Browsing by master's degree program "Geologian ja geofysiikan maisteriohjelma"
Now showing items 61-78 of 78
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(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
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(2022)Weak zones in bedrock might have an impact on the environment, safety and costs of rock construction projects. It is possible to locate them already in the pre-investigation stage with geophysical measurements. This study utilizes ground penetrating radar (GPR) data, seismic refraction data and the data from geological mapping aggregated during the first stage of the West Metro project, more specifically from two of its station areas (Keilaniemi and Otaniemi). The GPR and seismic refraction surveys are cost-effective ways to investigate the ground and the bedrock. Both methods are based on detecting waves – seismic and electromagnetic, respectively – on the surface after they have been transmitted and have travelled through the ground. In this study the West Metro geophysical data was re-examined with new methods to improve the analysis, specifically, the detection of the weak zones. Tomographic velocity models were produced from the seismic data. The processing of the GPR data was done so that especially the bedrock structures would be interpretable. It was noticed in the early stage of this study that the available refraction data was not necessarily suitable for seismic tomography. Despite this, processing of the data with new methods did produce new, improved results. From all the weak zones that were mapped in this study, eight were located close to the reviewed geophysical survey lines. From those eight, 75 % were detected with geophysical methods. Also, other possible structures of the bedrock were discovered with geophysical methods but were not detected during the geological mapping. Anomalies were detected in both the seismic tomography and the GPR results. These anomalies could be interpreted as weak zones. However, without reference data, the interpretation of the source of the GPR reflections and the seismic velocity deviations can not be confirmed. The most important conclusion of this study is that by using geophysical measurements it is possible to detect weak zones, and that such measurements should be used more in rock construction projects for bedrock assessments. The exact purpose for the use of geophysical methods should be taken into account already when planning the geophysical surveys to ensure best possible data for the purpose.
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(2022)Space weathering can be defined as the combination of physical and chemical changes that occur in material exposed to an interplanetary environment on the surface of airless bodies. This process produces amorphous surface layers often containing small opaque particles such as nanophase metallic iron (npFe0). This darkens the topmost layer resulting in alterations in material spectroscopic features.Eventually it can lead to misinterpretation of remotely sensed data in the visible- near-infrared (VIS-NIR) spectrum. The goal of this research is to simulate solar wind effects on asteroid spectra through low energy 1 keV hydrogen ion irradiation of meteorite powder samples and measure the changes in their reflectance spectra. This allows to understand how space weathering depends on the mineralogy of the material. We used Bjurböle (L/LL4), Avanhandava (H6) and Luotolax (Howardite) meteorites. H+ ion irradiation was carried out on powdered samples compressed into pellets. The pellets were placed into a vacuum chamber with pressure between 1.2 x 10 -7-2.4 x 10 -7 mbar for the whole experiment. To simulate solar wind irradiation, H+ ions were used with 1 keV under three fluences; 1 x 1017, 2 x 1017 and 5 x 1017 ions/cm2. Subsequently reflectance spectra of the samples were measured and processes using Modified Gaussian Model (MGM) to derive key spectral parameters. Both chondrites show significant reddening in the VIS region. Bjurböle being an LL, it is more oxidized than Avanhandava. The reddening in the NIR region is more significant in Avanhandava than in Bjurböle. My work indicates that even for low-energy solar wind conditions, the chondritic materials (Q/S-type asteroids) with high olivine content and/or higher fayalite (Fa) compositions are more susceptible to silicate absorption bands reduction. Luotolax meteorite being howardite rich in orthopyroxene and clinopyroxene, shows VIS reddening but not observable band depth changes with increasing exposure to H+ ion irradiation. The smaller change in Luotolax may be due to higher pyroxene resistance to low-energy ion irradiation. Overall, at short timescales and typical solar wind energies, VIS slope reddening is the most dominant factor in all three material compositions.
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(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.
