<abstract xmlns="http://www.w3.org/1999/xhtml">

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 (<italic>EuA</italic>). 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 <italic>EuA</italic>. 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.
</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.

Polymetallic tungsten skarn mineralisation related to the Periadriatic intrusion at Lienzer Schlossberg, East Tyrol, Austria

Austrian Journal of Earth Sciences

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

A regional tungsten anomaly was discovered and explored in the Lienzer Schlossberg area that is part of the crystalline Austroalpine nappe complex of the...

Polymetallic tungsten skarn mineralisation related to the Periadriatic intrusion at Lienzer Schlossberg, East Tyrol, Austria

Pubblicato online: 22 giu 2024

Pagine: 87 - 112

Ricevuto: 06 mar 2024

Accettato: 28 mag 2024

DOI: https://doi.org/10.17738/ajes.2024.0007

Parole chiave
Eastern Alps, scheelite, tungsten skarn, Periadriatic intrusion, trace elements, LA-ICP-MS

© 2023 Johann G. Raith et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Polymetallic tungsten skarn mineralisation related to the Periadriatic intrusion at Lienzer Schlossberg, East Tyrol, Austria

Pubblicato online: 22 giu 2024

Pagine: 87 - 112

Ricevuto: 06 mar 2024

Accettato: 28 mag 2024

DOI: https://doi.org/10.17738/ajes.2024.0007

Parole chiaveEastern Alps, scheelite, tungsten skarn, Periadriatic intrusion, trace elements, LA-ICP-MS

© 2023 Johann G. Raith et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Parole chiave
Eastern Alps, scheelite, tungsten skarn, Periadriatic intrusion, trace elements, LA-ICP-MS