Geophysical prospecting of the Las Águilas deposit, San Luis Province, Argentina

Abstract

The Las Águilas sulphide deposit is located in the southern part of the Sierra Grande of San Luis, Argentina. Geophysical exploration in this area is faced with several problems due to the geological structure and the varied mineral composition of the sulphides carried by mafic-ultramafic rocks. Induced polarization (IP) methods are very promising for the recognition of polymetalic disseminated sulphide mineralization, but they require the application of other geophysical methods to establish the influence of graphite, which clearly is an undesired element in evaluating the potential of a sulphide deposit. This contribution focuses on the evaluation and comparison of results obtained with both induced polarization (IP) and magnetic surveys. Our results show that, in the areas where the rocks have high magnetic susceptibility, it is due to the presence of the sulphide pyrrhotite. Graphite is irrelevant to magnetism because of its diamagnetic nature. When magnetic anomalies (total component) are compared with the results of the induced polarization method (resistivity, metallic factor and % frequency effect (PFE)) it is usually possible to deduce that the pyrrhotite is responsible for the magnetic anomalies, and pyrrhotite together with other sulphides are causing the IP anomalies, provided one assumes that the graphite and sulphides do not co-exist and, that there are no larger concentrations of magnetite.