Iwan Roelandts

Rare-earth data on monzonoritic rocks related to anorthosites and their bearing on the nature of the parental magma of the anorthositic series

Abstract Major and trace elements have been determined in monzonoritic rocks (hypersthene-monzodiorite or jotunite) from two intrusions belonging to the South Rogaland anorthositic complex (Norway). The rare-earth abundance pattern reveals no Eu anomaly, or only a very small one. This fact together with field observations suggest that these rocks represent the parental magma of the anorthositic suite. High Ti and P abundances, low Si content, high Fe/Mg and K 2 O/SiO 2 ratios are characteristics of the major element geochemistry. Absolute amounts of some trace elements abundances vary distinctly between the two intrusions. K/Rb ratios as high as 1700 are observed. Partial fusion of upper mantle kaersutite is proposed as a possible mechanism of magma generation. Partition coefficients between plagioclase phenocrysts and liquid are determined.

Rare Earth element patterns of the Central Indian Basin sediments related to their lithology

Rare earth element (REE) concentrations have been determined in terrigenous, siliceous (nodule barren and nodule bearing), calcareous, and red clay from the Central Indian Basin. The bulk distribution of REE, and in particular the relative cerium fractionation, in these surface sediments has been studied in relation to bottom water conditions. REE fractionations within a single depositional environment are found to be characteristic for each sediment type, with flat shale-normalized patterns associated with terrigenous sediments, positive Ce anomalies with siliceous sediments, negative Ce and positive Eu anomalies with calcareous sediments, and LREE-depleted patterns with pelagic red clays. There is no relation of any REE fractionation to bottom water redox conditions. Our results indicate that the REE signatures in marine sediments are not only related to depositional setting, but also to the lithological variations, and surficial diagenetic processes. Therefore, these further constraints on understanding REE behaviour indicate that REE fractionations for paleotectonic and paleoredox reconstructions should be used with caution.

Petrogenesis of monzonoritic dykes in the Egersund-Ogna anorthosite (Rogaland, S.W. Norway): trace elements and isotopic (Sr, Pb) constraints

Two major monzonoritic dykes occur in the Egersund-Ogna anorthositic massif (S.W. Norway): the Lomland dyke, which varies from norite to monzonite, and the Vettaland ferronoritic dyke. They are characterized by high Fe, Ti and P contents, low SiO2, variable K2O (0.5%–4.5%) and high Fe/Mg ratios. Small variations in REE distribution are observed inside the Lomland dyke [La/Yb=12; LREE ca. 150–180 (chondrite-normalized values), neutral to slightly positive Eu anomaly]. Part of the Vettaland dyke is severely depleted in Zr, Rb and REE and shows a positive Eu anomaly. All rocks are depleted in U and Th, and show very low Cr and Ni contents, as well as high Sr contents (400–600 ppm). Variation within the Lomland dyke is satisfactorily ex-plained through subtraction of an apatite-bearing noritic cumulate. The role of apatite is predominant in controlling the REE behaviour. Eutectic partial melting of a Fe-rich noritic cumulate (containing apatite) under low pH2O conditions is suggested for the Vettaland dyke by REE modelling. Sr isotopic initial ratios are different in Lomland (ca. 0.708) and Vettaland (ca. 0.706) dykes. These values preclude direct derivation from the mantle as well as comagmatic relationship with anorthosite. Contamination of a mantle derived magma by deep crustal material or anatexis of the LIL depleted lower crust is compatible with the low U and Th contents, and with the Pb isotopic ratios. The Vettaland partial melting process is extended to all monzonoritic types, the necessary heat being provided by the high temperature anorthositic crystal mush.

Geochemical constraints on the hydrothermal origin of ferromanganese encrustations from the Rodriguez Triple Junction, Indian Ocean

Abstract Ferromanganese crusts recovered from a spreading ridge north of the Rodriguez Triple Junction in the Indian Ocean were studied for their mineral and geochemical compositions. The crusts are highly porous, have maximum thickness of 2 cm, and occur on basaltic substrates. The composition of the crusts resembles that of hydrothermal ferromanganese crusts from other oceanic spreading centres. Compared to hydrogenous ferromanganese crusts and nodules, the hydrothermal crusts exhibit very low Mn/Fe ratios, lower transitional metal contents, low ΣREE contents and negaive Ce anomalies, which are all characteristics of hydrothermal origin. Geochemical discriminant plots of crust data show similarities to data for metalliferous sediment and hydrothermal deposits recovered from other areas. Shale-normalized REE patterns indicate that the hydrothermal contribution to the crusts is between 60 and 92%. Crusts have rarely been reported to occur at Indian Ocean spreading centers, and those described here are consistent with the earlier findings on water column temperature and chemical anomalies indicative of hydrothermal activity in the region. Some aspects of the crusts, such as δ-MnO2 mineralogy and middle REE enrichment, are not typical of hydrothermal Fe-Mn oxides. Microprobe studies show that some layers within the crusts have Mn/Fe ratios close to unity, suggesting a significant input from normal seawater. Growth rates, estimated from an algorithm based on Mn, Fe and Co contents, are orders of magnitude faster than rates determined for hydrogenous Fe-Mn oxides. The outer layers and some internal layers of the crust had relatively faster growth rates indicating that the crusts precipitated from distinct hydrothermal episodes.

