Browsing by Subject "Master's Programme in Geology and Geophysics"

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  • Wang, Yijun (Helsingin yliopisto, 2020)
    The Southern Andes is an important region to study strain partitioning behavior due to the variable nature of its subduction geometry and continental mechanical properties. Along the plate margin between the Nazca plate and the South American plate, the strain partitioning behavior varies from north to south, while the plate convergence vector shows little change. The study area, the LOFZ region, lies between 38⁰S to 46⁰S in the Southern Andes at around 100 km east of the trench. It has been characterized as an area bounded by margin-parallel strike-slip faults that creates a forearc sliver, the Chiloe block. It is also located on top of an active volcanic zone, the Southern Volcanic Zone (SVZ). This area is notably different from the Pampean flat-slab segment directly to the north of it (between latitude 28⁰ S and 33⁰ S), where volcanic activity is absent, and slip seems to be accommodated completely by oblique subduction. Seismicity in central LOFZ is spatially correlated with NE trending margin-oblique faults that are similar to the structure of SC-like kinematics described by Hippertt (1999). The margin-oblique faults and rhomb-shaped domains that accommodate strain have also been captured in analog experiments by Eisermann et al. (2018) and Eisermann relates the change in GPS velocity at the northern end of LOFZ to a decrease in crustal strength southward possibly caused by the change in dip angle. This project uses DOUAR (Braun et al. 2008), a numerical modelling software, to explore the formation of the complex fault system in the LOFZ in relation to strain partitioning in the Southern Andes. We implement the numerical versions of the analog models from Eisermann et al. (2018), called the MultiBox and NatureBox models to test the possibility to reproduce analog modelling results with numerical models. We also create simplified models of the LOFZ, the Natural System models, to compare the model displacement field with deformation pattern in the area. Our numerical model results in general replicate the findings from MultiBox experiment of Eisermann et al. (2018). We observe the formation of NW trending margin-oblique faulting in the central deformation zone, which creates rhombshaped blocks together with the margin-parallel faults. More strain is accommodated in the stronger part of the model, where the strain is more distributed across the area or prefers to settle on a few larger bounding faults, whereas in the weaker part of the model, the strain tends to localize on more smaller faults. The margin-oblique faults and rhomb-shaped domains accommodating strain is not present in the Natural System models with and without a strength difference along strike. This brings the question about the formation of the complex fault system in both the analog models and our numerical versions of them and hypothesis other than a strength gradient could be tested in the future.
  • Karpoja, Anna (Helsingin yliopisto, 2019)
    Kaapelinkulma is an orogenic gold deposit located in the Paleoproterozoic Vammala Migmatite Belt (1.91 – 1.79 Ma) in Valkeakoski municipality in Southwestern Finland, and it is considered to have been formed in microcontinent collision during Svecofennian orogeny and has been classified as an orogenic gold deposit. Kaapelinkulma comprises a set of sub-parallel lodes in a tight array hosted within a sheared quartz-diorite unit inside a tonalitic intrusion. Gold occurrence is hosted by an en echelon type sheared quartz-dioritic dyke which forms a large xenolith inside synorogenic tonalite intrusion, surrounded by mica gneiss. It is estimated that Kaapelinkulma gold deposit contains at least, 168 Kt of ore containing 3.8 g/t Au. Textural setting, mineralogical association form and assemblage of gold, sulphides and telluride grains in Kaapelinkulma were studied with field-emission scanning electron microscopy, with electron probe microanalyzer and scanning electron microscopy. Ore minerals observed in Kaapelinkulma are: arsenopyrite, löllingite, pyrrhotite, pyrite and chalcopyrite. Other ore minerals identified are native bismuth, gold, scheelite, bismuth-tellurides and maldonite, which were all found in abundant amounts. Ore minerals occur as dissemination in intergranular spaces between silicate matrix, as polycrystal aggregates in quartz-veins and quartz clusters; and within shear zones. Gold in Kaapelinkulma is present as two generations: as single free native gold grains and as polycrystalline gold aggregates. Polycrystalline gold aggregates are grains formed from several mineral association and their combinations. Most common polycrystalline gold aggregates are formed from combination of: maldonite-native Au, Au-Bi alloys, Au-Ag grains and Au-hedleyite. Single free native gold grains are pure gold or gold-silver alloys. Free native gold grains can be found as intergranular, single grains in silicate matrix and adjacent or as a part of disseminated ore together with polycrystalline gold aggregates, bismuth and bismuth tellurides. Polycrystalline gold aggregates are found in disseminated ore, which are in close contact with quartz-veins and sulphide aggregates, or as inclusions in arsenopyrite-löllingite contact zones- or in other sulphides. Concentration of Au varies in native-gold grain from 76.83 to 97.87 wt% according to EPMA analyzes and from 50.03 to 100 wt% according to FE-SEM analyzes. Minor to moderate amounts of silver and copper were identified within the grains. Grain sizes of gold varies significantly from 7µm2 to 5mm2. Ore mineral paragenesis were observed to start when arsenopyrite and löllingite crystallized first, followed, partly simultaneously by pyrrhotite, pyrite and chalcopyrite. This was followed by crystallization of maldonite, first occurrence of native gold and bismuth, bismuth-tellurides, hedleyite and finally tellurides and main occurrence of gold. General ore forming process in Kaapelinkulma has been open space filling.
