Browsing by Author "Räisänen, Milja"

As a part of Kumpula Campus Drill Hole Project, a 370 m deep drill hole was drilled on the University of Helsinki, Kumpula campus area in December 2015. Drilling took place on an amphibolitic outcrop, which is the main rock type of the area and part of the 1.9 Ga old Svecofennian orogenic belt. In this work, the geochemistry of the campus bedrock is analyzed, focusing on the amphibolite. Granite, actinolite rock and diopside-actinolite skarn are additional rock types described from the core in this work. The geochemical methods utilized are a portable X-ray fluorescence (P-XRF) spectrometer Niton XL3t GOLDD+ by Thermo Scientific and a laboratory wavelength dispersive X-ray fluorescence (WD-XRF) spectrometer PANAlytical Axios mAX 4kW. WD-XRF device is utilized in quantitative analysis and semi-quantitative Omnian scans. In addition to geochemical interpretation of the bedrock, feasibility of the P-XRF device in outcrop and drill core related studies is evaluated by comparing the methods. The surface of the drill core was analyzed with the P-XRF device. Representative samples of each rock type were sawed of the core and analyzed with both P-XRF and WD-XRF Omnian scans. In addition to surface analyses, a fused bead was prepared from one representative amphibolite sample and analyzed with WD-XRF quantitative method. Outcrop studies focused on the feasibility of the P-XRF device in in situ analyses. Compared to nearest temporally related amphibolite units, the amphibolite of the campus bedrock seems to be more felsic on average. All described rock types are connected to former petrogenetic interpretations of the local bedrock. However, further geochemical analyses are required to verify the interpretations. WD-XRF quantitative method and Omnian scans suggest almost similar results for fused bead of the amphibolite. Changing the sample type to solid rock surface introduces heterogeneity related problems to the quantitative determination of Omnian scans and quality of the results decreases almost to the level of P-XRF. Yet, the advantage of the Omnian scans method in rock surface analyses compared to P-XRF is better detection of light elements. For example, P-XRF device detects Mg, Al and K poorly and Na is not detected at all. On the other hand, SiO2 is on average detected quite accurately from rock surface with P-XRF when compared to WD-XRF quantitative method for fused bead. WD-XRF Omnian scans and quantitative application results of fused bead do not seem to differ remarkably. Broad rock type classification can be made with P-XRF device for drill core, but results cannot be considered quantitative. It should also be noticed, that the major element oxide sum values of P-XRF drill core surface analyses are quite low on average (84.00 wt.%). In outcrop analyses, different features lower the quality of the rock surfaces, resulting in even lower major element oxide sum values in analysis. Although major oxide sum values are very low on outcrops, relatively high amounts of for example Cl, S and P are detected for unknown reasons. Major advantages of the P-XRF device are the ease of use, light weight and rather good detection of for example SiO2. Developing the quantitativeness of the device would make it more comparable to laboratory XRF devices but it already has multiple features that are highly beneficial in a wide range of scientific fields.