Comparison of inductively coupled plasma and neutron activation analysis for precise and accurate determination of nine rare-earth elements in geological materials

Abstract The performance of inductively coupled plasma spectrometry (ICP) for the determination of nine rare-earth elements (REE) was evaluated by comparison with neutron activation analysis (NAA) data obtained for the same geochemical reference samples (GRS). Granite G-2, Andesite AGV-1, Granite GS-N, Diorite DR-N, Potash Feldspar FK-N and two apatite samples were chosen as test materials and analysed by the same operator. Granite NIM-G, Granite GA, Green River Shale SGR-1 and Granite AC-E were also included to access the accuracy and the precision of the combined cation-exchange-ICP method. For common silicate rocks and material rich in REE, the accuracy and the precision of both those techniques are within the requirements needed. These REE determinations show that ICP applied under the proper working conditions lives up to the expectations.

Distribution of Metals in Human Lung: Analysis by Particle Induced X-Ray Emission

Thirty-five lung pairs obtained during autopsy from randomly selected patients were investigated by particle induced X-ray emission for overall and regional elemental content determination. In each case the interbronchial lymph node was simultaneously processed. While homogenous distribution has been consistently observed for potassium, calcium, iron, copper, zinc, and rubidium, a very different distribution was recorded for titanium, chromium, nickel, and strontium. The significance of these results is discussed with regard to pollution hazards. Regional accumulation of this second group of elements seems to be related to air pollution peculiar to Liège. Advantages and limitations of the technique and the need for further research are stressed.

SOME NEW METHODS FOR THE DETERMINATION OF RARE-EARTH ELEMENTS IN GEOLOGICAL MATERIALS USING THERMAL AND EPITHERMAL NEUTRON ACTIVATION

Three procedures are outlined for the determination of rare-earth elements in geological materials. The irradiation of the samples is carried out by either thermal or epithermal neutrons. Two of the methods, one of which is especially suitable for ultramafic rocks are based on radiochemical separations, while in the third method non-destructive analysis is applied to apatites. The γ-ray activity measurements are performed by means of coaxial Ge(Li)-detectors.

Cerium anomaly variations in ferromanganese nodules and crusts from the Indian Ocean

Fifty analyses of rare earth elements as well as mineralogical studies have been carried out on a suite of manganese nodules and crusts from the Central Indian Basin and the Western Indian Ocean. The aim was to identify the processes controlling the REE patterns of the phases hosting the REE in the manganese nodules, with an emphasis on an understanding of the Ce anomaly. This has involved separating the encrusting layers and nuclei physically as well as Fe-Mn oxides from the aluminosilicate phase chemically (using a 2 M HCl leach) prior to analysis. The presence of nodule nuclei seems to have little influence (mostly <5% to a maximum of 30%) on the overall magnitude of the Ce anomalies in these nodules. The ratios of concentrations of elements in the acid leachates and the corresponding bulk values yield flat REE patterns indicating that the aluminosilicate phase contributes very little to the Ce anomalies. Interelement relations indicate that the Ce anomalies are largely controlled by the amorphous mineral phase FeOOH.xH2O. The relationship of Fe, Ce anomaly and δ-MnO2 further suggests that Ce is chemisorbed onto iron oxyhydroxides which are epitaxially intergrown with δ-MnO2. The regional distribution of the Ce anomaly values appears to depend on many of the factors responsible for the uptake of other minor metals in nodules and crusts.

Use of rutherford scattering on a secondary carbon target for correcting intermediate thickness sample PIXE measurements

Abstract A method is presented for correcting PIXE measurements on intermediate thickness targets. The correction deals with the X-ray attenuation and the incident proton energy loss. It is based on the simultaneous acquisition of the PIXE spectrum along with the energy distribution of protons elastically scattered by a thin secondary carbon foil located behind the PIXE target. These measurements allowed a linear correlation between the proton energy loss ΔE and the correcting factor for X-ray absorption XF to be demonstrated. The validity of these simplifying linear approximations is discussed. The method is applicable to inhomogeneous thickness samples like aerosol impactor stages.

Observations of serum trace elements in chronic lymphocytic leukemia.

Serum trace elements (STE) were measured in 50 patients with chronic lymphocytic leukemia (CLL) and 100 normal subjects. Copper was higher in patients than in controls (1.50 ± 0.06 versus 1.10 ± 0.02 μg/ml, P < 0.001), increased steadily from Stage 0 to Stage 4 (P = 0.002), and correlated with the lymphocyte count and serum lactate dehydrogenase (P < 0.01) but not with acute phase reactants. Zinc was lower in patients than in controls (0.94 ± 0.03 versus 1.10 ± 0.02 μg/ml, P < 0.001). Zinc (NS), selenium (P = 0.039), and calcium (P < 0.033), were decreased in Stages 3–4 as compared to Stages 0–2. The copper‐to‐zinc ratio (CZR) increased continuously from Stage 0 to Stage 4 (P < 0.001). Discriminant analysis between two groups, Stage 0–2 and Stage 3–4, based on serum copper, zinc, calcium, and protein levels, allowed for a correct classification of 94% of the patients. Moreover, the clinical staging of the remaining 6% was modified retrospectively according to the results of discriminant analysis. It was concluded that (1) serum copper and CZR are useful indices of the extent of disease, (2) they are independent of a nonspecific acute phase reaction, (3) STE determination could be helpful in the staging of a limited number of CLL patients, and (4) zinc deficiency could contribute to immune dysfunction in CLL.