  • Junna, Tuomas (Helsingin yliopisto, 2020)
    Pedogenic ferromanganese nodules and concretions are prevalent redoximorphic features in tropical and sub-tropical soils. The nodules are typically highly enriched in Fe and Mn that are present as oxides, hydroxides and oxyhydroxides. The formation of nodules happens via precipitation and translocation of metals as the soil redox state undergoes cyclical changes between reductive and oxidizing settings. As the nodule elemental distribution and structure is primarily and expression of the prevailing soil redox conditions, Fe-Mn nodules have the potential to be a useful tool of paleoclimatological analysis. The Chinese Loess Plateau (CLP) is a terrestrial archive for study of changes in the monsoon climate system. During Late Miocene, the intensification of the Asian Monsoon system caused an increase in warmth and humidity in inland Eastern Asia during a global trend of increased aridity and decreasing temperatures. Fe-Mn nodules from three different soil horizons, formed 8.07, 7.7 and 3.7 Ma ago in Lantian, southern CLP, were studied to compare nodules from varying sedimentary settings formed under different moisture regimes. Using electron microscopy methods, the structure and elemental distribution of nodules were described to compare their redoximorphic features. Large Fe-Mn nodules from floodplain sediments (8.07 Ma) show a well-developed structure, high metal enrichment and signs of variations in rate of formation and dominant redox states. The soil redox conditions are likely primarily controlled by the river flooding. Nodules from two eolian deposits (7.7 Ma and 3.7 Ma) were, on average smaller and showed less metal enrichment, less elemental differentiation and less variance in the dominant redox conditions. Only small, poorly developed nodules were found from older eolian sediments whereas younger soil horizon contained larger nodules with evidence of higher hydromorphism. While potential for using the nodules from eolian sediments to assess changes in precipitation exists, the lack of paleoclimatological information in smaller nodules, the small sample count, limitations of the methods and variance in depositional settings increase the uncertainty of the interpretation.
  • Markkanen, Minna (Helsingin yliopisto, 2021)
    The orbicular quartz monzonite from Kuohenmaa, Southwest Finland, is one of the most beautiful and well-known orbicular rocks in the world. The cores of the orbicules are peraluminous in composition, most likely of xenolithic metasedimentary origin. The cores are surrounded by orbicule mantles, which consist of several alternating biotite- and plagioclase-rich shells. There are three types of orbicules in Kuohenmaa orbicular rock: proto-, small-, and large-orbicular types. Proto-orbicules have only a few shells, small orbicules ~ 50 shells in average, and large orbicules over 250 distinct shells. In addition to shells, one sample was observed to be associated with comb layering in the contact of proto-orbicular and large orbicular types. Structures and textures of the comb layer resembles those of the outer shells of large orbicules. The orbicules are embedded in interstitial coarse-grained groundmass that forms locally almost pegmatitic patches. The petrographic observations were acquired from eight samples or sample photographs gathered from different collections. A mineral chemistry dataset was measured from a single large orbicule from the University of Helsinki collections. The main minerals of the Kuohenmaa orbicular rock are plagioclase, biotite, microcline, muscovite, and chlorite. The shell textures vary from branching plagioclase-rich shells to fine-grained plagioclase- or biotite-rich shells. Branching shells are mainly oligoclase, but a few granular andesine crystals were detected in the core. Peculiar interstitial fibrous allanite masses were found in the inner branching plagioclase-rich shells. The plagioclase compositions generally follow a regular fractional crystallization trend from core to groundmass, but some changes towards more primary compositions are observed in the orbicule mantle. Plagioclase crystals display only minor compositional zoning, suggesting rather quick crystallization. Biotite is very aluminous (Al2O3 17.63–18.53) in composition, and the compositional changes seem to have somewhat positive correlation with plagioclase compositions, suggesting changes in their crystallization conditions. Injections of primary melt from a deeper source most likely caused the observed changes to more primitive composition in plagioclase and biotite composition. Through the detailed petrographic and geochemical studies, a model of undercooling caused by decompression driven fluid saturation is proposed as a mechanism for orbicule formation in the Kuohenmaa orbicular rock. Branching plagioclase with interstitial fibrous allanite masses and several fluid inclusions in plagioclase indicates separate aqueous REE-enriched melt and rapid crystallization. Further studies of fluid inclusions and REE-enriched phases could provide information of the fluid origin and crystallization conditions.
  • Hakala, Heini (Helsingin yliopisto, 2021)
    A NW–SE trending dike swarm cuts Miocene volcanic rocks in the Ibex Hills and Precambrian to Cambrian cratonic rocks and sedimentary strata in the Saddlepeak Hills and Salt Spring Hills in southern Death Valley, California. These dikes are aligned with Jurassic and Cretaceous dike swarms of eastern California that are linked to the Mesozoic North American Cordilleran magmatism. The Ibex Hills dikes have been previously dated and yield K-Ar date of 12.7 Ma and are coeval with the early stage of the Miocene Basin and Range crustal extension in Death Valley. This Master’s thesis examines in detail the geology, petrography and geochemistry of the previously unstudied dikes of Ibex Hills, Saddlepeak Hills and Salt Spring Hills of southern Death Valley and a ~90 Ma dike of Mojave Desert to discuss (1) their petrogenetic link to each other and (2) their geologic significance. The samples and field observations were obtained in 2019. The Ibex Hills samples are relatively fresh compared to the dikes of Saddlepeak Hills and Salt Spring Hills which are pervasively altered by secondary minerals and have been subject to low-grade metamorphism. The sub-solidus processes that have modified the mineral assemblages of the metamorphic dikes are also reflected in various degrees of major element mobility and LOI. The whole-rock geochemical composition of the Ibex Hills and Mojave Desert samples is trachyandesite to trachyte, the Saddlepeak Hills and Salt Spring Hills samples are andesites. One Saddlepeak Hills sample is basaltic and, based on mineralogy, texture and composition, represents a 1.1 Ga diabase intrusion. All studied samples are enriched in LREEs and LILEs and have negative Ta-Nb anomaly, representing magmas with typical subduction zone characteristics with enriched lithospheric mantle component in source. EPMA and in situ LA-MC-ICP-MS analysis of plagioclase phenocrysts of two Miocene samples of Ibex Hills shows variation in anorthite content and 87Sr/86Sr ratios across phenocryst profiles indicating open-system magma chamber evolution with episodes of recharge, hybridization and assimilation during the crystallization. Variation in anorthite content and 87Sr/86Sr ratios between samples suggest heterogeneities in the source magmas. The studied dikes represent multiple episodes of dike emplacements in southern Death Valley. The Miocene dikes of Ibex Hills, coeval with the Basin and Range crustal extension, indicate an early period of southwest directed extension in the southern Death Valley. The metamorphosed dikes of Saddlepeak Hills and Salt Spring Hills represent one or more episodes of older dike emplacement and could be coeval with the Mesozoic magmatism of North American Cordilleran orogeny and the Cretaceous dike of Mojave Desert. However, geochronological analysis is needed to verify the exact ages of these dikes.
