Greisen formation is associated with the cooling of a highly fractionated H2O-rich granitic intrusion and the enrichment of incompatible volatile elements in the upper part of the intrusion such as F, Cl, B and Li during fractional crystallization. The main evolution stages of greisenized granitoids are as follows: (1) solidification and fissuring, followed by (2) formation of pegmatites (stockscheider) and K-feldspathization (microclinization), (3) Na-feldspathization (albitization), (4) greisenization and hydrothermal alteration (sericitic alteration and / or kaolinization) and final (5) formation of veins (SHCHERBA, 1970 [369]; POLLARD, 1983 [360]).

The Zinnwald / Cínovec deposit is a typical example of a granite hosted greisen deposit. Among a number of general characteristic features fulfilled by the ore deposit, most relevant for the classification as a greisen is the existence of subsequent post-magmatic alteration stages including greisenization in the endo-contact. The mineral assemblage of quartz, Li-F-mica (zinnwaldite), topaz, fluorite and the associated ore minerals cassiterite and wolframite prove the affiliation to this deposit type. The flat dipping greisen ore bodies are marked by the absence of feldspar indicating a complete succession of greisenization of the host rocks. Mineralogical and petrological characterization of the different rock types was conducted by macroscopic observation of outcrops (above and below ground), drill core (historic and recent) as well as microscopic investigation of thin sections made from selected drill core samples.

Greisen type mineralization at the Zinnwald / Cínovec deposit is related to flat dipping, sheet-like greisen ore bodies and veins in the apical part of a geochemically highly evolved granitic intrusion. Lithium, tin, and tungsten mineralization is potentially economic and occurs mainly as quartz-mica greisen.

Individual greisen beds show a vertical thickness between less than 1 m and more than 40 m. No other areas of significant mineralization are known at present at the Zinnwald property, but surface exposures and drillings indicate various preliminary investigated or untested anomalies in the vicinity. Li-Sn-W-(Mo) mineralization is also known to exist to the north at the Altenberg “Zwitterstock” deposit. Furthermore, a Sn-W-Nb-Ta mineralization was intersected by drilling in the southeastern portion of the deposit (NEßLER, 2017 [289], NEßLER et al., 2018 [290]).

The Zinnwald / Cínovec greisen deposit and subordinately the Teplice Rhyolite can be characterized by a number of different mineralization styles. The most important include:
I. Independent or vein adjoining greisen bodies
II. Flat dipping veins (so called “Flöze”)
III. Subvertical dipping veins (so called “Morgengänge”)
IV. Metaalbite granite Sn-W-(Nb-Ta) mineralization

Independent or vein adjoining greisen bodies
The lithium ore mineralization of the Zinnwald property is closely linked to the existence of metasomatic greisen ore bodies that are located at the endo-contact of the uppermost parts of the ZG stock (style I). They form curved, stacked and lensoidal compact greisen bodies that can be highly irregular in shape but commonly exhibit a larger horizontal and limited vertical extend. The presence of stock-like greisen, reported in literature (e.g. BOLDUAN & LÄCHELT, 1960 [249]), remains disputable owing to the lack of prove by drilling intersections. However, maximum intersected greisen thickness was about 44 m (ZGLi 06A/2013). This style of greisen mineralization occurs in the central uppermost part and along the flanks of the ZG and follows with subparallel dip the morphology of the granite’s surface. Frequency and thickness generally decrease with depth. True thickness of greisen bodies is consequently consistent with the vertical depth for the central parts where the dip angle is less than 10°. Towards the gently inclined (10° - 30°) flanks of the N, E and S and a steeply inclined (40° - 70°) W-flank the true vertical thickness needs to be recalculated, respectively. On average, thickness of potentially mineable greisen bodies in the property area is between 2 m and 15 m.

