3D reflection seismic imaging for open-pit mine planning and deep exploration in the Kevitsa Ni-Cu-PGE deposit, northern Finland

Abstract

A 3D reflection seismic survey was conducted over an area of about 9 km 2 at the Kevitsa Ni-Cu-PGE (platinum group elements) orebody, northern Finland, where open-pit mining started in mid-2012. The principal objective of the survey was to image major fault and fracture zones at depth that may have an impact on the mine stability and safety. Mine planning would then take into account the geometry of these zones at Kevitsa. Processing results, using conventional prestack DMO and poststack migration methods, show gently dipping and steeply dipping reflections from depths of approximately 2 km to as shallow as 150-200 m. Many of the reflections are interpreted to originate from either fault systems or internal magmatic layering within the Kevitsa main intrusion. Further correlation between the surface seismic data and VSP data suggests that numerous faults are present in the imaged volume based upon time shifts or phase changes along horizontal to gently dipping reflections. Some of these faults cross the planned open-pit mine at depths of about 300-500 m, and are therefore critical for geotechnical planning. In terms of in-pit and near-mine exploration, the magmatic layering internal to the intrusion controls the distribution of the bulk of economic mineralization. The ability to image this magmatic layering could therefore guide future drilling, particularly by constraining the presumed lateral extents of the resource area. Exploration also will target discrete reflectors that potentially represent higher-grade sulfide mineralization.

New constraints on an existing mineral resource through 3D seismic

“…Malehmir et al (2012) provide the full details of the acquisition and processing parameters. Source lines were spaced at 80 m and perpendicular receiver lines at 70 m. Source stations every 45 m and geophone groups every 15 m resulted in a fold of 60-75 over all but the margins of the survey area.…”

Late Cenozoic deep weathering patterns on the Fennoscandian shield in northern Finland: A window on ice sheet bed conditions at the onset of Northern Hemisphere glaciation

“…The Kevitsa intrusion hosts the eponymous Kevitsa Ni-Cu-PGE mine and is comprised of mafic to ultramafic rocks, including olivine pyroxenite, peridotite, gabbro, and granophyre. Mine cuts at Kevitsa are excavated mainly in saprock and fresh rock (Malehmir et al, 2012), and diamond drill cores from the nearby Sakatti prospect (Fig. 1B) demonstrate that fresh rock is extensive beneath thin till and saprock.…”

Seismic volumetric interpretation of a disseminated copper system in Kevitsa, northern Finland

“…They also interpret a deeper continuation of the intrusion than previously thought. Surface seismic reflection has generally failed to directly image steeply dipping to sub-vertical structures, but Malehmir et al (2012b) correlated 3D seismic data with the VSP data and suggested that steep reflections observed in the VSP data match steep or near-vertical faults displacing gently-to-moderately dipping reflectors (Figure 3). …”

“…density and seismic velocity . Improved mining technology and scarcity of large, near-surface deposits has led the mining industry to explore deeper for economic minerals in order to meet future needs (Malehmir et al, 2012b). Gravity and magnetic methods cannot resolve targets beyond 500 metres in depth, however, the seismic reflection method can delineate structures up to 1 km deep Snyder, 2007, Malehmir et al, 2012b).…”