Geological and geophysical sulfide prospection in the Virorco-La Bolsa area, San Luis province

Abstract

In the Virorco and La Bolsa mafic-ultramafic bodies, central block of San Luis range, polymetallic sulfides occur in veinlets and disseminated. The autopotential method in combination with geomagnetic studies, were utilized as geophysical prospection tools. The maficultramafic lenses are surrounded by high-grade gneissic-migmatitic country-rocks. A penetrative mylonitic foliation NNE-trending and dipping with high angle to the ESE, affects the basement rocks and also the borders of the mafic-ultramafic bodies. Towards the interior of the mafic-ultramafic bodies, sectors which preserve the igneous granular textures and a foliation dipping to the W, alternate with shear bands with mylonitic foliation dipping to the ESE. The geophysical study in Virorco indicates a correspondence between the negative autopotential values (-150 mV) and maximum values of the magnetic field (+350 nT). In the La Bolsa zone two autopotential profiles show a nucleous of negative autopotential in the range between -40 and -50 mV, slightly elongated and dipping to the ESE. On the eastern margin, a value of -90 mV constitutes the core of an elongated anomaly also dipping to the ESE. The spatial orientations of these anomalies are coincident with the orientation of the mylonitic foliation. The established correspondence with this prospection tool, support the remobilization and concentration of the disseminated primary sulfides during the mylonitic event, previously suggested on the basis of other study techniques.