Pb-isotope evidence for the origin of lead in strata-bound Pb-Zn deposits in triassic carbonates of the Eastern and Southern Alps

A comparison of ore-lead isotope ratios of Pb-Zn deposits hosted in Triassic carbonates of the Eastern and Southern Alps with the isotopic composition of trace leads of their host rocks, of Triassic volcanics, and of the underlying clastic sediments shows that these rocks could have supplied only part of the ore lead. The isotopic signature of feldspar lead from crystalline basement rocks, however, reveals that they must have contributed a significant amount of metal to these deposits. The presence of barite and of thallium is also indicative that feldspars were the main source of lead. Arsenic is one of the few important trace elements in these deposits and is known to occur in some areas of Lower Paleozoic metasediments in unusually high concentrations. Any model explaining the origin of these deposits must consider the extensive leaching of the basement and to some extent of the overlying clastic sediments as well. How the metal-bearing solutions entered the lagoonal back-reef areas is still open to question as feeder channels have not yet been positively identified. The results further demonstrate that the basement also acted as a metal source for galena-bearing deposits hosted in Permian sediments, vein-type deposits in Permian volcanics, and probably the barite-fluorite polymetallic deposits along a Devonian erosional surface in the Carnic Alps as well.