Abstract

MARTINEZ-REYES, Juan José et al. Geochronology of Mexican mineral deposits: II: Veta Madre and Sierra epithermal vein systems, Guanajuato district. Bol. Soc. Geol. Mex [online]. 2015, vol.67, n.2, pp.349-355. ISSN 1405-3322.

This paper presents two new high-resolution geochronological determinations for the epithermal deposits in the World-class Guanajuato mining district, in central Mexico. These are a Rb-Sr isochron age in illite at 28.47 ± 0.55 Ma for the Villalpando and San Juan de Dios low sulfidation veins of the Sierra group of veins, and a ⁴⁰Ar/³⁹Ar plateau age in adularia ("valencianite") at 30.20 ± 0.17 Ma for the La Valenciana ore shoot of the famous Veta Madre intermediate sulfidation vein. These determinations have greater accuracy, precision and trueness than the preexisting K-Ar determinations for similar adularia samples. The accuracy of such determinations supports the idea of a diachronic emplacement of intermediate and low sulfidation deposits in this district, the former being older than the latter, similar to other epithermal deposits in Mexico. Also, the ~2 m.yr. span between the Veta Madre and Sierra groups of epithermal veins is in agreement with other case studies, regardless of the size of the deposit.

Keywords : Guanajuato; Mexico; epithermal deposits; intermediate sulfidation; low sulfidation; Rb-Sr ages; illite; Ar/Ar ages; adularia.

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