Dados aerogeofísicos magnetométricos e gamaespectrométricos integrados com modelos geoelétricos em escala de detalhe na área da mina Cerro Rico – Lavras do Sul – RS

Abstract

The research area covers the Cerro Rico Mine and is located 7 km east of the city Lavras do Sul, delimited by the geographical coordinates longitudes -53, 81200 W - 53,83400 W and latitudes -30, 81100 S -30,81870 S. The mineral occurrence of Au, Ag and copper (Cu) is related to the presence of hydrothermal alteration zones and is conditioned to the existence of quartz veins that present northwest (NW) and east - west (E - W) preferential directions, present in the rocks characterized as tufts, andesites, rhyolitic spills and volcanic conglomerates of the Formação Hilário (604 - 590 Ma), belonging to the Bom Jardim Group, or Bom Jardim Alogrupo. The main objective of this research is to update the geophysical geological understanding of the area in a detail scale of 1: 5,000, integrating and interpreting aerial and terrestrial geophysical data in detail scale, in order to identify and characterize hydrothermal alteration areas associated with zones of failure and / or fractures, possibly related to metal mineralization (Ag and Cu and Au). Aerogeophysical data and lithological descriptions of drillholes were kindly provided by Amarillo Mineração do Brasil Ltda. The aerogeophysical data used in this research belong to the gamma-spectroscopic and aeromagnetometric aerogeophysical survey - Lavras do Sul Project - Rio Grande do Sul, 2007. The electrical resistivity and chargeability (IP) data form part of a geoelectric data set compiled from previous geophysical works in the study area, as well as the addition of new data to be acquired in two preferences directions NW-SE and SW-NE , aiming the creation of a spatial distribution mesh of the electrical resistivity and chargeability (IP) data for the study area in order to make a 3D geophysical model. Magnetic susceptibility data will be acquired in a regular grid with sampling intervals of approximately 60 meters in sectors of the study area characterized by high chargeability (IP) values and low resistivity values, as well as the characterization of anomalous Factor F, Anomalous uranium (Ud) and Anomalous potassium (Kd), indicative criteria that suggest the presence of hydrothermal alteration zones. The geoelectric results were efficient to delimit sectors of the study area with potential attractive targets for mineral prospecting, with values greater than 8 mV / V that coincide with the anomalies of Kd, Ud and Factor F. Rocks of the andesitic top are characterized by values greater than 3000 Ohm.m, resistivity values in the range of 200-500 Ohm.m characterize the presence of layers of agglomerated and derived rhyolitic volcanic tufts. According to the proposal 2D geophysical-geological model, for the Cerro Rico Mine area, it can be inferred from interpretative criteria that the andesitic top is at a depth of approximately 25 to 35 meters, characterized by the presence of an irregular relief, affected by failures and/or fractures. Layers of soil with volcanic rock fragments and the presence of silty clay soils characterize a depth of 2 to 15 meters. According to geophysical criteria it is suggested that the preferred direction of mineralized geological structures presents a Trend in the NW direction.