  • Hankaankorpi, Tuuli (Helsingin yliopisto, 2021)
    The study area is Hyrylä groundwater area, located in southern Finland, in the city center of Tuusula. Hyrylä groundwater area is class 1 groundwater area, and it is classified as a chemical risk area. The Koskenmäki water pumping plant, owned by Keski-Uudenmaan Vesi Kuntayhtymä, is in the groundwater area, where on average 1000 m3 of water is pumped daily for domestic use. The groundwater area is situated in a southwest to northeast orientated esker which is a part of a bigger esker series starting from I-Salpausselkä in Hyvinkää. There is a big southwest to northeast orientated shear zone in the bedrock under the groundwater area where Lake Tuusulanjärvi and Tuusula-river follow the shear zone. The aim of this study was to research the interactions between river water and groundwater in the Hyrylä groundwater area and to get a better understanding of the geology of the area. Additionally, the movements of the groundwater were studied. Based on earlier studies the groundwater is discharging to the Tuusula-river near the Koskenmäki water pumping plant and the river water has been recharging to the groundwater. There are contaminated areas surrounding the old gas station in Hyrylä, where the soil and groundwater are contaminated with oil hydrocarbons, hence it was important to study where the water to Koskenmäki water pumping plant is coming from. Effects of the shear zone to the movements of the groundwater and to the amount of water available for pumping were also examined. The groundwater-river water interactions were studied with thermal methods and seepage meters. Isotopic and chemical tracers were analyzed from the water samples, which were collected from the groundwater observation wells, groundwater discharging to Tuusula-river and from the river water itself. A 3D geological structure model of the groundwater area was made based on earlier gravimetric measurements and drillhole data. The water table measurements from the observation wells were taken at the same time when the water samples were collected. Based on the 3D structure model a groundwater flow model was made to explain the movements of groundwater in Hyrylä. The geology of the groundwater area was examined with ground-penetrating radar, but the measurements were not successful and did not give any useful data for making the 3D model. The results of this study show that the groundwater is discharging to the Tuusula-river near the Koskenmäki water pumping plant. Based on the water analyses done, there was only one water sample with surface water mixed in it. 3D modeling gave a clear picture of the bedrock surface and cross-sections of the soil structure. According to the groundwater flow model, groundwater is flowing to the Koskenmäki water pumping plant from southeast. To the shear zone groundwater flows mostly from east and southeast. From the northwest part of the groundwater area the groundwater is flowing via northeast to the northern parts of the shear zone. The contaminated areas are not in the flow path to Koskenmäki water pumping plant. Based on the water analyses, groundwater discharging to the western parts of Tuusula-river is from a different source than the water discharging to the eastern parts of the river. In the shear zone the groundwater flow direction is to the south and the groundwater discharges to the river southwest of the Koskenmäki water pumping plant.
  • Laasio, Emmi (Helsingin yliopisto, 2020)
    As a part of constructing the upcoming repository for spent nuclear fuel ONKALO®, Posiva Oy is investigating the hydrogeological structures of Olkiluoto bedrock. Posiva Flow Log (PFL) drillhole measurements are an important part in characterization of bedrock’s hydraulic properties. The measurements are conducted both from the surface and in the study site of ONKALO tunnel network. Results are used widely at the site from the planning of construction to the water conducting fracture characterization. PFL equipment are capable of measuring groundwater flow originating from a single fracture which enables small scale detection of transmissive fractures in bedrock. Equipment measures temperature variations in a water flow inside an isolated test section to determine the flow rate. Several other equipment for groundwater flow measurement are introduced to highlight the accuracy of PFL. Fractures measured with PFL DIFF were 3D modelled in twelve ONKALO pilot holes (ONK-PH13-20, ONK-PH23, ONK-PH26 and ONK-PH28-29) using FracMan software suitable for fracture network modelling. 3D model described the fracture locations with fracture orientation and pilot hole transmissive fracture traces projected to tunnel walls. Brittle fault zone intersection between the chosen pilot holes were also modelled. Three of the pilot holes (ONK-PH23, ONK-PH28 and ONK-PH29) were selected for the fracture correlation. Pilot hole transmissive fractures were connected with tunnel wall water leaking fractures located with systematic mapping and water leakage mapping. Criteria for connecting the fractures were fracture location, water leakage and fracture orientation. Structure intersections with brittle fault zones were studied individually for each pilot hole. 433 meters of ONKALO tunnels were included in the correlation with total 20 of pilot hole transmissive fractures and 18 tunnel wall water leaking fractures according to systematic mapping. 100 % of ONK-PH23, 75 % of ONK-PH28 and 16,7 % of ONK-PH29 pilot hole transmissive fractures were correlated with tunnel wall water leakages in the corresponding depths. Counterparts were found for nine fractures of total 20 studied fractures based on the listed attributes. Fracture correlation was unsuccessful with 11 of the observed transmissive fractures. Study produced new data for the possible fracture correlations and hydraulic connections were produced in the pilot hole areas. Views and opinions described in this thesis are interpretation of the author and do not necessarily represent Posiva’s views.
