Lead Isotope Constraints on the Sources of Ore Metals in Deposits from the Guerrero Terrane, West-Central Mexico

New sampling has been undertaken to determine whether there is any systematic difference in ore metal sources among the proposed exotic tectonostratigraphic terranes of southern Mexico, and to what extent ores in this region represent new additions of lead to the crust from an enriched mantle source. New TIMS lead isotope analyses are presented for samples from the metamorphic basement rocks of the Guerrero Terrane, the Late Cretaceous clastic sedimentary rocks, and for mid-Cretaceous igneous rocks, as well as for samples from the Oligocene La Verde and Esmeralda copper prospects.

Whole rock samples of schist from the Arteaga Complex (with a poorly constrained Triassic age, underlying the Zihuatanejo subterrane), as well as of phyllite and slate from the Tierra Caliente Complex (of most probable Mesozoic age, underlying the Teloloapan and Arcelia-Palmar Chico subterranes) contain radiogenic lead relative to bulk earth models, with 206Pb/204Pb ranging from 18.981-19.256. These values are substantially more radiogenic than published data on metagabbro and charnockite from the Grenvillian-age Oaxaca Terrane. Sandstones, siltstones, and marls belonging to the Huetamo Sequence (Huetamo subterrane) have 206Pb/204Pb values ranging between 18.630 to 18.998, close to the published data for the sediments from IPOD-DSDP Sites 487 and 488, Cocos Plate. The sedimentary rocks are less radiogenic than the metamorphic basement, suggesting they are not simply derived from the basement and that other rocks were involved in their provenance. Whole rock analyses of granodiorite collected from La Verde and El Malacate have 206Pb/204Pb ranging from 18.764 to 18.989, clustering between the compositions of the sedimentary and the metamorphic rocks, suggesting assimilation of lead from these components. Ore samples from La Verde and Esmeralda have 206Pb/204Pb between 18.685 and 18.731 and plot within the field defined by the sedimentary rocks suggesting a dominant component of sedimentary rock-derived lead.