The Peninsular Ranges Orogenic Gold Belt: Supporting Evidence from the San Pedro Mártir Goldfield (Baja California, Mexico)

Abstract

The gold deposits in northern Sierra San Pedro Mártir are located around the Main Mártir thrust in the Peninsular Ranges batholith (PRB). This middle-Cretaceous regional structure represents the suture zone of the Alisitos island arc against the continental margin of North America. Mineralizations show affinities with orogenic gold deposits and consist in shear zone-related gold-bearing quartz-carbonate veins, with minor contents of sulfides, which are hosted in plutonic and metamorphic rocks (greenschist to amphibolite facies). We have dated four selected deposits by the 40Ar/39Ar method using hydrothermal white micas from the auriferous veins and altered wall-rocks: 106.2 ± 0.2 Ma (Valladares mine), 100.5 ± 0.2 Ma (La Fortuna mine), 94.2 ± 0.2 Ma (El Socorro mine), and 92.2 ± 0.2 Ma (Corazón de Oro de Jesús prospect). The first two data represent very accurate age determinations of the orogenic gold event, whereas the other data were reset by a slightly younger large La Posta-type pluton (~97‒90 Ma). Three additional U-Pb zircon ages of plutonic host rocks constrain the maximum age of the mineralizations, and fluid inclusions were analyzed from six gold deposits. Gold mineralizations were formed after the initial collisional phase, in a setting of concomitant regional metamorphism and pluton emplacement. At least some (synorogenic) pluton-hosted deposits were formed under a transient dextral transpressive regime, intercalated between the regional orthogonal compression. A connection is established between these deposits and other historical gold districts along the exhumed axis of the PRB (e.g., El Álamo), and we propose that all form part of the ‘Peninsular Ranges orogenic gold belt’.

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