Browsing by master's degree program "Geologian ja geofysiikan maisteriohjelma"

In this study, single-grain rutile techniques (rutile U-Pb geochronology, Zr-in rutile thermometry, rutile Nb-Cr systematics and trace element composition) are applied on Red Clay samples from Lingtai, central-southern Chinese Loess Plateau (CLP), to reveal more detailed information on provenance of the Red Clay and wind regimes responsible for transporting the particles from source to sink between 7 Ma and 2.6 Ma. The new rutile data are combined with previous zircon U-Pb data from Lingtai and nearby Chaona to strengthen the interpretations with multi-proxy approach. The results suggest that from 7.05 Ma to 6.23 Ma the westerlies and the East Asian Winter Monsoon (EAWM) were relatively equally responsible for the sediment transportation to the CLP. At 5.55 Ma, the Red Clay was mostly derived from the westerly sources. At 3.88 Ma, contribution from northeastern Tibetan Plateau was most dominant suggesting enhanced East Asian Summer Monsoon (EASM) and surficial drainage from the source regions. At 3.20 Ma, the Red Clay was mainly sourced from proximal areas and fluctuation between EAWM and EASM had begun. This study demonstrates that single-grain rutile techniques have strong potential to aid a more precise distinction between individual primary and secondary sources for aeolian dust in the CLP region, especially when combined with zircon geochronology or other single-grain techniques. However, at present the applicability of rutile in provenance studies is hindered by scarcity of rutile data from the potential primary as well as secondary source regions, and lack of truly homogenous rutile standards for the analysis.

Eutrophication and harmful substances of anthropogenic origin threaten the state of the Baltic Sea and especially its geochemistry and oxygen levels near the seafloor. Water exchange between the Baltic Sea and the Atlantic Ocean can affect oxygen circulation and sedimentation rates, but they are considered very sporadic and it is unclear how the water circulation and flow rates affect element concentrations and sediment deposition in the near seafloor environments. One of the less studied basins is the Western Gulf of Finland and its seafloor environment. During the 2019 voyage, the seafloor located to the south of the city of Hanko was investigated through bathymetric sounding tools and other measurements in which element concentration and sediment deposition rate data was acquired. The sounding revealed a large channel cutting the seafloor which was hypothesized to influence the nearbottom conditions. The obtained data consisted of samples from 13 short, 40 cm sediment cores which were analysed for 137Cs activity, organic content, and grain size distribution. The goal of the thesis was to determine the intensity of water exchange taking place in the seabed channels between the mid-Baltic Sea and the Western Gulf of Finland and investigate the effect of the seafloor channel and flow rates on sediment and element deposition, their relationships, and how they affect the overall conditions in the study area. These relationships were analyzed through spatial and statistical methods by utilizing GIS-tools to interpolate the data obtained from the study locations by using the Inverse Distance Weighting (IDW) method, and by multielement analyses in the R-environment, namely Principal Component Analysis (PCA) and Partial Least Regression (PLS) to analyze grain size and element concentration correlations and combine them with obtained flow rate data. The results showed strong correlation in flow rate intensities between the Western Gulf of Finland and the mid-Baltic Sea, and they are strongly linked with sedimentation and element deposition rates. However, no long-term trend was identified for the seafloor channel velocity frequencies. The Cs-activity shows stronger sedimentation activity on the western side of the seafloor channel. The overall element and sediment deposition in the study area was largely controlled by monthly and seasonal current velocity fluctuations among other processes. The element concentration comparison showed weakened oxygen conditions in the study area with increased eutrophication and carbon burial since the 1950s. The principal Component Analysis showed smaller grain sizes (0.15 - 2 mm) having a stronger influence on the datasets with Mo, N, and C providing largest variation in the data. Interpolation showed oxygen, pH, and H2S to have more fluctuation in the study area, which can indicate changes in the vertical gradients in each sample point. It could also be determined that other measured concentrations, such as temperature, turbidity, and salinity do not respond very sensitively to water inflow fluctuations or sedimentation rate changes. The results indicate that harmful substances and eutrophication are most likely going to increase in the near-bottom environment in the Western Gulf of Finland, contributed by anthropogenic activity. Water exchange is likely to become more and more uneven, thus affecting the flow rate effects to the sediment deposition in the Baltic Sea. Further studies are needed to link these processes to large-scale global changes and the general state of changes happening in the Baltic Sea and its surrounding areas. The seafloor of the Western Gulf of Finland could also be studied further to gain a better understanding of longer timescale changes on the seafloor channel currents, and element and sediment deposition rates.

