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Browsing by study line "Berggrundsgeologi och ekonomisk geologi"

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  • Dimakopoulos, Georgios (2022)
    The metamorphosed Kutemajärvi gold deposit is located near the town of Orivesi, at the eastern flank of the Tampere Schist Belt, which constitutes part of the Svecofennian domain of southern Finland, and it is hosted in the volcanic rocks of the Koskuenjärvi formation. Previous isotopic studies have mainly focused on the igneous and metamorphic rocks of the Tampere Schist Belt and only a few of them have presented ages for the area of Kutemajärvi. This study aims to shed light on the timing of mineralization by employing the single-grain U-Pb dating method of monazite and zircon, in order to evaluate the relationship between the ore and its host rocks. Based on the results from the SEM mineral identification, monazite grains are divided into metamorphic and hydrothermal grains. In the case of zircon grains, a third magmatic type has been identified. Results from U-Pb dating of single monazite and zircon grains are well constrained and document four distinct stages of geodynamic evolution in the region. Ages older than 1.91 Ga represent detrital material transported during the stage of rifting that led to the opening of the Tampere basin. Subsequent subduction resulted in active volcanism which is expressed with the extrusion of the Koskuenjärvi formation at 1904 Ma. At the late stages of subduction or at the outset of the collision stage, the subvolcanic Pukala porphyry intruded into the volcanic sequence of the Tampere Schist Belt at 1890 Ma, which provides the maximum mineralization age. Release of hydrothermal fluids, due to the crystallization of the Pukala intrusion caused pervasive hydrothermal alteration of the Kutemajärvi host rocks and deposition of epithermal gold and other elements. However, the participation of hydrothermal fluids, released by high-temperature metamorphism of the lower crust, cannot be ruled out. Ages between 1890‒1878 Ma record the syn-collision stage, during which the deposit, the Pukala intrusion and its adjoining rocks were deformed and metamorphosed at greenschist to lower-amphibolite facies. The majority of ages fall within the 1880‒1878 Ma time-interval, characterizing the metamorphic peak that marks the culmination of the Svecofennian orogeny and provides a minimum age of the mineralization. This major orogenic event is partly overlapped by the collision of the Central Svecofennian Arc Complex with the Southern Svecofennian Arc Complex that transpired at 1880‒1860 Ma, as indicated by ample age data. Monazite and zircon also yield lower ages (<1860 Ma), which record retrograde metamorphic and subordinate cooling events, and resonate recurring tectonothermal activity, associated with the syn- and post-collisional magmatism of Southern Svecofennia and the emplacement of rapakivi intrusions in southern Finland. Single-grain U-Pb dating of monazite and zircon from polished thin sections, in tandem with collation of the obtained ages with earlier published data, establishes a spatial and temporal framework with respect to the tectonometamorphic evolution of the Kutemajärvi gold deposit and the Tampere Schist Belt. Precise temporal constraints substantiate the intricate geological history of the area and can be used to discriminate magmatic, metamorphic and hydrothermal events, with a view to breaking ground on the exploration of other epithermal deposits in the metamorphic terranes of southern Finland.
