Adakite-like signatures of Middle-Late Miocene intrusions at the Altar porphyry Cu-(Mo-Au) deposit (31º 29' S, 70º 28´ W) in the Andean Main Cordillera of San Juan, Argentina

LAURA MAYDAGÁN; MARTA FRANCHINI; MASSIMO CHIARADIA; GRACIELA MAS; AGNES IMPICCINI

Keystone

Conferencia; SEG 2010 Conference; 2010

SEG

In the Andean Cordillera several recent studies have highlighted a link between large-scale geodynamic changes (e.g., slab flattening and aseismic ridge collision with the trench), magma chemistry changes (from normal to adakite-like, i.e., high Sr/Y) and the formation of giant porphyry Cu mineralization (Cooke et al., 2005; Richard and Kerrich, 2007; Chiaradia et al., 2009). Because the profound reasons of this association remain elusive, it is important to understand the temporal and spatial pattern of the association between geodynamic setting changes, magma chemistry transitions to adakite-like and porphyry Cu mineralization. Kay et al. (1991) have emphasized the high Sr contents of Miocene volcanic rocks from both the El Indio belt and the Maricunga Au–Ag district and have proposed petrogenetic models involving melting of thickened metabasaltic crust to form these magmatic suites. Gutscher et al. (2000) suggested that in El Indio belt anomalous heating of the leading edge of the shallowing slab could lead to slab melting and eruption of small volumes of adakitic magma. Kay and Mpodozis (2002) challenged Gutscher et al.’s (2000) proposal that these rocks were derived from flat-slab melting. Adakite-like features have been recognized in the Middle-Late Miocene porphyritic intrusions of the Altar porphyry Cu-(Au-Mo) prospect (31º 29' S, 70º 28´ W). This region is located within the southern portion of the Andean flat-slab segment (28–33ºS) of the Andean Main Cordillera, Argentina, 25 kilometres north of the world-class porphyry Cu-Au-Mo deposits of Los Pelambres (Chile) and El Pachon (Argentina), and nearby other recently discovered Cu- Au prospects like Piuquenes, La Coipa, Calderón, Rincones de Araya and Los Azules. Kay et al. (1991) have emphasized the high Sr contents of Miocene volcanic rocks from both the El Indio belt and the Maricunga Au–Ag district and have proposed petrogenetic models involving melting of thickened metabasaltic crust to form these magmatic suites. Gutscher et al. (2000) suggested that in El Indio belt anomalous heating of the leading edge of the shallowing slab could lead to slab melting and eruption of small volumes of adakitic magma. Kay and Mpodozis (2002) challenged Gutscher et al.’s (2000) proposal that these rocks were derived from flat-slab melting. Adakite-like features have been recognized in the Middle-Late Miocene porphyritic intrusions of the Altar porphyry Cu-(Au-Mo) prospect (31º 29' S, 70º 28´ W). This region is located within the southern portion of the Andean flat-slab segment (28–33ºS) of the Andean Main Cordillera, Argentina, 25 kilometres north of the world-class porphyry Cu-Au-Mo deposits of Los Pelambres (Chile) and El Pachon (Argentina), and nearby other recently discovered Cu- Au prospects like Piuquenes, La Coipa, Calderón, Rincones de Araya and Los Azules.