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

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.

In this thesis, fossilized teeth of herbivores from four sites in Western Mongolia (Altanteel, Chono-Kharyakh, Oshin-Boro-Udzyur-Ula and Khrigis Nur) are examined for their stable carbon and oxygen isotope record. The fossils date to the Late Neogene period (ca. 10-3 Ma). The aim of the thesis is to reconstruct the palaeoclimate and palaeoenvironment of Western Mongolia during the Late Neogene using the isotopic records obtained from the fossilized teeth. The enamel of fourteen teeth from Rhinoceros, Equids, and a possible Giraffid was sampled and analyzed for δ13C and δ18O-values. The analyses were conducted using well-established methods with Isotope Ratio Mass Spectrometry. The stable carbon isotopes (13C and 12C) can be used to determine, the types of plants that these animals consume. Plants can be categorized into three groups based on their photosynthesis pathways. This study focuses on the C3 -plants, typically found in moister environments, and the C4-plants, which thrive in dry conditions. Specific δ13C-values have been established for these groups: –34‰ to –24‰ for C3-plants, and –20‰ to – 9‰ for C4. The δ13C-values obtained from the teeth of herbivores can be compared to these limits, allowing evaluation of the mammals’ diets (whether they consisted of C3 or C4-plants). If C3 plants dominate the die, this would indicate a moister climate, and likely a forested environment. Conversely, the presence of C4 plants would suggest grassland areas with more arid climatic conditions. The stable oxygen record in the teeth relates to the δ18O-composition of meteoric water in the area. Analysing δ18O-values facilitates the reconstruction of the mean temperatures of the habitats and allows for a comparison of climatic factors affecting precipitation and temperature over time. The stable carbon and oxygen records are compared to reconstruct the climate and environment of Western Mongolia during the Late Neogene. The results suggest an increase in the δ13C-values over time, which indicating a shift in the animals’ diets towards a more drought-stressed C3 and C4 plant-based one. The δ18O-values, on the other hand, remain stable and do not indicate a change in temperature during the Late Neogene. Comparing both the δ13C- and δ18O- values with studies conducted in China indicates a gradual aridification in Western Mongolia and China during the Late Neogene. However, the temperatures did not change significantly, although there were most likely alternating cooler and warmer periods during the time span of 10-3 Ma.

A significant amount of carbon has been stored in the northern peatlands during the Holocene. These peatlands are an important part of global carbon cycle by sequestering and releasing carbon dioxide (CO2) and methane (CH4) into the atmosphere. The development of high-latitude peatlands begun at the beginning of the Holocene, about 11,700 years ago after the retreat of the continental ice. To some extend, the carbon accumulation rate history has followed Holocene climate phases. Due to the high primary production during the warm periods, their carbon sequestration has been high and lower during the colder periods as primary production decreased. Perhaps the most important factor determining peatland carbon dynamics moisture conditions, i.e. water table depth. The climate is predicted to warm much faster in the north than elsewhere, making the northern peatlands particularly vulnerable to the effects of climate change. In the future, climate change is expected to change the humidity and temperature conditions, which likely affecting the carbon dynamics of the peatlands. However, the ultimate effects are not yet fully known. This thesis studies changes in the hydrological conditions of the subarctic Lompolojänkkä peatland in Finnish Lapland over the past 900 years. Based on a testate amoeba analysis of two peat profiles, a quantitative water table depth reconstruction was created using a transfer function based on the surface samples reference data. The supporting plant macrofossil data was available supplemented by chronology based on radiocarbon and lead dating. The results show that the hydrology of Lompolojänkkä has adapted changes in climate conditions over the past 900 years and the data show that the surface of the peatland is now drying. The observed current trend towards drier conditions is in line with previous observations from northern peatlands. Changes in the Lompolojänkkä's plant community indicate extensive peatland lateral growth as well as a small-scale development resembling fen-bog-transition. In contrast to prevailing understanding, changes in the testate amoeba community followed changes in the plant community. This may be due to relative change in water level whereas a result of warming the plant growth accelerated and peat accumulation increased, which resulted in deepening of water table depth. The number of testate amoebae in different peat layers gives the slightly conflicting indications of the development of the carbon sequestration capacity of the peatland over the time studied, and there are some uncertainties associated to applicability of such data. However, the observed vegetation shift suggests future increase in carbon sequestration potential in Lompolojänkkä.

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.

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.

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.

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.