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Abstract: Porphyry Mo and Cu mineralization in the California-Vetas mining district is contemporaneous with 10.9 to 8.4Ma granodiorite porphyry stocks and overprinted by Au–Ag mineralization of epithermal affinity. Mineralization is hosted by Grenvillian aged paragneisses (Bucaramanga Gneiss of the Santander Massif) and late Triassic to early Jurassic granitic rocks. All intrusive rocks are high-K calc-alkaline. Late Triassic to early Jurassic rocks include peraluminous granites with more than 70wt.% SiO2 as well as metaluminous diorites, tonalites and granodiorites with SiO2 between 54.9 and 60.4wt.%. Late Miocene rocks are weakly peraluminous granodiorite porphyries with SiO2 between 61 and 67wt.% SiO2. Late Miocene rocks share some characteristics with adakite-like rocks which are widely associated with porphyry and epithermal style mineralization elsewhere in the Andes. They have high Ba (930 to 1500ppm) and high Ba/La (28 to 50), high Sr (850 to 1100ppm) and Sr/Y (48–78) and depleted middle rare earth elements (MREE) compared to the Mesozoic granites, which have 400 to 700ppm Ba (Ba/La 14 to 25) and 80 to 150ppm Sr (Sr/Y 2.5 to 14), and Mesozoic diorites and tonalites, which have ~900 to 1200ppm Ba (Ba/La 20 to 32) and ~610 to 750ppm Sr (Sr/Y 22 to 25). Miocene granodiorite porphyries, in contrast to Mesozoic intrusive rocks have only weak negative Eu anomalies. The Miocene rocks have 87Sr/86Sr ratios of 0.7052 to 0.7067 and ε Nd of −1.9 to −5.4 and are significantly more isotopically primitive than all other rocks in the study area including the Mesozoic diorites to tonalites (87Sr/86Sr=0.7082 and 0.7092; ε Nd =−6.7 and −7.2), granites (87Sr/86Sr=0.730 (n =2); ε Nd =−8.2 and −8.3) and Bucaramanga Gneiss (0.718 to 0.743; ε Nd =−10.8 to −14.1). Lead isotope data are broadly consistent with the Sr and Nd isotope data and the Miocene porphyries have the lowest 207Pb/204Pb ratios but overlap with the Mesozoic diorites to tonalites in their 206Pb/204Pb and 208Pb/204Pb ratios. The geochemical signature suggests that late Miocene granodiorite porphyries represent oxidized and water-rich melts. However, in contrast to many other porphyry districts in the Andes, they do not have low Y (<15ppm) or depleted HREE, which together with the high Sr, Al and Na content indicates that neither plagioclase nor garnet were important residual phases in the MASH zone at the base of the crust. The trough shaped MREE suggest that amphibole was present in the source. The 87Sr/86Sr values of the Miocene rocks are consistent with a mantle derived melt which interacted with the radiogenic continental crust. The magmatism occurred above the shallow subducting Caribbean slab attributed to subduction of part of the Caribbean plateau (a.k.a. proto-Caribbean oceanic complex). It may be related to slab break-off and incursion of hot asthenospheric mantle, but dehydration of the Caribbean slab probably provided additional volatiles which made amphibole a major residual phase and provided water for the hydrous porphyry related magmas. [Copyright &y& Elsevier]

Abstract: The Vetas-California Mining District (VCMD), located in the central part of the Santander Massif (Colombian Eastern Cordillera), based on U–Pb dating of zircons, records the following principal tectono-magmatic events: (1) the Grenville Orogenic event and high grade metamorphism and migmatitization between ∼1240 and 957 Ma; (2) early Ordovician calc–alkalic magmatism, which was synchronous with the Caparonensis–Famatinian Orogeny (∼477 Ma); (3) middle to late Ordovician post-collisional calc–alkalic magmatism (∼466–436 Ma); (4) late Triassic to early Jurassic magmatism between ∼204 and 196 Ma, characterized by both S- and I-type calc–alkalic intrusions and; (5) a late Miocene shallowly emplaced intermediate calc–alkaline intrusions (10.9 ± 0.2 and 8.4 ± 0.2 Ma). The presence of even younger igneous rocks is possible, given the widespread magmatic–hydrothermal alteration affecting all rock units in the area. The igneous rocks from the late Triassic–early Jurassic magmatic episodes are the volumetrically most important igneous rocks in the study area and in the Colombian Eastern Cordillera. They can be divided into three groups based on their field relationships, whole rock geochemistry and geochronology. These are early leucogranites herein termed Alaskites-I (204–199 Ma), Intermediate rocks (199–198 Ma), and late leucogranites, herein referred to as Alaskites-II (198–196 Ma). This Mesozoic magmatism is reflecting subtle changes in the crustal stress in a setting above an oblique subduction of the Panthalassa plate beneath Pangea. The lower Cretaceous siliciclastic Tambor Formation has detrital zircons of the same age populations as the metamorphic and igneous rocks present in the study area, suggesting that the provenance is related to the erosion of these local rocks during the late Jurassic or early Cretaceous, implying a local supply of sediments to the local depositional basins. [Copyright &y& Elsevier]

Abstract: An Early Ordovician magmatic event has been documented in the Santander Massif (north-Eastern Cordillera, Colombia). Three U/Pb laser ablation ages of 477 ± 2 Ma (Arenig), were obtained from metamorphosed and foliated calc-alkaline diorites. The 176Hf/177Hf values in zircons from these meta-diorites, yielded epsilon Hf values (ɛ Hft) > 0 (Mean = 2 ± 1, at 477 Ma). These data allow interpretation of the origin of these zircons from a radiogenic initial Hf isotope source, which is characteristic of the Earth''s mantle. This, together with the fact that the rocks have been affected subsequently by tectonometamorphic processes, suggests that the early Ordovician diorites have been emplaced in a supra-subduction tectonic setting, related to onset of the Iapetus Ocean closure. [Copyright &y& Elsevier]