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Wolfsberg
Austria
Main commodities: Li


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The Wolfsberg lithium deposit is located in the Carinthia Province of south-central Austria, ~200 km SSW of Vienna and 20 km by road east of the industrial town of Wolfsberg (#Location: 46° 50' 21"N, 14° 59' 31"E).

The deposit was discovered in 1981 by Minerex, an Austrian government owned entity. Following extensive exploration, and technical and commercial studies, a pre-feasibility study was completed in 1987. Minerex completed exploration work that comprised initial surface geological mapping, 9 940 m3 of surface trenches, 17 000 m of diamond drilling from surface and underground and 1 400m of underground access decline and drifts. Trial mining was succesfully undertaken by Boliden Contech. In 1988 the Austrian Government decided not to proceed with development. Minerex was wound up and the Project was transferred to the government owned lead-zinc miner, Bleiberger Bergwerksunion. The latter was also closed by the Austrian government in 1991 and the project was on-sold to a private company, Kärntner Montanindustrie GmbH who kept the mining development under care and maintenance. In 2011 ASX listed Global Strategic Metals and Exchange Minerals, acquired the Project and spent a further €1.83 m on exploration and development, including drilling, a scoping study and the extraction of two 500 tonne bulk samples in October 2013. After a range of reorganisations of the holding companies, by 2014, ownership passed to the demerged European Lithium Limited which is now listed on the Australian Securities Exchange (ASX) and Vienna Stock Exchange (VSE). Subsequently, the Minerex data has been confirmed and drilling and sampling completed to bring the resource to JORC compliance, and a Definitive Feasibility Study completed. Construction was commenced in 2023, when first production was anticipated by quarter 4 of 2024 (European Lithium Limited, 2021).

Regional Setting

The deposit lies within the ~400 x up to 75 km, east-west oreinted, Austroalpine Unit Pegmatite Province in the Koralpe Region of the Eastern Alps (Göd 1989; Knoll et al., 2023). The Koralpe Region is, in turn, part of the Saualpe-Koralpe Complex, one of several lithostratigraphic complexes within the Koralpe-Wölz Nappe System of the polymetamorphic Austro-alpine Unit nappe stack. The dominant lithologies of this complex are kyanite-bearing paragneiss and garnet-bearing mica schist with intercalations of eclogite, amphibolite, quartzite and marble (Miller et al., 2005). Magmatic rock found within the region include 255 to 247 Ma MORB-like metagabbro (Miller and Thöni 1997), granite of the 258 ±11 Ma Wolfsberg granitic orthogneiss (Morauf 1980), 250.4 ±5.3 Ma; leucogranite (Knoll et al., 2018), and late Permian to Triassic spodumene-free and spodumene-bearing pegmatite (Heede 1997; Thöni and Miller 2000; Thöni and Miller 2010; Knoll et al., 2018).

A Permian event and the Cretaceous Alpine Orogeny are the dominant metamorphic episodes affecting the region. The Permian event involved lithospheric extension along the western embayment of the Neotethys Ocean, accompanied by basaltic underplating, which is interpreted to have led to high-temperature, low-pressure metamorphism up to granulite-facies throughout the Austroalpine Unit (Schuster and Stüwe 2008). This coincided with partial melting of metasedimentary rocks at lower crustal levels and emplacement of granitoid and pegmatite at middle to upper crustal levels within the attenuated crust throughout the Austroalpine Unit Pegmatite Province at amphibolite- to greenschist-facies conditions (Knoll et al., 2023). The subsequent Cretaceous Alpine Orogeny involved subduction and then collision during closure of the Meliata Ocean (Schmid et al., 2004), resulting in variable greenschist- to eclogite-facies metamorphism throughout the Austroalpine Unit. Eclogite-bearing rocks of the Saualpe-Koralpe Complex are both under- and overlain by basement units of lower metamorphic grade indicating an inverted metamorphic gradient such that they resemble the core of a recumbent fold within the extrusion wedge (Schmid et al., 2004).

Pegmatites within the Austroalpine Unit Pegmatite Province were predominantly emplaced during the Permian to Triassic in age (Schuster et al., 2001; Schuster and Stüwe 2008). However, there are also pegmatites of i). Ordovician age related to crustal melting during a 'Caledonian' magmatic event (Thöni and Miller 2004; Gangl et al., 2005; Tropper et al., 2016), ii). Late Devonian age, associated with early Variscan magmatism (Mandl et al., 2018), and iii). emplaced during Cretaceous decompression melting at the end of the Alpine orogeny (Thöni and Miller 2010). Most pegmatite bodies are simple, composed of quartz + feldspar + muscovite assemblages, although a small number are Nb-Ta-Sn-bearing spodumene pegmatite, including the most economically important Wolfsberg pegmatite.

Geology and Mineralisation

The Wolfsberg lithium deposit is situated on the northern limb of a WNW-ESE-striking 'Wolfsberg Anticline' (Göd 1989) that dips at ~60°NNE and was the result of regional deformation associated with Alpine metamorphism. The immediate host sequence is characterised by metre-thick intercalations of mica schist within eclogite-amphibolite (referred to as 'amphibolite'), and tens of centimetre-scale graphite and marble layers within both. In the main pegmatite-hosting section, the mica schist unit dips beneath the amphibolite unit, and comprises an assemblages of muscovite + garnet + biotite + kyanite. Kyanite crystals are up to centimetre-scale and display textures that indicate pseudomorphic replacement of pre-existing andalusite. The amphibolite consists of amphibole + plagioclase + quartz ±garnet ±pyroxene, and calcite which is a primary component, as well as minor stratabound scheelite. When present, pyroxene has a symplectic textures with extensive replacement by amphibole.

