Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, PR China
Distribution, timing, and tectonic setting of Cretaceous porphyry Cu-Au and IOCG deposits in the Mesozoic Coastal Cordillera of northern Chile. (a) Geographic distribution of deposits and spatial relationship to the Atacama fault system; ages of deposits in Ma are shown in parentheses. (b) Temporal and tectonic separation of porphyry and IOCG deposits. Sources of data are provided in Table 1 and Appendix 1.
Photomicrographs of apatite crystals in samples from (a) Candelaria (CAN-2), (b) Casualidad (CAS-2), and (c, d) Carmen de Andacollo (CDA-8, CDA-2). Concentrations of SO3 in apatite crystals are shown in red (wt %); higher concentrations are observed in apatite from porphyry-related samples (Carmen de Andacollo) compared to the IOCG-related samples (Candelaria, Casualidad). Some apatite microphenocrysts from Carmen de Andacollo show zonation from SO3-rich cores to SO3-poorer rims (d). Abbreviations: Amph = amphibole, Ap = apatite, Chl = chlorite, Plag = plagioclase, Qz = quartz.
Total alkali-silica diagram (Le Maitre et al., 2002) showing the compositions of Cretaceous igneous rocks associated with porphyry (blue symbols) and IOCG deposits (red symbols) in the Coastal Cordillera of northern Chile; Productora (purple symbol) shows characteristics of both porphyry and IOCG deposits. Data are from Table 3, excluding the following samples for reasons of extreme alteration or lack of correlation with the main suites: CAS-4 (clasts in igneous breccia); CAS-8, 9, 10, 11 (regional plutons, relationship to Casualidad deposit unclear); CDA-7 (Quebrada Marquesa Formation, andesitic country rock); MV-10 (strong potassic alteration); MV-11, MV-12 (altered volcanic rock outcrops, relationship to Mantoverde deposit unclear); PR-1 (Cachiyuyito stock, possibly unrelated). All of the remaining samples shown are nevertheless altered to varying degrees, and we attribute the apparently alkaline compositions of some rocks to this effect.
Zr/Ti vs. Nb/Y discrimination diagram (Winchester and Floyd, 1977) for Cretaceous igneous rocks from the Coastal Cordillera of Chile between 25° and 34°S. Regional igneous geochemical data from the literature are grouped according to the three temporal-tectonomagmatic groups, as defined in the text. Igneous rocks related to mid-Cretaceous IOCG and late Cretaceous porphyry deposits collected during this study are plotted for comparison. Regional Cretaceous data from Irwin et al. (1988), Vergara et al. (1995), Cisternas et al. (1999), Parada et al. (1999, 2002), Grocott and Taylor (2002), Morata and Aguirre (2003), Creixell (2007), Hasler (2007), and López et al. (2014).
Primitive mantle-normalized extended trace element diagrams (normalization values of Sun and McDonough, 1989) for selected igneous rocks associated with (a) porphyry and (b) IOCG deposits in the Coastal Cordillera of northern Chile.
C1 chondrite-normalized extended trace element diagrams (normalization values of Sun and McDonough, 1989) for selected igneous rocks associated with (a) porphyry and (b) IOCG deposits in the Coastal Cordillera of northern Chile.
(a) Sr/Y versus Y and (b) La/Yb versus Yb plots for selected igneous rocks associated with porphyry and IOCG deposits from the Coastal Cordillera of northern Chile. The more “adakite like” compositions of many of the porphyry rocks compared to many of the IOCG-related rocks likely reflect the more felsic compositions and greater degrees of fractionation (especially of amphibole) of the former. Note that, with only one exception, all of these rocks have lower La/Yb ratios than adakites. Fields for adakite-like rocks from Richards and Kerrich (2007); regional Cretaceous data from Irwin et al. (1988), Vergara et al. (1995), Cisternas et al. (1999), Parada et al. (1999, 2002), Grocott and Taylor (2002), Morata and Aguirre (2003), Creixell (2007), Hasler (2007), and López et al. (2014).
εNd vs. initial 87Sr/86Sr ratios for Cretaceous igneous rocks from the Coastal Cordillera of Chile between 25° and 34°S. Mid-Cretaceous rocks associated with IOCG deposits mostly fall at the primitive end of a range of data reflecting various degrees of crustal contamination of mantle-derived magmas, whereas early and late Cretaceous rocks associated with porphyry deposits range to significantly more isotopically evolved compositions. Data from Parada et al. (2005), Hasler (2007), Morata et al. (2008), and Girardi (2014). Depleted MORB mantle field at ~110 Ma from Pilet et al. (2011). Jurassic igneous rock field from Parada et al. (1999), Creixell (2007), and Girardi (2014). Paleozoic intrusive rock field from Parada et al. (1999).
Schematic model illustrating the evolution of the tectonomagmatic setting along the margin of northern Chile between 25° and 34°S during the Cretaceous, and its relationship to porphyry and IOCG deposit formation. SCLM = subcontinental lithospheric mantle.
↵1 Normalized to 100 wt % (Supplementary Table S1)
↵2 Apatite saturation temperature (AST) calculated from whole-rock SiO2 and P2O5 concentrations using the equation of Piccoli and Candela (1994), recast from the data of Harrison and Watson (1984)
↵3 Average of all igneous apatite analyses (Supplementary Table S4)
↵4 Average log fo2 calculated from MnO contents of igneous apatite crystals (Supplementary Table S4) using the equation of Miles et al. (2014): log fo2 = −0.0022 (± 0.0003) Mn (ppm) − 9.75 (± 0.46)
↵5 Average log fo2 value relative to the fayalite-magnetite-quartz (ΔFMQ), where the value of FMQ at different temperatures (provided by the AST estimate) is calculated using the equation of Myers and Eugster (1983): log fo2 = −24,441.9/T (K) + 8.290 (± 0.167); the ΔFMQ error is the sum of the ±0.167 error on FMQ and the uncertainty in the sample log fo2 estimate from the previous column
↵6 Estimated from apatite SO3 contents (Supplementary Table S4) using the temperature-dependent apatite-melt partition coefficient formula of Peng et al. (1997): lnKD = 21,130/T − 16.2 (where T is in Kelvin)
↵7 Estimated from apatite SO3 contents (Supplementary Table S4) using the apatite-melt partition coefficient formula of Parat et al. (2011): SO3 apatite (wt %) = 0.157 × ln[SO3] (melt, wt %) + 0.9834 (r2 = 0.62)
8 SiO2 and P2O5 compositions for this sample taken from sample CDA-9 (same lithology as CDA-8 but less altered)