Abstract

LAZCANO, Javier et al. The La Felipeña Upper Cretaceous gold deposit on the eastern edge of the Peninsular Ranges batholith (Baja California, Mexico): Preliminary study. Bol. Soc. Geol. Mex [online]. 2023, vol.75, n.3, e011123.  Epub May 28, 2024. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2023v75n3a011123.

The La Felipeña prospect and other mineral occurrences located in the periurban area of San Felipe (Baja California) consist of quartz-carbonate veins with low sulfides, white mica, and tourmaline, which are characterized by anomalous Au contents. The veins are hosted in Paleozoic greenschist facies metasedimentary rocks and in quartz-dioritic dikes that intrude the former. In this study, we present two radiometric dates that constrain the age of mineralization in La Felipeña between ~94 and 83 Ma. A sample from a hosting dike yielded a U-Pb zircon age of 94.0 ± 0.8 Ma. The lower limit corresponds to a 40Ar/39Ar age for hydrothermal white mica of 82.73 ± 0.14 Ma. Fluid inclusion studies in hydrothermal quartz yielded trapping temperatures between ~400° y 530 °C, trapping pressure at ~210 MPa, and salinities of ore-bearing fluids between 5 and 14 wt.% NaCl equiv. The formation of this deposit was partially associated with effervescence. The La Felipeña deposit exhibits similar characteristics to those of the orogenic gold type and is the first documented case of this style of mineralization formed during the transition between the Peninsular Ranges orogeny (~110−90 Ma), which is related to the culmination of the construction of the Peninsular Ranges batholith, and the Laramide orogeny sensu lato (~90−40 Ma), associated with an increased convergence rate between the Farallon and North America plates. The gold mineralization in the San Felipe area provides evidence for the spatial-temporal continuity between the Peninsular Ranges (~106−92 Ma) and Caborca (~77−36 Ma) orogenic gold belts at the easternmost Peninsular Ranges batholith.

Keywords : Peninsular Ranges batholith; Caborca orogenic gold belt; regional metallogeny; geochronology.