Orogenic Gold Belt Overlap in the Eastern Peninsular Ranges Batholith: La Rumorosa District (Northern Baja California, Mexico)

Abstract

Gold deposits of the La Rumorosa district (eastern Peninsular Ranges batholith; PRB) consist of auriferous quartz-(carbonate) veins hosted by brittle-ductile shear zones in metamorphic and synorogenic plutonic rocks. A combination between U-Pb zircon geochronology of country rocks and 40Ar/39Ar dating of hydrothermal and metamorphic white micas, in conjunction with the structural characterization of the main orebodies has allowed to differentiate two mineralization events in the study area. The oldest deposit (>93 Ma) was formed during the ultimate compressional phase of the PRB development (~110‒90 Ma), and it is part of the yet poorly known Peninsular Ranges orogenic gold belt. Other mineralizations were dated at ~77‒75 Ma, that correspond to the beginning of the Laramide tectonism instead and represent the oldest and westernmost deposits from the Caborca orogenic gold belt (~69‒36 Ma). The Laramide gold deposits at La Rumorosa are contemporaneous with the first generation (~76‒74 Ma) of copper porphyries at the southern North American Cordillera belt, located immediately east on the opposite margin of the Gulf of California-San Andreas fault system. Both gold and copper deposits show an eastward migration during the early Upper Cretaceous similar to the best-known shift in magmatism and deformation. The apparently continuous formation of orogenic gold deposits in southwestern North America linked to the convergence between the subducted Farallon plate and the continent during the Cretaceous-early Paleogene suggests a connection between the two gold belts, and we visualize that both conform a large gold province in western Mexico.

Keywords: Orogenic gold deposits, Dating of ore deposits, Peninsular Ranges orogenic gold belt, Caborca orogenic gold belt, Peninsular Ranges batholith