In the area of South Kuusamo, in the middle of Finland close to the Russian border, an deep geophysical anomaly has puzzled researches since the 1970’s. Now, a deep research borehole is drilling the boundary, which will hopefully confirm the cause of the anomaly.
As Esme Whitehouse explains in the blog she dedicated to this project, the theory most favoured at the moment is that the anomaly is an extension of the Näränkävaara and the Koillismaa Intrusive Complexes at depth, surrounded by lighter Archaean gneisses. These two complexes are comprised of 2.4 Ga old mafic to ultra-mafic layered intrusions and they sit approximately 60km part, with this mysterious gravity anomaly between. Other less probable suggestions for the origin of the anomaly include an Archaean greenstone belt, granulites, Ni-Cu-PGE mineralisation, or even an Archean-age impact crater.
Heavily fractured basement
Drilling commenced in September this year. The first stage was to drill through the till to the top of the bedrock. Then, the first 300m of bedrock turned out to be heavily fractured, causing loss of drilling fluids. In her blog, Esme Whitehouse also describes that around a depth of 900 m, overpressures were encountered, which prevented the use of injector tools.
Currently, the well is at a depth of around 1,500 m and based on a marked change of reddish grey granitic rock to a dark green to black rock it appears that the gravitational anomaly has been intersected at 1423m. The darker rocks are currently interpreted as a metamorphosed ultramafic cumulate rock in which olivine has altered to talc, and pyroxene altered to amphibole.
In addition to investigating the geophysical anomaly, the borehole will also offer potential to carry out further research and innovation in geothermal energy and deep geothermal gradients.
GTK‘s investment budget for the project for this year and next is a total of approximately EUR 860,000. The project will enable GTK and its partners to develop their existing research equipment to meet the needs of deep hole research as well as a completely new type of research technology in a deep hole environment.
The Arctic Drilling Company (ADC) from Rovaniemi is the drilling contractor for the research project. It is using a drilling machine developed and built by the company itself.
Read Esme’s blog here.