(III)-rich zone is controlled by barite-pyrite while the reduced zone contains graphite or pyrrhotite-pyrite and formally zerovalent As. The As(III)-rich zone is characterised by a mineral assemblage consistent with fO₂ in the stability field of barite+pyrite. An As-(Pb, Tl)-rich sulphide melt coexisted with a hydrothermal fluid at >kk300 °C in this zone. Mineralised dolostones are anomalous in As, Pb, Ag, Tl, Hg, Zn, Ba, Cd, Fe, Cu, Mo, U, V, B, Ga, Cr and possibly Sn and Au (in order of decreasing enrichment). As, Pb and Zn are present in the 0.1 to 1% range, Tl and Ag reach several hundred ppm. Uraninite is concentrated in silicate-rich bands and yields a late Alpine U-Pb age of 18.5±0.5 Ma. Pb- and S isotopic variations are interpreted by metamorphic overprinting and re-equilibration within an isochemically metamorphosed mineralisation. Hydrothermal sulphides are more strongly affected by uranogenic Pb than massive Pb-As-sulphides representing a former sulphide melt. The least overprinted mineralisation is characterised by ²⁰⁶Pb/²⁰⁴Pb U003U=18.44−18.56, ²⁰⁷Pb/²⁰⁴Pb=15.60−15.75, ²⁰⁸Pb/²⁰⁴Pb =38.44−38.84 and δ³⁴S (sulphide)=−25±2‰. S isotopic variations are largely a result of sulphide-sulphate re-equilibration yielding temperatures of 450± 30 °C. ⁸⁷Sr/⁸⁶Sr ratios of mineralised samples are lower than or equal to host dolostones, precluding major infiltration of basement-derived fluids during Alpine metamorphism. The Sr source (⁸⁷Sr/⁸⁶Sr close to 0.708) probably was seawater with a radiogenic, detrital mineral component. The genesis of the unique Lengenbach mineralisation is interpreted as the result of isochemical metamorphic overprinting of a carbonate hosted stratiform sulphide mineralisation. Well-crystallised sulphide minerals in fissures and druses formed during retrograde cooling of a sulphide melt in equilibrium with a hydrothermal fluid. The primary mineralisation was probably formed at or close below the sea floor and fed by sulphide-poor hydrothermal fluids. Sulphide was largely derived from seawater by open system bacterial sulphate reduction. U, V and Mo may be seawater-derived. Received: 1 February 1995/Accepted: 10 January 1996     

Mineralogy and geochemistry of the hydrothermally altered archaean granodioritic rocks of the ventersdorp dome,Western Transvaal,South Africa

Summary Archaean granodioritic rocks from the Ventersdorp Dome have been hydrothermally altered in two stages: epidotization and K-feldspatization. The alteration locally is both pervasive or occurs along veins. Mass balance calculations reveal CaO, Fe₂O₃, Sr and Y addition and loss of Na₂O,K₂O, MgO, Pb and Ba during epidotization. The combined epidotization and K-feldspatization involved a gain in SiO₂, Fe₂O₃, CaO, K₂O, Ba, Sr and Rb. A1₂O₃ and Nb were immobile during both alteration stages. The alteration is accompanied by a change in the An-content of the plagioclase (An₁₁ to An₁).

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Mineralogie und Geochemie der hydrothermal veränderten, archaischen Granodiorite des Ventersdorp Domes (westliches Transvaal, Südafrika)

Zusammenfassung Archaische Granodiorite des Ventersdorp Domes sind durch zwei Typen hydrothermaler Verdnderung, Epidotisierung und Kalifeldspatisierung überprägt worden. Die Veránderung tritt sowohl durchdringend als auch auf Adern auf. Massenvergleichsberechnungen ergaben, daß während der Epidotisierung CaO, Fe₂O₃, Sr und Y angereichert und Na₂O, K₂O, MgO, Pb und Ba abgeführt worden sind. Während der kombinierten Epidotisierung und Kalifeldspatisierung treten eine Zufuhr von SiO₂, Fe₂O₃, CaO, K₂O, Ba, Sr und Rb auf. A1₂O₃ und Nb verhielten sich während beider Verdnderungen immobil. Die hydrothermale Veränderung wurde von einer Verminderung des Ca-Gehaltes der Plagioklase begleitet (An₁₁ zu An₁).

