Passive seismic imaging of ore deposits using coda wave interferometry: a case study of Akanvaara V-Cr-PGE deposit in Northern Finland

Abstract. In this study, we present an innovative method to image the inner structure of orthomagmatic ore deposits using P-wave coda of regional seismic events. We combine data processing and interpretation schemes from conventional passive seismic interferometry and teleseismic receiver function (RF) method. We hypothesize that correlation of P-wave coda recorded by three-component sensors can be used to evaluate body wave part of empirical Green's tensor, from which arrivals of reflected and converted waves could be extracted. To test our hypothesis, we installed a high-resolution seismic array (profile) with 606 seismic instruments on the Akanvaara V-Cr-PGE deposit in Northern Finland above the inclined zones of V-Cr mineralization, placed inside ultramafic intrusion. From the regional seismic catalogue, provided by the Institute of Seismology, University of Helsinki, we selected the P-wave coda of 363 regional seismic events to evaluate body wave part of empirical Green's tensor by passive seismic interferometry. Further interpretation of the tensor allowed us to identify arrivals of PS and SP waves, converted at Cr and V mineralization zones. We conducted numerical simulation of plane wave interaction with the synthetic Akanvaara deposit model compiled from geological and drilling data and found that Green's tensors evaluated from synthetic seismograms and from seismic data contain similar converted PS and SP arrivals. To calculate depths to the conversion boundaries, we obtained S-wave velocity model using MASW method. According to calculated depths and geological model compiled from drilling data we suggest that the converted arrivals correspond to continuation of the Cr and V mineralized zones. Therefore, using the empirical Green's tensor, evaluated from P-wave coda of regional seismic events can be an effective tool for orthomagmatic ore deposits exploration in both greenfield and brownfield cases. In this paper we are describing details of the passive seismic experiment, numerical simulation, data processing and interpretation.