New stratigraphic, geochronological, and structural data from the southern Guanajuato Mining District, México: implications for the caldera hypothesis

A new geological map and geochronological data reveal that the volcanic activity in the southern Guanajuato Mining District (GMD) occurred between approximately 33.5 and 31.3 million years ago, coinciding with NW–SE normal faulting. This activity is linked to the formation of the Bufa, Calderones, and Cedro formations, which are part of a volcanic center that also contributed to the world-class silver ore deposits in the region. The study suggests that the Chichíndaro Rhyolite, though sparsely present in the area, is more extensive outside it and postdates major faulting. Structural analysis indicates an extensional phase that continued throughout the Oligocene, with the hydrothermal event beginning shortly after the emplacement of the Cedro Formation and lasting for at least two million years due to the subsequent rhyolitic volcanism.

Nieto-Samaniego, Á. F., Báez-López, J. A., Levresse, G., Alaniz-Alvarez, S. A., Ortega-Obregón, C., López-Martínez, M., Noguez-Alcántara, B., & Solé-Viñas, J. (2015). New stratigraphic, geochronological, and structural data from the southern Guanajuato Mining District, México: implications for the caldera hypothesis. International Geology Review, 58(2), 246–262. https://doi.org/10.1080/00206814.2015.1072745