  • Liimatainen, Toni (2022)
    Graphite is formed mainly by graphitization processes from organic precursor in high-grade metamorphic conditions, or precipitation of carbon from carbon-bearing fluids. Quality of the graphite, i.e. crystallinity, flake size and purity, determines its use and commercial value. Demand for graphite has been on the rise and is expected to increase more in the near future. The Korsnäs region in Ostrobothnia, Western Finland, is a prominent target for a graphite exploration based on the region’s geological history, i.e. the Svecofennian accretionary orogeny and high-grade metamorphic conditions. Graphite is ubiquitous in the area, and has been enriched mainly in the metapelitic schists intercalated within the paragneisses. The aim of the master’s thesis is to study the mineralogical characteristics and quality of the graphite, as well as estimate the economic importance of the graphite occurrences in the area of Korsnäs. Additionally, the origin of the graphite formations and their relationship to the regional metamorphic conditions are considered in this research. Mineralogical characteristics and quality of the graphite flakes were studied from the polished thin sections with optical microscopes and scanning electron microscope. Crystallinity of the graphite flakes was analyzed by a Raman spectroscopy, which has been used widely to measure orderly structure of a carbonaceous material. Peak temperatures of the metamorphic conditions were estimated from the Raman results using geothermometers. Based on the petrographic analysis, graphite is abundant, and the morphology refers to a flake graphite. Large proportion of the flakes are over 0.3 mm on their c-axis, which can be considered as large and the most valuable type of a flake graphite. Crystallinity of the graphite was determined from the Raman spectra using the peak intensity ratio (R1) of the graphite band and the main disordered band. The analyzed graphite flakes show good values for the R1 parameter (mean value 0.05 ± 0.05), indicating high crystallinity, and consequently, high-grade metamorphic conditions or precipitation from carbon-bearing fluids for the formation mechanism. The estimated peak temperatures are ranging from 650 to 695°C, which are consistent with the mineral assemblages of the migmatite and paragneiss samples, but inconsistent with the graphite-bearing metapelitic schists. The biotite-garnet and biotite-garnet-cordierite (sillimanite) paragneisses does not show any meaningful evidence of a retrograde overprint, but it is apparent that the graphite bearing samples have experienced retrograde metamorphism and hydrothermal alteration. This is evident from the lack of high-grade metamorphic minerals, presence of lower metamorphic grade minerals, and the estimated high peak temperatures for the formation of the graphite. Consequently, the R1 parameter suggests that the graphite in these rocks has not been affected by the retrograde metamorphism. The origin of the high-crystalline graphite appears to be a graphitization of biogenic material, but fluid-deposited graphite cannot be completely ruled out. Some carbon enrichment may have occurred by fluid-rock interactions. Further studies and detailed analyses, such as locating the possible high-grade deposits and determining the purity of the graphite, are needed. In conclusion, the high-crystalline graphite in the Korsnäs region is of good quality and shows prominent results for the commercial value.
  • Kettunen, Ilkka Henrikki (2022)
    Aim of this study is to develop biogeochemical exploration methods for cobalt. Several different samples were collected from study area, analyzed, and compared to each other. This study took place at Rautio village at North Ostrobothnia and more accurately over the Jouhineva mineralization. Jouhineva is well-known high-grade cobalt-copper-gold mineralization. Elements examined in this study are cobalt, copper, arsenic, zinc, selenium, and cadmium. Samples were collected from three different study profiles from the area. From these three profiles samples collected are: soil, pine, lingonberry, birch, rowan, and juniper. Water samples were collected around the study area from every location possible. Soil samples were analyzed with four different methods: Ionic leaching, aqua regia, weak leaching and pXRF. Ionic leaching and aqua regia had both elevated concentrations of cobalt, but in different locations depending on study profile. Ionic leaching detects rising ions from the ore and therefore elevated concentrations are found at different locations compared to aqua regia. Aqua regia results proved how different orientation of study profile, direction of the ore and glacial flow can affect to the anomalies of elemental concentration. Profile-2 was oriented differently to ore and glacial flow than Profile-1, and therefore elevated concentrations of cobalt and copper were not drifted away from the ore on Profile-2 like they were on Profile-1. Aqua regia and pXRF have very similar copper, arsenic and zinc results. Pine and lingonberry turn out to be the most promising plant species applied for cobalt exploration, and rowan appears to be most suitable for copper exploration. Lower detection limit could significantly improve pine analyses as exploration method and more extensive sampling could remove some of the uncertainties about the method. Lingonberry samples have elevated concentration of copper and arsenic. Birch and juniper produced somewhat unclear results. Despite this, cobalt and copper concentrations in birch leaves were elevated when compared to concentrations found in other studies. In addition to this birch is suitable for arsenic exploration. Juniper had elevated copper concentration in the study area compared to other studies. Water samples collected from the Jouhineva area yielded concentrations of cobalt, copper and arsenic that were above the average concentration in the Kalajoki area waters. Copper and arsenic were above the average concentration of the Kalajoki area in every sample collected from the study area. Cobalt was above the average concentration in all samples that were not collected directly from the pond formed in the old test mine. Zinc concentration was below the average limit in all samples collected from the area. Zinc concentration in the water samples collected from the pond is significantly lower compared to the other samples collected from the area.