Other greisenized lithologies
Zinnwaldite is not restricted solely to greisen ore bodies. Subsequent greisenization affected various rock types of the ZG cupola and adjacent wall rocks to a different degree. Therefore, the term “greisenized” is used for rocks that are not completely transformed into a greisen, meaning that they exhibit remnants of feldspar. In terms of volume the ZAG is by far the most influenced lithology. Progressive greisenization produced an enormous amount of greisenized ZAG that exhibits typical features, e.g. beginning replacement of feldspar by the growth of metablastic quartz and zinnwaldite as well as advanced argillic, sericitic and haematitic alteration.

Metaalbite granite Sn-W(-Nb-Ta) mineralization
Moderate to intermediate greisenization of albite granite associated with significant mineralization of Sn-, W- and Nb-Ta-oxides (style IV) represents an unusual mineralization style of the Zinnwald deposit. Spatially independent from major greisen ore bodies this style is characterised by greisenized albite granite of common appearance but with a disseminated ore mineralization.

A continuous body of metaalbite granite Sn-W(-Nb-Ta) mineralization with 20 m of apparent thickness was intersected at drill hole ZGLi 06A/2013 (depth from 299 to 319 m). The mean ore grades are 0.26 wt.% Sn, 520 ppm W, 130 ppm Nb and 40 ppm Ta. Maximum grades amount to 0.39 wt.% Sn, 1200 ppm W, 160 ppm Nb and 50 ppm Ta. Located below a stacked quartz-mica greisen ore body of exceptional thickness and grade (50 m at 0.47 wt.% Li), the presence of this mineralization was indicated by geochemistry rather than by macroscopically significant features on the drill core. The identical style of mineralization was observed in the adjacent drill hole (ZGLi 07/2013) with less thickness and grade.

The mining operation for the Project is planned as an underground mine development using a main ramp for the access to the mine and for ore transportation from the mine to the surface and straight to Freiberg, 50 km away from Zinnwald. The mine technology will be a common load-haul-dump (LHD) room and pillar technology with subsequent backfill using self-hardening material. Furthermore, the design of the underground mine has to consider that there are no impacts on the surface.

Based on the key figures of the overall project, the mine has to be designed for an annual output of 1,800 t of Li metal. With reference to the reserve estimation (see Item 15) this corresponds to an annual ore production between 500.000 to 600.000 t.

The inclined development ramps are planned with a cross section of 5.0 by 4.5 m and will be constructed along the footwall boundaries of the ore bodies by conventional drilling and blasting technology. The different sublevels are planned in a vertical distance of 8.0 m. At first, a sublevel crosscut will be prepared through the ore body up to its hanging wall boundary. With respect to the mining technique, turning radii are to be met for the development ramps with an inner radius of not less than 6 m and an outer radius not less than 11 m. In the extraction level the inner radius should not be below 5 m.

With respect to the best possible adjustment to the deposit structure and the prevention of mining losses, a mining technology consisting of sublevel stoping with longitudinal stopes and optimized self-hardening backfill was chosen. Mining consists of two extraction steps:
- 1st Extraction Step: Construction of pillar roads with a standard cross section of 5.0 by 4.0 m with permanently stable dimensioning (e.g. 5.0 m width on +560 m level) and a horizontal roof pillar thickness of 4.0 m. This extraction step is still accompanied with 70 % systematic mining losses.
- 2nd Extraction Step: Systematic reduction of pillars and horizontal roof pillars depending on the local conditions (deposit shape, geotechnical conditions, etc.) to a dimension of up to 7,0 by 7,0 m. Thus, it is possible to reduce the systematic mining losses down to 30 %.

The first extraction step can be downward and upward directed, whereas the second step has to be upward directed beginning at the deepest part of the deposit.

For an optimal development of the mine and a steady output of ore material, the initial development of the mine within the first years will be focused onto the deeper ore bodies (below +560 m) of the north and east field. The deepest planned sublevels are in the north field at +392 m (ore slice +388 to +396 m level) and in the east field at +360 m (ore slice +356 to +364 m level). The uppermost mineable sublevel will be at +688 m (ore slice +684 to +692 m level), to guarantee a minimum distance towards the historic mine workings. Furthermore, as long as a safety pillar of at least 25 m towards the historic mine workings is maintained, it is also possible to mine the ore bodies above the +688 m sublevel.

