Mineralogy, origin and commercial value of the zeolite-rich tuffs in the Petrota-Pentalofos area, Evros County, Greece

Abstract

The zeolite-rich tuffs of the Petrota-Pentalofos area were deposited in the Orestias Basin during the Eocene. They are up to 100 m thick and extend more than 15 Km in a long axis. Most of the outcrops consist of frequent alternations of very fine grained tuff with pumice and lapilli tuffs, the latter containing detrital fragments of the Mesozoic substrate of the basin. X-ray Diffraction, Scanning Electron Microscopy and light microscopy analysis on quarry and borehole samples has shown that the tuffs are composed mainly of clinoptilolite and minor cristobalite, with a small proportion of detrital constituents (quartz, mica-schist) and pyrogenic crystals (feldspar, quartz, biotite). Minor amounts of mordenite randomly occur in some of the northern outcrops, closer to the occurrence of lava. ICP-AES chemical analysis of the tuffs gives evidence that the original magmas were of quartz-latite composition. The tuffs rest on pre-Cenozoic metamorphic basement and pass gradationally upwards into sandstone and limestone. Evidence is give for deposition of the tuffs in a supra to infra-littoral environment. The zeolitic tuffs originated as epiclastic volcanic sediments, transported by water from the source of the eruption. The transformation of the volcanic glass of the tuffs to zeolite and cristobalite has taken place by meteoric waters in an open hydrological system existed during tghe Tertiary. The zeolitic rocks are currently being expoited as an animal feed supplement.