Browsing by discipline "Geologi"

The Jokisivu gold deposit is a structurally controlled orogenic gold deposit that was formed during the Svecofennian orogeny when the Pirkanmaa belt, a turbidite dominated subduction zone complex, was pushed below the Tampere schist belt in the north. The Jokisivu gold deposit formed in a brittle-ductile shear zone and gold mineralization is related to the youngest deformation stage. The main focus of this study was in fluid inclusions in quartz veins. Quartz grains host fluid inclusions that carry information of the prevailing P–T–X conditions during fluid events in the quartz veins. According to the properties of fluid inclusion assemblages (FIA), six fluid inclusion types were distinguished. Fluid inclusion types A1, A2 and A3 are aqueous and fluid inclusion types B1, B2 and B3 are aqueous–carbonic. Relative chronology of the fluid inclusion types was determined by cross cutting relationships of fluid inclusion assemblages. Relative chronology of fluid inclusion types from oldest to youngest is A1, A2 and A3, B3, B1 and B2 indicating that aqueous fluids came in first and aqueous–carbonic fluids followed them. Microthermometry was conducted for all the FIAs. The melting point of CO2 was generally below the CO2 triple point ranging from -59.15°C to -56.73°C indicating the presence of other gaseous phases that were later confirmed with Raman spectroscopy to be CH4, N2 and even H2S. Raman spectroscopy was conducted for qualitative analysis of the phases presentn the inclusions. Quartz crystallization temperatures were calculated using titanium in quartz geothermometer (TitaniQ). TitaniQ was well suited for Jokisivu samples because titanium concentrations in the hydrothermal quartz were quite constant. Combining TitaniQ P–T slopes and fluid inclusion assemblage isochores from microthermometry and Raman spectroscopy yielded a good estimate for P–T conditions of fluid entrapment of 390–470°C and 170–345 MPa. The estimated temperature range is higher than the previous studies have suggested. However, the P–T range estimated for Jokisivu is in accordance with the P–T conditions of other Svecofennian orogenic gold deposits. Judged by the mineralogy of the quartz vein - host rock contact, the most important factor triggering gold precipitation in Jokisivu has probably been fluid-rock interaction. Strong sulfidation of host rock reduced the sulfur fugacity and enabled gold precipitation.

Out of all igneous rocks, carbonatites are perhaps the ones most sensitive to changing chemical environments and P-T conditions. As a result, their primary chemical and textural characteristics are more often than not altered by secondary processes. Discerning between the two is essential in order to make correct petrogenetic inferences from textural and chemical data. In this study, the 1.3 Ga siderite carbonatite of the Grønnedal-IÌ ka alkaline complex of South Greenland is used as a natural laboratory to identify mineral chemical and textural fingerprints of hydrothermal alteration in iron-rich carbonatites, with a second aim of describing the paragenesis of a high-grade magnetite mineralization in the locality. Trace element chemistry of magnetite, calcite, siderite and ankerite-dolomite is analyzed in situ by electron-probe microanalysis (EPMA) and laser ablation inductively coupled mass spectrometry (LA- ICP-MS). Magnetite is shown to be a product of oxidation of siderite and is exclusively of hydrothermal origin, characterized by low Ti (1-12000 ppm) and V (1-200 ppm) concentrations. High Nb/Ta (up to 1000) and Zr/Hf (up to 300) ratios in magnetite suggest formation mediated by fluorine-rich fluids. Hydrothermally reworked siderite is enriched in Mn and light rare earth elements (LREEs) and has a depleted Y/Ho ratio. In contrast, hydrothermally reworked calcite is enriched in Y/Ho and depleted in LREEs. A secondary mineral assemblage of apatite, strontianite, barite, REE-fluorocarbonates and ankerite-dolomite is associated with the alteration, which increases toward the contact to a 55 m wide basaltic dike that cuts the carbonatite. Unusual mineral compositions are found close to the dike contact, including magnetite with up to 1 wt.% Nb and calcite with 1 wt.% REEs, both the highest reported values in the literature. Together, the data point to the dike intrusion as a heat source of a hydrothermal convection cell, driving hot F and CO2 rich fluids that mobilized P, Sr, Ba, Mn, LREE, Nb and Ta and reacted with and altered the composition of the carbonatites up to a distance of 40 m from the intrusion contact. The results underscore the necessity of a careful textural and mineral chemical assessment in studying the petrogenesis and subsolvus evolution of ferrocarbonatites.