  • Uusikorpi, Juuso (2020)
    The geochemical regolith data gathered from Dzhumba, a gold prospect in eastern Kazakhstan, was analyzed using factor analysis and then integrated into ArcGIS as spatial data. Principal axis factoring method was used for factor extraction combined with varimax orthogonal rotation and Kaiser normalization. Five clear factors were extracted from the data set of 47 elements in 3942 regolith samples. Kriging interpolation was used to generate spatial data surfaces from factor scores. The generated factors are composed of the geochemical associations in the raw data, and represent the underlying geological processes and formations of the area. The fourth factor generated represents gold mineralization with As, Sb, Au, Zr, Sc, Mn, Mo, Cu, K and Ni being the elements that are positively loaded onto factor 4. Therefore, single element maps of these elements have been produced alongside the factor maps in order to examine factor 4 more intensely. Also maps about structural geology and alteration in the Dzhumba project area have been produced in order to give better understanding of the factor maps. The data suggests that the deposit type is an orogenic gold deposit. Other factors created interesting results as well, and they gave information about the different geological units of the area. Factor 1 represents granitic rocks by their feldspar and trace element content, factor 2 represents black shales with possible mafic rock constituents, factor 3 represents a sulfide rich mafic mineral group or graphitic rocks that are most likely black shales and factor 5 possibly represents calcite alteration. Factor 4 is the main interest of this study. The most intense loadings for factor 4 are in Brigadnoe, Svistun and Dzhumba with a small peak in Belyi. Single element map for gold mostly corresponds to factor 4 for Svistun and Dzhumba, but Brigadnoe is represented with a small peak. However, gold has a major presence in Fedor-Ivanovskoe, which is absent from factor 4. Further exploration in Fedor-Ivanovskoe could be performed in order to clarify if this is due to an unrelated gold-only deposit or some other event. Possible future exploration in the area could benefit from factor 4 results, using As and Sb, or a combination of As, Sb, Zr, Sc, Mn, Mo, Cu, K and Ni as pathfinders for possible gold occurrences.
  • Sandström, Joonas (2021)
    Aijala-Metsämonttu volcanogenic massive sulphide ore deposit belongs to Orijärvi regional volcanogenic massive sulphide mineralisation, localised within the schist zone southwestern Finland. Aijala-Orijärvi zone is an island-arc structure formed during the Paleoproterozoic (1895-1891 Ma). The mining operation in Aijala took place in 1949–1958 and Metsämonttu in 1952–1958 and 1964–1974. The Aijala and Metsämonttu deposits were 1 km apart. The main ore types were massive vein-like pyrite, sphalerite, pyrrhotite, chalcopyrite, and galena. The purpose of this thesis was to produce modern geological 3D models of the Aijala and Metsämonttu volcanogenic massive sulphide ore deposits and numerical grade models of the utilised minerals (copper, lead, zinc, silver, and gold) using historical material and to interpret the occurrences and emplacements of precious metals and base metals. In addition, compare the accuracy of the 3D models with digitised historical material. Geological 3D and numerical grade models were created using implicit modelling. Historical data used in this thesis consist of 266 drill holes from Aijala and 274 drill holes from Metsämonttu. Also, 61 mine tunnel maps and 47 cross-sections were used to create the geological models. The Aijala-Metsämonttu volcanogenic massive sulphide ore deposits are in the same stratigraphic zone between the footwall quartz-feldspar-porphyry and hanging wall amphibolite. Sulphide lenses of both deposits are vertically on the south side of the footwall and hanging wall contact. The main host rocks to sulphide ores are skarn and cordierite-gneiss. Several local faults intersect the deposits. The most significant faults displaced overlying blocks to the south in Aijala and to the north in Metsämonttu. The Aijala-Metsämonttu deposit belongs to the Zn-Pb-Cu group. The occurrence style and concentrations of metals vary between deposits. Copper ore is present in Aijala but absent in Metsämonttu, whilst zinc-lead ore is present in Metsämonttu but absent in Aijala. Precious metals occur in both deposits with a companion of base metals. The Metsämonttu deposit is rich in precious metals compared to the Aijala deposit, and the presence of high content of precious metals correlates with the incidence of lead ore. Precious metals concentrations increase from east to west and deeper in Metsämonttu.
