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Zugl.: Potsdam, Univ., Master Thesis, 2016
Abstract:
The Collisional Orogeny in the Scandinavian Caledonides (COSC) project supported by the International Continental Scientific Drilling Program (ICDP) and the Swedish Scientific Drilling Program (SSDP) drilled a borehole through the Seve Nappe in Sweden to investigate mountain building processes. It recovered 2.5 km of drill core. Five core samples from the depth from 1682 to 2469 m were analyzed in this thesis. A hyperspectral imaging spectrometer (HySpex) was used to conduct the measurements. It is a two sensor system which combines a VNIR and a SWIR sensor. The measurements were taken with a resolution of 0.22 mm/ pixel. As a comparison, mineral maps based on Laser Induced Breakdown Spectroscopy (LIBS) element measurements of approximately the same resolution were used. This thesis developed a working process chain which includes 1) the adjustment of the measurement parameters of the sensors to acquire optimal data cubes, 2) the "unrolling" of a drill core to depict and analyze the whole core mantle surface and to map the distribution of minerals accurately not only over the length but also the whole surface of the core and 3) the mineral mapping based on spectral absorption features with the EnGeoMap algorithm. This can be seen as the beginning of the development of a stand-alone drill core scanner including the geological evaluation by EnGeoMap. The measurements revealed a basic approach to determine the integration time for the VNIR and the SWIR sensor based on the signal-to-noise ratio of the white reflectance standard. An approach of a step-wise rotation of the core and a translation measurement and a mosaicking based on the rectification of the core surface was developed. The stitching of several core images via key points was deployed. The duration of the unrolling amounts to 22 h/ m of core and results in an hyperspectral mosaic of the core mantle surface. Relative to the approximately 550 h needed to measure the surface area of 1 m of core with the LIBS system, 22 h seems tolerable. The feasibility of the unrolling and the mosaicking of drill cores varies. In scientific operations the accuracy is valued higher than the time-consumption, in industrial operations the time is a big factor to make a project profitable. The mineral mapping with EnGeoMap proved to be very precise in case of detecting the abundance of single minerals. When mapping multiple minerals, a bias towards a few minerals showed which were mapped with higher abundances than in reality. This is due to mineral-dependent fit value thresholds and has to be investigated further. When choosing few but distinct proxy minerals, EnGeoMap is a valuable tool to evaluate the mineral abundances and the distribution over the course of a drill core, to highlight changes and to give information about mineral assemblages.
