PALEOMAGNETISM AND MAGNETIC MINERALOGY IN EL TENIENTE SUPERGIANT PORPHYRY CU-MO DEPOSIT, CENTRAL ANDES, CHILE

El Teniente mine, a world-class Cu ore deposit is located in the southern edge of the Pampean Flat Slab segment of the Central Andes and directly to the east of the Juan Fernandez Ridge. We have carried out a detailed paleomagnetic-mineralogical study in order to obtain local tectonic information, syn or post mineralization. El Teniente ore body is hosted within Miocene-Pliocene basaltic-andesitic volcanic and gabbroic intrusive rock and multiple events of alteration/mineralization have been recognized and penetrative potassic and chloritic alteration are overprinted by phyllic alteration. Mineralization is related to small felsic apophyses, dykes (quartz diorite to tonalite) and porphyritic stocks and occurs as stockwork of mineralized veins and hydrothermal breccias. Magnetic analysis suggests the presence of prevailing magnetite and subordinates quantities of maghemite, hematite and scarce Fe-Ti oxides. These magnetic minerals are associated with heterogeneous alteration conditions and country rock behavior. We have recognized at least five stages of generation of magnetic minerals. Magnetic mineralogical phases can be distinguished optically and are characterized by differences in size, shape and mineralogical association. The correlations between available alteration ages and our characteristic magnetic directions show that an early penetrative biotitization and phyllic alteration is related with a reverse polarity interval. In contrast, a late hydrothermal stage of alteration is related to a normal polarity interval. The calculated paleomagnetic direction shows no evidence of block movement post 4 Ma in the orebody. In this context our results suggest that the Juan Fernandez Ridge has no drive a paleomagnetic recognizable tectonic rotations at least in this area.