     

内蒙古苏尼特左旗东苏A型花岗岩的锆石U-Pb年龄、地球化学特征及地质意义

位于苏尼特左旗东部的东苏二长花岗岩是索伦缝合带重要组成部分,具有高硅(SiO_2=69.76%~75.58%)、高碱且相对富钾(K2O+Na2O=6.99%~9.16%,K2O/Na2O=0.70~1.69)、相对富铝(铝饱和指数A/CNK=1.04~1.13)、高TFeO/MgO值(3.43~11.26)、贫镁(MgO=0.08%~0.50%)的特征;微量元素地球化学性质表现出相对富集轻稀土,Ba、Sr、Nb、Eu强烈负异常,Rb、Th、Ta等不相容元素富集的特征。主量和微量元素均表现出铝质A型花岗岩的特征。采用锆石LA-ICP-MS U-Pb法获得206Pb/238U值的加权平均年龄为221.5±0.81 Ma(MSDN值为0.57),表明该岩体为晚三叠世岩浆活动的产物。结合区域地质资料及地球化学信息可以判断该东苏花岗岩为后造山伸展阶段长英质地壳物质(变杂砂岩)部分熔融的产物。它的出现,标志着古亚洲洋演化的结束,索伦缝合带在晚三叠世的碰撞已达末期。     

Redox equilibria and the structural role of iron in alumino-silicate melts

The relationship between the redox ratio Fe⁺²/(Fe⁺²+Fe⁺³) and the K₂O/(K₂O + Al₂O₃) ratio (K₂O^*) were experimentally investigated in silicate melts with 78 mol% SiO₂ in the system SiO₂-Al₂O₃-K₂O-FeO-Fe₂O₃, in air at 1,400° C. Quenched glass compositions were analyzed by electron microprobe and wet chemical microtitration techniques. Minimum values of the redox ratio were obtained at K₂O^*0.5. The redox ratio in peralkaline melts (K₂O^*>0.5) increases slightly with K₂O^* whereas this ratio increases dramatically in peraluminous melts (K₂O^*<0.5) as K₂O is replaced by Al₂O₃. These data indicate that all Fe⁺³ (and Al⁺³) occur as tetrahedral species charge balanced with K⁺ in peralkaline melts. In peraluminous melts, Fe⁺³ (and Al⁺³) probably occur as both tetrahedral species using Fe⁺² as a charge-balancing cation and as network-modifying cations associated with non-bridging oxygen.     

Geochemistry and zircon U–Pb chronology of charnockites in the Yinshan Block,North China Craton: tectonic evolution involving Neoarchaean ridge subduction

The Yinshan Block, part of the Neoarchaean basement of the Western Block of the North China Craton, is composed of granite–greenstone and granulite–charnockite complexes. We report research on a suite of charnockites from the granulite–charnockite complex and characterize their geochemistry, zircon U–Pb geochronology, and Hf isotopic composition. The charnockites can be divided into intermediate (SiO₂ = 59–63 wt.%) and silicic (SiO₂ = 69–71 wt.%) groups. U–Pb zircon data yield protolith formation ages of 2524 ± 4 Ma, 2533 ± 15 Ma, followed by metamorphism at 2498 ± 3 Ma, 2490 ± 11 Ma, respectively, for these groups. Although the intermediate charnockites are characterized by higher Al₂O₃, TiO₂, Fe₂O₃^T, MnO, MgO, CaO, P₂O₅, K₂O, Sr, and ΣREE content than the silicic charnockites, the ages and Hf isotopic composition of zircons and REE patterns of both intermediate and silicic charnockites are remarkably consistent, which indicates that they are genetically related. These charnockites are predominantly metaluminous to slightly peraluminous, calc-alkalic to calcic, and magnesian – characteristics generally related to a subduction setting. High-Sr + Ba granites with low K₂O/Na₂O characteristics, shown by these charnockites, imply a mixture of mafic and felsic magmas generated from an enriched mantle + lower crust. High MgO, Ni, Cr and Mg#, low K₂O/Na₂O, and metaluminous to slightly peraluminous natures imply that the source rocks most likely were amphibolites. Coeval calc-alkaline magmatism and high-T granulite-facies metamorphism under low-H₂O activity in the area lead us to propose a model involving mid-ocean ridge subduction within a Neoarchaean convergent margin. The arc-related rocks accreted along the continent margin, and became a barrier when the lithospheric mantle ascended through the slab window. Melt derived from the decompressing mantle mixed with melt derived from the overlying, juvenile lower crust melt, which was warmed and metamorphosed by the ascending lithospheric mantle.     

