Xenotime in the Lower Buntsandstein of Central Europe: Evidence from cathodoluminescence investigation

doi:10.1016/j.sedgeo.2005.09.017

Sedimentary Geology

Volume 183, Issues 3–4, 15 January 2006, Pages 261-268

https://doi.org/10.1016/j.sedgeo.2005.09.017 Get rights and content

Abstract

Xenotime and zircon in heavy mineral separates of siliciclastic sediments can easily be distinguished by means of cathodoluminescence (CL). All shades of bright blue, yellow and grey to white colours have been reported for zircon while only bottle green to greenish yellow colours have been found in xenotime in heavy mineral separates of Lower Buntsandstein samples as well as in two samples from crystalline rocks from Bahia (Brazil) and the Karpaty Mts. (Slovakia). The CL-spectra of both minerals are commonly dominated by narrow emission bands of rare earth elements, especially Dy³⁺. The two different crystal lattices induce differences in the intensity ratios of the emission lines that are thought to be the reason for the different CL-colours. Additionally, intrinsic broad bands that may occur in the CL-spectra of zircon are missing in the xenotime spectra. The possibility to distinguish minerals with similar optical properties underlines the large potential of cathodoluminescence in sedimentary petrology.

Introduction

Xenotime is a rare species in heavy mineral separates (e.g., Boenigk, 1983, Füchtbauer, 1988). Under transmitted light, it is possible to distinguish xenotime reliably from minerals with similar optical properties such as monazite and zircon only by means of an additional absorption spectrometer (Hering and Zimmerle, 1963, Zimmerle, 1972). Commonly, xenotime is not mentioned in analyses of siliciclastic rocks carried out to determine their provenance, probably because of the similarity in the optical properties of the isostructural zircon in the tetragonal system. Xenotime (YPO₄) occurs in small quantities in acidic and alkaline igneous rocks, pegmatites, gneisses, and schists. Commonly it occurs as an accessory component of titanium and tin minerals in beach sands and placer deposits, e.g., in Malaysia (Mariano, 1989a). Apart from a short report of Mange and Maurer (1991), it has not yet been described from heavy mineral separates dominated by zircon/tourmaline/rutile (± apatite) in the Bundsandstein (Bunter) of central Europe (e.g., Sindowski, 1958, Schnitzer, 1986, Klare, 1989). In contrast to transmitted light microscopy, the differentiation between zircon and xenotime appears to be easy by means of cathodoluminescence. This is due to the incorporation of rare earth elements (especially heavy rare earth elements, HREE) that are known to fit well into the xenotime lattice (Mariano, 1989a) and are important activators in many minerals (zircon, apatite and others, see summary in Marshall, 1988). Mariano (1989b), for example, found Dy³⁺, Eu³⁺ and Tb³⁺ as activators in xenotime from the Thor Lake peralkaline granite–syenite complex, and he pointed out the absence of intrinsic CL-bands which are typical for zircon spectra.

In this study we demonstrate how to distinguish zircon and xenotime by means of CL using examples of heavy mineral analyses of medium-grained siliciclastics from the Lower Buntsandstein of southern Germany (NE Bavaria and Black Forest).

Section snippets

Sample localities and preparation

The samples were taken, during preliminary heavy mineral studies analysis by means of CL, from sandstones of the German Triassic of Central Europe (Fig. 1). The four samples are from outcrops of the upper Lower Bunter (Buntsandstein) of NE Bavaria (1, 2) and the Black Forest (3, 4): 1. Sample HA-A, sand pit east of Haig, Geologic map of Bavaria 1 : 25,000, Sheet Kronach 5733, coordinates R 444938 H 557175; 2. Sample EB-TI, Tiefenlohe about 1 km NNE Immenreuth, Geologic map of Bavaria 1 : 25,000,

CL-Method

The CL-microscopic and CL-spectroscopic examinations were carried out with a “hot cathode”-luminescence microscope HC1-LM (Neuser et al., 1996). To avoid electrical charging the double-sided polished thin sections were carbon- or gold-coated. An acceleration voltage of 14 kV and a beam current density between 5 and 10 μA/mm² was used for the CL-measurements.