Lake Pyhäjärvi, the largest lake in southwestern Finland, has been under considerable external nutrient loading for the past decades. Rivers Pyhäjoki and Yläneenjoki are the only major input rivers of the lake and are the source of most of the external nutrient loading to the lake. The hydrogeochemistry of the Lake Pyhäjärvi catchment, as well as the catchments of the two input rivers, and groundwater-surface water interaction were evaluated using a wide array of geochemical tracers (major ions, dissolved silica, stable isotopes of oxygen and hydrogen, electrical conductivity and radon-222). Additionally, the feasibility of using mass balance based methods to separate river waters of the two input rivers to their respective source components was evaluated independently with each tracer analysed. In the context of this study, stable isotopes alone were deemed plausible and were only usable in the River Pyhäjoki catchment as there was not enough difference between river water and precipitation (new water) stable isotope proportions in River Yläneenjoki. Employing the stable isotopes of oxygen, mass balance based modelling was attempted to separate the hydrograph of River Pyhäjoki to its end-members (new water and old water). Based on the obtained data, the hydrogeochemical content of the surface waters of each subcatchment (Pyhäjärvi, Pyhäjoki and Yläneenjoki) differed significantly. Additionally, the groundwaters were clearly distinguished from surface waters. Differences were most apparent in stable isotope proportions as well as dissolved silica, and in the case of groundwaters in radon-222 concentrations. This categorization was further supported by a hierarchical cluster analysis. Surface waters showed varying signs of evaporation, whereas groundwaters retained the stable isotope characteristics of mean annual precipitation. Dissolved silica concentrations appeared to be mostly affected by the amount of easily soluble silica in the sediment, water residence time, as well as biological uptake in the surface waters. Lithology seemed to be the controlling factor in radon concentrations, with areas of granitic bedrock having the highest concentrations. The hydrograph separation of River Pyhäjoki gave results between 66–88% of old water in the river at the time of sampling, consisting likely mostly of groundwater. Though this result corresponds well with recent similar studies in the area, there were considerable sources of uncertainty, therefore making the result best thought of as indicative. However, there was clear evidence of groundwater-surface water interaction in all of the subcatchments of Lake Pyhäjärvi, with clear evidence of groundwater discharging into the lake, lake water infiltrating into an aquifer near the shore of the lake, as well as signs of groundwater discharging into the two input rivers.

The Finnish spent nuclear fuel repository is currently under construction by Posiva Oy, and the repository will be located in Olkiluoto Island, western Finland. After intensive research of the site from surface drillholes, construction of underground rock characterisation facility named ONKALO began in 2004 in the same location for the purposes of detailed site characterization. Additionally, to ONKALO and research drillholes, 58 deep drillholes provide a large database for the geological, geochemical, geophysical and rock mechanics site characterisation. One of the key aspects of rock mechanics site characterisation is to determine the in situ stress field prevailing at Olkiluoto. Mathematically, the stress field is represented as a tensor with both direction and magnitude. The effect of excessive magnitudes of the tensor can be manifested by oriented fractures on the walls of the drillholes forming a phenomena of borehole breakouts along the drillhole length. The breakouts form when compressive stress, induced by the concentration of the in situ stress around the drillhole, exceeds the rock strength. The breakouts occur on the opposite sides of the walls. Due to the breakouts occurring in the areas of maximum compression around the drillhole walls, both the direction of the minimum (σh) and maximum (σH) horizontal in situ stress components can be inferred along the drillhole. This Master's thesis was set to identify and map the breakouts in the deep drillholes in Olkiluoto using the acoustic and optical imaging data of the deep drillholes. Acoustic and optical televiewers are two of the several geophysical measuring methods used in the drillholes. They produce images of the walls of the drillholes by wave reflection. During the study, different types of breakouts were identified along the drillholes in Olkiluoto: dotted, zipper-like and a mix of the two previous types with different intensities. The locations of the identified breakouts and other features (direction of σh, rock type, foliation) were recorded in a mapping form developed during this work. The mapping results show that in the total of 19 imaged drillholes, 40 breakout sections exist in only 5 drillholes. Geophysical data show that the breakouts are highly dependent on the geology and the majority of the breakouts occur in veined gneiss and in less competent rock types such as deformed or fractured rocks. Most of the breakouts were observed below 600 meters depth. Major group of directions of calculated σH from the mapped breakouts is oriented NE-SW (60-90°/245-270°) and secondary groups are oriented 107-150°/285-325° and 10-40°/190-220°. In some drillholes, the directions are rotated about 40° due to a significant brittle fault zone separating the site of Olkiluoto into stress field domains.

