Seismically active fracture zones and distribution of large accumulations of metals in the central part of Andean South America

The analysis of the geometry of distribution of earthquake foci in the cent ral part of Andean South America between 18 degrees and 34 degrees S made t he delineation of several seismically active fracture zones in the continen tal wedge overlying the subducting Nazca plate possible. Correlation of the ir position with the distribution of hypogene accumulations of metals revea led that the majority of large mineral deposits and mining districts are si tuated in the outcrops of these fracture zones. We present geometrical docu mentation (map of epicentres, vertical and longitudinal cross sections) of the most important fracture zones and data on mineralogical composition, ge netic type and available radiometric ages of mineral deposits. Sixteen mini ng districts in Chile, and 24 in Argentina, were attributed to the seismica lly active fracture zones. Major mining districts and individual large mine ral deposits occur in six seismically active fracture zones roughly paralle l to the axis of the Peru-Chile trench (Carachas-Portillo, Choquelimpie, Iq uique, Domeyko, Rio Blanco-Los Bayos and Farellones F.Z.), in six fracture zones roughly perpendicular to the trench (El Salvador. Maricunga, Jaroma, Ujina, Tumbaya and Incahuasi-Leon Muerto F.Z.) and in two fracture zones or iented at an angle of about 45 degrees in relation to the direction of the presently active Andean subduction (Aconcagua and Sierra der Volcan F.Z.). The occurrences of large mineral deposits of different ages show that these fracture zones were also active in the geological past and represent sites of permanent reopening of paths allowing ore-bearing solutions and long-te rm accumulation of large amounts of metals to occur in relatively restricte d domains of the Earth's crust. The mining districts with dated mineral dep osits are arranged into four periods of hypogene mineralization: Upper Mioc ene-Pliocene, Upper Oligocene-Middle Miocene? Upper Eocene-Middle Oligocene , Lower Paleocene-Upper Eocene, These periods of metallogenic activity corr elate well with four supposed Andean subduction cycles active in the Tertia ry. The occurrence of mineral deposits of different ages in recently active fracture zones can be used as an important evidence in favour of long-term spatial permanence and activity of these zones and as a guide for the disc overy of further mineral deposits hidden under young sedimentary and volcan ic cover in the fracture zones.