Adakite-like signature of Late Miocene intrusions at the Los Pelambres giant porphyry copper deposit in the Andes of central Chile: metallogenic implications

Abstract

Adakite-like features are recognized in the Late Miocene ($10 Ma) porphyritic intrusions of the Los Pelambres giant porphyry copper deposit, central Chile (32°S). Located within the southern portion of the flat-slab segment (28-33°S) of the Chilean Andes, the Al-and Na-rich porphyries of Los Pelambres display distinctly higher Sr/Y ($100-300) and La N /Yb N ($25-60) ratios than contemporaneous and barren magmatic units (e.g., La Gloria pluton, Cerro Aconcagua volcanic rocks) of the same Andean magmatic belt. Strong fractionation of heavy rare earth elements (HREE), absence of Eu anomalies, high Sr/Y and Zr/Sm and low Nb/Ta ratios suggest melt extraction from a garnet-amphibolite source. The Late-Miocene adakitelike porphyritic intrusions at Los Pelambres formed closely related in time and space to the subduction of the Juan Ferna´ndez Ridge (JFR) hotspot chain along the Chilean margin. Current tectonic reconstructions reveal that, at the time of formation of the Los Pelambres rocks, a WE segment of the JFR started to subduct beneath them, producing a slowdown of a previously rapid southward migration of a NE-ridge-trench collision. These particular tectonic conditions are favorable for the origin of the Los Pelambres porphyry suite by melting of subducting young hotspot rocks under flatslab conditions. The incorporation of crustal components into the oceanic lithopheric magma source by subduction erosion is evidenced by the Sr-Nd isotope composition of the Los Pelambres rocks different from the MORB signatures of true adakites. A close relationship apparently exists between the origin of this adakite-like magmatism and the source of the mineralization in the Los Pelambres porphyry copper deposit.

Geochemical differences between subduction- and collision-related copper-bearing porphyries and implications for metallogenesis

“…The second phase of metallogenesis occurred during the Miocene, and was associated with the formation of the Bajo de la Alumbrera porphyry Cu-Au deposit in Argentina (e.g., Müller and Forrestal, 1998;Ulrich and Heinrich, 2001), the giant El Teniente Cu-Mo deposit (e.g., Cannell et al, 2005;Stern et al, 2007Stern et al, , 2010Vry et al, 2010) and the giant Los Pelambres porphyry Cu deposits in central Chile (e.g., Reich et al, 2003), the porphyry Cu-Au deposits of the Refugio District in northern Chile (e.g., Muntean and Einaudi, 2000), and porphyry Cu-Mo deposits in…”

Late Cretaceous (ca. 90Ma) adakitic intrusive rocks in the Kelu area, Gangdese Belt (southern Tibet): Slab melting and implications for Cu–Au mineralization

“…Reich et al, 2003;Cooke et al, 2005;Wang et al, 2006aWang et al, ,b, 2007cRichards and Kerrich, 2007;Chiaradia et al, 2009;Liu et al, 2010a,b;Sun et al, 2010;Tang et al, 2010). The three largest super-giant porphyry Cu-Au deposits in the world, i.e., the E1 Teniente, Chuquicamata and Río Blanco-Los Bronces deposits, all occur in the central Andes arc and are considered by many workers to have been related to the adakites derived by partial melting of subducted oceanic crust (Skewes and Stern, 1994;Oyarzun et al, 2001;Reich et al, 2003;Cooke et al, 2005).…”

“…The three largest super-giant porphyry Cu-Au deposits in the world, i.e., the E1 Teniente, Chuquicamata and Río Blanco-Los Bronces deposits, all occur in the central Andes arc and are considered by many workers to have been related to the adakites derived by partial melting of subducted oceanic crust (Skewes and Stern, 1994;Oyarzun et al, 2001;Reich et al, 2003;Cooke et al, 2005). Subduction zones have been considered as uniquely favorable tectonic settings for the generation of Cu-Au deposits (Oyarzun et al, 2001;Defant et al, 2002;Reich et al, 2003). The upper part of subducted oceanic crust has very high intrinsic fO 2 due to equilibration with seawater during hydrothermal alteration and the deposition of terrigenous sediments (Mungall, 2002).…”

“…Subduction zones have been considered as a uniquely favorable tectonic setting for the generation of Cu-Au deposits (Oyarzun et al, 2001;Defant et al, 2002;Mungall, 2002;Reich et al, 2003;Cooke et al, 2005;Sun et al, 2010). Most known porphyry/hydrothermal Cu-Au deposits in the world occur in subduction zones or arc settings (Sajona et al, 1993;Skewes and Stern, 1994;Akira, 2002;González-Partida et al, 2003;Reich et al, 2003;Cooke et al, 2005;Richards and Kerrich, 2007;Sun et al, 2010;Tang et al, 2010).…”

“…Most known porphyry/hydrothermal Cu-Au deposits in the world occur in subduction zones or arc settings (Sajona et al, 1993;Skewes and Stern, 1994;Akira, 2002;González-Partida et al, 2003;Reich et al, 2003;Cooke et al, 2005;Richards and Kerrich, 2007;Sun et al, 2010;Tang et al, 2010). These include super-giant porphyry CuAu deposits such as the E1 Teniente, Chuquicamata and Río Blanco-Los Bronces deposits in the Andes arc related to the subduction of oceanic crust or ridges (Skewes and Stern, 1994;Oyarzun et al, 2001;Reich et al, 2003;Cooke et al, 2005).…”