Boletín de la Sociedad Geológica Mexicana Volumen 70, núm. 2, 2018, p. 531 ‒ 547 http://dx.doi.org/10.18268/BSGM2018v70n2a13

Geochronology of Mexican mineral deposits. VI: the Tayoltita low-sulfidation epithermal Ag-Au district, Durango and Sinaloa

Erme Enríquez^1,*, Alexander Iriondo², Antoni Camprubí^3,**

¹ Minera Canasil S.A. de C.V. Alhelí 142, Fraccionamiento Jardines de Durango, 34200 Durango, Dgo., Mexico.
² Centro de Geociencias, Universidad Nacional Autónoma de México. Boulevard Juriquilla 3001, 76230 Santiago de Querétaro, Qro., Mexico.
³ Instituto de Geología, Universidad Nacional Autónoma de México. Ciudad Universitaria, 04510 Coyoacán, CDMX, Mexico.

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Abstract

The Tayoltita district (Durango, Mexico) is one of the major silver and gold producers in the world with over 745 million ounces of Ag and 11 million ounces of Au in the entire lifetime of the mine. These high-grade Ag-Au deposits are of low-sulfidation epithermal type, and formed during the final stages of igneous and hydrothermal activity of small Eocene quartz monzonitic and andesitic intrusions. The veins are hosted by tuffs, flows, and agglomerates of Paleocene age that belong to the Lower Volcanic Complex of the Sierra Madre Occidental, and are unconformably overlain by the Miocene Upper Volcanic Supergroup. Three episodes of intrusion have taken place in the district. The presently available ages of the Piaxtla intrusions indicate that the batholithic complex was emplaced between 46.31 and 45.1 Ma. The second event is represented by the so-called Intrusive andesite, which yielded ages that range between 39.9 and 37.9 Ma. The last intrusion event is represented by the Arana diorite. K-Ar ages of these rocks range between 38.1 and 36.6 Ma. Ages obtained in this study and in the available literature allow to establishing that the formation of epithermal veins in the district ranged between 41.01 and 31.9 Ma. Hydrothermal alteration and mineralization occurred within a 0.3 to 3.4 M.yr. time-span after the emplacement of the Intrusive andesite and the Arana diorite, respectively. Such intrusive events are generally acknowledged to have triggered ore formation in this district, thus implying the genetic association between the intrusive rocks and the epithermal deposits. The available ⁴⁰Ar/³⁹Ar and K-Ar ages of adularia from vein material indicate that vein formation occurred episodically in distinct periods separated by intervals of about 3.18 M.yr., albeit magmatic-hydrothermal activity in the area experienced few lull periods. The total duration of mineralization from the margin to the center of the Tayoltita district was ~10 M.yr., which makes it one of the longest lived known epithermal deposits. However, there is no apparent correlation between the longevity of epithermal deposits and their size.

The age of an unaltered tuff of the Upper Volcanic Supergroup that unconformably overlies the Lower Volcanic Complex of the Sierra Madre Occidental indicates that tilting of the units and the activity of the paleo-hydrothermal system had ceased by 20.3 Ma. The temporal and spatial coincidence of volcanism, faulting, and high-grade mineralization may reflect the importance of contributions from deeper fluid reservoirs containing magmatic components or highly exchanged meteoric waters. In this sense, it is worth noting that the 0.3 M.yr. time-span between the emplacement of hypabyssal rocks and immediately subsequent epithermal mineralization is much narrower than the common ~2 M.yr. time-span in most (low and intermediate sulfidation) epithermal deposits in Mexico that are proven to be associated with magmatic fluids, as it is the case of the giant deposits in the Fresnillo district. The short time-span suggests that the emplacement of hypabyssal rocks and epithermal deposits was known to date to have occurred in association with high-sulfidation deposits alone.

Keywords: Tayoltita, epithermal, low sulfidation, Ar/Ar ages, timing of mineralization, magmatic-hydrothermal cycling, Sierra Madre Occidental.