Lithium v granitoidech Ceskeho masivu

Bulk-rock contents of Li in granitoids were assessed within several projects of the Czech Geological Survey (CGS) and the Institute of Geology of the Czech Academy of Sciences (GLÚ) in 1985-2019. Lithium was determined mostly by the AAS method in laboratories of the CGS. Analyses of micas can be divided into three groups according to the methodology: (i) classic wet complete chemical analyses of mica concentrates (from years 1985-90); (ii) a combination of AAS-Li analyses of mica concentrate and determination of other elements using a microprobe in thin sections (mostly from years 1990-2010); and (iii) a combination of Li analyses and trace element analyses using laser-ablation ICP-MS and major elements using a microprobe. The method of laser ablation was performed at Faculty of Sciences, Masaryk University in Brno, microprobe analyses in GLÚ and wet chemical analyses in CGS.
Pre-Variscan granitoids in the Bohemian Massif are generally Li-poor (Fig. 2). Relatively highest Li values (0.08 wt.% Li₂O + elevated P, B, and Sn) were found in the Blaník-type orthogneiss in the NE part of the Moldanubicum. Lithium is hosted in micas: ca. 0.1-0.6 wt.% Li₂O in biotite and 0.2-0.4 wt.% Li₂O in muscovite.
Among Variscan igneous rocks (Fig. 3), Li is slightly enriched in some two-mica and muscovite granites in the Moldanubicum, particularly in Li-biotite and zinnwaldite granites in the Krušné Hory - Erzgebirge (Saxothuringicum). Two-mica granites of the Eisgarn type in the South Bohemian pluton in the Moldanubicum contain up to 0.05 wt.% Li₂O; small bodies of late muscovite granites near the Czech-Austrian border up to 0.16 wt.% Li₂O. Biotite and muscovite from the two-mica granites contain about 0.1-0.5 wt.% Li₂O and 0.03-0.14 wt.% Li₂O, respectively. Muscovite of the Homolka muscovite granite contains up to 1.0 wt.% Li₂O. In the Kreuzstein granite (0.12 wt.% Li₂O), situated at Czech-Bavarian border in the NW edge of the Moldanubicum, zinnwaldite is the Li carrier; this makes this granite more similar to evolved Saxothuringian granites.
Variscan granites in the Erzgebirge should be divided into two groups. The first group includes strongly peraluminous granites which dominate the western part of the area forming the Smrčiny-Fichtelgebirge, Nejdek-Eibenstock and Slavkovský les plutons (Fig. 4). These granites evolved from biotite to zinnwaldite facies containing 0.04-0.20 wt.% Li₂O. Hydrothermal greisens, forming cupolas in the uppermost part of granite intrusions at Krásno, are also enriched in Li (0.6 wt.% Li₂O), while vein-shaped and pericontact greisens in northern and northeastern parts of the Nejdek pluton are Li-poor (usually below 0.1 wt.% Li₂O).
The second group, only slightly peraluminous A-type granites, form a large volcano-plutonic complex of the Teplice caldera in the eastern Erzgebirge (Fig. 5). While early rhyolite tuffs are Li-poor (< 0.05 wt.% Li₂O), later granites contain up to 0.2 wt.% Li₂O in zinnwaldite facies in the upper parts of the cupolas at Cínovec and Krupka. Hydrothermal greisenization in the uppermost parts of cupolas increased the Li contents up to 0.4-1 % wt.% Li₂O (0.6 wt.% Li₂O on average). The only Li carrier is represented by trioctahedral Li-Fe micas with the contents from 0.25 wt.% Li₂O in biotite to 4.8 wt.% Li₂O in zinnwaldite (Fig. 6). The Cínovec-Zinnwald represents the only potential Li deposit in the Czech Republic.