Xenotime in the Lower Buntsandstein of Central Europe: Evidence from cathodoluminescence investigation
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)
Schwermineralanalyse
Über Kreuzschichtung im deutschen Buntsandstein
Nachrichten von der Gesellschaft der Wissenschaften zu Göttingen, Mathematisch-Physikalische Klasse, Fachgruppe 4: Geologie und Mineralogie
(1933)- et al.
Ein Ordinationsverfahren zur Charakterisierung von Zirkonpopulationen
Neues Jahrbuch für Geologie und Paläontologie. Monatshefte
(1987) Contributions to molecular physics in high vacua
Phylosophical Transactions of the Royal Society
(1879)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)Sandsteine
- et al.
Laser-induced time-resolved luminescence as a tool for rare-earth element identification in minerals
Physics and Chemistry of Minerals
(2001) - et al.
Laser-induced time-resolved spectroscopy of visible broad luminescence bands in zircon
Mineralogy and Petrology
(2002) - et al.
High-resolution cathodoluminescence combined with SHRIMP ion probe measurements of detrital zircons
Mineralogical Magazine
(2001) - et al.
Simple method of distinguishing zircon, monazite, and xenotime
Journal of Sedimentary Petrology
(1963)
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