Simultaneous Determination of Cd,In, Tl and Bi by Isotope Dilution‐Internal Standardisation ICP‐QMS with Corrections Using Externally Measured MoO+/Mo+ Ratios

A method for the simultaneous determination of Cd with In, Tl and Bi by isotope dilution‐internal standardisation (ID‐IS) ICP‐QMS using the same aliquot for rare earth element and other trace element determinations was developed. Samples mixed with an enriched ¹⁴⁹Sm spike were decomposed using a HF‐HClO₄ mixture, which was evaporated and then diluted with HNO₃. After determination of Sm by ID‐ICP‐QMS and Cd, In, Tl and Bi concentrations were determined using the ¹⁴⁹Sm intensity as an internal standard. The interference of MoO⁺ on Cd⁺ was corrected using the MoO⁺/Mo⁺ ratio separately measured using a Mo standard solution, and the validity of the externally determined oxide‐forming ratio correction was evaluated. The MoO⁺/Mo⁺ ratios measured using the standard solution and samples were ～ 0.0002 and < 0.002, respectively. Detection limits for Cd, In, Tl and Bi in silicate samples were at levels of < 1 ng g^?1 with a total uncertainty of < 7%. Cadmium in the carbonaceous chondrites, Orgueil (CI1), Murchison (CM2) and Allende (CV3) as well as Cd, In, Tl and Bi in the reference materials, JB‐2, JB‐3, JA‐1, JA‐2, JA‐3, JP‐1 (GSJ), BHVO‐1, AGV‐1, PCC‐1 and DTS‐1 (USGS) and NIST SRM 610, 612, 614 and 616 were determined to show the applicability of this method.     

Terrestrial geochemistry of Cd,Bi, Tl,Pb, Zn and Rb

About 2000 common magmatic, metamorphic and sedimentary rocks and rockforming minerals contained in 465 individual samples have been analyzed for 6 trace metals and potassium with high precision, mainly by combined distillation and AAS methods. Estimates of average abundances in the continental crust are: 98 ppb Cd. 82 ppb Bi. 490 ppb Tl, 14.8 ppm Pb, 77 ppm Zn and 98 ppm Rb (K/Rb: 223). These averages are close to the mean concentrations of the 6 elements in sedimentary and in low to medium grade metamorphic rocks. In relation to the upper mantle the earth's crust has very effectively accumulated Rb, Pb, Tl (and Bi). Cd and Zn are equally distributed between the upper and lower crust. Bi, Tl, Rb, Pb and K are accumulated in the upper relative to the lower continental crust by factors between 3.5 and 1.4. This is mainly due to higher concentrations in granites and lower abundances in granulites relative to gneisses and schists. The five metals form large ions with bulk coefficients less than one for the partition between metamorphic rocks and anatectic granitic melts. The major hosts of Rb, Tl, Pb and Bi in rocks are minerals with 8- to 12-coordinated sites such as mica, K-feldspar, plagioclase etc. (except for some preference of Bi for sphene and apatite). As examples of significant correlations those of Pb with Tl, K, Bi and Rb in mafic rocks and of Bi with K, Rb, Tl and Pb in sedimentary rocks can be reported. In granites and gneisses hydroxyl containing Fe²⁺-Mg-silicates are major host minerals for Zn and Cd. Except in some carbonate rocks Cd has no preference for Ca minerals.     

Trace Elements and Sr,Nd Isotope Geochemistry of the Lajimiao Norite-Gabbro from the North Qinling Belt1

Abstract The Lajimiao norite-gabbro complex, as a part of the ophiolites on the southern side of the North Qinling belt, consists of gabbro and norite-gabbro. They were derived from different magma series: the gabbro was derived from tholeiitic magma series with higher TiO₂, REE abundance and Fe³⁺ / Fe²⁺ ratio; norite-gabbro was derived from calc-alkali magma series with lower TiO₂, Fe³⁺ / Fe²⁺ ratio and REE abundance and much lower HREE abundance, which suggests that the source of the norite-gabbro magma was deeper and controlled by eclogite facies. Geochemical characteristics of both plutonic rocks are similar to those of island-arc basalts, such as relatively high contents of Ba, Pb and Sr and relatively low contents of Nb, Zr and Ni. The Sr, Nd isotopic characteristics of the Lajimiao norite-gabbro complex are similar to those of ophiolites. Its 8_Nd values are constant, about +2; whereas 8_Sr values have wide variation from — 6.4 to +31.2 and positively correlate with Na₂O, H₂O⁺ and CO₂ contents and the Fe³⁺ / Fe²⁺ ratio. The ?_Nd—Nd / Th, ?_Nd—La/Nb and ?_Nd—Ba/Nb diagrams clearly show that there were significant components of terrigenous sediments in the mantle source of the Lajimiao norite-gabbro complex. It suggests that large amount of sediments had been carried into the mantle by the subducted ancient Qinling sea plate during the Palaeozoic.     