  • Galvin, Keith (Helsingin yliopisto, 2020)
    A seismic reflection survey was carried out at the Hannukainen-Rautuvaara Iron (Fe), Copper (Cu), and Gold (Au) deposits as part of the HIRE (High Resolution Reflection Seismics for Ore Exploration, 2007-2010) project. The main discovery from this survey was a regional structure showing three reflective layers dipping to the southwest. The top of this package of reflectors is currently planned to be mined at Hannukainen. The deeper parts of this package may have potential continuation of the economically viable deposits seen at shallow depths. In this work, a target-specific, amplitude-preserving workflow for profiles E1 and V5 of the Hannukainen-Rautuvaara HIRE seismic data will be formulated and applied. Then seismic amplitude vs. offset (AVO) and attribute analyses will be used to analyse the reflective layers and identify potential areas of interest for further study. This is a burgeoning area of seismic research, AVO analysis is typically used in hydrocarbon exploration and has only been sparsely used in hard rock settings for mineral exploration. Attribute analysis is more common in hard rock environments, but still underutilised. The seismic reflection data were re-processed focusing on retaining the high-frequency content of the seismic signal, this is key for further analysis. The results of the AVO analysis consist of determining the AVO class of the responses seen across the CMPs of two selected AVO horizons. AVO product and Poisson’s ratio change across the horizons were calculated, and an area of interest was identified from the correlation of these parameters. Attribute analysis was done using the seismic attributes envelope, first derivative envelope, Hilbert Transform, relative impedance, phase, weighted instantaneous frequency and dip. The amplitude attributes (envelope, first derivative envelope, Hilbert Transform, relative impedance) were useful in determining the areas of the reflector package that showed the strongest amplitudes and selecting horizons on the uppermost reflector for AVO analysis. Phase and weighted instantaneous frequency helped determine the continuity of the reflector package which revealed a clear four-layer signature, differing form the earlier three-layer interpretation. The dip attribute showed vertical anomalies, some of which correlated with mapped faulting in the area. Detailed interpretation of the geophysical results requires better borehole coverage, and petrophysical work, to tie in the seismic data results to the alteration and mineralisation. With open pit mine planning ongoing in the study area, the identification of deep-seated mineral deposits will have direct impact on the planning of the mine and the future of exploration in Hannukainen-Rautuvaara.
  • Rinne, Lauri (Helsingin yliopisto, 2021)
    Kappa-parameter (κ) is used to estimate the decay of seismic spectral amplitudes with frequency and is the sum of regional kappa (κr) and site-specific kappa (κ0). The site-specific kappa (κ0) parameter in Olkiluoto (Southwestern Finland) is generally small, approximately 0.002 to 0.004. These values, although smaller, are in the same range that have been found in Eastern North America, where kappa is around 0.006. In Western North America kappa is around 0.04. In Europe, e.g., in alpine region, kappa value is around 0.025. The kappa-value was studied by analysing microearthquake recordings gathered by Posiva Oy’s seismic monitoring network from 2016 to 2019. From these microearthquakes 51 microearthquakes were selected and used in the analysis. All these microearthquakes occurred relatively close to the monitoring stations, from tens of meters to few hundred meters. Each of the events were detected by multiple sensors and the total number of microearthquake registrations used in this study was 297. From these recordings the κ0 was calculated for each component (two horizontal and one vertical). Total number of calculated κ0 values was 473. The kappa-method used was the original introduced by Anderson and Hough in 1984. Besides using earthquake data, the site-specific kappa was also calculated from excavation blasts in Olkiluoto for comparison. Blasting related kappa was smaller than the one calculated from microearthquakes, with average values between 0.0012 and 0.0017. The number of blasts used to calculate κ0 was quite small and the results may not be statistically relevant. Results are in line with similar study areas around the world – harder rock has lower κ0 values
  • McKevitt, Bláthnaid (Helsingin yliopisto, 2020)
    Phosphate is reported to be subject to “high supply risk” by the EU Commission (European Commission 2017). At present, the Siilinjärvi mine in Finland is the only mine in the EU producing phosphate. Optimising the productivity of the Siilinjärvi mine is crucial to address the demand for phosphate within the EU. The current production prognosis of the mine is to the end of 2035. To improve the prognosis of the mine, an exploration program is being undertaken to investigate the extent of the deposit and possible locations for new pits. The main area of interest is the area south of the current Särkijärvi pit. Exploration drilling is limited in this area due to obstacles created by infrastructure of the mine, including the factory area and gypsum pile. To address this, 3D passive source seismic, 2D active-source reflection seismic, Ground Penetrating Radar (GPR) and magnetic surveys were conducted at the Siilinjärvi mine site as part of the H2020 Smart Exploration project. This study focuses on two of the acquired active-source seismic reflection profiles, SM2 and SM3. The aim of the study is to determine the depth and lateral extent southern continuation of the deposit in the area south of the Särkijärvi pit, next to the gypsum pile, and create a 3D model of the Siilinjärvi deposit based on the obtained results. In addition, obtaining information on waste rocks and zones of weakness, such as shear and fracture zones, is also of interest as this information is critical for mine planning. The main focus for seismic data processing was to improve the signal-to-noise ratio. Strong amplitude S-waves and unclear first-breaks were limitations found in the data. As a consequence, in addition to bandpass filtering, seismic line SM2 required a combination of attenuation and muting to supress the impact of S- waves. Seismic line SM3 had a lower data quality in comparison to that of SM2. The suppression of S- waves had a negative impact on the near-surface reflections along SM3 and therefore was not carried out. The GPR and magnetic data were processed using standard workflows. The active-source seismic survey was successful in determining the depth and the lateral extent of the southern continuation of the Siilinjärvi deposit. A 3D model of the deposit was created based on the obtained seismic images. This model expands on the previous model and indicates that the carbonatite- glimmerite deposit expands towards the W, beneath the gypsum pile. This information can be used as a guide for future drilling in the area. In addition, information was obtained on zones of weakness and the waste-rock dike network. Sub-horizontal to gently dipping reflections observed in the seismic data were interpreted as diabase dikes. On a smaller scale, GPR measurements detected shallower near-surface features which are also interpreted to possibly be dikes. For some features, a correlation could be made between the various geophysical measurements. The carbonatite-glimmerite deposit was found to be associated with elevated magnetic total field (nT) values.