  • Jokela, Eetu (2020)
    The Sukseton area is located in the northern part of Kittilä municipality, Central Lapland Greenstone Belt, approximately 15 km N from Suurikuusikko gold mine and 5 km NW from Iso-Kuotko orogenic gold deposit, between several large crustal scale thrust and shear zones. This area is a mix of different volcanic formations of Kittilä suite, felsic intrusion of Vuotso Complex and Paleoproterozoic intrusive rocks in the north. In addition to this, several porphyry dykes cut the Kittilä suite volcanic rocks around the area. Exploration work in this area started in the 1980’s when Outokumpu Oy found two minor gold and gold-copper mineralizations. In 2017, Agnico Eagle Finland Oy continued exploration in this area, intending to define the regional geology and the extent of the mineralizations. As a result of this exploration work, this study investigates more closely the regional geology, geochemistry, metamorphism and structural geology of the Sukseton area, as well as the geochronology of associated porphyry dykes. To understand and define the geology of the area, the following methods were used: geological bedrock and exploration trench mapping, interpretation of drill core loggings and several geophysical surveys, optical studies of polished thin sections and U–Pb dating a porphyry dyke sample. The metamorphic conditions of the area were studied through thorough petrological studies. In addition, an extensive geochemical and geotectonic classification of the rocks in the area was conducted. The Sukseton area composes mainly of different tholeiitic basalts and pyroclastic rocks with minor sulphide rich graphitic volcanic sediment and chert sections. Based on this study, these volcanic rocks originate from island arcs and mid-ocean ridges. With the help of geophysical surveys and field measurements, a couple of large fold structures were identified from the eastern part of the study area as well as a large shear zone in the middle of the area striking NE–SW. Porphyry dykes cut the volcanic rocks all around the area giving the minimum age of 1940±18 Ma for the volcanic rocks. Composition of porphyry dykes vary from rhyolites to basalt and they have similar geochemical characteristics with Nyssäkoski type felsic veins. The peak metamorphic conditions in the area represent high-P amphibolite facies metamorphism. Also, hydrothermal alteration is common in Sukseton and it can be metamorphic and magmatic in origin.
  • Georgi, Jaakko (2019)
    This study consists of a comprehensive characterization of the geology, geochemistry, alteration, and mineralization at the Ronaldo prospect as well as an evaluation of its ore potential. Previous mapping campaigns of the prospect, which lies in the Central Andes in Peru at an elevation of 4300 metres, have identified intrusions overlain by a volcanic package. The intrusions are crosscut by silicified ridges that host epithermal mineralization. Satellite imagery reveals that the topographically elevated areas exhibit strongly altered rocks identified as an advanced argillic-altered lithocap. The methods used to define and better understand the geology and the evolution of the hydrothermal system included reconnaissance field mapping, whole-rock geochemistry, short-wave infrared spectroscopy, petrography, and geochronology. Previous studies have shown that only high-sulfidation epithermal mineralization can be spatially and temporally linked to porphyry Cu mineralization, and therefore this study investigates – among other aspects – what type of epithermal mineralization is present at Ronaldo in order to evaluate the potential for concealed at-depth porphyry Cu mineralization. Two separate lower Miocene intrusive units were identified, a porphyritic diorite and a porphyritic granodiorite, whose average age difference is 1.79 Ma. The intrusive units display intermediate argillic alteration. The overlying extrusive units are Sacsaquero Formation basaltic andesites and ignimbrites that are either unaltered or display propylitic alteration. The basaltic andesite roof pendants observed at Ronaldo indicate that the tops of the intrusions are preserved. At high elevations, advanced argillic alteration composed of pyrophyllite, kaolinite, and dumortierite was observed. This area is the remnant, deeper zone of a larger lithocap. The steeply dipping silicified ridges that display sericitic alteration were inferred to be the root zone of this lithocap. Elevated values of trace elements such as Te, Bi, As, and Sb suggest that the Ronaldo prospect is mostly situated in a sericitic alteration zone related to a porphyry-like magmatic-hydrothermal source located at greater depth. Isolated magnetite aggregates were observed in magmatic-hydrothermal breccia, which indicates that the sericitic alteration may have overprinted potassic alteration. A few intermediate-sulfidation epithermal veins and porphyry-related veins, including a banded molybdenite quartz vein, were observed in the creek near the major fault. At Ronaldo, high silica content and sericitic alteration correlate well with elevated concentrations of Ag, Au, and Mo, whereas Cu concentration does not correlate well with any alteration type or with silica content. Quartz veinlets in the silicified ridges that host abundant Ag and Au mineralization were interpreted to have formed at a slightly later stage and to be unrelated to the magmatic-hydrothermal system. This mineralization was interpreted to be low-sulfidation epithermal in origin due to features such as abundant adularia, lattice-textured bladed calcite replaced by quartz, crustiform banding, banded quartz-chalcedony veins, druse-lined cavities, and high Ag/Au ratios. In conclusion, the Ronaldo prospect comprises a hydrothermal system in which the deep, root zone of an advanced argillic lithocap is exposed. The exploration potential for low-sulfidation epithermal mineralization in the silicified ridges is rather significant, whereas the potential for porphyry Cu mineralization is minor due to the lack of appreciable Cu and Mo mineralization, typically shallow-depth porphyry-related hydrothermal alteration, and the lack of high-sulfidation epithermal mineralization.
