The Sarmatian bentonite occurrences from the Tétény Plateau (Hungary)

Abstract

The investigated area is situated on a calcareous plateau to the south-west from the centre of Budapest. The bentonite occurrences are intercalated with Sarmatian limestones of the Tinnye Formation. There are 1–6 bentonite strata with
respective thicknesses of 0.1–0.8 m.Given their stratigraphical position, mineral composition, and total silica vs. alkali content, it is clear these strata were produced by the hydrodiagenetic alteration of dacitic tuffs (e.g. the Galgavölgy
Rhyolite Tuff).
According to the X-ray and thermal analyses the montmorillonite content of the bentonite samples is between 58–96 wt%. The other mineralogical components of the samples are biotite, quartz, zircon and apatite. These bentonites are
characterized by the absence of cristobalite.
According to the K-Ar dating on biotite the age of these bentonites is between 11.7 (Sóskút) and 13.2 (Budatétény) My. Frequently Sarmatian Foraminifera association of Elphidium (E. macellum, E. aculeatum) and Cibicidoides
lobatulus is present in the samples.
The bentonite and the limestone in this region were mined underground at Budatétény (Endre-Gallery) and Nagytétény between 1934 and 1965. The main product was limestone blocs, which were used in construction.
The predominant exchangeable cation is Ca2+, and subordinately Na+. The respective cation exchange capacities (meqv/100g) of the samples are as follows: Ca2+ (0.57–0.75), Mg2+ (0.12–0.24), Na+ (0.02–0.33) (Budatétény) and Ca2+
(0.90–0.95), Mg2+ (0.06), Na+ (0.05–0.07) (Sóskút).
The swelling capacity ranges from 6.6 to 14.0 (natural) and from 14 to 29 (activated, ml/2g). The bentonite was used predominantly to purify mineral oils and bond foundry sands, and it was exported as activated bentonite to Germany (former East Germany), Poland and former Czechoslovakia.