  • Huovari, Iiris (Helsingin yliopisto, 2021)
    Espoossa Nuuksion kansallispuiston lähettyvillä sijaitsevan Suomen luontokeskus Haltian kävijämäärät ovat jatkuvasti nousseet sen avaamisesta lähtien. Nuuksion geologinen historia on todella mielenkiintoinen, ja sitä voisi tulevaisuudessa saada luontokeskuksen kävijöiden tietoisuuteen. Alueen geologista historiaa tutkitaan tässä tutkielmassa laajasta näkökulmasta ottaen huomioon erityisesti viime jääkauden loppuvaiheen vaikutus alueen maa- ja kallioperään sekä selvittämällä jääkauden jälkeisen maaperän, ilmaston ja kasvillisuuden kehitystä. Erityistä huomiota kiinnitetään alueelta löytyvään pieneen suohon, jonka kehitystä selvitettiin siitepölyanalyysin sekä raekoon ja orgaanisen aineksen määrän muutosten avulla. Suon keskeltä kairatusta profiilista tehtiin lisäksi kolme ajoitusta, jotta sen syvyysulottuvuus saatiin kiinnitettyä aikaan. Samalla saatiin ikä suoaltaan turpeen muodostumiselle. Uurrehavaintojen sekä rannansiirtymisen avulla pyritään selvittämään suoaltaan ja Haltian ympäristön kehitystä. Rannansiirtymisaineiston perusteella tuotettiin karttoja ja video, jotka havainnollistavat alueella vallinneen muinaisen Itämeren vaiheiden vaikutusta maisemankehitykseen. Uurteiden perusteella jäätikkö virtasi alueen yli ensin pohjoisluoteesta ja lopuksi luoteesta. Suoaltaan pohjalla tavataan karkeampaa materiaalia soraisesta diamiktonista karkeaan silttiin, joka viittaa Baltian jääjärven laskeneen äkillisesti valtamerenpinnan tasolle. Tuotetusta rannansiirtymiskäyrästä selviää, että tutkittava suo on kuroutunut Yoldiamerestä noin 11 400 vuotta sitten. Alueelta löytyvän muinaisrantakivikon alatason perusteella Ancylusjärvivaiheen maksimi sijaitsee Nuuksiossa korkeudella 65 m mpy. Suosta löytyneet siitepölyt kertovat alueella vallinneen aluksi metsätön ja avoin kasvillisuus, jossa vähitellen koivut lisääntyivät. Koivun ollessa valtapuulajina ei alueen ympäristö kuitenkaan ollut vielä täysin metsittynyt suuren ei-puumaisten maakasvien osuuden perusteella. Leppä yleistyi alueella 10 300–9 800 vuotta sitten. Lehmus saapui alueelle 8 500–8 300 vuotta sitten ilmaston lämmetessä. Ilmasto alkoi tästä hieman yli 2 000 vuotta myöhemmin kuitenkin vähitellen viilentyä, ja kuusi yleistyi alueella noin 5 100–4 600 vuotta sitten. Tällöin jalopuut väistyivät vähitellen kuusen tieltä. Metsä muuttui kuusen saapumisen myötä ensin havupuuvaltaiseksi ja lopulta nykyisenlaiseksi sekametsää muistuttavaksi metsäksi. Suoaltaan umpeenkasvu ja sitä kautta soistuminen alkoivat sen reunoilta, ja umpeenkasvu oli todennäköisesti pääosin pohjanmyötäistä. Suoaltaan keskiosat ovat soistuneet kokonaan viimeistään 3 300 vuotta sitten turpeen silmämääräisesti määritetyn alaosan ajoitusiän ollessa 3 375 ± 30 vuotta. Suon turve muuttui lopullisesti saravaltaisesta rahkavaltaiseksi aikaisintaan 2 250 vuotta sitten.
  • Kettunen, Kia (Helsingin yliopisto, 2021)
    Ilman saastuminen on maailmanlaajuinen ongelma ja ihmisen toiminta lisää merkittävästi kohonneita epäpuhtauksia ilmakehässä. Merkittävimpiä päästölähteitä ovat fossiilisten polttoaineiden käyttö, energiantuotanto, teollisuus, maatalous, kotitaloudet ja jätehuolto. Happamoittava rikki-, typpi- ja ammoniumlaskeuma on ollut yksi suuri ongelma lisääntyneiden päästöjen myötä, mutta erityisesti rikin ja typen oksidien päästöjä on pystytty vuoden 1990 tasosta vähentämään onnistuneesti. Vuonna 1975 aloitettiin valtakunnallinen lumen seurantatutkimus 53 eri pohjaveden seuranta-asemalla. Tämän tutkielman tarkoituksena oli tarkastella valituilla asemilla talviaikaisen ilmaperäisen laskeuman pitoisuuksia ja havainnoida niiden mahdollisia vaikutuksia alueen pohjaveteen. Lisäksi haluttiin tarkastella, sopiiko tämänkaltainen pitkäaikainen seuranta-aineisto tilastolliseen tarkasteluun. Seuranta-asemista valittiin kuusi asemaa siten, että ne kattavat Suomen maantieteellisesti mahdollisimman laajasti, asemia olisi sekä hiekka- että moreenialueilla ja näytteenotto olisi aloitettu ainakin osalla asemista jo vuonna 1975. Asemista päädyttiin valitsemaan Valkealan, Parikkalan, Haapajärven, Kuusamon, Lumiahon ja Sodankylän asemat. Aineisto saatiin valmiina Suomen ympäristökeskukselta ja se on saatavissa myös pohjavesitietojärjestelmästä (POVET). Lumi- ja pohjavesinäytteistä mitatuista muuttujista valittiin ne, joita oli mitattu molemmista näytetyypeistä tarpeeksi pitkältä aikaväliltä tilastollisen tarkastelun onnistumiseksi. Analyysituloksia tarkasteltiin ensin asemakohtaisesti, jonka jälkeen lumi- ja pohjavesinäytteille tehtiin erilaisia tilastollisia analyyseja: ei-parametrinen ja parametrinen t-testi, pääkomponenttianalyysi sekä korrelaatioanalyysi. Lisäksi aineistoa tarkasteltiin visuaalisesti laskeuman ja pohjaveden välillä mahdollisesti esiintyvien yhteyksien löytämiseksi. Selvin yhteys laskeuman ja pohjaveden välillä löytyi happamoittavan laskeuman ja pohjaveden happamoitumista indikoivien muuttujien välillä. Happamoittavan kuormituksen lasku näkyi pH:n sekä alkaliniteettipitoisuuden