  • Teräs, Oliver (2022)
    This MSc thesis is built on drill core and outcrops data at the Haukivuori area where fluorite bearing granitoids cut sharply the country rocks (mafic volcanic rocks). This thesis presents new whole-rock geochemical and zircon uranium-lead age data for Haukivuori granitoids in southeast Finland, which provide insights into the distribution of post-collisional granitoids in this region. The purpose of this thesis is to classify a granitoids in Haukivuori and to determine the conditions of their formation. Tectonic evolution of the central and southern Finland is also reviewed and the relationships between Haukivuori whole-rock geochemical data and already published whole-rock data from southern Fin-land post-collisional granitoids are discussed. In the present thesis, the focus is on the 1.815–1.77 billion years post-collisional granitic magmatism across the southern Finland. Haukivuori granitoids modal compositions vary from quartz-monzonite through granite to granodiorite. The contents of quartz, K-feldspar and plagioclase remain consistent all in all, covering about 95 % of the mineral assemblage. The accessories are biotite, muscovite, fluorite, calcite, apatite and zircon as well as oxides. Granitoids show high-K calc-alkaline to shoshonitic affinities and are metaluminous to weakly peraluminous with enrichment in light rare earth elements (example lanthanum normalized to chondrites shows ratios between 93 to 4263) and granitoids lack significant europium anomalies. Granitoids show enrichment in large-ion lithophile elements such as barium (1359–10000 ppm) and strontium (827–8318 ppm), and they display negative anomalies on chondrite normalized spider diagrams in high field strength elements such as niobium, tantalum, zirconium, and titanium. Concordia-intercept age from zircons uranium-lead data of 1794 ± 13 million years is the best crystallization age estimate for the Haukivuori granitoids. Haukivuori granitoid’s age, their undeformed nature, and the fact that granitoids cut country rocks clearly put granitoids into the post-collisional group. Thus, Haukivuori granitoids can be classified as post-collisional granitoids. Haukivuori granitoids display all features of typical high Barium-Strontium granitoids. Thus, granitoids are interpreted to represent a high-level expression of the mantle magmatism that was derived from depleted mantle source which was enriched during an earlier subduction episode.
  • Lahermaa, Petri (2022)
    Kimberlites are a primary source of diamonds. However, not all kimberlites contain diamonds, let alone in the abundance that enable economically profitable exploitation. To assess the diamond potential of kimberlites, the study of kimberlite/diamond indicator minerals (i.e. mantle-derived xenocrysts) can be utilized. In this study the diamond potential of Liqhobong kimberlite cluster in Lesotho, Southern Africa, was studied. Indicator mineral grains (chromian diopside, garnet, chromite, ilmenite) from Liqhobong kimberlites were analysed for major and minor elements using electron microprobe. Results were used to examine formation conditions (P/T) and chemical characteristics of indicator minerals, to define local geotherm and diamond window and to provide general overview to diamond potential of the Liqhobong kimberlite cluster. Based on single clinopyroxene thermobarometry (using Cr-diopside grains as a thermobarometer), the local Liqhobong geotherm is estimated to be ~41 mW/m². It corresponds reasonably accurately to the reference geotherm 40 mW/m², which is widely considered being a decent “average” geotherm at Kaapvaal-Kalahari Craton area. Analysed xenocrysts are principally from the peridotitic source rock. Geochemistry of the indicator minerals show that there is a significant diamond potential in Liqhobong kimberlites. Specifically, Ni-in-garnet thermometry, using the formation depth of the G10 garnets combined to the relevant 40 mW/m² reference geotherm, displays the existence of a significant diamond window at the depth interval of ~140-230 km below the Liqhobong area.