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(2023)The island of Suur-Pellinki is located near the town of Porvoo in the southern Finland. The bedrock in the area consists of different rock types such as plutonic rocks and rock types that are rare in the southern Finland, for example agglomerate and different kinds of metavolcanites. The bedrock has undergone several tectonic events, of which Svecofennian orogenesis (1.9-1.8 Ga) has been the most notable. The orogenesis caused compression, extension and shearing of the bedrock, and signs of these stresses can be seen as fractures, folds, foliations and faults. The development of unmanned aerial vehicles, such as drones, has been significant in recent years. Thus, usage of them has increased in different fields of science, of which geosciences are not an exception as drones are used in data collecting. In this study, a drone was used to study outcrops of Suur-Pellinki. Four outcrops were photographed by a drone, and photographs were used to build three-dimensional models. The models were built in Pix4D and Metashape software using Structure-from-Motion photogrammetry. In addition, the models were exported to GeoVis3D software, in which orientation of fractures was studied. The aim was to study the bedrock with traditional fieldwork methods and technology that has not been used in the area. It was studied if three dimensional modelling can provide any significant additional benefits over traditional fieldwork methods. Moreover, the aim was to find ways to operate a drone efficiently and build three-dimensional models straightforwardly. The bedrock was found to be undergone extensional and differently oriented compressional events during the orogeny, and the maximum principal stress (σ1) orientations had been firstly NW-SE and later NE-SW. These stress orientations formed the main structures of the bedrock such as fractures, folds, and foliation, which is prevalent in metavolcanites of the area. In addition, some strike-slip faults were seen in the area, which have not been studied significantly in the previous studies. The three-dimensional models turned out to be useful in order to study the bedrock. Critically, building of the models was not fast and straightforward. The final resolution of the models is under three centimetres, which let to study even the smallest structures of the bedrock.
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(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.
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(2022)Korroosio voi heikentää kallioperään sijoitettavien ydinpolttoainejätteen säiliöinä toimivien kuparikapselien kestävyyttä. Kalliopohjavedessä esiintyvät sulfaatinpelkistäjäbakteerit pelkistävät sulfaattia korroosiota aiheuttavaksi sulfidiksi. Tämän vuoksi ydinjätteen loppusijoitukseen liittyen on tärkeää selvittää, kuinka paljon ja missä muodossa rikkiä esiintyy kalliopohjavedessä ja mistä sitä päätyy sinne. Sulfaatinpelkistäjäbakteerien esiintyvyys ja sulfaatinpelkistyksen intensiteetti on myös oleellista selvittää loppusijoitukseen liittyvien uhkien minimoimiseksi. Tutkimuskohteena oli Tupoksella sijaitseva 1033 metriä syvä Tupos 001 -kairareikä, joka sijaitsee Muhos-muodostuman savikiviympäristössä, joka muistuttaa ominaisuuksiltaan kuparikapseleiden bentoniittipuskuria. Kairareiän pohjavedestä oli 80-luvulla tehty mittauksia sulfaatin määrästä ja sen isotooppikoostumuksesta. Nyt kairareiän pohjavedestä oli määrä selvittää sulfaattisen, sulfidisen sekä muiden rikkiyhdisteiden eli niin kutsutun X-faasin pitoisuus ja isotooppikoostumus eri osissa kairareikää. Isotooppikoostumuksen perusteella oli tarkoitus selvittää rikin lähteitä ja sulfaatinpelkistyksen intensiteettiä kairareiässä. Pohjavesinäytteet kerättiin letkuprofiilimenetelmällä 100 metrin pätkissä. Pohjavesinäytteistä analysoitiin muun muassa alkuaineiden ja ionien pitoisuuksia spektrometrilla ja ionikromatografilla. Rikin isotooppikoostumus selvitettiin eri rikkifaasien erottelun jälkeen massaspektrometrisin menetelmin. Tupos 001 -kairareiän pohjavedestä havaittiin runsaasti sulfaattia noin 800 metrin syvyyteen asti. Myös sulfidia mitattiin kairareiästä kaikilta syvyyksiltä, minkä lisäksi sulfidipitoisuuksissa havaittiin selkeä piikki 600-700 metrin syvyydellä. Sulfaattisen, sulfidisen ja X-faasin sisältämän rikin δ34S-isotooppikoostumus oli samankaltainen kairareiän ylä- ja keskiosissa vaihdellen noin 6-10 ‰:n (CDT) välillä. Kairareiän pohjalla sulfidinen rikki muuttui selvästi köyhemmäksi ja sulfaattinen ja X-faasiin sitoutunut rikki puolestaan rikastuneemmaksi 34S-isotoopin suhteen. Tupokselta saadut mikrobiologiset tulokset osoittavat sulfaatinpelkistäjäbakteerien runsaan esiintyvyyden pohjavedessä. Tässä tutkielmassa havaittu korkea sulfaattipitoisuus ja sen lasku kairareiän alaosissa, sulfidipiikki sekä sulfaatin ja sulfidin isotooppikoostumus varsinkin kairareiän pohjalla tukevat mikrobiologisia tuloksia. Etenkin tutkimuksessa havaitun sulfidipiikin perusteella sulfaatinpelkistys voi paikoitellen tuottaa huomattavasti kohonneita sulfidipitoisuuksia, minkä perusteella mikrobiologinen sulfaatinpelkistys voi lisätä ydinjäte-säiliöinä käytettävien kuparikapselien korroosion riskiä. Rikkifaasien pitoisuuksiin ja niiden isotooppikoostumukseen on sulfaatinpelkistyksen ohella todennäköisesti vaikuttanut myös merivesi ja rikkimineraalit niin sedimenttikivessä kuin kiteisessä kallioperässäkin. 80-luvulla suoritettuihin rikkitutkimuksiin verrattuna tässä tutkielmassa kolmen eri rikkifaasin ja kattavamman näytemäärän tutkiminen tuotti aiempaa tarkempia tutkimustuloksia rikin geokemiasta Tupoksen kalliopohjavedessä.