Documentation of the CL-spectra was made with a EG&G-spectrograph connected to a nitrogen cooled CCD-Camera. The CL-microscope is linked by

Results

Stable to ultrastable minerals dominate the heavy mineral associations of all samples. Disregarding authigenic anatase, the ZTR (zircon–tourmaline–rutile)-index which refers to the sum of the common percentage of zircon, tourmaline and rutile in a heavy mineral assemblage and is interpreted to be an indicator of the compositionally maturity of a sediment ranges between 80 and 93 (see Table 1). For further provenance interpretation using CL-analyses only “zircons” can be used, because in the

Discussion and conclusions

According to Boenigk (1983) xenotime is a rare species in heavy mineral samples of siliciclastic deposits. Up to now, xenotime has only locally been reported from the Buntsandstein of Central Europe (Mange and Maurer, 1991), probably because of the similar optical properties to zircon in transmitted light. In this study of the 63–90 μm heavy mineral fraction, which is dominated by zircon, xenotime was identified for the first time in sandstones from the German Triassic by means of

Acknowledgements

We are grateful to H.P. Schertl and M. Hrdlièka who kindly supplied the xenotime samples from crystalline rocks. The laborious preparation of polished thin slides of the heavy minerals by S. Schulz and M. Born is gratefully acknowledged. We also thank R. Hesse for constructive criticism of the manuscript and for help with the English language. J. Götze and two unknown referees kindly reviewed the manuscript.

References (23)

W. Boenigk
Schwermineralanalyse
R. Brinkmann
Über Kreuzschichtung im deutschen Buntsandstein
Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen, Mathematisch-Physikalische Klasse, Fachgruppe 4: Geologie und Mineralogie
(1933)
M.R. Brix et al.
Ein Ordinationsverfahren zur Charakterisierung von Zirkonpopulationen
Neues Jahrbuch für Geologie und Paläontologie. Monatshefte
(1987)
W. Crookes
Contributions to molecular physics in high vacua
Phylosophical Transactions of the Royal Society
(1879)
H.J. Förster
The chemical composition of REE-Y-Th-U-rich accessory minerals in peraluminous granites of the Erzgebirge-Fichtelgebirge region, Germany: Part II. Xenotime
American Mineralogist
(1998)
H. Füchtbauer
Sandsteine
M. Gaft et al.
Laser-induced time-resolved luminescence as a tool for rare-earth element identification in minerals
Physics and Chemistry of Minerals
(2001)
M. Gaft et al.
Laser-induced time-resolved spectroscopy of visible broad luminescence bands in zircon
Mineralogy and Petrology
(2002)
J. Götze et al.
High-resolution cathodoluminescence combined with SHRIMP ion probe measurements of detrital zircons
Mineralogical Magazine
(2001)
O.H. Hering et al.
Simple method of distinguishing zircon, monazite, and xenotime
Journal of Sedimentary Petrology
(1963)

Klare, B., 1989. Gliederung und Paläogeographie des Buntsandsteins im SE-Teil der Süddeutschen Scholle. PhD-Thesis,...