Pegmatite occurs as generally NW-SE striking dykes hosted within the mica schist and amphibolite, and is concordant with the foliation of the host sequence. Pegmatite dykes have been traced over a length of 1300 m, width of up to 200 m, and to a depth of 350 m, with an average thickness of 2 m, but can reach up to 5 m in width. The pegmatite dykes generally lack zoning and have sharp contacts with host rock. However, amphibolite-hosted pegmatites have irregularly-shaped internal aplitic domains, and a ~10 to 20 cm thick spodumene-poor aplitic border along dyke margins. They also have an up to 50 cm contact aureole characterised by biotite alteration of the host amphibolite and formation of holmquistite, tourmaline and garnet. Irrespective of host rock, the pegmatites are composed of quartz + feldspar + muscovite + spodumene and a range of other accessory minerals. The modal abundance of spodumene is higher in amphibolite-hosted pegmatite than in mica schist-hosted pegmatite, resulting in a ~ 0.5 wt.% higher Li
2O whole-rock composition (Göd 1989). Both pegmatite types are interpreted to have crystallised from the same highly fractionated melt, and consequently, differences between them are attributable to melt reactivity with different host rocks and degree of metamorphic overprint resulting from different host rock competence (Göd 1989). The limited geochronological data for the Wolfsberg pegmatites include 240 ±1.5 Ma (U-Pb of zircon from pegmatite; Heede 1997) interpreted to represent the timing of emplacement. Spodumene-whole rock isochron ages of 242.8 ±1.7 and 238.5 ±2.6 Ma have been returned for pegmatite samples (Thöni and Miller, 2000) that were also suggested to represent the timing of pegmatite emplacement. However, Sm-Nd mineral isochron ages of 87 and 65 Ma from the aplitic border zone of an amphibolite-hosted pegmatite (Thöni and Miller, 2000) were interpreted to reflect local eclogite-facies remobilisation and recrystallisation of the Permian protolith during the Alpine orogeny.

The amphibolite-hosted pegmatite has a coarse-grained magmatic texture and is composed of up to 5 cm greyish spodumene crystals with dark mm scale mica flakes within a matrix of white feldspar and greyish quartz. The spodumene-free aplitic border zones along its margins, as described above, are ~10 cm thick, and they and the irregular aplitic domains are interpreted as the products of albitisation. These aplitic zones are mostly composed of albite, muscovite, quartz, and in the border zones, tourmaline. They have contact aureoles of biotite-holmquistite and tourmaline. Mica schist-hosted pegmatites are generally fine-grained and have a distinct gneissic appearance the product of alternating quartz- and feldspar-rich bands with dark aligned micas.

The spodumene has a relatively consistent composition with respect to Al
2O3 and Li2O, irrespective of the host rock. Other elements present with concentrations of <1.0 wt.% include FeO, MnO and Na2O. Trace element analysis of spodumene within the two pegmatite types (i.e., the amphibolite and the mica schist hosted variants) consistently encountered concentrations of B, Mg, P, Ti, Cr, Mn, Zn, Ga and Sn of >10 ppm; Be, Sc, V and Ge of between ~1 and 10 ppm; and Cs, Nb, Ta and Pb of <1 ppm. The ΣREY (rare earth element and Yttrium) of spodumene is <1 ppm with almost all elements below detection levels. Significant differences between spodumene from the mica schist and amphibolite hosted pegmatite types are higher concentrations of Mg, P, Ti, Sn, Cs, Nb and Ta in spodumene from the latter compared to that of the former, which was comparably more enriched in Mn, Sc and Zn. Both pegmatite types have rare earth patterns that are interpreted to suggest derivation by partial melting of basement mica schist during the Permian HT/LP extensional event. However, the Cretaceous Alpine metamorphism modified the mica schist hosted variety more strongly, as compared to the amphibolite hosted varieties, resulting in recrystallisation of primary mineralogy to metamorphic assemblages with lower rare-metal concentrations, and development of a strong foliation, during which remobilised elements (e.g., Li, Cs) were concentrated along localised shear zones.

Resources

An estimated JORC compliant Measured + Indicated + Inferred Mineral Resource within Zone 1 has been published of 12.88 Mt @ 1.0% Li
2O (European Lithium Limited, 2021). Preliminary drilling within the adjacent Zone 2 suggest the possibility of substantially increasing resources (European Lithium Limited 2022). In 2023, Wolsberg was rated as the third largest lithium pegmatite resource in Europe.

The most recent source geological information used to prepare this decription was dated: 2023.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


Wolfsberg

  References & Additional Information
   Selected References:
Keyser, W., Müller, A., Steiner, R., Erambert, M., Kristoffersen, M. and Unterweissacher, T.,  2023 - Alpine eclogite‑facies modification of Li‑Cs‑Ta pegmatite from the Wolfsberg lithium deposit, Austria: in    Mineralium Deposita   v.58, pp. 1191-1210. doi.org/10.1007/s00126-023-01176-w.


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