nousuna ja sulfaattipitoisuuden laskuna. Raskasmetallipitoisuuksissa havaittiin myös yhteys laskeuman ja pohjaveden välillä. Muiden muuttujien osalta selvää yhteyttä pitoisuuksissa ei havaittu. Laskeuman ja muiden pohjaveden koostumukseen vaikuttavien tekijöiden suhteen arviointi havaittiin hankalaksi, mutta esimerkiksi metsähakkuiden vaikutus pohjaveden nitraattipitoisuuksiin löydettiin. Jotta tilastollinen tarkastelu oli luotettavaa, tuli aineistosta ensin poistaa tai korjata erilaisista virhelähteistä johtuvat poikkeamat. Aineiston todettiin sisältävän monia erilaisia virhelähteitä liittyen näytteenottoon, näytteiden analysointiin ja tuloksien kirjaamiseen. Lisäksi muutokset määritysrajoissa, mittaustarkkuuksissa ja menetelmien tarkkuuksissa vuosien varrella tuli ottaa huomioon. Ennen tilastollista käsittelyä virheet ja poikkeamat tuli havaita sekä korjata tai poistaa. Toimiviksi jo toteutetuiksi parannuksiksi todettiin Suomen ympäristökeskuksen vuonna 2013 julkaisema laatusuositus ympäristöhallinnon vedenlaaturekistereihin vietäville tiedoille sekä vuoden 2016 jälkeinen keskitetympään analysointimalliin siirtyminen. Poikkeamiin aineistossa voisi kuitenkin jatkossa kiinnittää huomiota jo analyysivaiheessa ja erityisesti tuloksia kirjatessa, jotta aikaa vieviltä korjausprosesseilta jatkossa vältyttäisiin. Korjausten jälkeen aineisto on kuitenkin hyvin käyttökelpoista ja mahdollistaa laajamittaisenkin laskeuman ja pohjavesien pitoisuuksien tilastollisen tarkastelun.
  • Laakso, Viveka (Helsingin yliopisto, 2019)
    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 currently being investigated to ensure continuation of the mining operations also after 2035. The Siilinjärvi carbonatite-glimmerite deposit has been intruded by multiple waste-rock diabase dykes crosscutting the deposit and by a tonalite-diorite intrusion, creating a complex geological setting. To study the depth and lateral extent of the deposit, the diabase dykes, tonalite- diorite, major zones of weakness and the geophysical anomalies related to these features, active-source 2D reflection seismic, Ground Penetrating Radar (GPR) and magnetic surveys were conducted at the Siilinjärvi mine site in fall 2018 as part of the H2020 Smart Exploration project. Understanding the locations of the waste rocks and fracture and shear zones is crucial for mine planning and optimising the production prognoses. The interest of this study is in particular on imaging the sub-horizontal diabase dykes, whose locations and continuation are harder to predict. The focus area of this study is in the southern end of the Särkijärvi pit and the area just south of the pit, where the well-known geology of the pit can be used to constrain the interpretation. Processing of the reflection seismic data focused especially on the static corrections and the methods used to improve the signal-to-noise ratio. This was done so that the processed data could serve as a reference for new processing methods, focused on these aspects, developed within the Smart Exploration project and planned to be tested with the Siilinjärvi data. The static corrections were constrained by the limited number of first-break picks clear enough for picking from the data. In addition to the bandpass filtering, suppressing the S-wave arrivals was found to be crucial for increasing the signal-to-noise ratio, particularly in the near subsurface which is the main interest area of this study. The GPR and magnetic data were processed with standard processing workflows. The lateral and depth extent of the Siilinjärvi carbonatite-glimmerite deposit, the large-scale sub-horizontal waste- rock dykes and the major zones of weakness are imaged with the active-source reflection seismic data. The ore deposit is associated with a complex reflectivity pattern due to the intruded diabase dykes and tonalite-diorite, and the fracture and shear zones. The interpreted diabase dykes correlate with a large-scale sub-horizontal waste-rock dyke model created from the production drilling data as part of the Smart Exploration project, supporting the continuation of the sub-horizontal diabase dykes south of the pit. With GPR data, the smaller- scale sub-horizontal dykes within the shallow subsurface (<30 m) are imaged. The GPR data correlates with a detailed waste-rock dyke model created as part of the Smart Exploration project from the southern end of the Särkijärvi pit based on geological mapping, GigaPan images and a 3D photogrammetry model. The reflection seismic, GPR and magnetic data have very different scales and these different data are suitable for different purposes in mineral exploration and mine planning at Siilinjärvi. The carbonatite-glimmerite ore is associated with elevated magnetic total field values and at a larger scale the deposit could possibly be followed with magnetic surveys. With reflection seismic method, the large geological structures can be imaged at depth, and the 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.
