Sulfur-rich monazite with high common Pb in ore-bearing schists from the Schellgaden mining district (Tauern Window, Eastern Alps)

• Published in: Mineralogy and petrology Vol. 102; no. 1-4; pp. 51 - 62
• Main Authors: Krenn, Erwin, Putz, Hubert, Finger, Fritz, Paar, Werner H.
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01.10.2011; Springer Nature B.V
• Subjects: Crystals; Earth and Environmental Science; Earth Sciences; Geochemistry; Inorganic Chemistry; Mineralogy; Minerals; Mining; Orogeny; Special Issue Accessory Minerals; Sulfur; Alps; Scheelite; Molybdenite; Pyrite; Tourmaline; Galena
• ISSN: 0930-0708; 1438-1168
• DOI: 10.1007/s00710-011-0170-x

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.% SO 3 ), which enter the monazite structure together with Ca and Sr as “anhydrite-celestine” component replacing P and REEs. The exchange reaction is S 6+ + (Ca, Sr) 2+ = REE 3+ + P 5+ . 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 (0.1–1 wt.% SO 3 , < 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.