Seismic reflection profiling of the Pyhäsalmi VHMS-deposit: A complementary approach to the deep base metal exploration in Finland

Abstract

In the Pyhäsalmi case study, the seismic data is used in direct targeting of shallowly dipping mineralized zones in a massive sulfide ore system that was deformed in complex fold interference structures under high-grade metamorphic conditions. The Pyhäsalmi volcanic-hosted massive sulfide (VHMS) deposit ([Formula: see text]) is located in a Proterozoic volcanic belt in central Finland. Acoustic impedance of Pyhäsalmi ore ([Formula: see text]) is distinct from the host rocks ([Formula: see text]), enabling its detection with seismic reflection methods. Drill-hole logging further indicates that the seismic imaging of a contact zone between mafic and felsic volcanic rocks possibly hosting additional mineralizations is plausible. Six seismic profiles showed discontinuous reflectors and complicated reflectivity patterns due to the complex geology. The most prominent reflective package at 1–2 km depth was produced by shallowly dipping contacts between interlayered felsic and mafic volcanic rocks. The topmost of these bright reflections coincides with high-grade zinc mineralization. Large acoustic impedances associated with the sulfide minerals locally enhanced the reflectivity of this topmost contact zone which could be mapped over a wide area using the seismic data. Seismic data enables extrapolation of the geologic model to where no drill-hole data exists; thus, seismic reflection profiling is an important method for defining new areas of interest for deep exploration.