Abstract

CAMPRUBI, Antoni; CABRERA-ROA, Miguel Ángel; GONZALEZ-PARTIDA, Eduardo  and  LOPEZ-MARTINEZ, Margarita. Geochronology of Mexican mineral deposits. VIII: the Zacatepec polymetallic skarn, Oaxaca. Bol. Soc. Geol. Mex [online]. 2019, vol.71, n.1, pp.207-218. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2019v71n1a11.

The Zn-Pb-Ag(-W) skarn deposits at Zacatepec (or Mɨɨygɨxy) in Oaxaca are associated with rocks of the Sierra Madre del Sur (SMS) magmatic province, and located in its easternmost part, in southern Mexico. This region consists of Eocene to Miocene calc-alkaline hypabyssal and volcanic rocks, with intermediate to felsic compositions that intrude or overlie Cretaceous carbonate sequences. Prograde mineralization in the Zacatepec skarn deposits was dated by means of the40Ar/39Ar method in a sample of the granitic hypabyssal body, with which the formation of these deposits is directly associated. The isochron ages thus yielded are 17.52 ± 0.14 Ma for biotite and 17.33 ± 0.40 Ma for hornblende. Such ages are in accordance with several other magmatic-hydrothermal deposits (epithermal, skarn, and porphyry-type deposits) that are hosted by Miocene rocks in central Oaxaca state. Deposits in the region with known ages for Miocene hypabyssal rocks with which they are closely related are Taviche, Lachigalla, Cobre Grande, Aurena, Natividad, Altagracia-Águila-Arista, Santa Margarita-Azucena, and Guielavazar. The plausible ages for these ore deposits determine a time bracket between <23.8 and <13.01 Ma (early to middle Miocene) that can be considered as favorable for the finding of magmatic-hydrothermal ore deposits. The latter can be tentatively used to define a new metallogenic period that corresponds to a new metallogenic province, for which the rocks derived from the Miocene magmatism of the SMS constitute the metallotect. Although such metallogenic activity has not been altogether overlooked, no previous papers have focused on its relevance and extent in space and time. Therefore, this province constitutes the fifth Miocene mineralized region known in Mexico, besides the southernmost Sierra Madre Occidental, the Trans-Mexican Volcanic Belt, the Gulf of California, and the alkaline province in Chiapas.

Keywords : Oaxaca; Mexico; skarn; ⁴⁰Ar/³⁹Ar ages; prograde associations; early Miocene; Sierra Madre del Sur.