  • Ruhanen, Hanna-Kaisa (2022)
    The 1.64 Ga Ahvenisto complex in the southeastern Finland, is an anorthosite-mangerite-charnokite-granite (AMCG) suite, which has been discovered to host conspicuous magma interaction structures formed in magma mixing and mingling. These structures form areas where the consequences of mingling are found as monzodioritic pillows and granitic veins forming net-veined complexes. Mixing of monzodioritic and hornblende granitic magmas has produced hybrid rocks with intermediate composition. The main goals of the study were to report the major element mineral chemistry of the main minerals (plagioclase, alkali-feldspar, amphibole, and pyroxene) from the hybrid rocks, hornblende granite, and monzodiorite and to test the suitability of geothermobarometric methods for the rock types related to the different magma interaction structures and to evaluate crystallization pressures and temperatures of the pertinent magmas. The magma interaction structures of the Ahvenisto complex are recognized in the mineral chemistry of the mingling and mixing related rocks. The mineral chemistry confirms that the hornblende-granite represents the most primitive granitic phase in the mixing set and the composition of the minerals change as the mixing proceeds towards the final hybrid rock. The mineral chemistry from the monzodiorites reveals that the monzodiorites from different areas of the Ahvenisto complex have distinguished features and they can be separated by their composition. Hornblende-plagioclase thermobarometers and two-pyroxene thermometers were used, and the results were compared to the previous studies related to the emplacement conditions of the Ahvenisto complex. The hornblende-plagioclase thermobarometers suggest that the crystallization of the mixing related rocks took place at ~790–860°C. For the temperature results, pressures of 100 MPa and 300 MPa were used based on earlier studies and a conclusion is drawn that the pressure has had only minor impact on the temperature. The two-pyroxene thermometers show similar regional difference for the crystallization temperatures of the monzodioritic rocks as recognized in the mineral chemistry. The results from the two-pyroxene thermometers show wider variation in the temperatures, which leaves some uncertainty on the liability of the results. The variation is mainly explained by the mineral chemistry of the mafic silicate minerals in the Ahvenisto complex rocks being very iron-rich and outside the calibration standards of the geothermobarometers.
  • Rantanen, Aleksi (2021)
    Vulkaanisten kaarten magmaattinen aktiivisuus nostaa maankuoren lämpötilaa ja laskee sen kestävyyttä, mutta näiden muutosten suuruutta tai muutosten erinäisiä tekijöitä, kuten latenttilämpöä, sulamisesta aiheutunutta viskositeetin laskua sekä intruusioiden koostumusta, lämpötilaa ja sulan määrää ei ole laajemmilta osin tutkittu. Pro gradu tutkielman tarkoitus on kvantifioida näitä kuoressa tapahtuvia muutoksia sekä tutkia erinäisten tekijöiden vaikutusta kallioperän kestävyyteen, kuten sitä kuinka kestävyys muuttuu lämpötilan nousun seurauksena kiinteässä tilassa verrattuna siihen miten se muuttuu kiven sulaessa. Näitä näkökulmia tutkitaan mallilla, joka perustuu kaksiulotteiseen lämpöyhtälöön, joka ratkaistaan differenssimenetelmällä. Kuoren kestävyyden muutoksia lasketaan sarjalla yksiulotteisia kuoren kestävyyskriteerimalleja. Kivien sulamislämpötilat saadaan termodynaamisella ohjelmalla, joka laskee sulafraktiot eri paine ja lämpötilaolosuhteissa ja näitä sulia käytetään hyväksi mallissa, joka laskee efektiivisen viskositeetin osittain sulaneelle kivelle. Kuoren kestävyyttä ja lämpötilan muutoksia tarkastellaan tekemällä useampia simulaatioita, jotka jäljittelevät magmaattisen kaaren vulkanismia. Maankuoren integroitu kestävyys laskee magmakammioiden läheisyydessä jo muutaman miljoonan vuoden kuluttua ~80 % eikä tämä arvo muutu huomattavasti jatkuvan magmaattisen aktiivisuuden seurauksena. Magmakammioita ympäröivä maankuori kuitenkin jatkaa heikentymistä