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(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.
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(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.
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(2022)Peatlands are complex ecosystems that not only respond to external changes but also influence their environment. Permafrost peatlands have an important role in the global carbon (C) cycle as they store about 200 Pg of C. As permafrost thaws this C can be released either as methane (CH4) or carbon dioxide (CO2). In addition to these peatlands also emit nitrous oxide (N2O). Climate warming may change this sink-source balance of peatlands. Hydrological conditions are an important factor in peatland C dynamics. As permafrost thaws it can shift these ecosystems towards wetter or dryer conditions. Peat decomposition under dry conditions can have a strong positive feedback to climate change due CO2 emissions. Though wetter conditions can increase CH4 emissions. Through topography and hydrology, permafrost also affects vegetation dynamics. In this thesis I am examining peat profiles collected from two subarctic permafrost peatlands located in Kevo, Finland and Karlebotn, Norway. The profiles included an un-frozen active layer profile and a permafrost sample collected from inside a palsa mound. These samples were analysed for vegetation composition and peat properties (C and N content, C/N ratio and bulk density), they were also 14C dated and incubated. The purpose was to simulate a warmer climate to which these ecosystems will be exposed to in the future and observe how they will respond. The observations focused on the three most common GHGs of peatlands, CH4, CO2 and N2O. The permafrost samples showed potential for CH4 and CO2 emissions, whereas the active layer only emitted CO2. The CH4 emissions were interpreted to represent old CH4, whereas the CO2 was interpreted to be produced by the peat.
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(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.
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(2023)Macquarie Island is a subaerial fraction of oceanic crust where lithology from mantle peridotites to crustal gabbro, dolerite, and extrusive rocks are present, thus providing a unique opportunity to study geochemistry and petrology of the oceanic crust. Macquarie Island represents a mid-ocean crust ophiolite in which the potential geochemical modification of continental crust and effects of subduction initiation are absent. A genetic link between plutonic and extrusive rocks and processes leading to formation of the ophiolite sequence were studied in this thesis. A set of samples representing different rock types of the oceanic crust were studied petrographically as well as for whole-rock major and trace element geochemistry. Selected samples were studied for chromian spinel, silicates, and apatite major and minor component geochemistry. Harzburgites of Macquarie Island are depleted in trace element composition and are not a straightforward residue for the source of the crustal section of the island. Melt infiltration of basaltic melt into potentially former lherzolitic mantle source has been dominating process leading to formation of Macquarie Island oceanic crust. As a consequence to melt infiltration plagioclase-bearing wehrlites recrystallized and these rocks probably acted as a more enriched source for crustal rocks.Major and trace element data show that fractional crystallization has not been significant process forming the island. Extrusive basalts are more primitive in MgO and SiO2 contents and more enriched in REE contents compared to gabbroic rocks of the island. This could be explained by porous fluids migrating through oceanic crust modifying both major and trace element compositions of the samples or extrusive and gabbroic rocks forming from different mantle sources. This study shows that formation of oceanic crust is much more complex than often assumed simple model of fractional crystallization from mantle melt leading to formation of the oceanic crust, or a hypothesized gabbro-dolerite-basalt plumbing system forming the genetically linked crustal rocks.
