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The geochemical evolution and chronology of the Breitenau sparry magnesite deposit has been investigated by means of major and trace element abundances, stable C–O isotope, and Sm–Nd isotope analysis. Chemically separated magnesite fractions (leachates) show consistent light-REE depleted REY patterns (marine carbonate normalized) and nearly constant normalized values for the middle and heavy REE without significant Ce, Eu or Y anomalies. Non-carbonate residues (composed of dark matrix material) are high in Al 2 O 3 and show variably light to middle REE enriched REY patterns similar to shales. Leachates of limestone from nearby country rocks have normalized REY patterns similar to marine carbonates. Only Ce and Y are slightly fractionated. Based on their trace element chemistry and normalized REY patterns, leachates of dolomite from the margin of the deposit closely resemble either limestone (Type A) or magnesite (Type B). With one exception, δ 18 O VPDB for both dolomite types is within the range of the respective magnesite values (δ 18 O VPDB c. − 14.2 to − 15.7‰). Leachates of dolomite from druses within the deposit (Type C) show low REY abundances with normalized patterns similar to those of magnesite. Sm–Nd isotope data for magnesite leachates yield a well-defined isochron age of 222.5 ± 9.8 Ma (MSWD 3.1). Isochron calculations for leachate(s) and residue(s) from individual magnesite samples (“internal isochrons”) yield ages between 236 ± 16 Ma and 193.5 ± 8.6 Ma with a low degree of scatter (MSWD 18 O VPDB c. − 15‰), 2) 37.9 ± 5.4 Ma (δ 18 O VPDB c. − 12.5‰), and 3) − 1.7 ± 6.8 Ma (δ 18 O VPDB c. − 11‰). Type C dolomite data indicate that druses were formed by open-system fluid flow throughout the deposit. |
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