The Geological Setting of Base Metal Mineralisation in the Rhodope Region, Northern Greece

Abstract

The Rhodope region of NE Greece is made up of a complex Lower Palaeozoic (?) basement sequence (metasediments, gneisses and amphibolites) unconformably overlain by Mesozoic and Tertiary formations. There is evidence for ophiolitic sequences in the structurally higher parts of the eastern basement and in the Mesozoic, Circum-Rhodope Belt. Metamorphic grades reach upper-amphibolite facies in the central Rhodope. Base metal mineralisation (Pb, Zn, Cu, Fe, Mn) occurs throughout the region in a variety of environments. Within the basement, sulphides are found associated with marbles (in the west) and amphibolite-serpentinites (in the east). Important base metal occurrences are found in the eastern Tertiary volcano-sedimentary basins, both as strata-bound, syngenetic sulphides and often as fault-controlled Pb-Zn deposits. All of the major deposits, both within the basement and cover sequences, appear to result from a major mineralisation event in the Tertiary. Evidence for this view comes from their homogeneous lead isotope values and the overall mineralisation style which appears to be controlled by large-scale fracture systems. Field and remotely sensed data provide the basis for a dynamic model in which extensional tectonics associated with arc magmatism, resulted in hydrothermal solutions migrating through well-defined fracture systems. Isotope data from the major sulphide occurrences support the model of large-scale homogenisation of crustal lead which was scavenged from the basement and cover sequences. The metals were subsequently dumped in chemically and physically favourable environments such as marble horizons or into actively depositing basins. Although the region is dominated by Pb-Zn occurrences, there is evidence from the Cu sulphides within the amphibolite-serpentinite sequences that local control did play an important role. Pb isotope data leave no doubt, however, that the mineralising solutions circulated through very large rock volumes outside of the mafic sequences. Overall, the study illustrates the potential of an exploration programme which uses remotely sensed data in combination with well-constrained ground studies.