ALBERT

Description: Highlights • Regional investigation of precious and base metal-rich deposits in the Cyclades • Pb-isotope and trace element analyses in galena by laser ablation ICP-MS • Galena inherits the Pb-isotopic signature of the underlying basement. • Distinct Pb-isotope signatures in the west and north-central Cyclades, Greece. • 206Pb/204Pb line follows the trace of known tectonostratigraphic units. Polymetallic ore deposits of the Aegean Sea, Greece, are temporally and spatially associated with the emplacement of Miocene granitoids and Pliocene to Quaternary volcanic units along the active volcanic arc and occur adjacent to the crustal-scale detachment systems. A variety of mineral deposits (e.g., carbonate-replacement, skarn, porphyry, vein-type, and low- to high-sulfidation epithermal deposits) formed during different stages of back-arc evolution and can be found in the footwall and hanging wall of the major detachment systems and all tectono-stratigraphic units. New galena Pb-isotope data collected by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis exhibit a range of isotopic ratios: 206Pb/204Pb: 18.68–18.91, 207Pb/204Pb: 15.67–15.75 and 208Pb/204Pb: 38.83–39.18, with a resolvable geographic pattern. Together with compiled Pb-isotope data of Cycladic galena, large-scale regional similarities in the Pb-isotope signatures are recognized, suggesting distinct sources of lead in the underlying basement. Base metal-rich deposits in the west Cyclades have a common lead source with a more radiogenic signature, whereas lead in the deposits in the north-central Cyclades was derived from a less radiogenic source. Similarities between the Pb-isotopic signature of galena and regional host rocks suggest, that the pre-Alpine Cycladic Basement was the main source of lead for the deposits in the north and central, and the metamorphosed volcano-sedimentary Lower Cycladic Blueschist Nappe was the source of lead for the deposits in the west. Moreover, there is a close spatial relationship of the 206Pb/204Pb 18.84 line and trace of the proposed Trans-Cycladic Thrust. Regional trends were also observed in the new LA-ICP-MS trace element analysis in galena. Galena in carbonate-replacement and skarn deposits in the west is enriched in base metals and silver, whereas galena in vein-type deposits in the north and low- to high-sulfidation epithermal deposits along the active volcanic arc is enriched in gold, tellurides and selenium. Combined trace element and isotopic data of galena indicate distinct metal sources in the Cyclades. Heterogenous rock assemblages of mixed provenance and age account for the differences in lead isotopes. Whereas the base metals and silver are ultimately sourced from the basement, the precious metals might be derived from the metasomatized lithospheric mantle.