This diploma thesis was carried out in the course of the ÖAW project "Trace element analyses and dating of scheelite ores in the Tauern Window", supervised by Ao. Prof. Dr. Johann G. Raith. The Au-(W) mineralisation of the Schellgaden type has been investigated in the areas Pöllatal (Carinthia) and Schellgaden (Salzburg). Scheelite was dated with the Sm-Nd method and trace elements in scheelite were analysed using LA-ICPMS techniques. The abandoned Au-(W) ore deposits of the Schellgaden type are located along the eastern margin of the Tauern window and belong to pre-Alpine sequences forming the upper parts of the Storz-Kareck complex. The sulfide bearing gold quartz veins are hosted by metamorphosed magmatic and sedimentary rocks, which formed in an Early Palaeozoic island arc system. Scheelite occurs only in concordant quartz veins (Type 1), which are strongly deformed (quartz mylonites). In remobilised subconcordant to discordant quartz veins (Type 2 and Type 3) scheelite is lacking. Bigger scheelite crystals (Scheelite 1) are deformed and to some extent show metamorphic recrystallisation (Scheelite 2). All scheelites are Mo-poor and they do not show a zonation in cathodoluminescence images. The chondrite normalized Rare Earth Elements (REE) patterns show an enrichment in MREE (Sm-Gd) and a relative depletion of LREE (La-Nd) as well as HREE (Tb-Lu). This results in konvex (bell-shaped) REE patterns that have been previously described from mesozonal, hydrothermal gold deposits. Scheelite 1 was dated with the Sm-Nd method. The concentrations of Sm (65-171ppm) and Nd (111-365ppm) are remarkable high for scheelites. However, Sm/Nd ratios vary only in a narrow range from 0.1836 to 0.2623. Thus, the calculated isochron ages have very high uncertainties. An age of 322+/-140Ma can be calculated from all (n=12) analysed samples. The calculation for a single specimen (SSHF) yielded an age of 336+/-190Ma. The epsilon Nd values of all analyses are slightly positive (+1,9 to +2,9). Hence, highly radiogenic, crustal sources can be ruled out as source of the mineralisation. An Alpine age of the mineralisation can also be excluded on the basis of these ages and field relations. An epigenetic hydrothermal formation of the Au-(W) deposits during the Variscan orogeny is favoured, although because of the age uncertainties a pre-Variscan syngenetic (?) origin cannot be excluded.
|Translated title of the contribution||Samarium-neodymium dating and trace element analyses of scheelite from the Au-(W) deposit Schellgaden/Salzburg|
|Award date||26 Mar 2010|
|Publication status||Published - 2010|
Bibliographical noteembargoed until null
- Tauern Window Schellgaden Scheelite Sm-Nd dating Rare Earth Elements LA-ICPMS analyses