Metallogeny of the Triassic‐Jurassic Rift‐Related Mineralizations in Argentina

Abstract

The Triassic-Jurassic NNW-SSE extensional phase affected the western margin of Gondwana and marked the beginning of the fragmentation of this supercontinent. Extensional faulting began in the Late Permian in the northern areas, becoming younger to the south, i.e. Jurassic in Patagonia. During this stage extensive rhyolitic ignimbrite magmatism developed. The rift system, was filled with continental sediments that locally have intercalated bimodal, predominantly mafic, volcanic rocks. The region affected by the Triassic-Jurassic rifting in the Argentine territory hosts a number of deposits that have no direct link with magmatic activity and whose age has previously been attributed, in general, to the Mesozoic (Zappettini, 1999), or are herein ascribed to this event. These include the Se-rich polymetallic deposits, five elements deposits, Pb-Zn-Ag simple veins, epithermal Mn, fluorite and barite veins. The various types of deposits analyzed have a wide regional distribution reflecting the extent of the processes of rifting that started during the Triassic and reached the Cenozoic, generating thermal and fluid flow anomalies leading to hydrothermal mineralizing processes. Where there was a favorable source, fluids collected selected elements resulting in a mineralogical specialization and inhomogeneities in the distribution of the mineralization types along the belt affected by rifting. Characteristically, where the rifting affected Paleozoic or older sedimentary sequences, polymetallic and barite type deposits were generated. Where rifting affected acidic Triassic-Jurassic volcanic and volcaniclastic sequences the fluids originated fluorite mineralization. In the cases where there was an associated restricted basic magmatism or by leaching or volcanic sequences Mn ore bodies were formed. In all cases, this rift environment has been favorable for the emplacement of alkaline to subalkaline acid magmatic rocks. In these cases, besides the presence of fluorine and fluorine-rich fluids, evidenced by the presence of fluorite and / or topaz, there are associated REE mineralizations (Rodeo de los Molles, Sierras Pampeanas of San Luis and Rangel district, Puna of Salta), Mo-rich stockworks (Elsiren and German) and epithermal gold deposits (Pantanito, and, in general, the Au-Ag epithermal deposits of the Deseado Province). In this context the Pb-Ag polymetallic mineralization of the Navidad deposit formed in relation to a rift-related magmatism represented by volcanic and pyroclastic deposits associated with biochemical and epiclastic sediments deposited within the Canadon Asfalto hemigraben (e.g. Fernandez et al., 2008). From a global point of view, the fluorine, manganese and polymetallic deposits related to extensional environments may be associated with precious metal mineralization (Au-Ag) and Mo-rich porphyries, so that their presence can be used regionally as an exploration guide (e.g. Wallace, 2010).