Geology, Mineralogy and Genesis of Yenidoğan (Sivrihisar) Sepiolite Deposit

Abstract

In addition to the lump sepiolite known as the meerschaum, it has been known that there also exist some layered sepiolite deposits in the Eskişehir Neogene basin since 1960's. Sepiolite deposit, which is found nearby the Yenidoğan village, southern Sivrihisar is one of the most important one among them. Here, sepiolite occurs as two separate beds in the upper part of the Pliocene sequence, which is made up of the alternation of dolomites and dolomitic marls. The lower sepiolite bed is up to 3 m. thick and consists of sepiolite clay and dolomitic sepiolite. The upper one has maximum thickness of 10m. and it regularly extends over 750 000 square meters. It is made up of the alternation of sepiolite clay and sepiolite-rich layers and lenses. Sepiolite clay consists of over 90 % sepiolite mineral and also organic material in varying proportions but not exceeding 10 %. It may also contain quartz, feldspar, illite, dolomite and pumice grains less than 5 %. Dolomitic sepiolite is the most abundant sepiolite-rich material in the upper bed. Its dolomite content is less than 50 %, and in some cases, illite and quartz grains may also be found in trace amounts. Sepiolite has been deposited at the shallow margins of alkaline lake, shortliving ponds and marshlands. Si4+ and Mg 2+-rich solutions with 8-8.5 pH values have probably favoured sepiolite formation. Under these conditions, sepiolite was formed by direct crystallization and precipitation from the lake water. It was also formed from the solutions circulating through the intergranular space and along the desiccation cracks during and after diagenesis.