Sulfur-rich monazite with high common Pb in ore-bearing schists from the Schellgaden mining district (Tauern Window, Eastern Alps) |
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| Authors: | Erwin Krenn Hubert Putz Fritz Finger Werner H Paar |
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| Institution: | 1. Department of Materials Engineering and Physics, University of Salzburg, Hellbrunnerstrasse 34, 5020, Salzburg, Austria
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| Abstract: | The compositional variation of accessory monazite in ore bearing micaschists from the Schellgaden mining district, Tauern Window, Eastern Alps, was studied by means of the electron microprobe. In ore-rich domains monazite yields unusually high sulfur contents (up to 2.5?wt.% SO3), which enter the monazite structure together with Ca and Sr as ??anhydrite-celestine?? component replacing P and REEs. The exchange reaction is S6++ (Ca, Sr)2+ = REE3++ P5+. Sulfur-rich monazite is intergrown with anglesite, pyromorphite or galena and shows oscillatory zoning indicating growth from S-bearing fluids. This type of S-enriched monazite yields very high common lead contents (up to 0.5?wt.% PbO) and unrealistic high apparent Th-U-total Pb single dates (> 1?Ga). However, S-enriched monazite grains provide a flat trendline in the Th* vs. Pb isochron diagram similar to the trendline defined through low-S, and low-Pb monazite crystals (0.1?C1?wt.% SO3, < 0.05?wt.% PbO), which were observed in ore-poor parts of micaschists. Results from this study imply an Alpine rather than a pre-Alpine formation age for monazite and a strong S-rich fluid activity during the Alpine orogeny. Apart from this geological aspect, the current study also shows that the detection of sulfur in monazite may serve as a warning for a possible presence of common Pb. |
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