Re-processing of reflection seismic data from line V2 of the HIRE Seismic Reflection Survey in the Suurikuusikko mining and exploration area, northern Finland

Sammanfattning: The Suurikuusikko gold deposit is located in northern Finland; it is the largest known gold resource in northern Europe. The acquired high resolution reflection seismic data along the c.30 km long profile V2 of the HIRE reflection survey in the Surrikuusikko gold mining and exploration area have been re-processed. A 15.4 ton Geosvip was used as the source, with a receiver spacing of 12.5 m and source spacing of 25 or 50 m. It was aimed to obtain more detailed structural information of the upper 5 – 6 km crust, and to study the seismic response of the important geological and tectonic structures (e.g. Suasselkä PG fault) along the line V2. The line V2 runs from south to north; in the north, it cuts the mafic graphitic tuffic rocks, which are buried under a layer of tholeiite. It is almost perpendicular to the surface trace of the Suasselkä PG fault in the north. The obtained seismic image showed significant improvements compared with the previous work. The seismic response of the major rock units generated strong reflections, and they can be traced down to at least 3 km depth; the reflections correlate well with the surface geology. The moderately dipping reflections from the PG fault are clearly imaged; the dip direction of the fault is towards the SE with a dip of about 50o, possibly decreasing with depth down to about 35o, the fault can be traced down to about 3 km depth. The reverse movement of the fault most probably caused the neighboring sub-horizontal layers to be folded and generated a duplex structure. The dip direction of the major structures in the southern parts is towards NE; this together with the mentioned information about the fault, can be utilized in order to define the major geological structures and most importantly the tectonic evolution of the area; such information can be used in many crucial aspects such as prediction of the future movements of the bedrock and discovery of new resources.