Pre-Crushing
The run of mine (ROM) material is fed into the processing plant by dump trucks. The material has a maximum particle size of 500 mm and a maximum moisture content of 6 wt.%. The ore is fed to the feed hopper which has a storage capacity of approximately 60 t and thus can store up to 2 truckloads to ensure a continuous material flow into the plant. During dumping of the ROM into the hopper, fine water mist is sprayed onto the material to prevent excessive dust generation.

The material is discharged from the hopper by a variable speed vibrating feeder, which continuously feeds the raw material at a controlled rate via a scalping screen to the jaw crusher. The jaw crusher is equipped with a hydraulic jack hammer to break large rocks that block the inlet of the crusher. The area is monitored remotely and controlled from the control room.

The fine material from the scalping screen and the crushed product from the jaw crusher are collected by a belt conveyor and transferred to a bucket elevator, which elevates the material to the crushing circuit vibrating screen.

The screen separates the material into fines below 25 mm particle size and coarse plus 25 mm. The coarse material is fed to the bucket elevator, which feeds the feed hopper of the cone crusher. The feed hopper is equipped with load cells to monitor the material level in the bin and material continuously feeds the cone crusher by a vibrating feeder which is controlled by the plant operator. The crushed material from both crushing stages is circulated back to the screen by belt conveyor and bucket elevator. A belt conveyor collects the crushed materials from the first and the second comminution step, this belt is equipped with a magnetic separator to remove tramp metal. The fine screen product is transferred via a belt conveyor and bucket elevator to the drying section.

HPGR Grinding and Screening
The dried and cooled material is discharged from the cooler by belt conveyor and fed to two parallel screens. The belt conveyor is equipped with two belt scales, one to measure the material flow from the cooler and a second scale that measures screen feed that also includes the high pressure grinding roll (HPGR) product. A magnet is used to remove tramp metal from the HPGR feed.

Each screen is equipped with a vibrating feeder to ensure proper material distribution over the complete screen width. The double-deck screens separate the material flow into 3 fractions - the coarse fraction (plus 4 mm), the middle fraction (between 1.25 and 4 mm) and the fines fraction (below 1.25 mm). After screening the coarse fraction and the middle fraction are combined.

The plus 1.25 mm coarse fraction is collected from both screens by a belt conveyor and fed to the HPGR feed hopper via a bucket elevator and belt conveyor. The minus 1.25 mm fines are collected from each screen with belt conveyors and fed to the fine magnetic separation section via a bucket elevator and belt conveyor. The belt conveyor is equipped with a belt scale.

Pyrometallurgy
Prior to the thermal processing of zinnwaldite, the concentrate is ground to a coarse powder (< 315 µm). This is done to facilitate the mixing with additives and enables the mixed powder to be granulated. Test work showed that the best option for grinding the lamellar zinnwaldite concentrate is by a vertical roller mill. The 1.8 m diameter vertical roller mill selected for this aplication includes a 60,000 m³/h air classifier.

Hydrometallurgy
The roasted product, which is stored in two 120 t bins, is conveyed to a mill (e.g. a hammer mill) in order to reduce the particle size of this material to less than 1 mm.

The Zinnwald Lithium Process Plant is designed to process 573,362 t/a of ROM feed, at an average grade of 0.314 wt.% Li, to produce a minimum 5,112 t/a of battery grade LiF (equivalent to 7,285 t/a LCE or 8,274 t/a LiOH·H2O) and 31,950 t/a of K2SO4 byproduct. The potassium sulfate produced is expected to be sold as a sulfate of potash (SOP) fertilizer.

Magnetic Separation
The magnetic separation circuit is fed by belt conveyor which feeds the material onto a drag conveyor. This conveyor distributes the complete material flow equally to 9 magnetic separator lines, each line consists of two magnetic separator units. The drag conveyor is equipped with nine slide gates so that each line can be isolated. Below the slide gates, every line has a feed hopper which serves as a buffer for the magnetic separators and enables the material distribution to the several lines.

The magnetic separators consist of three stages. The first stage includes magnetic drum separators ........