The Zinnwald Lithium Project is wholly owned by Zinnwald Lithium GmbH (ZLG), which is fully controlled and financed by Zinnwald Lithium Plc (ZLP). ZLP acquired 50% of ZLG in October 2020 and the remaining 50% in June 2021. Therefore, ZLG is a wholly owned subsidiary of ZLP.
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Summary:
The Zinnwald deposit is typical of a greisen-related lithium deposit, whereby zinnwaldite mica is the lithium host. Greisenisation is the host of the zinnwaldite micas, with the term “greisen” derived from the Saxony region of Germany, and Zinnwald being the type locality of the zinnwaldite mica mineral. As such, the Zinnwald-Cínovec deposit is in fact the type locality of all greisen-hosted zinnwaldite deposits. Greisen related lithium-mica systems occur throughout the Erzgebirge province. They trend northwest–southeast, which is perpendicular to the general Erzgebirge belt (Burisch, et al., in review). The lithium-mica greisens are often associated with the G4 high F and low P2O5 granites, which are typically later stage, highly fractionated granites, and regularly intrude into older rhyolites or granites.
The predominant surface outcrop within the licence area is the Teplice rhyolite, which is cut by a surface expression of the Zinnwald lithium-mica albite granite. The Zinnwald albite granite forms a north-south trending stock, which intrudes the rhyolite, and the contact is sharp and well defined. Dimensions of the surface outcrop of the albite granite are approximately 1.4 km x 0.3 km; however, this is reduced to 0.4 km x 0.25 km on the German side of the licence. The granite dips shallowly between 10° and 30° to the north, east and south (the southern limb is cut by the national border). The western contact of the granite dips at a steeper angle, between 50° and 80° (Burisch, et al., In Review). The granite essentially forms a dome structure underlying the villages of Zinnwald and Cínovec.
Vertical fractionation and subsequent alteration within the intrusion control major and minor mineral abundances, as well as distribution of rare metals. The vertical zonation can be described as:
• Uppermost 30 m: Fine-grained albite granite with lepidolite mica hosting lithium, which is not necessarily observed in the Zinnwald deposit due to dip of the granite to the north. Observed at Cínovec.
• Uppermost 700 m: Medium-grained and porphyritic varieties of the albite granite with zinnwaldite the dominant lithium-mica. Zones of microgranite are evident. There is enrichment of zinnwaldite associated with greisenisation; and a mica transition at approximately 700 m depth. Average mineral content of 35% albite, 33% quartz, 23% alkali feldspar, 6% zinnwaldite, and 2% muscovite.
• 700 m to >1,600 m depth: Medium-grained albite granite with lithium annite as the dominant dark mica. Absence of greisenisation and a reduction in albitisation.
Greisenisation is the key hydrothermal alteration package and is responsible for lithium enrichment. It is a high temperature alteration suite and often associated with final cooling of felsic magmas. Key replacement minerals include quartz and muscovite, with lithium-micas, fluorite, topaz and tourmaline as additional minerals dependent on conditions.
Lithium mineralisation is hosted entirely within the albite granite and is strongly associated with greisen beds (complete replacement of original granite textures and minerals), or greisenisation of the granite (weaker alteration and generally lower grades of lithium).
Tin (cassiterite) and tungsten (wolframite) mineralisation is also associated with the greisen beds but is infrequent and grades of both tend to decrease with depth. Tin and tungsten mineralisation is zoned and occurs predominantly toward the roof zone of the albite granite and is generally hosted in quartz veins.
Low-grade greisenisation of the granite is common and can be laterally and vertically continuous over tens of metres. The intensity of greisenisation is directly proportional to increases in zinnwaldite mica content/lithium grade and this can change abruptly over short distances (Burisch, et al., In Review).
High-grade greisen alteration occurs in narrow beds or lenses. These beds are commonly 1 m to 10 m in thickness and can be laterally continuous over 10 m to 100 m. The greisen beds are flat lying or mirror the dip of the granite/rhyolite contact. Greisen beds can be hosted within the broad zone of greisenised granite, as well as within granite that is not greisenised, the former termed internal greisens and the latter termed external greisens.
Host rock alteration is considered local but commonly associated with flat lying greisen beds or vertical fault structures. Common post mineralisation alterations include kaolinisation, sericitisation and haematisation.
The predominant host of lithium is zinnwaldite mica. Alteration of the micas is not common but is present and usually occurs along grain boundaries resulting in loss of iron and lithium.