Lead isotope studies of the Guerrero composite terrane, west-central Mexico: implications for ore genesis

摘要

New thermal ionization mass spectrometry and multi-collector inductively coupled plasma mass spectrometry Pb isotope analyses of three Cenozoic ores from the La Verde porphyry copper deposit located in the Zihuatanejo-Huetamo subterrane of the Guerrero composite terrane are presented and the metal sources are evaluated. Lead isotope ratios of 3 Cenozoic ores from the E1 Malacate and La Esmeralda porphyry copper deposits located in the Zihuatanejo-Huetamo subterrane and of 14 ores from the Zimapan and La Negra skarn deposits from the adjoining Sierra Madre terrane are also presented to look for systematic differences in the lead isotope trends and ore metal sources among the proposed exotic tectonostratigraphic terranes of southern Mexico. Comparison among the isotopic signatures of ores from the Sierra Madre terrane and distinct subterranes of the Guerrero terrane supports the idea that there is no direct correlation between the distinct suspect terranes of Mexico and the isotopic signatures of the associated Cenozoic ores. Rather, these Pb isotope patterns are interpreted to reflect increasing crustal contribution to mantle-derived magmas as the arc advanced eastward onto a progressively thicker continental crust. The lead isotope trend observed in Cenozoic ores is not recognized in the ores from Mesozoic volcanogenic massive sulfide and sedimentary exhalative deposits.