Magmatic Evolution of Granodiorite Intrusions at the El Salvador Porphyry Copper Deposit, Chile, Based on Trace Element Composition and U/Pb Age of Zircons

摘要

Uranium-lead ages and trace element compositions of zircon from a series of shallow porphyry intrusions document the temporal, chemical, and thermal magmatic evolution of magmatic-hydrothermal porphyry Cu (Mo-Au) ores in the El Salvador district, Chile. Zircons (n = 240) from 15 Eocene age diorite, granodiorite, and granite porphyry intrusions were analyzed by SHRIMP-RG ion microprobe. The weighted means of Pb-207-corrected Pb-206/U-238 zircon ages span 3 m.y. from about 44 to 41 Ma, with peak magmatic flux at 44 to 43 Ma. The granodiorite porphyries at the Turquoise Gulch copper deposit record waning stages of magmatism at 42.5 to 42.0 Ma and were followed by postmineral latite dikes at about 41.6 Ma. Porphyry copper ores formed contemporaneously with porphyry intrusion centers that progressed temporally from north to south, from the small deposits at Cerro Pelado (similar to 44.2 Ma), Old Camp (similar to 43.6 Ma), and at M Gulch-Copper Hill (similar to 43.5-43.1 Ma) to the main ore deposit at Turquoise Gulch (similar to 42 Ma). The Eocene porphyry intrusions contain a few Mesozoic (n = 9) inherited zircons and numerous (n >= 19) antecrystic zircons about 1 to 2 m.y. older than the host intrusion that provide evidence of extensive Eocene magmatic recycling.