A 2-D resistivity modeling of the southern sector of the Pringles Metamorphic Complex, Sierra de San Luis, Argentina

POMPOSIELLO, C LÓPEZ DE LUCHI M, FAVETTO, A.

Perugia, ITALIA

Congreso; IUGG XXIV General Assembly IAGA; 2007

Ultramafic-mafic igneous intrusions of the Virorco district form part of a NNE trending belt of Ordovician mafic plutonic lenses located in the Pringles Metamorphic Complex (PMC) the central basement domain of the Sierra de San Luis (Eastern Sierras Pampeanas),where high temperature low/medium pressure (5.7-6.4 kbar/740-790C) granulite facies rock constitute their host rock. Whole rock major and trace element compositions indicate that the parent magma was gabbroic/basaltic and was generated in a subduction-related arc, or back-arc settings. The belt of mafic-ultramafic intrusions host nickel sulfide resources and contain significant Cu, Co and PGE mineralization. Using pre-existing resistivity and chargeable data 2D and 3D models were obtained. Resistivity anomalies are located along two eastern and western parallel corridors located outside the area of most continuous outcrops of the orthopyroxene gabbro. These anomalies could be controlled either by a particular enriched rock facies or by a structural feature, being in this last case an indication of a secondary mineralization. Model output shows that the bodies that are responsible for the PFE% and FM anomalies extend down to 200 m. The vertical attitude and location of the eastern anomaly are coincident with ductile shear zones that affect the contact between the mafic intrusion and the host rocks .In this area a 150 m vertical sounding cut across the metamorphic host. The western anomaly is located below an area in which the metamorphic host is interlayered with horblendiferous diorites. It is possible that this contact surfaces between rocks of different rheology could act as weakness zones in which ductile deformation was concentrated. Ductile shear zones could have channelized fluid circulation that mobilized the original mineralogy and led to its concentration. Therefore in the southern sector of the Virorco ultramafic-mafic unit the mineralization is associated with the regional steep high- temperature shear zones, the activity of which is Ordovician. Furthermore, MT sites using two commercial wideband receivers (EMI MT-24) with a data bandwidth of 0.01 to about 300 s were collected around the bodies. Resistivity anomalies are found at approximately 5000 m depth. It is not clear if these deeper anomalies have the same origin that the shallower ones.