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In addition, luminescence from the REE-bearing minerals can be detected without a polishing procedure [21], indicating that no pretreatment of mineral ores is required for acquiring the CL images. Intense green luminescence was observed in CL images of xenotime [22,23], whereas no luminescence was observed from monazite or bastnäsite [9]. However, the author previously reported a dark red luminescence originating from monazite and bastnäsite in CL images that were acquired using a custom SEM–CL system [24], and the author has recently demonstrated a method to identify most of the xenotime and to determine the rough monazite content in mineral ores from their luminescence colors in CL images [21,25].
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Identification of rare earth element (REE)-bearing minerals in ores is important for the efficient exploration of mines that reserve REEs. This study presents a method to identify monazite, which is one of the principal REE-bearing minerals, and determines its content in ores via cathodoluminescence (CL) imaging. Monazite emitted pale red luminescence in CL images at 850–920 nm wavelengths in ores annealed at 1300 °C. No luminescence in 420–680 nm wavelength was observed. Apatite, xenotime, cheralite, quartz and potassium feldspar in the annealed ores emitted intense luminescence in CL images at 850–920 nm but also 420–680 nm wavelengths. Hence, we are able to distinguish monazite from other minerals by first finding areas with pale red luminescence in CL images in the 850–920 nm and subsequently in the 420–680 nm wavelengths. Areas with pale red luminescence in CL image in the 850–920 nm and no luminescence in the 420-680 nm wavelengths imply the presence of monazite. From the areas, monazite content in ores can then be estimated. The CL images can be obtained within 10 s. Therefore, the CL imaging method proposed in this study is applicable to the selection of ores with high content of monazite, which are needed in the precise quantitative analysis of ICP–MS, leading to a reduction in time to explore mines containing REEs.
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In mineral ores, the identification of monazite, bastnäsite, and xenotime, which are currently exploited rare earth element bearing minerals, is important for the development of the mines that reserve rare earth elements. A conventional method for their identification, an electron probe microanalysis, is time-consuming. Here a method to rapidly identify these minerals is presented by acquiring cathodoluminescence (CL) images and spectra. Monazite, xenotime, and bastnäsite emitted red, blue-green, and red luminescence in their CL images, respectively. We detected CL peaks related to some rare earth elements, such as Ce, Tb, Pr, Sm, and Nd for monazite; Gd, Ce, Tb, Er, Tm, Dy, Sm, and Nd for xenotime; and Pr, Sm, and Nd for bastnäsite using our custom CL spectrometer. Monazite, bastnäsite, and xenotime are distinguishable from other minerals that coexist with these three minerals based on their CL colors, intensities, peak wavelengths, and peak intensity ratios. The analysis time to acquire the CL images and spectra was within 100 s. Therefore, the acquisition of CL images and spectra contributes to the development of the rare earth element reserving mines and the sustainable supply thereof.
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For this, however, comprehensive PL-spectral databases are needed. Examples of quick mineral identification by luminescence have already been proposed in igneous/metamorphic and sedimentary petrology (Richter et al., 2006, 2008), and gemmological (Bersani et al., 2012; Fritsch et al., 2012) and mineral provenance studies (Andò and Garzanti, 2014). Also, the availability of reliable, highly resolved reference PL spectra provides the opportunity to identify specific REE species in a specific host mineral, even in cases of mineral unknowns whose emissions consist of multiple, strongly interfering REE centres (see e.g., Fig. 3).
Laser-induced photoluminescence of trivalent rare-earth elements (REEs), which is obtained as analytical artefacts in Raman spectra of selected accessory minerals, was studied. Spectra of natural titanite, monazite—(Ce), xenotime—(Y), and zircon samples from various geological environments were compared with emission spectra of synthetic, flux-grown analogues doped with REEs. The latter is of great importance to identify potentially mistakable bands as either Raman or PL signal, and to assign them to certain REE centres. In the samples investigated, various REE centres are excited selectively using 473, 514, 532, 633, and 785 nm laser excitation. Their assignment was verified by photoluminescence-excitation experiments. Luminescence spectral patterns of zircon and titanite vary in dependence of trace-REE concentrations, hence reflecting geochemical growth conditions. “REE artefacts” in Raman spectra of accessory minerals may be used as fingerprint tool for mineral phase-identification. The distribution of REE emission-intensities, revealed by hyperspectral mapping, opens up the opportunity to visualise mineral textures, complementary to cathodoluminescence imaging-techniques.
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In this study it is applied for the first time to detrital quartz grains, and significant differences with respect to the nature and amount of the OH defects are revealed. The novel technique furnishes complementary information to other state-of-the-art techniques such as chemical analysis of accessory minerals (Morton et al., 2004; Zack et al., 2004; Richter et al., 2006; von Eynatten and Dunkl, 2012) and CL on quartz grains. The fact that no correlation between water content and CL colour was revealed, underlines the potential and sensitivity of IR spectroscopy to add news aspects for the characterisation of quartz grains of unknown origin.
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Xenotime in the Lower Buntsandstein of Central Europe: Evidence from cathodoluminescence investigation

Abstract

Introduction

Section snippets

Sample localities and preparation

CL-Method

Results

Discussion and conclusions

Acknowledgements

Schwermineralanalyse

Über Kreuzschichtung im deutschen Buntsandstein

Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen, Mathematisch-Physikalische Klasse, Fachgruppe 4: Geologie und Mineralogie

Ein Ordinationsverfahren zur Charakterisierung von Zirkonpopulationen

Neues Jahrbuch für Geologie und Paläontologie. Monatshefte

Contributions to molecular physics in high vacua

Phylosophical Transactions of the Royal Society

The chemical composition of REE-Y-Th-U-rich accessory minerals in peraluminous granites of the Erzgebirge-Fichtelgebirge region, Germany: Part II. Xenotime

American Mineralogist

Sandsteine

Laser-induced time-resolved luminescence as a tool for rare-earth element identification in minerals

Physics and Chemistry of Minerals

Laser-induced time-resolved spectroscopy of visible broad luminescence bands in zircon

Mineralogy and Petrology

High-resolution cathodoluminescence combined with SHRIMP ion probe measurements of detrital zircons

Mineralogical Magazine

Simple method of distinguishing zircon, monazite, and xenotime

Journal of Sedimentary Petrology