A hydrothermal sepiolite occurrence at Măgureni Hill, Preluca Veche (Maramures County, Romania)

Abstract

In the Măgureni Hill, situated in the Preluca Mts (NW Transylvania, Romania) proterozoic metamorphosed carbonatic rocks (dolomites and limestones) occur. During the latest phase of regional (Hercynian) metamorphism in this area, a great number of “hot” pegmatite bodies were intruded into these rocks. The consolidation of pegmatites was accompanied by the diopside-tremolite-phlogopite skarn formation and was followed by hydrothermal processes. The SiO₂-bearing, alkaline or neutral aqueous solutions reacted with the Mg-rich wall rocks, resulting in the formation of a magnesian clay mineral association. Sepiolite is the most interesting among the constituents of this association, both from a mineralogical and from an economic point of view.
The sepiolite of the Măgureni Hill occurs as thin veinlets and lenses. The accompanying minerals are talc, saponite, chlorite, kaolinite, marcasite, calcite and opal. The chemical, X-ray diffraction, thermoanalytical, IR-spectroscopy and electron microscopic studies reported in this paper proved the presence of nearly pure, magnesian sepiolite, with a very small amount of alumina and iron oxide. Mg-coordinated and free (zeolitic) water were also indicated.
Also presented here are the technological experiences related to the extraction and enrichment of the sepiolite and the possibility of its utilisation.