Influence of structural and lithological controls in ore-shoots formation and morphology from Julieta vein, Casposo district, Cordillera Frontal, San Juan, Argentina.

JOVIC, S.M.; PALMA DIEGO S; PERMUY VIDAL C.; LÓPEZ, L.; GUIDO, D.M.; MONGAN MARCO, MARIANO; SOTARELLO GUSTAVO

Salta

Simposio; 15th Quadriennial IAGOD; 2018

IAGOD

The Casposo district is located in the Cordillera Frontal, in the centre-west of the San Juan province, Argentina(Fig. 1a). It is characterized by the presence of low sulfidation epithermal veins, hosted in volcanic rocks of theChoiyoi Group (Sotarello et al. 2002). The structural trend that controls the Au-Ag mineralization has a main NW-SEdirection, with Kamila and Mercado as the main mineralized sectors (mined by open pits, and actually by undergroundmining). In Kamila sector, 3 structures with different orientations were recognized, 2 subparallel structures, Incaand B-vein with a NW-SE orientation and a SW dip, and Aztec vein with N-S orientation and W dip, between B-veinand Inca, developing a dextral jog. Julieta is one of the most important targets of Casposo district and will be inproduction at the end of 2018. The vein is located 5 kilometres to the NW of the operations zone (Kamila/Mercado),within the same NW regional structural corridor (Fig. 1b). The target was discovered by Intrepid Minerals in 2005and explored by Troy Resources until 2013. Austral Gold resumed exploration of the target since the end of 2016until the middle of 2017, performing tasks of geological mapping, mineralization mapping, surface sampling, loggingof drill survey. The mineralization is hosted within volcanic rocks composed of two thick crystaloclastic ignimbritesequences with andesitic (lower section) to dacitic (upper section) compositions, intruded by a series of pre- andpost-mineralization subvolcanic intrusions including dykes, and cryptodomes.Julieta vein is composed of carbonate and quartz with banded and brecciated textures, which participate inthe filling of the vein in different proportions. Nine pulses of mineralization are summarized in 4 events: a barreninitial carbonate hydrothermal event, a siliceous hydrothermal event that provides Au and Ag to the system, a newbarren carbonate hydrothermal event, and a final tectonic-hydrothermal event that remobilized metals (Palma etal. 2017).