  • McDonald, Isabel (Helsingin yliopisto, 2020)
    Talc is a problematic alteration mineral at the Kevitsa Ni-Cu-(PGE) mine in Sodankylä, Finland, and its distribution and control were assessed in this thesis. Kevitsa is a polymetallic mine hosted in an ultramafic intrusion, extracting Ni, Cu, Co, Au, Pt and Pd, which are of increasing importance in green energy technologies. Talc – a common alteration product in ultramafic rocks – detrimentally interferes with the recovery of copper in the flotation stage of ore processing when concentrations exceed 5 wt. %, thus affecting the economics of mine operations. It was found different talc concentrations had different spatial associations and controls, with three dominant styles identified, and a multi-stage genesis of talc alteration is proposed. The talc styles identified in the study are as follows: (style 1) pervasive talc-chlorite alteration, (style 2) talc-dolomite alteration haloes proximal to dolomite veins and (style 3) talc on brittle structures, associated with magnetite. Low values of talc between 0.2-0.5 wt.% (style 1) were found to have no preferential spatial distribution, occurring as background alteration throughout the intrusion. Intermediate values (between 1-5 wt. %) were associated with late brittle fractures and structures (style 3), with a notable association with the NE-flt-rv1 fault zone. Style (2) was found to have a dominant structural control, specifically being associated with north-south trending structures. Dominant structures with this association identified are NS-flt1_flt-002 and NS-flt-2_flt-009. Highest values (commonly exceeding >10 wt. %) manifest themselves as alteration haloes proximal to veins, where talc-carbonate replaces the intercumulus mineral phases. Here it is proposed that ‘low talc’ alteration, style (1), was the first talc association to occur, generated by late magmatic fluids or regional metamorphism accompanying amphibole and serpentine alteration. The association observed as style (2) was likely generated by the infilling of north-south trending structures by carbonate-talc veins through metasomatism by a CO2 rich metamorphic fluid, perhaps delivered by a deep-seated structure, often generating talc values in excess of 10 wt.%. The third stage is proposed to be talc enrichment via meteoric fluid percolation, after exhumation. This generated talc along brittle structures associated with magnetite style (3), and talc-carbonate concentrations may also be upgraded at this stage. Further enrichment of talc is observed at the surface, attributed to freeze thaw-cycles of permafrost upgrading talc values. The identification of these processes and controls on talc will not only have implications for the economics of Kevitsa as high talc zones can be avoided, but findings may have useful applications for mining of similar deposits in the Central Lapland Greenstone belt such as the nearby Sakatti Cu-Ni-(PGE) project, when it enters production.
  • Barron, Pelayo (Helsingin yliopisto, 2020)
    Sakatti is one of the most significant magmatic Ni-Cu-PGE deposits discovered in the last decade. With a reported 44.4 Mt resource, is a polymetallic deposit with grades of: 1.90 % Cu, 0.96 % Ni, 1.40 g/t PGE; Anglo American ltd. report (2019). Sakatti is located within the Early Proterozoic Central Lapland Greenstone Belt (CLGB), Finland. The deposit is hosted by three ultramafic magma–derived olivine cumulate bodies: Main body, North-East body and South-West body. Very distinctive ore types can be recognized according to several academic studies: A) Massive ore containing an average 3.04 % Ni and 7 % Cu and showing a wide range in Ni/Cu (average of 1.42) and Pt/Pd of 0.98 (Ahvenjärvi 2015); B) Stockwork ore that is extremely copper-rich containing an average 0.68 % Ni and 26.17 % Cu, with Ni/Cu of 0.03 and Pt/Pd of 0.85 (Fröhlich 2016); C) Disseminated ore, where sulfides form a wide halo around the massive and stockwork ores, again being highly copper-dominated containing an average 0.07 % Ni and 0.61 % Cu. Ni/Cu and Pt/Pd values for disseminated ore are 0.13 and 1.83 respectively. The aim of this study is to shed some light on the genesis of the Sakatti´s disseminated ore and the massive sulfides from the NE and SW bodies. The disseminated mineralization was studied more in depth. Moreover, a comparison with other major Ni-Cu-(PGE) magmatic deposits in the world was done. Overall the disseminated ore seems to be dominated by a patchy texture with low connectivity but high wettability. Chalcopyrite is the predominant sulfide mineral and forms intergrowths with the texturally earlier pyrrhotite and pentlandite. These primary phases are widely altered to secondary phases like marcasite, millerite, violarite, pyrite, bornite, covellite and magnetite. Only a few platinum-group minerals (PGM) were found. They all are tellurides or bismuth-tellurides of which the merenskyite-moncheite-melonite series minerals are the most abundant. The chemical composition of the disseminated ore revealed compositional and fractionation similarities with both the massive and stockwork ores. When recalculated to 100 % sulfides and normalized to mantle values, the disseminated ore showed a moderate content in Ni, Co, IPGE and Rh close to the massive mineralization, and a higher enrichment in PPGE, Au and Cu with similar evolution patterns as the stockwork vein sulfides. This led to a fractionation path of the disseminated sulfide phase that seemed to be a mixture of the other two main ore types. Thus, it is suggested that the disseminated ore is formed by a combination of monosulfide solid solution (MSS) and intermediate solid solution (ISS), which originated from a sulfide melt genetically linked to the one that gave rise to the massive and stockwork ores. The massive sulfides from the NE and SW bodies show compositional similarities with the massive ore from the Main body that suggest a share origin and genesis. The Oktabr'sky, Noril'sk-Talnakh, disseminated ore, when normalized to mantle values, shows similar Ni, Co, PGE, Au and Cu distribution as the Sakatti´s disseminated sulfides. Moreover, the Oktabr'sky deposit seems to have similar S/Se vs Pt+Pd evolution trend to the one from Sakatti deposit.
