ISOTOPIC COMPOSITION OF PB IN ORE-DEPOSITS OF THE BETIC CORDILLERA, SPAIN - ORIGIN AND RELATIONSHIP TO OTHER EUROPEAN DEPOSITS

The Betic Cordillera in southern Spain is a complex Alpine fold belt t hat resulted from the Cretaceous through Cenozoic collision of Africa with Europe. The region is illustrative of one of the characteristics of the Alpine-Mediterranean orogen: the occurrence over a limited area of mineral deposits with a wide variety of host rocks, mineralization ages, and styles. The metamorphic basement in the Betic zone is chara cterized by a nappe structure of superimposed tectonostratigraphic uni ts and consists of lower Paleozoic to Lower Triassic clastic metasedim entary rocks. This is overlain by Middle to Upper Triassic platform ca rbonate rocks with abundant strata-bound F-Pb-Zn-(Ba) deposits (e.g., Sierra de Gador, Sierra Alhamilla). Cretaceous to Paleogene subduction -related compression in southeastern Spain was followed by Miocene pos tcollisional extension and resulted in the formation of the Almeria-Ca rtagena volcanic belt and widespread hydrothermal activity and associa ted polymetallic mineralization. Typical Miocene hydrothermal deposits include volcanic-hosted Au (e.g., Rodalquilar) and Ag-rich base metal (e.g., Cabo de Gata, Mazarron) deposits as well as complex polymetall ic veins, mantos, and irregular replacement bodies which are hosted by Paleozoic and Mesozoic metamorphic rocks and Neogene sedimentary and volcanic rocks (e.g., Cartagena, Sierra Almagrera, Sierra del Aguilon, Loma de Bas). Lead isotope compositions were measured on sulfide samp les from nine ore districts and from representative fresh samples of v olcanic and basement rock types of the region. The results have been u sed to evaluate ore-forming processes in southeastern Spain with empha sis on the sources of metals. During a Late Triassic mineralizing even t, Pb was leached from Paleozoic clastic metasedimentary rocks and inc orporated in galena in strata-bound F-Pb-Zn-(Ba) deposits (Pb-206/Pb-2 04 = 18.332 +/- 12, Pb-207/Pb-204 = 15.672 +/- 12, Pb-208/Pb-204 = 38. 523 +/- 46). The second episode of mineralization was essentially cont emporaneous (late Miocene) throughout the region and did not involve r emobilization of less radiogenic Triassic ore Pb. Lead isotope data in dicate a dominantly Paleozoic metasedimentary source for polymetallic vein- and manto-type deposits that formed by hydrothermal circulation through the Betic basement, driven by Miocene intrusions (Pb-206/Pb-20 4 = 18.860 +/- 20, Pb-207/Pb-204 = 15.685 +/- 9, Pb-208/Pb-204 = 39.02 6 +/- 37). Lead in Au-(Cu-Te-Sn) ores is isotopically indistinguishabl e from that of the calc-alkalic volcanic host (Pb-206/Pb-204 = 18.860 +/- 9, Pb-207/Pb-204 = 15.686 +/- 8, Pb-208/Pb-204 = 38.940 +/- 27). I n contrast, the Pb in volcanic-hosted Pb-Zn-Cu-(Ag-Au) veins was deriv ed from Paleozoic metamorphic and Miocene volcanic rocks (Pb-206/Pb-20 4 = 18.786 +/- 5, Pb-207/Pb-204 = 15.686 +/- 2, Pb-208/Pb-204 = 38.967 +/- 9). A comparison of the Pb isotope data from southeastern Spain w ith published data from selected Pb-Zn deposits in southern Europe (in cluding Les Malines, L'Argentiere, and the Alpine, Iglesiente-Sulcis, and Montagne Noire districts) indicates the importance of a meta-sedim entary basement as a common source of ore Pb.