koko magmaattisen aktiivisuuden ajan (10 Ma) eikä tämä ei ole ainoastaan seurausta hitaasta lämmönjohtumisesta. Magmaattisen aktiivisuuden päätyttyä maankuori jäähtyy ja kiteytyy, jolloin intruusioiden mekaaniset ominaisuudet saattavat joko heikentää tai kestävöittää kallioperää suhteessa maankuoren alkuperäiseen kestävyyteen riippuen intruusioiden ja niitä ympäröivän kiven mekaanisista ominaisuuksista. Mafiset intruusion kykenevät kestävöittämään kallioperää helpommin syvemmällä, missä kuori alun perin deformoitui plastisesti, kun taas felsiset intruusiot kykenevät mekaanisesti heikentämään maankuorta matalammilla syvyyksillä. Pitkällä aikavälillä intrudoituvan magman lämpötila on vähemmän tärkeä tekijä kuoren kestävyydelle, kuin intruusioiden mekaaniset ominaisuudet. Kiven sulamisella ei näytä olevan huomattavaa vaikutusta kuoren kestävyyden muutoksiin. Suurin osa simulaatioista osoittaa, että kuoren integroitu kestävyys on pudonnut jo yli 99.9 % lämpötilan nousun seurauksena ennen kuin kuori alkaa sulamaan. Jopa äärimmäisimmissä skenaarioissa kuoren sulamisesta aiheutuva integroidun kestävyyden lasku pysyy pääsääntöisesti 0.5 % alapuolella. Mitä enemmän magmassa on sulaa, sitä suurempi vaikutus latenttilämmöllä on kuoren lämpötiloihin. Magmaattisen aktiivisuude aikana intrudoituvalla magmalla minkä sulamäärä on 10–100 %, latenttilämmön osuus lämpötilan noususta on 12–34 %. Latenttilämpö vaikuttaa enemmän kuoren kestävyyteen magmakammioiden läheisyydessä ja laskee kuoren kestävyyttä enemmän magmaattisen aktiivisuuden päätyttyä. Maximissaan latenttilämmöstä aiheutunut kuoren integroidun kestävyyden lasku on 10–30 % magmakammioiden läheisyydessä ja keskiarvo on 5–17.5 % 50 km säteellä magmakammioista, riippuen magman alkuperäisestä sulan määrästä. Tektoniikan kannalta on tärkeää ymmärtää miten magmaattinen aktiivisuus vaikuttaa maankuoren kestävyyteen. Maankuori on heikoimmillaan suoraan magmakammioiden läheisyydessä magmaattisen aktiivisuuden aikana, joka saattaa aiheuttaa paikallisia muutoksia kuoren deformaatiossa ja hiertovyöhykkeiden muodostumisessa, mutta pitkällä aikavälillä intruusioiden koostumus ja niiden mekaaniset ominaisuudet saattavat vaikuttaa huomattavasti kuoren kestävyyteen. Koska kuoren sulamisesta aiheutunut viskositeetin lasku ei ole huomattava tekijä kuoren kestävyydelle, niin muut magmaattiseen aktiivisuuteen ja vulkanismiin liittyvät tekijät ovat todennäköisesti tärkeämmässä osassa, kuten kiven sulamiseen liittyvä tiheyden lasku ja tilavuuden kasvu, joka taas johtaa uusiin maankuoreen syntyviin jännityskenttiin, kallioperän murrosten syntymiseen sekä magman liikkumiseen.
  • Wiberg, Meri (2023)
    The need for renewable energy sources is continuously increasing due to the prevailing climate change. The temperature of the Earth's crust increases with depth, providing more energy than humanity can utilize. Geothermal energy is a low-carbon form of energy, and its potential is being increasingly exploited. The design of an energy well requires geological investigations and knowledge of geothermal properties such as thermal conductivity, energy well thermal resistance, and heat capacity. Preliminary studies and modeling of energy wells have utilized in situ measurements, such as thermal response testing and active distributed temperature sensing, to determine thermal conductivity and energy well thermal resistance. By using information on mineral composition and mineral distribution in the rock formation, the thermal conductivity and heat capacity of the rock can be calculated. In the modeling of geothermal fields, thermal conductivity, energy well thermal resistance, and heat capacity are utilized. Both computational and in situ methods provide two of these factors, with thermal conductivity being a common factor. However, the methods differ in terms of ecological impact, implementation time, and cost-effectiveness. In the thesis, comparisons have been made between the results and differences of the methods, as well as a cost estimate comparison between the methods.
