Lithium bearing silicates in Upper Permian salt rocks of the Morsleben site (Germany)

Li can be detected in salt rocks, although no known naturally formed salt mineral incorporates Li in the crystal lattice [1]. Very low Li concentrations (few µg/g) are related to fluid inclusions, but higher concentrations must originate from other sources, e.g. phyllosilicates [1, 2]. To verify the Li-hosted minerals, samples from the upper Staßfurt-Formation (Deckanhydrit, z2DA) to the lower Leine-Formation (Grauer Salzton, z3GT; Leinekarbonat, z3LK; Hauptanhydrit, z3HA) were investigated. The succession contains salt clays, anhydrite and carbonate bearing salt rocks of the Upper Permian (Zechstein) from the Morsleben site (Germany).

The samples were investigated using ICP-OES, ICP-MS, XRD, SEM and thin section microscopy.

The z2DA shows Li concentrations of ca. 4 µg/g to 159 µg/g. The sample with the highest Li content consists of quartz, illite-muscovite, chlorite (clinochlore), halite, anhydrite, magnesite, kaolinite, koenenite, biotite and hydrotalcite. The z3GT is composed of quartz, illite-muscovite, halite, sylvite, anhydrite, carnallite, hydrotalcite, chlorite (clinochlore), anatase, biotite and tourmaline, with a Li content of 146 to 154 µg/g. In the z3LK, the Li content varies from 11 to 46 µg/g and in the z3HA from 5 to 116 µg/g. Al, K and Rb show positive relations to Li in all samples.

In the z2DA, Li probably originates from illite-muscovite, in the z3GT probably from illite-muscovite and a Li-bearing variety of a tourmaline (elbaite). The Li content of these minerals will be verified in future work.

[1] Braitsch (1971) Salt Deposits, Their Origin and Composition 4, 297.

[2] Mertineit & Schramm (2019) Minerals 9, 766; doi:10.3390/min9120766.