The physical-chemical regime of argillaceous interseam sediments in the Emet borate district, Turkey: A transition from non-metallic volcano-sedimentary to metallic epithermal deposits

Among the world-class borate deposits, the borate deposits at Emet Espey and Hisank in Western Anatolia, Turkey, stand out by their enrichment in As-bearing minerals realgar and orpiment. In terms of abundance these Turkish deposits are on a par with the world-class borate deposits in North America. In Turkey As-bearing base and precious metal deposits of epithermal low-sulfidation type developed adjacent to these nonmetallic deposits under consideration. The borate deposits formed during the Miocene under arid climatic conditions within intermontane basins. The latter were filled with volcano-sedimentary series, which host a playa lake at the center. If we use the non-borate minerals, mainly phyllosilicates, as marker minerals and as a link to the equivalent shallow metal deposits, we can distinguish six paragenetic mineral associations (PAS). They reflect the following intrabasinal processes responsible for the formation of the deposits: (1) siliciclastic detrital input into the depocenter, (2) basic volcanic input into the depocenter, (3) felsic volcanic input into the depocenter, (4) evaporation in the depocenter, (5) hot brine activity in the depocenter and at its rim, and (6) oxidation. The physical-chemical regime of the various stages, including the temperature of formation, and the Eh and pH conditions are discussed in the current study indicating the interaction of intrabasinal and extrabasinal fluids