Genesis of the Kremikovtsi deposit and metallogenic perspectives of the Sredec iron ore region

Abstract

A detailed review of arguments used to confirm different genetic hypotheses for the Kremikovtsi deposit shows that the sedimentary-exhalative version is able to interpret logically highly varied mineralogical, geochemical and geological features of the deposit without getting into apparent contradictions typical of all other versions. According to this hypothesis, the Kremikovtsi deposit was the result of two-stage (sedimentary-hydrothermal and hydrothermal-metasomatic) Middle Triassic metallogenesis located along the margin of the adjacent to the West Balkan Early Paleozoic accreted block grabenshaped structure and realized in an extensional embryonal rift-related setting characterized by a high geothermal gradient, permeable fault-disturbed basement rocks, arid climate in the beginning of marine transgression and depressions on the epicontinental seafloor. An ore-forming recycling model of hydrothermal convection better conforms to the data obtained so far. The Kremikovtsi deposit can be defined as a zonal deposit of SED EX-type (Atasu-type in the Russian classifications) composed of stratiform barite and MECS-IF-type iron ores with lowgrade strata-bound sulphide mineralization, accompanied by contemporaneous, but epigenetic, vein and stockwork barite-sulphide mineralizations in the stratiform ores and underlying rocks. Substantial reasons there exist the Kremikovtsi deposit in its present boundaries to be considered as a distal and upper Fe( +Mn)-Ba equivalent of richer sulphide mineralization in depth. The most suitable exploration strategy for a similar type of ore bodies and deposits in the region described, based on the summary of geological parameters, must have a following sequence: lower levels of Iskar Carbonate Group → facies of reef and relatively shallow-water dolomitic limestones precipitated into fault-bounded basins with low energy and partly evaporitic environment → wallrock alterations; primary, secondary and superimposed dispersion haloes of Mn, Fe, Ba, Pb, Zn, Cu, Ag, Hg; geophysical anomaly of magnetic, gravitational or electric fields; lowgrade oxide/carbonate or barite-sulphide ore occurrences → intersection of ore horizons and determination the type and the economic perspectives of the ore mineralization.