The use of geochemical indicator elements in the exploration for hot water sources within geothermal fields

Soils, rocks, altered rocks, hot and cold waters, and hot spring precipitates were sampled within and on the outskirts of geothermal fields in China. The contents of thirty trace elements in soils and rocks show that Hg, As, Sb, Bi, Li, Rb, Cs, Au, Ag, B, W, Sn, Pb, Zn, Mn, Ni and Co can serve as direct and indirect indicators for geothermal field exploration. Large amounts of data indicate that Hg, As and Sb are the best indicators of hot water sources. Altered rocks contain higher Hg, As, Sb, Bi and Be than unaltered rocks. Based on their abundances in hot waters, it is suggested that the following elements may be used as hydrochemical indicators of high-temperature hot-water geothermal systems: K⁺, Na⁺, Ca²⁺, Mg²⁺, SO²⁻₄, HCO⁻₃, F⁻, Cl⁻, SiO₂, HBO₂, CO₂, pH, total dissolved solids and hydrochemical types, as well as Hg, As, Sb, Be, Li, Rb and Cs. Modern precipitates associated with hot springs have high contents of Ba, Be, Fe, Ti, Hg, As, Sb and Bi. Using these geochemical data, the authors have had much success in locating hot water drill sites within geothermal fields. Case histories are described for five geothermal areas.     

Mineral chemistry and chemical zoning in tourmalines, Pampa del Tamboreo, San Luis, Argentina

Tourmalinites that are distally associated with tungsten deposits of the Pampa del Tamboreo area, San Luis, Argentina, contain tourmalines retaining evidence for its origin and evolution. Tourmaline grains uncommonly contain small grains of detrital tourmaline. Analysis of a single detrital tourmaline grain reveals that it is a Ca-rich “oxy-dravite”. Proximal to the detrital cores there are inner domains of asymmetric tourmaline overgrowths that developed during low grade metamorphism. Volumetrically dominant tourmaline overgrowths in the outer domain are concentrically zoned aluminous dravite and “oxy-dravite” with Al/(Al + Fe + Mg) = 0.71–0.74 and Mg/(Mg + Fe) = 0.64–0.71. Variability of Al is primarily controlled by the deprotonation substitution R + OH⁻ = Al + O²⁻ (where R = Fe + Mg), and is a function of the activity of H₂O. A likely evolutionary scenario is one in which volcanogenic material is altered by hydrothermal fluids in the sea floor resulting in an aluminous and magnesian residuum. With further hydrothermal circulation and incipient metamorphism, boron-rich fluids are expelled from metasedimentary and metavolcanic basement rocks and develop Mg-rich tourmalinites in the aluminous, magnesian host rocks. The tourmalinization process occurs over a range of metamorphic conditions and with fluids of variable activity of H₂O.     

Geochemistry of soils derived from black shales in the Ganziping mine area, western Hunan, China

The geochemistry of major and trace elements (including heavy metals and rare earth elements) of the fresh and weathered black shales, and the soils derived from black shales in the Ganziping mine area in western Hunan province (China) were studied using the following techniques: X-ray fluorescence (XRF), inductively coupled plasma mass spectrometer (ICP-MS) and X-ray diffraction (XRD). The results show that the black-shale soils are significantly enriched with Al₂O₃ and Fe₂O₃, and depleted of mobile elements CaO, Na₂O and K₂O. The soils are also highly enriched with heavy metals U, V, Ni, Ba, Cu, Zn and Pb, that may cause potential heavy-metal contamination of the soils. Composition of the soils is homogeneous compared to the weathered black shales, for which the concentrations of major elements except CaO and Na₂O, and trace elements except heavy metals (U, V, Ni, Ba, Cu, Zn and Pb) as well as the mobile Sr, show lower variations than in the weathered black shales. Ratios of Zr/Hf, Ta/Nb, Y/Ho, Nd/Sm, and Ti/(Ti + Zr), of the soils are also less variable, with values constantly similar to that of the fresh and weathered black shales correspondingly. Thus, components of the soils are believed to be contributed from the parent black shales through weathering and pedogenesis. It is concluded that the soils were formed by at least two stages of geochemical processes: the early stage of chemical differentiation and the later stage of chemical homogenization. The chemical differentiation that was taken during black-shale weathering might have caused the depletion of CaO and Na₂O, and the enrichment of Al₂O₃ and Fe₂O₃; while the chemical homogenization that was taken during pedogenesis led to the depletion of SiO₂ and K₂O, and to the further enrichment of Al₂O₃ and Fe₂O₃. The heavy-metal enrichment (contamination) of the soils was then genetically related to the enrichment of Al₂O₃ and Fe₂O₃ in the soils.     