Bedrock fracturing is considerably extensive and distinct in Finland, and the fractures that are open, conductive and interconnected usually control the groundwater flow paths in fractured bedrock. This highlights the importance of knowing the locations and hydraulic connections of water conducting fracture zones particularly in mining areas, because they can transport adverse substances outside the mining area. In this study, it is focused on examining possible hydraulic connections of bedrock groundwater by using the stable isotopes of oxygen (δ18O) and hydrogen (δ2H). The study was carried out in the Talvivaara mining area in Northeastern Finland alongside a project from the Geological Survey of Finland (GTK). After November 2012, when a leakage of acidic, metal-containing waste water occurred in the gypsum ponds, there was an urgent need to study the groundwater transport routes in the bedrock fractures. The aim was to find hydraulic connections between surface water and groundwater, and to study the flow of the groundwater in the fracture zones based on the different isotopic characteristics of waters from different sources and isotopic similarities. Most of the materials used in this study were obtained from the results of the project from the GTK. These materials included geophysical interpretations of the locations and water content of the main fracture zones and the results from the geochemical analyzes. Together with the interpretations of groundwater flow direction based on hydraulic heads these materials formed a frame for this study. The isotope composition of 39 water samples from bedrock wells, shallow wells and surface water was analyzed using cavity ring-down spectroscopy (CRDS) method. The surface waters were clearly distinguished based on their evident evaporation signal, but no significant such a signal was observed in the bedrock and shallow groundwaters. However, similarities between groundwater from different depths of same well were found, in addition to similarities between different wells along same fracture zones. Although the isotopes did not indicate surface water contamination, groundwater contamination with smaller amounts of water is possible, in which case the changes in isotope composition are not yet significant, while certain elements have elevated concentrations. A NE-SW oriented fracture zone passing in the center of the study area was concluded to have the most important role in collecting and transporting groundwater outside the mining area. More detailed interpretations would require regular sampling for a longer period of time to better distinguish naturally and artificially induced changes both in the isotopic but also geochemical compositions. Also the usage of packer tests possibly together with pumping tests would be useful in obtaining more comprehensive image of the groundwater flow in the fracture zones and their hydraulic connections.

