The Lokve Barite Deposit, Croatia: an Example of Early Diagenetic Sedimentary Ore Deposits

摘要

Syngenesis versus epigenesis in the Kupferschiefer genetic model is still a matter of controversy. The title of the article seems to be a paraphrase of a well-known paper by WEDEPOHL (1971), “Kupferschiefer as a prototype of syngenetic sedimentary ore deposits”. It is intended, however, more as a paradigm for the genesis of the hydrogen-sulphide geochemical barrier, an important ore formation episode prior to heavy metal accumulation, which shows the utility of RENFRO’s (1974) epigenetic model. Barite mineralization in Lokve is a stratabound ore deposit conformably situated at the Permian-Triassic boundary. It bears only two ore minerals, barite and pyrite exclusively, separated into two distinct, juxtaposed horizons stretching for tens of kilometers. The discovery of cryptalgal fabrics and other conspicious sedimentary features in underlying siliciclastics with massive pyrite and surmounting barite-bearing dolomites supports their affiliation to a tidal flat facies and sabkha environment. Barite and pyrite accumulation were formed by an early diagenetic, bacteriogenic sulphate reduction in a peritidal muddy environment, concommitant to a widespread process of evaporative dolomitization. The early diagenetic model is supported by an analysis of the sedimentary facies, trace element geochemistry and sulfur isotope distribution along two vertical profiles across the stratabound barite and pyrite mineralization.