Abstract

In northern Chile, between latitudes 17.5° and 19.5°S, three major Andean metallogenic belts play a critical role in the concentration of porphyry copper deposits. These belts, ranging from Paleocene-Early Eocene, Middle Eocene-Early Oligocene to Miocene-Early Pliocene, are essential for the formation and distribution of porphyry copper deposits, mainly associated with a thick crust, wide magmatic arcs and regional mineralization events. This greenfield exploration-scale case study on the use of passive seismic tomography as a technique to study porphyry copper deposits focuses on the Lluta Valley, located near the axis of the Bolivian Orocline in the Arica and Parinacota region, with particular emphasis on the known Dos Hermanos and Campanani deposits. A seismological network composed of 38 short-period stations was implemented to perform passive seismic tomography and the Regressive ESTimator (REST) algorithm was applied to analyze a preliminary seismic catalog. This catalog revealed 28,793 P-wave and 19,243 S-wave phases associated with 1,011 seismic events, providing a robust basis for joint inversion and obtaining 3D models of P-wave velocity (Vp), S-wave (Vs) and Vp/Vs ratio. Our preliminary results indicate a correlation between high Vp/Vs ratio anomalies and the location of the Dos Hermanos and Campanani deposits. These anomalies may indicate the influence of complex geological processes, such as intense fracturing, that facilitate the emplacement and migration of mineralizing fluids associated with porphyry copper deposits. On the other hand, low Vp/Vs anomalies cover a large part of the crust, which could be related to rigid rheology bodies associated with Paleoceno-Eocene intrusives and Paleozoic basement. The low Vp/Vs anomalies are strongly linked to rigid bodies emplaced along regional N-S faults linked to the Altiplano Uplift, while the high anomalies correlates with the change of strike of these same faults, due to the oroclinal bending. These anomalies could play an important role in differentiating the size of the copper porphyry deposits in this area from other world-class Chilean porphyries in the same metallogenic belts such as Chuquicamata.