HR: 15:00h
AN: T23A-05    [Abstracts]
TI: Hydrothermal precious-metal deposits related to graben-calderas of the Sierra Madre Occidental
AU: * Aguirre-Diaz, G J
EM: ger@geociencias.unam.mx
AF: Centro de Geociencias, Universidad Nacional Autonoma de Mexico, Campus UNAM Juriquilla, Querétaro, Qro 76230, Mexico
AU: Labarthe-Hernandez, G
EM: labarthe@uaslp.mx
AF: Instituto de Geologia, UASLP, Universidad Autonoma de San Luis Potosi, San Luis Potosi, SLP , Mexico
AU: Nieto-Obregon, J
EM: nieto@servidor.unam.mx
AF: Centro de Geociencias, Universidad Nacional Autonoma de Mexico, Campus UNAM Juriquilla, Querétaro, Qro 76230, Mexico
AU: Tristan-Gonzalez, M
EM: mtristan@uaslp.mx
AF: Centro de Geociencias, Universidad Nacional Autonoma de Mexico, Campus UNAM Juriquilla, Querétaro, Qro 76230, Mexico
AU: Gonzalez-Partida, E
EM: egp@geociencias.unam.mx
AF: Centro de Geociencias, Universidad Nacional Autonoma de Mexico, Campus UNAM Juriquilla, Querétaro, Qro 76230, Mexico
AB: The Sierra Madre Occidental (SMO) covers the NW portion of Mexico and it is the host for several important precious metal mine operations, such as Tayoltita, Cienega, Topia, Fresnillo, Zacatecas, Guanajuato and Bolaños, just to mention a few. The southern part of the Basin and Range extension affected also NW Mexico and formed NW- to NE-trending normal faults that bound many large grabens, which are particularly long and deep in the southern SMO. Both graben formation and mid-Tertiary silicic volcanic activity coincided in space and time, particularly for the 38-23 Ma period, the Ignimbrite Flare-up event, but this activity dates back to Eocene and was as young as Miocene. This volcanism included large rhyolitic domes, too. At the southern SMO, the vents of this silicic volcanism are related to graben's master faults and we have named them graben-calderas. Evidences include large pyroclastic dikes and post-ignimbrite aligned rhyolitic domes and lava dikes. All these features were found along the graben-caldera walls or on the graben's shoulders. Some of these vents are related to gold and silver hydrothermal mineralization. In most cases a paleo-lake filled the graben-caldera for a period of time, either during the ignimbrite emplacement or after it. Some of the graben-caldera ignimbrites were deposited in subaqueous environments and post-ignimbrite rhyolitic domes and dikes were intruded in non-consolidated water-saturated tuffs or sedimentary deposits. This lacustrine environment provided the necessary water for the hydrothermal system. The combination of all these factors in space and time, grabens+volcanism+water, resulted in the development of precious-metal hydrothermal ore deposits. Bolaños mine in the Bolaños graben represent our case-study, but we have confirmed the same tectono-volcanic-lake relationship at other mine-districts along the SMO. We conclude that locating the fissural vents of the silicic ignimbrites by means of just geologic mapping is be the best and most economical first approach to locate the associated hydrothermal mineralization.
DE: 8109 Continental tectonics: extensional (0905)
DE: 8110 Continental tectonics: general (0905)
DE: 8178 Tectonics and magmatism
DE: 8185 Volcanic arcs
SC: Tectonophysics [T]
MN: 2007 Joint Assembly