Geochemistry and origin of massif-type anorthosites

Samples of Proterozoic anorthosite complexes from the Adirondack Mountains of New York, Burwash Area of Ontario, and the Nain Complex of Labrador, ranging in composition from anorthosite to anorthositic gabbro, have been analyzed for major elements, Rb, Sr, Ba and nine rare-earth elements (REE), in order to set limits on the compositions and origins of their parent magmas. Similar rock types from the different areas have similar major and trace element compositions. The anorthosites have high Sr/Ba ratios, low REE abundances (Ce about 10, Yb about 0.5–1.5 times chondrites) and large positive Eu anomalies. The associated anorthositic gabbros have lower Sr/Ba ratios, REE abundances nearly an order of magnitude higher than the anorthosites, and small to negligible positive Eu anomalies.Model calculations using the adcumulate rocks with the lowest REE abundances and published distribution coefficients yield parent liquids having REE abundances and patterns similar to those of the associated anorthositic gabbros with the highest REE abundances. Rocks with intermediate REE abundances are the result of incorporation of a liquid component by a plagioclase-rich cumulate similar to the adcumulate samples. The analytical data and model calculations both suggest parent liquids having compositions of 50–54% SiO₂, greater than 20% Al₂O₃, about 1% K₂O, atomic Mg/(Mg+Fe²⁺) ratios (Mg No.'s) of less than 0.4, 15–30 ppm Rb, 400–600 ppm Sr and 400–600 ppm Ba, 40–50 times chondrites for Ce and 8–10 times chondrites for Yb.The low atomic Mg/(Mg+Fe²⁺) values for these rocks combined with geophysical evidence suggesting there are not large quantities of ferromagnesian material at depth, indicate that the anorthositic masses are not products of fractional crystallization of mafic melt derived from melting of the mantle. Rather, it is suggested that they are a result of partial melting of tholeiitic compositions at depths shallower than the basalt-eclogite transformation, leaving a pyroxene-dominated residue.     

Effects of alteration on element distributions in archean tholeiites from the Barberton greenstone belt,South Africa

Major and trace element and modal analyses are presented for unaltered, epidotized, and carbonated tholeiite flows from the Barberton greenstone belt. Au, As, Sb, Sr, Fe⁺³, Ca, Br, Ga, and U are enriched and H₂O, Na, Mg, Fe⁺², K, Rb, Ba, Si, Ti, P, Ni, Cs, Zn, Nb, Cu, Zr, and Co are depleted during epidotization. CO₂, H₂O, Fe⁺², Ti, Zn, Y, Nb, Ga, Ta, and light REE are enriched and Na, Sr, Cr, Ba, Fe⁺³, Ca, Cs, Sb, Au, Mn, and U are depleted during carbonization-chloritization. The elements least affected by epidotization are Hf, Ta, Sc, Cr, Th, and REE; those least affected by carbonization-chloritization are Hf, Ni, Co, Zr, Th, and heavy REE. Both alteration processes can significantly change major element concentrations (and ratios) and hence caution should be used in distinguishing tholeiites from komatiites based on major elements alone. The amount of variation of many of the least mobile trace elements in the altered flows is approximately the same as allowed by magma model calculations. Hence, up to about 10% carbonization and 60% epidotization of tholeiite do not appreciably affect the interpretation of trace-element models for magma generation.     

