Imaging Mineralizing Fluids of Porphyry Cu Deposits Using Local Earthquake Tomography: Northern Chile Case Study

An essential part of the world's remaining mineral resources is now expected to reside deep in the crust or under thick post-mineralization cover. Deep penetrating geophysical methods are thus becoming a crucial exploration tool that can greatly improve our current understanding of ore genesis. In the case of porphyry Cu-Mo deposits, the world's primary source of Cu and Mo, identifying the dynamic processes that control the emplacement of porphyries in the upper crust will guide future exploration. Seismic tomography shows promise in imaging deep-seated ore control structures in porphyry systems including fluid pathways related to faults and/or granitic intrusions, as well as mineralization sites. In this study, a three-dimensional model of Vp/Vs obtained from seismic tomography reveals low, near-surface anomalies of Vp/Vs ~1.55-1.65 in the proximity of the Cerro Colorado porphyry Cu deposit in northern Chile, and near a range of historical porphyry prospects included in the study area (e.g., Mocha). These low Vp/Vs anomalies, which extend to 10-12 km depths, are interpreted as ore-associated intrusive bodies in agreement with previous tomography results of hydrothermally altered and mineralized bodies. Deep-seated magma chambers that irregularly underlie ore bodies are characterized by slightly higher Vp/Vs ratios of ~1.68-1.7 that extend down to ~ 15 km depth. Imaging these precursors and/or parental plutons in the deep crust is crucial as the latter ultimately act as the source of fluids for porphyry Cu generation in the shallow crust. This study confirms seismic tomography as a powerful tool to image ore-controlling structures in porphyry Cu magmatic systems and provides valuable clues for the identification of future exploration targets.