Genesis of manganese oxide mineralization in the Boleo region and Concepción Peninsula, Baja California Sur: constraints from Pb-Sr isotopes and REE geochemistry

Manganese oxide mineralization on the eastern coast of Baja California Sur is intimately related to the Neogene tectonic evolution of the Gulf of California. Manganese is closely associated with the Cu-Co-Zn mineralization of the Boleo district and nearby deposits of Santa Rosalía region and Concepción peninsula. Trace element and rare earth element geochemistry of the manganese oxides provides clear evidence of a hydrothermal origin and excludes the hydrogenous nature for these deposits. Lead isotope data suggest that metal sources for the manganese mineralization along the eastern coast Baja California Sur are mostly the Miocene Andesite of Sierra Santa Lucía volcanics and the Peninsular Ranges batholith rocks. The strontium isotope data indicate that the mineralizing fluids involved in the manganese mineralization from Boleo district resulted from the interaction of two end-members: (1) the Sierra Santa Lucía volcanic rocks and (2) the gypsum member of the Boleo Formation. The geological observations and the available isotope and geochronological data suggest a southward migration of the hydrothermal processes in response to the evolving tectonic context of the opening of the Gulf of California.