Monsuuni-ilmastoa luonnehtivat vuodenaikojen mukaan suuntaansa vaihtavat ilmamassojen liikkeet sekä niihin liittyvät sadekaudet. Aasian monsuunisysteemi on yksi maapallon merkittävimmistä ilmastosysteemeistä ja sen vaikutusalue ulottuu Arabian meren länsiosista Itä-Aasiaan sekä Australian pohjoisosiin. Se jaetaan kahteen ala-systeemiin: Intian monsuuniin ja Itä-Aasian monsuuniin. Monsuunialueella asuu yli puolet maapallon ihmisistä ja näiden yhteiskuntien hyvinvointi on täysin riippuvainen kesämonsuuni sateiden maantieteellisestä jakautumisesta sekä voimakkuudesta. On esitetty, että käynnissä oleva ilmastonmuutos on jo vaikuttanut monsuunisysteemeihin. Tässä tutkimuksessa perehdyin holoseenin aikaisiin monsuunivaihteluihin. Omia tuloksiani vertasin muualta monsuuni alueelta peräisin oleviin monsuuni-ilmastoa käsitteleviin tuloksiin sekä myös Pohjois-Atlantin alueen ilmastorekonstruktioihin. Tutkimuskohteeni on Kumphawapi järvi, joka sijaitsee Koillis-Thaimaassa. Thaimaa on ihanteellinen kohde monsuunitutkimuksille, koska se sijaitsee molempien monsuunin ala-systeemien vaikutusalueella. Järven syvimmästä kohdasta noudettiin 3.81 metriä pitkä sedimenttisarja, josta määritin orgaanisen aineksen määrän sekä analysoin kasvimakrofossiili koostumuksen. Sedimenttisarja ajoitettiin radiohiili menetelmällä suhteellisen tiheällä näytevälillä ja ajoitusten perusteella luotiin ikä-syvyys malli. Tätä aineistoa käytin menneiden vedenpintojen vaihteluiden eli holoseenin aikaisen monsuunin voimakkuuden rekonstruoimiseen. Laskin näytteistä myös makroskooppiset hiilipartikkelit. Näiden avulla arvioin ihmistoiminnan mahdollista vaikutusta ympäristöön. Omaa aineistoani tukemaan minulla oli käytettävissäni aiempaa paleoekologista aineistoa samasta järvestä. Tutkimustulokseni paljastivat, että järven hydrologiset olosuhteet olivat holoseenin aikana vaihdelleet huomattavasti. Holoseenin alussa järvi oli suhteellisen syvä, ja tämä viittaa kosteisiin olosuhteisiin eli voimakkaaseen kesämonsuuniin. Keski holoseenin aikana veden syvyys oli matala, joka taas viittaa heikkoon kesämonsuuniin. Myöhäisholoseenin aikana veden syvyys vaihteli. Tämä viittaa monsuuni-ilmastossa tapahtuneisiin lyhyempikestoisiin vaihteluihin. Omat tulokseni vertautuvat hyvin muihin ilmasto rekonstruktioihin Aasiasta. Kumphawapi-järven aineisto myös viittaa siihen, että alueellinen monsuuni-ilmasto on ollut yhteydessä pohjoisten leveysasteiden ilmastoon. Lisäksi Aasian monsuuni-ilmasto näyttäisi kytkeytyvän trooppiseen nk. ENSO systeemiin. Kumphawapi-järven sedimentaatiossa esiintyi usean tuhannen vuoden katkos, joka ajoittuu keski holoseeniin, Siksi tulkinta siitä oliko keski holoseenin veden pinnan lasku ilmaston vai ihmisen aiheuttama, jää tässä tutkimuksessa selvittämättä. Joka tapauksessa aineistoni viittaa siihen, että myöhäisholoseenin vaihtelut veden pinnoissa oli ilmaston eikä ihmistoiminnan aiheuttamaa. Kasvimakrofossiilimenetelmä yhdistettynä hyvään kronologiaan ja litologiseen analyysiin, muulla paleoekologisella aineistolla tuettuna, osoittautui hyväksi tavaksi tutkia holoseenin aikaisia kosteusolosuhteita. Eri tutkimusten tulkintojen välillä esiintyi kuitenkin epäyhtenäisyyttä ja siksi lisätutkimukset ovat tarpeellisia; ja näissä tutkimuksissa kannattaa hyödyntää myös kasvimakrofossiili menetelmää.

