Abstract
The Minas Azules gold deposit, located in the northernmost part of the Sierra de Rinconada, Argentina, is hosted by low-grade metamorphosed turbidites of Middle Ordovician age. Quartz veinhosted, stockwork and disseminated gold mineralization is structurally controlled and intimately associated with a large cylindrical-type anticline that developed during the Upper Ordovician-Lower Silurian Ocloyic orogeny. Several styles of gold-bearing quartz veins were emplaced during folding and the later stages of episodic thrust faulting, but the main gold mineralization episode occurred at a particular stage in the deformation history and can be shown to be related to pressure solution reactions that occurred following cleavage development and prior to the onset of transpressional deformation. Due to post-ore faulting, mineralization is confined entirely to the eastern flank of the Minas Azules anticline. Petrological and geochemical studies reveal that, within the eastern flank, hydrothermal alteration of the wallrock is well-developed and, together with low-grade disseminated mineralization, extends for at least 70 meters from the vein system. Alteration in the Minas Azules deposit includes chloritization, sericitization, (de)silicification, sulfidation, and carbonatization. Lithogeochemical changes related to alteration are characterized by the addition of K2O, CO2, As, Au, S, and concomitant depletion of SiO2, MgO, and Na2O. Based on the style of mineralization, relative timing of ore formation, and characteristic alteration features, the Minas Azules deposit bears many similarities with well-documented orogenic gold deposits in Phanerozoic fold belts elsewhere (e.g., Tasmanides, eastern Australia; Meguma Terrane, Nova Scotia; Tien Shan, Central Asia; Mongol-Okhotsk fold belt, Russian Far East) and highlights the potential of the Sierra Rinconada as a significant producer of orogenic lode-gold and disseminated mineralization in the Andes.
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