Polymetallic tungsten skarn mineralisation related to the Periadriatic intrusion at Lienzer Schlossberg, East Tyrol, Austria
Author:
Raith Johann G.1ORCID, Hutter Florian12, Altenberger Florian1ORCID, Weilbold Julia3, Auer Christian3, Krause Joachim4ORCID, Berndt Jasper5, Neinavaie Hassan6
Affiliation:
1. Chair of Resource Mineralogy, Montanuniversitat Leoben , Peter Tunner-Strase 5 , Leoben , Austria 2. geo.zt gmbh – poscher beratende geologen , Saline 17, 6060 Hall in Tirol 3. GeoSphere Austria , Hohe Warte 38 , Vienna , Austria 4. Helmholtz-Zentrum Dresden-Rossendorf, Helmholtz Institute Freiberg for Resource Technology , Chemnitzer Strase 40 , Freiberg , Germany 5. Institute for Mineralogy , University of Munster , Corrensstrase 24 , Munster , Germany 6. Rennfeld 28 , Kitzbuhel , Austria
Abstract
Abstract
A regional tungsten anomaly was discovered and explored in the Lienzer Schlossberg area that is part of the crystalline Austroalpine nappe complex of the Eastern Alps in the 1970/80-ties. Tungsten is present as scheelite, which occurs in steeply SSW dipping WNW-ENE oriented quartz veinlets and joints within the porphyritic dioritic to tonalitic/granodioritic host rocks of the Oligocene Lienz/Edenwald intrusion and in the exoskarn, which developed at the contact of the intrusion with Ca-rich lithologies. The skarn system is characterised by two stages: (1) a primary high-temperature calc-silicate stage characterised by grossular, diopside-hedenbergite, vesuvianite, wollastonite and Ca-plagioclase and (2) a retrograde skarn stage including scheelite-bearing massive sulphide ores (pyrrhotite, chalcopyrite, tremolite-actinolite, diopside-hedenbergite) and scheelite-rich fault rocks with calcite, sericite and chlorite. The two ore stages, the mineral paragenesis and composition is like that of a reduced tungsten skarn; i.e., garnet is grossular-rich, clinopyroxene is diopside-hedenbergite. Vesuvianite contains up to 1.8 mass % fluorine. Scheelite has been studied by cathodoluminescence (CL), electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. Three types of scheelite (Scheelite 1–3) are distinguished. In short-wave UV light, all types show blue fluorescence but CL revealed internal micro-textures in scheelite grains which are dominated by oscillatory zoning. Prolonged hydrothermal activity is indicated by dissolution-replacement and overgrowth textures affecting the primary zonation and trace element composition of scheelite. The distribution of rare earth elements (REE) in Scheelite 1 in tonalite-hosted quartz veinlets shows a convex (i.e., middle REE-enriched), heavy REE-depleted pattern with negative Eu anomalies (EuA
). The evolution of REE patterns from skarn-hosted Scheelite 2 and 3 illustrates a gradation of convex REE patterns with high ΣREE and distinct negative Eu anomalies to relatively flat REE patterns with small to no EuA
. Scheelite at Lienzer Schlossberg has one of the highest ΣREE+Y contents of all scheelite-bearing ore settings in the Eastern Alps but incorporates minor Mo and the least Sr. High Na and Nb contents together with the positive correlation of REE+Y vs. Na+Nb+Ta suggests that the main exchange vectors for REE incorporation in scheelite is via a combined coupled substitution mechanism. Results of this study confirm the genetic similarity with reduced tungsten skarns and highlight the tungsten potential of this area.
Publisher
Austrian Geological Society (OGG)
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