Mineralización argentífera asociada al volcanismo cenozoico en la faja Puquio-Cailloma

Abstract

In the western Cordillera highlands of Southern Peru argentiferous mineralization occurrences have been known since the Spanish conquest time; several mines are still at work in the area: San Juan de Lucanas, Arcata, Orcopampa Cailloma. Argentiferous mineralization mostly related to veins hosted by mainly andesitic rocks that we correlate with the Tacaza volcanic group of lower middle Miocene age (20·14 m. y.). Geochimical datas of Tacaza rocks compared with the ones of other main volcanio units from the same area Sencca and Huaylillas acid volcanics and Barroso andesitic volcanics) show that: -There is no difference between the three volcanic groups respect to the mejor-elements chemistry. All of them are characteristic of calcoalcalio series with high potassium contents. Minor elements average contents for each volcanic group are similar to those published for rocks from similar geotectonic environment. However, the 1.5. ppm silver content of the Tacaza lavas is higher than the common 0.07 ppm of the intermediate lavas. The length of the veins in the different mines lies generally between 500 m and. 3 km. The Veins have three main directions: NW-SE, NE-SW and E-W. These directions appear to be related to a single period of brittle tectonics characterized by an E-W directed compression; this tectonio phase is itself subsequent to a widespread folding episode that affects the Tacaza beds. Mineralized veins show mains structures: brecciated, banded and cockade structures, and display successive stages in ore minerals deposition. Paragenesis contains sulphides (pyrite, galena, sphalerite) copper compounds (tetraedrite, chalcopyrite) copper silver sulphide-salts, silver sulphide salts, argentite, native silver, deposited in· a mesothermal to epithermal environment.