A high-resolution grain size analysis was carried out on a 2,5 meter long marine core series from Isvika Bay, Nordauslandet, Svalbard. Grain size analysis was performed with a Malvern Mastersizer 2000 laser grain size analysator. The analysis of the results was determined by the relative proportions of sand (greater than 63 microns), silt (8-63 microns) and clay (less than 8 microns). Clay, silt and sand proportions were made in to a triangle diagram. On certain depths a model diagram was taken and its curves were examined. The material was determined by the following standard deviations (d₁₀, d₂₅, d₃₀, d₅₀, d₆₀, d₇₅ ja d₉₀), which were calculated to parameters: the coefficient of uniformity (Cu), the coefficient of curvature (Cc), standard deviation (So), skewness (Sk), and kurtosis (K). The modes were obtained directly from the Malvern software results. In addition, graphs of interpenetration rates dd₅₀ and d₉₀ were made. The grain size of the marine sediment core gave a comprehensive picture of the sedimentation of the last 11700 years in Isvika Bay. IRD-material of over 500 microns accumulates almost the entire time series. IRD's minimum sections describe a momentarily colder period in the climate, which lead to the freezing of the sea and the perennial sea ice. These colder periods prevented sea ice and icebergs importing IRD-material to Isvika Bay. These cold 25-80 years lasting periods have been 10300, 8300, 6700, 5700, 2000, 1200, 500, 300 and 200 cal. years BP. The intervals of cold phases have been on an average of 1150 years. Based to grain size distribution 11700 – 9400 cal. years BP, stable sedimentation environment and cold climate prevailed. 9500 cal. years BP there has been strong warming. 9500 – 7500 cal. years BP, there has been a warm climate, which led to an intensive glacier melting. 7500 – 4500 cal. years BP, the climate got colder for several thousands of years. 4500-4000 cal. years BP the climate got warmer for a period of about 500 years. The climate cooled down gradually between 4000 – 500 cal. years BP toward the present time. The last 500 years the climate has been warmer than the previous, but very variable. During this time, the presence of the multi-annual sea ice has declined.

University of Helsinki, precisely the Department of Geology and Geography installed a groundwater station on Lammi Biological Station, to be used for academic research and education purposes. The main principle of this study was to collect basic properties of the soil and groundwater circumstances on the site and to test the main functions of the groundwater station. The groundwater station includes six groundwater monitoring wells, installed in January 2015. To describe the groundwater circumstances as widely as possible, the wells were installed on places where groundwater both recharges and discharges. Soil samples were collected and a field estimation of the layer order was made during the installation of the wells. Grain size distribution and hydraulic conductivity were defined in the laboratory and multiple other hydraulic conductivity measurements of the soil were made in the field. Also groundwater samples were collected and the chemical composition of the water examined. Besides elevated concentration of iron, manganese and uranium the quality of the groundwater was good. pH-values were close to neutral, alkalinity normal and electrical conductivity low. There was a regional variation in the quality. Continuous measurement devices were installed to the monitoring wells in June 2015, to follow the temperature, groundwater level and in one of the wells electrical conductivity. This data was followed from the early summer to the next spring, to receive versatile data due to climate factors. Groundwater level seems to react to the amount of precipitation. Similar variation pattern were noticed in the groundwater levels in all of the wells. An estimation of groundwater table, bedrock surface and soil thickness were made using data from this and the earlier studies. The soil on the site consists for the most of stony sand till overlaid by 1 – 4 meter thick layer of fine sediment. The hydraulic conductivity and grain size distribution of till variated largely even in the same spot. The hydraulic conductivity variated between 4,8 * 10-6 – 1,0 * 10-1 ms-1, normal values from silt to gravel. The groundwater table is situated without exception in the till layer, thus its thickness and depth variates regionally. The site was divided in two zones based on the contours, field observations and old and new drilling data.