Biogeochemistry of trace metals (Mn, Sr, Rb, Ba, Cu, Zn, Pb and Cd) in a river-wetland-lake system (Balaton Region, Hungary)

Mn, Sr, Ba, Rb, Cu, Zn, Pb and Cd concentrations have been measured seasonally in the water and deposited sediments of the system comprising: Zala river (main input) — Lakes Kis-Balaton 1 and 2 (small artificial lakes created in a former bay of Lake Balaton) — Keszthely bay (hypertrophic part of Lake Balaton). The concentrations of the trace elements together with pH, alkalinity, dissolved cations (Ca²⁺, Mg²⁺, Na⁺, and K⁺), dissolved inorganic ligands (Cl^–, SO₄ ^2–), particulate Al, Ca, inorganic and organic carbon are used to assess the contamination of the study area and biogeochemical processes controlling trace element concentrations. Thermodynamic speciation calculations have also been utilized to enhance our understanding of the system. In the sediments Rb, Ba, Cu and Zn concentrations were mainly controlled by the abundance of the aluminosilicate fraction. Strontium was mainly associated with the calcium carbonate fraction. The aluminosilicate fraction constitutes a major sink for Mn and Cd but the concentration of these elements are also strongly related to calcite precipitation. The main processes that control the dissolved distribution of trace elements in the Balaton system were: solid phase formation (carbonate) for Mn; coprecipitation with calcite for Sr, Ba, Rb and possibly Mn and Cd; adsorption/desorption processes (pH dependent) for Zn and Pb; solubilization of Mn and precipitation of Cd and Cu in reed covered wetland areas where anoxic conditions were probably existing during the warm season. A preliminary budget of atmospheric and river input to Lake Balaton has also been outlined. Although Lake Balaton, is subjected to anthropogenic inputs mainly from agricultural and domestic activities, their impact on trace element concentrations in the Balaton system is very limited due to the efficiency of removal processes (i.e. adsorption and co-precipitation) and to high sedimentation rates and strong sediment re-suspension. Anthropogenic inputs are only detected for Pb.     

Heavy metal concentrations in sultana-cultivation soils and sultana raisins from Manisa (Turkey)

This paper describes the concentrations of heavy metals in soils and in raisins (sultanas) cultivated upon the Gediz Plain (Manisa), western Turkey, which is cut by major roads from ?zmir to ?stanbul and ?zmir to Ankara. A total of 212 samples of surface soil and 82 raisin samples were analysed. Soil samples have nearly same mineralogy, quartz, calcite, magnetite, pseudo-rutile and clay minerals. Dolomite is seen especially in areas close to Neogene sediments. Clay minerals are mainly mica (illite?Cmuscovite), chlorite/kaolinite, smectite and mixed layers (Sm-Il). The concentrations of 21 elements (Ba, Ni, Mo, Cu, Pb, Zn, Co, Mn, As, U, Sr, Cd, Sb, Bi, Cr, B, W, Hg, Sn, Li and organic C) were determined in the surface soils. The degree of element enrichment in soil can be measured in many ways, the most common of which are the geoaccumulation index (Igeo), enrichment factor and the pollution index. Arsenic and Sb showed the highest Igeo values, corresponding to Igeo classes 3?C4. Hence, the area is characterised as ??being heavily contaminated to polluted?? by As and Sb. Arsenic contamination has been reported from all over world. Arsenic-related pollutants enter the groundwater system by gradually moving with the flow of groundwater from rains and irrigation. Gediz Plain forms the main groundwater supply of ?zmir city. The enrichment factor (EF_arsenic) of the analysed soil samples is around 76, which corresponds to ??extremely high enrichment??. The concentrations of 33 elements (Al, Sb, As, Ba, Be, Bi, B, Cd, Ca, Cr, Co, Cu, Fe, Pb, Li, Mg, Mn, Hg, Mo, Ni, K, Se, Ag, Na, Sr, Ta, Th, Sn, Ti, U, V, Zn and Zr) were determined in the raisin samples. The Pb and Cd contents of raisins are of great concern due to their toxicity. Pb contents ranged between 0.05 and 0.46?mg?kg^?1, and average Cd content was 0.04?mg?kg^?1. Only one sample contained high level of Cd, 0.23?mg?kg^?1. After cleaning the raisins, the heavy metal concentrations were low as in the European Community (EC) regulation No: 466/2001 for allowable levels of Pb (0.2?mg?kg^?1) and Cd (0.05?mg?kg^?1).     

Origin and geochemistry of Pan-African granitoid rocks in the Gabal Um Shomer area,Southwestern Sinai,Egypt

Geological, petrological and geochemical studies indicated that there are two distinct types of granitoid rocks: older quartz diorites to granodiorite assemblage and younger granitoids, the latter occurring in two phases. The older granitoids have a meta-aluminous chemistry and a calc-alkaline character, with high MgO, Fe2O3, TiO2, CaO, P2O5, Sr and low SiO2, K2O, and Rb. Their major and trace elements data, together with low 87Sr/ 86Sr ratios (0.7029±0.0008) are indicative of I-type affinities. The second-...