Occurrence of sepiolite in the Hirsizdere sedimentary magnesite deposit, bozkurt-denizli, SW Turkey

Abstract

The Hirsizdere magnesite deposit is found in the upper Miocene-Pliocene lacustrine sediments of the cameli formation in the western Aegean depression zone, which was uplifted to form a broad anticline and in which consecutive faults and fractures developed due to the neotectonic activities. Thick alternation of carbonate cemented and weakly cemented conglomerate, sandstone, mudstone intercalated with a few thin dolomite and magnesite layers is exposed at the lower part of the sequence. These units are overlain by magnesite and dolomite in association with thin claystone and sandstone layers and lenses. Green and claret red-brown smectite is observed in detrital materials as well as in sandy carbonate units, and is accompanied by serpentine, amphibole, illite, feldspar and quartz, whereas sepiolite is developed in the form of 3–5 cm thick, yellow and greenish brown colored veins, or as thin films liming parallel to the vein axis within the magnesite unit. SEM studies show that sepiolite fibers are grown in the form of meshworks and bridges between relict carbonate mineral grains. The presence of plant stem imprints, and the abundance of gastropod and ostracode shells in carbonate units indicate shallow and alkaline lake conditions. Field observations and detailed mineralogical, chemical and micromorphological determinations indicate that sepiolite is formed by diagenetical transformation of magnesite during the movement of silica-rich meteoric water through the fractures of carbonate units under near-surface alkaline conditions.