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(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.
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(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.
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(2023)A new three-dimensional crustal and upper mantle P-wave velocity model and a Moho depth map of Finland and the surrounding area were constructed using kriging interpolation. The models are based on the latest wide-angle reflection and refraction (WARR) data from the Fennoscandian shield. The Moho depth map agrees with previous Moho maps but also shows new details in the large Moho depression in central Finland compared to the previous Moho maps. The new Moho features include a new Moho depth local maximum near the center of the depression and increased Moho depths extending to the northwest and south of the depression. The three-dimensional crustal and upper mantle P-wave velocity model differs from previous models by showing a non-existent high-velocity lower crust beneath the Wiborg Rapakivi Batholith. Both the Moho map and the velocity model exhibit distinct features within the tectonic provinces in the Fennoscandian Shield. The uppermost velocity model layer is shown to roughly correlate with general features of surface geology. Statistical analysis of Moho depth and P-wave velocity data was performed, and variogram models were fitted to capture spatial autocorrelation. Ordinary kriging was used to generate a Moho model with a 25 × 25 km grid cell size. The three-dimensional P-wave velocity model was constructed in two parts, with separate universal kriging schemes for the crustal and upper mantle velocities. The velocity model has a grid cell size of 50 × 50 × 1 km in the uppermost 4 km and a lower resolution of 50 × 50 × 2 km below 4 km depth. The presented models can be utilized for a variety of applications, including seismic source location, crustal effect correction for seismic tomography and teleseismic studies, and general modeling of large-scale tectonic processes.
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Using Three-Component Data for Seismic Interferometry Studies at the Kylylahti Mine, Eastern Finland (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.
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(2024)The traditional method for identifying sulfate soils has been the incubation method, which typically takes 9-19 weeks. However, in collaboration, the Finnish Environment Institute (SYKE), Geological Survey of Finland (GTK), and Åbo Akademi developed a faster hydrogen peroxide oxidation method for identifying sulfate soils and assessing acidity potential. This method allows for sulfate soil identification and acidity potential estimation in just a few hours. The hydrogen peroxide oxidation method was used to identify sulfate soils in the Helsinki region and to evaluate the method. The study areas included the Sunnuntaipalsta-field area in Malmi, the area associated with the relocation of Gasgrid’s gas pipeline in Pihlajamäki, and the Hermanninranta- Kyläsaari area. Sulfate concentrations determined by the oxidation method were compared with concentrations obtained through water extraction at the Helsinki geophysical, environmental and mineralogical laboratories (Hellabs) of the University of Helsinki's Department of Geology and Geophysics, and acid extraction at ALS Finland Ltd. In Malmi, the method worked well and reliably, indicating naturally acidified soil with relatively low sulfur concentrations. Deeper layers revealed potential acidic sulfate soil materials. In Pihlajamäki, the method was effective, identifying clear potential acidic sulfate soils even with samples consisting of clay fillings. Challenges arose in the Hermanninranta-Kyläsaari area due to contaminated fill soils with high pH values and various hydrocarbons. The lower layers of the samples were rich in organic matter (LOI > 10%), causing the hydrogen peroxide oxidation method to overestimate sulfate concentrations, resulting in deviations with both acid and water extraction results. Based on the results, the hydrogen peroxide oxidation method performs most reliably when loss on ignition (LOI) is < 10% and the pH change (ΔpH) after oxidation is less than 5 units. The method could be a valuable addition to soil investigations conducted by the City of Helsinki's construction services public enterprise, Stara, in their Street and ground laboratory. The method is effective and enables the rapid identification of potential acidic sulfate soils.
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(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.
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