Landstreamer seismics and physical property measurements in the Siilinjärvi open-pit apatite (phosphate) mine, central Finland

Abstract

We tested the applicability of a newly developed broadband (0–800 Hz) digital-based seismic landstreamer for open-pit mine planning in the apatite-bearing Siilinjärvi mine in central Finland. Four seismic profiles, in total approximately 2.5 km long (2–4 m source and landstreamer receiver spacing), two inside the pit and two on its margins, were acquired in combination with wireless recorders connected to 10 Hz geophones and fixed at every 10 m spacing along the seismic profiles while the streamer data were being acquired. Downhole logging and laboratory physical property measurements on core and rock samples were carried out to not only support the seismic interpretations but also to provide information about the possible geophysical signature of these unique types of deposits. In spite of a highly noisy mining environment, seismic data of high quality were acquired; however, reflection processing and interpretations were challenged by the geologic complexities of several generations of basic and carbonatite dikes. To complement the reflection data imaging and to account for the steep elevation changes and crookedness of some of the seismic profiles, 3D first-arrival traveltime tomography and 3D swath reflection imaging were also carried out. Clear refracted arrivals from the open-pit profiles suggest the possibility of low-velocity zones associated with either blasting or several shear zones intersecting the seismic profiles. In terms of reflectivity, reflections have a different appearance from short and flat to longer and steep ones. The downhole- and borehole logging data suggest that some of these reflections are associated with diabase dikes and some are likely from zones of weaknesses in the alkaline-carbonatite complex. We determine the potential of using seismic streamers for cost- and time-effective open-pit mine planning and encourage further testing in simpler geologic settings to be established.

Integrated Geological and Geophysical Mapping of a Carbonatite-Hosting Outcrop in Siilinjärvi, Finland, Using Unmanned Aerial Systems

“…The photogrammetric 3D outcrop model and ground measurements provide constraints on strike/dip and azimuth of the source bodies. Magnetic susceptibility values assigned to the modeled bodies are taken from published literature [27,28,44] and from additional measurements collected with a handheld susceptibility sensor over selected rock samples.…”

“…Our area of investigation is the Siilinjärvi apatite ore mine in Finland [25]. The site is an ideal testing ground due to the wealth of existing evaluation data, including geophysical [26][27][28][29] structural-geological [30][31][32], geochronological, and mineralogical information [33,34]. We used two on-site survey days to acquire high-resolution UAS data and ground validation in an area of about 1 km 2 .…”

High‐resolution reflection seismic imaging for the planning of a double‐train‐track tunnel in the city of Varberg, southwest Sweden

“…Spectral balancing using a 40‐60‐170‐280 Hz filter helped to partly balance the amplitudes between the two different‐type sensors. In normal seismic processing flows, the integration (to velocity for the MEMS sensors) is embedded into a deconvolution filter provided that the input data are minimum phase (i.e., impact sources and not vibroseis) and that deconvolution is surface consistent (see Malehmir et al ). No amplitude matching or data integration from velocity (geophones) to acceleration (MEMS), and vice versa, was considered since we did not aim to study amplitude variations of reflections in the data.…”

Unravelling the internal architecture of the Alnö alkaline and carbonatite complex (central Sweden) using 3D models of gravity and magnetic data

“…Therefore an estimate about their depth, lateral extent and the geological factors that have contributed to their formation can have implications for potential mineral resources. Our earlier studies using AMS data (Andersson et al, 2016) suggested that magnetite is a dominant magnetic mineral within the carbonatites that give rise to their high magnetic susceptibility (see also Malehmir et al, 2017). However, these types of rocks are not expected to comprise the main bulk volume of the complex and to produce the large positive gravity anomaly observed over the intrusion (Figure 2a).…”

“…Note that these types of complexes are not only unique in terms of their petrology but also because they are sometimes rich in REEs (Rare Earth Elements) and apatite minerals, which are in high demand in today's society. In fact most REEs in the world are mined from carbonatites, e.g., Bayan Obo in China, Lovozero in Russia, Mount Weld in Australia, Mountain Pass in USA, and Strange Lake in Canada (see Berger et al, 2009;Zaitsev et al, 2014), whereas Siilinjärvi carbonatite complex is an apatite 10 mine in Finland (Malehmir et al, 2017). Therefore an estimate about their depth, lateral extent and the geological factors that have contributed to their formation can have implications for potential mineral resources.…”