Publications – Master’s Thesis

Testing of Reflection Seismic, Ground Penetration radar and Magnetic Methods for Mineral Exploration and Mine Planning at the Siilinjärvi Phosphate Mine Site in Finland

MSc Thesis by Laakso, V., University of Helsinki

ABSTRACT

Siilinjärvi mine in Finland is the only mine within the European Union producing phosphate rock, a critical raw material for the European Union. With the current mining plans, the production is estimated to continue until 2035. The extent of the ore deposit and new locations for open pits are presently being investigated to ensure continuation of the mining operations also after 2035. The goals of this work were to study the depth and lateral extent of the phosphate-bearing Siilinjärvi carbonatite-glimmerite deposit, major zones of weaknesses, waste-rock diabase dykes and a tonalite-diorite intrusion cutting the deposit south of the current main pit, and in particular the geophysical anomalies related to these features. Detailed 3D geological models created for the current main pit area by Smart Exploration PhD student Tuomas Kauti from the University of Turku were used as a reference for the interpretation of the new geophysical data. The carbonatite-glimmerite ore is associated with elevated magnetic total field values, and at a larger scale the deposit can be tracked with magnetic surveys. With reflection seismic method, the large geological structures can be imaged at depth (see Figure 38), and 3D seismic data could be used for detailed planning of a new open pit. The higher resolution GPR measurements could then be implemented in the operating phase of the mine in a more routine manner to aid creation of reliable production prognoses (see Figure 39).

Figure 38. 3D views of the Smart Exploration reflection seismic data and the waste-rock dyke, i.e., diabase dyke, network model created by T. Kauti based on production drilling data (Kauti et al. manuscript in preparation). Figure a) shows all the modelled waste-rock dykes. The different colours present different dyke populations. The sub-horizontal diabase dyke population is presented in green. Figure b) shows the sub-horizontal dyke population with reflection seismic line SM1. The dashed black line outlines the shapes of a modelled diabase dyke, and a diabase dyke interpreted from the reflection seismic data. The shapes resemble an anticline and a syncline of folding structures.

Figure 39. A comparison between the GPR data acquired along the southern edge of the Särkijärvi pit (line 203) and the high-detail waste-rock dyke model created by T. Kauti (Kauti et al. manuscript in preparation). Figure a) shows the 3D photogrammetry model together with the modelled diabase dykes looking towards the south. The pit location corresponds approximately to the distance between 700–900 m in the GPR line 203 (Figure 37). Figure b) shows the 3D photogrammetry model and the diabase dykes together with the GPR data looking towards the north. The different colours of the diabase dykes refer to the positions of the dykes. The orange dyke in the near subsurface, denoted with the orange arrows, is dipping towards the south and the green dyke, denoted with the green arrows, is dipping towards the north. The two dykes are cutting each other somewhere between the pit wall and the GPR line which is why the dykes change order when the viewing angle changes from south to north. In this figure, the GPR data has been plotted to a constant datum, i.e., no elevation variation. The black dashed line shows the true zero position of the GPR line. Figure made by T. Kauti.

The full thesis is available here.