Integração de dados geofísicos aéreos e terrestres e a sua contribuição para prospecção aurífera na área da Mina Cerro Rico, Lavras do Sul (RS)

Abstract

The Cerro Rico Mine is located approximately 7 km east of the Lavras do Sul city, in the central region of the state of Rio Grande do Sul and is under mineral exploration license of the Amarillo Mineração do Brasil company. The research area is 15,758 km², delimited by longitudes 53º 47 '42.7 "W - 53º 50' 56.4" W and latitudes 30º 48 '5,7 "S - 30º 49' 46" S. The occurrence of gold, silver and cooper minerals in this area are related to the presence of hydrothermal alteration zones characterized by quartz filaments through NW and EW directions, intruded in the volcanic rocks of the Hilário Formation (~ 580 Ma). The aerogeophysical data belongs to the Lavras do Sul Gammaspectrometric Survey Project, which was executed by Prospectors Aerial Surveys and Systems in 2007. The sectors was identified by the characterization of geophysical anomalies through the processing of aerogamaespectrometric data, in this area the geophysical surveying was made on a scale of approximately 1: 3.000 and defined with the geoelectric methods of Eletroresistivity and Induced Polarization using the techniques of 2D Horizontal Profiling and Vertical Electrical Sounding. The aerogamaespectrometric data allowed the identification of five radiometric domains that suggests the presence of differents lithologies in terms of possible variations in the radioelements (K (%), eU (ppm), eTh (ppm)), texture and mineralogy of the rocks and soils present in the area. The gamma spectrometric profiles integrated with the geoelectric data allowed the identification of possible zones of fractures and/or faults, with probable percolation of hydrothermal fluid and/or presence of metallic mineralizations. The 2D geophysical-geological model proposed for the Cerro Rico Mine area, suggests that the depth of the top of the andesitic basement is between 20 and 30 meters, characterized by the presence of irregular relief, affected by fractures and/or faults. According to the integration of the results from the resistivity and chargeability data, the anomalous levels with a resistivity value around 200 Ohm.m and chargeability of 8 mV/V to 12 mV/V are associated with the presence of fracture zones with possible metallic mineralization. The sectors of the area with presence of fractures filled by quartz veins and probable mineralization, results in attractives potentials, to give continuity and guide future research related to gold prospecting in the Cerro Rico Mine.