The role of karst in the genesis of sulfur deposits, Pre-Carpathian region, Ukraine

Most of exogeneous epigenetic sulfur deposits are clearly associated with intensely karstified carbonate and sulfate rocks. This paper demonstrates, using the Pre-Carpathian region as an example, that karstification is one of the most important processes controlling the formation of sulfur deposits. This is determined by a coincidence of some major prerequisites of these two processes. In the Podol'sky and Bukovinsky regions the Miocene aquifer system is well drained by erosion valleys; the giant network caves known here in gypsum formed under past artesian conditions. In the region of sulfur deposits, associated with the same karstified gypsum strata, true artesian conditions still prevail. Hydrogeologic data show that abundant cavities detected in the vicinity of sulfur deposits can be interpreted as having the same origin as the fossil caves of the Podol'sky and Bukovinsky regions. The current widespread belief that the gypsum/ anhydrite stratum in the region is aquifuge separating the Miocene aguifers is inadequate. This belief caused much controversy with regard to the genetic interpretations of sulfur deposits in the region. Caves formed by the upward water flow through the gypsum/anhydrite stratum govern the water exchange between the aquifers within the aquifer system. A new karst model for the formation of sulfur deposits is suggested. It agrees well with the hydrogeological features of the Miocene sequence and with biogeochemical mechanisms of sulfur origin in low-temperature diagenetic environments.