Hyvinkäänkylä pumping station extracts groundwater from a local esker aquifer and supplies drinking water within the Hyvinkää municipality. There have been problems with the aquifer’s water quality, when surface water from the Vantaa river has mixed with groundwater during flooding season. As a result of the mixing, the pumping at the station must be periodically stopped. For more effective groundwater acquisition, management and protection it is critical to gain better understanding of the structure of the aquifer better. In addition, more knowledge of the groundwater-surface water interaction is needed and information on the possible routes of groundwater flow, particularly those which most affect the groundwater supply coming to the pumping station. The purpose of this study is to gather the previous research on the area and to create a 3D hydrogeological structural model using the Leapfrog Geo program. The model in this study visualizes the hydrogeological structures and serves as input for a groundwater flow model. The data in this study can be categorized into three groups: the structure of the bedrock and sediments, the level of the groundwater and the groundwater discharge. The structure of the bedrock and sediments was surveyed by geophysical methods, using previous data as well as some additional data gathered by field measurements. Data on the groundwater level measurements were obtained from both the Finnish Environment Institute and the Hyvinkää Water station. Additional data were collected using field measurements. To measure the amount of groundwater discharge, data were collected using flow measurements in the Vantaa River and the results compared with previous research. The geological and geophysical data were compiled and georeferenced first in ArcGis and then transferred into Leapfrog, which was used to build the 3D hydrogeological structural model. On the basis of the geological units of the drill data, five hydrogeological units were formed: coarse glaciofluvial material, fine glaciofluvial material, fine grained material, till and other. The hydraulic conductivity of the drill core sediment samples were calculated, and then used to estimate the hydraulic conductivity within and between the different sediment layers. Since one purpose for the 3D structural model was to serve as a base for the flow model, it was simplified into a 2-layer model. The study area was divided into smaller subareas, which were visualized with cross sections that were sliced from the 3D model. The measured groundwater levels were interpolated to demonstrate the groundwater flow direction in the study area. The groundwater monitoring levels were examined over a five year period and compared with weather and groundwater pumping data. The flow measurements obtained from the Vantaa River were compared to previous research to estimate the amount of groundwater discharge into the Vantaa River. The contribution of this study is five new significant observations about the structure of the aquifer: 1) the north and south part of the aquifer are connected to each other 2) the three-dimensional shape of the esker is different from its geomorphologic shape 3) most of the groundwater flowing to the pumping station is from the south side of the river 4) the amount of groundwater flowing to the pumping station is very high compared to the surface area of the aquifer 5) thick glaciofluvial layers underneath the Hirvisuo bog allow groundwater flow from the first Salpausselkä to the esker.

Tropical Africa has been under intense land cover change during the last decades. Human activities have had an impact on natural ecosystems and this has accelerated changes in them. Soil can be considered as an ecosystem and changes in natural soil formation can lead to soil loss and erosion. Taita Hills located in south-east Kenya are no exception. Almost all recoverable land is used for agriculture in these subtropical hills despite the great altitude differences and steepness of the hill slopes. Wundanyi catchment at the altitude 1400 - 2100m above sea level was studied in order to identify certain physical parameters of the soil in the hills and to define if these could be explained by changes in the physical environment like alteration in altitude, slope angle and land uses. A total of 68 study points were selected within the catchment in order to represent different physical environments. At each study point, the slope angle was measured, an approximately one meter deep soil cut was dug into the hill slope of which the soil profile was drawn and the subsamples were taken for the grain size analysis and bulk density determination. At 21 study points, the soil was not sampled due to a thick humus layer. The soil hydraulic conductivity was determined experimentally at three study points with an infiltration ring and theoretically for the rest of the study points by estimation, using other physical soil properties obtained from grain size analysis. The soil at the Wundanyi catchment was found to be massive, chemically weathered fine residual soil originating from the weathered gneissic bedrock. It was discovered that generally the soil is quite homogeneous within the catchment area and the physical parameters of the soil are similar despite the different land cover classes. The most common soil type at the catchment is fine sand. The deepness of the organic layer varied greatly, the mean being 0.7 meters. The thickest organic layers were found in indigenous forests and in places that had not been used for agricultural purposes. Soil hydraulic conductivity at the studied area is low. The degree of correlation between soil grain size distribution and varying physical environments was found low. However, there seems to be moderate correlation between the elevation and the proportion of clay and the aspect and the proportion of clay. Topographic environment mainly defines the land use and land cover within the studied area. Only the steepest slopes and areas that are not accessible have avoided the excessive exploitation of the soil. The vegetation protects the mineral soil and, therefore, the removal of natural vegetation exposes the soil to impacts of climatic conditions. The exposition of the soil together with fine soil texture can reduce the infiltration making the soil compacted. This increases the surface runoff, which can increase the sediment transportation and can lead to environmental problems such as erosion, gullying, silting of rivers and transportation of nutrients to rivers. Signs of these environmental problems can already be seen at the Taita Hills, proving that soil exploitation is not sustainable.