  • Ioannou, Christos (Helsingin yliopisto, 2020)
    The Siivikko-Kellojärvi area forms the southern part of the Kuhmo greenstone belt. The rocks in the area are mainly tholeiitic and komatiitic lavas. In some occasions primary textures can still be observed in the rocks, including spinifex and pillow lavas in mafic and ultramafic volcanic rocks, evident of marine environment. The purpose of this M.Sc. thesis is to investigate the possible hydrothermal alteration processes involved in the formation of the Siivikkovaara Ni-Cu-Zn-Pb mineralized sulfide body. The goal of the M.Sc. thesis is to examine the Siivikkovaara Ni-Cu-Zn-Pb mineralized body using mineralogy, whole-rock geochemistry, mineral chemistry and sulfur isotope geochemistry (δ34S values). Komatiites in the present study have a Cr content of 0.28-0.62 wt.% and show a positive correlation between MgO and Cr, following a cotectic olivine-chromite cumulate trend. Analyses of the studied samples show an average Pd + Pt value of 300 ppb. Given the results, the mineralization represents an enriched body in Pd + Pt, relative to the majority of deposits in Finland. Samples presented in the current study are mildly depleted in (La/Sm)N and generally LREE, relative to chondrite values. The analysed minerals show an average δ34S value of 0.45‰. The source of sulfur is magmatic and cannot be related with any other geological setting. Enrichment in some elements may be attributed to later post-magmatic modification of the mineralization and remobilization of the elements. Komatiitic rocks of the studied samples were derived from Cr-saturated magmas. Cr depletion in tremolite rock may be related with alteration processes or post-magmatic modification. REE data suggest a rather primitive and uncontaminated magma for the studied samples. The studied komatiites are principally of Aluminum-Undepleted komatiite-type. Owing to the poor exposure and extensive post-magmatic modification, any solid conclusions on the origin of the mineralized body are rather difficult. Therefore, more work can be done in the studied samples to further examine the assumption of a possible black-smoker setting.
  • Väkevä, Sakari (Helsingin yliopisto, 2019)
    The reflection seismic surveying method is useful when conducting mineral exploration in the crystalline bedrock because of its good depth extent and resolution. However, the traditional experiments with active sources are expensive and difficult to carry out, especially in remote areas or in conservation areas where mineral exploration is limited due to environmental reasons. Recently, a number of theoretical advances have proven that passive soundings utilizing ambient seismic noise can provide new opportunities for seismic imaging and contribute to data generation for reflection seismic surveys, without the need for explosive or vibratory sources. One of the most promising new methods is seismic interferometry (SI), where the impulse response between two receivers is reconstructed by correlating their signals with each other. COGITO-MIN is a joint project between the University of Helsinki, the Geological Survey of Finland, Polish Academy of Sciences, and industrial partners with the aim of investigating and developing new cost-effective seismic exploration methods in the crystalline bedrock. Within the framework of the project, a passive seismic experiment was carried out in which 45 three-component geophones were deployed for a month in the vicinity of the polymetallic Kylylahti Mine in Polvijärvi, northern Karelia, where the mining operator is the Swedish metal company Boliden. The original purpose of these geophones was to collect data suitable for detecting underground cavities related to underground nuclear explosions. The institute that collected the data was CTBTO (Comprehensive Test Ban Treaty Organization) whose task is to monitor the treaty in the pre-ratification stage. The purpose of this Master's thesis was to develop an SI workflow for the three-component data and to investigate the method's performance in an area where local geology is known after nearly 40 years of exploration and consequent mining operations. The specific scientific objectives of the thesis are (1) to demonstrate the usefulness of collecting three-component data in conjunction with or instead of single-component data, (2) to assess the noise-based SI methods used in previous studies and to improve their stability in the crystalline bedrock, and (3) to investigate the possibilities of SI from an operational perspective. Seismic velocities obtained through laboratory measurements were merged with geological and density models of the target area provided by Boliden. The resulting velocity and density grids were then used as the basis for waveform modelling, and the results from SI were validated against them. The starting point for SI was the noise-driven approach where 'each sample matters'. The interferometric workflow is built on the Seismic Unix suite together with self-written algorithms that are based on theoretical evaluations. SI is followed by an imaging workflow, which provides the basis for the reflectivity profiles. The thesis work focuses on five components of the Green's tensor and the vertical, radial and transverse component of the impulse response. With the horizontal components, one can access the S-wave patterns in addition to the P-waves. As a specialty, the so-called sign bit normalization (SBN) method was also tested. The technique involves destroying much of the amplitude information of the original seismograms by only retaining the sign bit of each sample. According to the results outlined in this thesis, SBN can make it easier to image the weak reflectors of the subsurface. This type of seismic interferometry seems particularly suitable for the early stage of mineral exploration, where the explorer does not yet fully understand the target they are studying. The most important advantage of seismic interferometry, however, is its cost effectiveness, and its potential for reducing risks for the environment.
  • Harjama, Noora (Helsingin yliopisto, 2020)
    The seismic reflection methods produce high-resolution images from the subsurface, which are useful in structural studies of geology. Northern Finland features a complex Precambrian geological history, including massive extension and compression stages, which has been extensively studied. The xSoDEx survey is the most recent seismic survey carried out in northern Finland by the Geological Survey of Finland (GTK). The XSoDEx concluded four survey lines, which are located in Central Lapland Greenstone Belt (CLGB) in Sodankylä, Lapland. This thesis aims to find out whether the strong reflections shown in the xSoDEx Alaliesintie reflection profile, underneath the outcropping Archaean basement indicate a lithological contact or a fault zone. The Alaliesintie profile is characterized by Koitelainen intrusion, Archaean outcrops, and layers of younger Paleoproterozoic group rocks. The work was carried out in stages, with the use of the SKUA - GOCAD 3D modeling software. The four stages are: 1. Create a 3D geological model based on the Alaliesintie reflection section and geological bedrock observations. 2. Use gravity and magnetic geophysical data from the study area to improve model reliability. 3. Use the geological 3D model and petrophysical data to build a synthetic seismic forward mode. 4. Analyze and evaluate the modeling result for understanding the possible origins of the reflections. In the geological 3D model, I presented that the reflection would present lithological contacts and that the Archean bedrock would have folded and partly overthrust on top of the younger Proterozoic rocks. The seismic forward model is used as an experiment to test the geological 3D model’s lithological contact respondence to the synthetic seismic signal and to discover the possible reflector underneath the Archaean basement. The results present that the seismic forward model can be used to perform the reflections and that the geological 3D model presented similar reflections in the seismic forward model comparing to the original Alaliesintie reflection data.