Geological evolution and metallogenetic relationships of the Farallón Negro volcanic complex, NW Argentina
The 700 km2 region encompassing the Farallón Negro Volcanic Complex and associated outlying intrusive centres represents the locus of the greatest metal endowment currently recognized in Argentina. It is host to two world-class deposits (Bajo de la Alumbrera and Agua Rica), two producing mines (Capi...
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Detalles Bibliográficos
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- Formato:
- Tesis Libro
- Lenguaje:
- inglés
- Publicado:
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Kingston, Ontario, Canada
Queen's University
1997
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- Bibliografía al final de v.1
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v.1: Texto con láminas incluídas
v.2: Apéndices
nº de orden interno: TDG-34 - Materias:
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| Sumario: | The 700 km2 region encompassing the Farallón Negro Volcanic Complex and associated outlying intrusive centres represents the locus of the greatest metal endowment currently recognized in Argentina. It is host to two world-class deposits (Bajo de la Alumbrera and Agua Rica), two producing mines (Capillitas and Farallón Negro - Alto de la Blenda), five additional porphyry Cu-Au prospects (Bajo de Agua Tapada, Bajo el Durazno, Bajo de San Lucas, Bajo las Juntas and Bajo las Pampitas) and an epithermal Au-Ag prospect (Cerro Atajo).- The early volcanc history of the region is characterized by the extrusion fron discrete centres from 12.56 to 8.51 Ma of basalt, basaltic andesite and dacite flows of the Farallón Negro Group. These precursor volcanic events were subsequently covered byflows and breccias of the Main Farallón Negro Stratovolcano, centred on Alto de la Blenda, which erupted from ca. 8.51 to 7.49 Ma, but with the minor extrusion of pyroclastics persisting as late as 6.72 Ma. The stratocone-building event was accompanied by intrusive activity, of the Farallón Negro Intrusive Suite, which peaked between 6.8 and 8.6 Ma and continued until 5.2 Ma with the emplacement of dacite and rhyolite dykes representing the terminal stages of magmatic activity in the region. Porphyry Cu-Au and epithermal Au-Ag alteration-mineralization formed early in this terminal stage.- The geochemical continuun represented by the Farallón Negro high-K calc-alkaline and shoshonite suites strongly suggests that they originated from a common source. Whereas shoshonitic units represent some of the oldest dated units at Farallón Negro, they are interbedded with high-K calc-alkaline units. The absence of features commonly interpreted to be indicative of magma mixing (e.g., sieve-textured plagioclase) in the shoshonites suggests a lesser involvement of deep-crustal MASH processes for the more potassic members. This would imply either thinner crust at the time of eruption and/or rapid emplacement of shoshonitic melts with minimal crustal interaction. The calc-alkaline melts show evidence for mixing and may have experienced greater interaction with the lower crust through slower magma ascent and/or longer crustal residence time. Thery were erupted quasi-continuously throughout the igneous history at Farallón Negro.- The igneous rocks of the Farallón Negro region were emplaced in a pull-apart basin related to coalescing zones of transtension, nucleated at the intersection of N-S striking faults and the NE-trending dextral Tucumán Transfer Zone. Initiation of the localized extension occurred in a stress regime dominated by E-W compression related to the convergence of the Nazca and South American Plates. A reorientation of stress regimes at ca. 8.0 Ma, evident from the NW orientation of the Aguila dyke swarm, heralds the overriding of the subduction-related stresses by NW-SE directed stresses related to the uplift of the Puna.- The study-area delimits the eastern extension of a transect of Chile and Argentina centred at ca 27º S which hosts a definable, world-class, concentration of Cu-Au deposits. It constitutes the northern boundary of a distinct Cu-Au metallogenetic sub-province. A unique geodynamic setting is also proposed for this latitude. Tears in the subducted slab, possibly nucleated on inhomogeneities in the oceanic crust related to the Easter Island volcanic chain, allowed asthenosphere to traverse the slab and rise into the overlying mantle wedge. This provided higher heat flow and possibly allowed greater devolatilization of the subducter slab, which in inferred to have resulted in the generation of melts which record the Middle Miocene arc broadening at this latitude.- The coincidence of a unique geodynamic environment with the unusually intense Cu-Au metallogenetic signature of this transect implies a significant and fundamental role of "provenance" in the formation of ore deposits at this latitude.- |
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| Descripción Física: | 2 v. il.color ; 28 cm. |