  • Vatanen, Jonna (2022)
    The Kiimala Trend in Central Ostrobothnia, western Finland hosts orogenic gold de-posits. According to earlier studies conducted in the area by the GTK and Ou-tokumpu Exploration, the orogenic gold deposits contain varying amounts of gold ranging from 1.19 to 2.5 ppm and minor amounts of sulfides. In the Kiimala Trend area, the gold deposits of interest are Kiimala, Ängesneva, Vesiperä, and Pöhlölä. Fel-sic porphyries located in these areas are host rocks for orogenic gold, but little petro-logical and mineralogical information on the porphyries exists, and the available in-formation lacks both details and up-to-date data. During this study, the rocks in the Kiimala trend were mainly categorized as plagio-clase porphyries, plagioclase-porphyritic amphibolites, amphibolites, schists, sulfide veins, and diorites. Geochemically the rocks represent various types of gabbros and diorites. The rocks have been metamorphosed in amphibolite facies conditions during the Svecofennian orogeny. During the metamorphic events, low-salinity hydrothermal fluids altered the rocks resulting in saussuritization, sericitization, alkalization, calcifi-cation, epidotization, and chloritization. Hydrothermal fluids also caused the minerali-zation of gold-, iron-, arsenic-, and copper-bearing sulfides as well as the mineraliza-tion of various metals, most common being bismuth, lead, electrum, silver, and anti-mony. Common oxides are rutile that appears often as rims surrounding ilmenite, and hematite that is associated with hydrothermal veins. Most sulfides and oxides can be found as inclusions or in association with quartz and feldspars, exception being ilmen-ite, that can be found in biotite or chlorite.
  • Lumppio, Toni (2023)
    Cobalt is a strategic metal whose production is dominated by a handful of countries and mines. The Terrafame (formerly known as Talvivaara) black-shale hosted Ni-Cu-Zn-Co deposit in North-Eastern Finland is a globally significant deposit for cobalt containing 1 453 Mt of ore averaging 0.02% Co. The enrichment of cobalt has likely taken place during multiple phases throughout the geological history of the deposit with both the depositional phase and the orogeny phase having a key effect on concentrating cobalt. Scanning electron microscope based automated mineralogy (SEM-AM) and electron probe microanalyses (EPMA) were applied to study the mineralogy of 15 thin sections from Kuusilampi ore body. The results from SEM-AM were further enhanced by applying a python programming language-based data processing procedure that was created specifically for this study. The main Co-containing sulfide minerals at Terrafame are pyrite, pyrrhotite and pentlandite. The Co concentration in pyrite is controlled by the grain type, with pyrites that exsolved from the monosulfide solid solution having the highest average Co concentration. The Co concentration in pentlandite appears to be controlled by the host rock with Mn-rich calc-silicate rocks having an average of 2.77 wt.% Co and black shales 0.47 wt.% Co in pentlandite. Co-rich, with up to 27 wt.% Co sulfarsenide group minerals also occur in the deposit, but their abundances were calculated to be too low to be considered a major contributor to the bulk cobalt concentration at the Terrafame deposit.
  • Rantanen, Hanna (2021)
    The Paleoproterozoic (1.87 Ga, ɛNd -3.7) Suvasvesi granitoid intrusion in southeastern Finland is considered to be a part of the Heinävesi intrusive suite. Inner parts of the lithologically zoned Suvasvesi intrusion are variably alkali feldspar porphyritic biotite granitoid rock and the margins are composed of a more biotite-rich equigranular granitoid rock variety. The Paleoproterozoic metasedimentary rocks of the Viinijärvi suite adjacent to the Suvasvesi intrusion are intruded by leucocratic pegmatite dikes. Potential sources and possible contamination of the granitoid melt are considered with the help of structural and textural observations, petrography, whole-rock geochemistry, mineral chemistry, and petrophysical data. The data were acquired from 34 rock samples collected during a bedrock mapping campaign and combined with the pre-existing mapping, petrographic, and geochemical data from the Suvasvesi and surrounding areas. The Suvasvesi granitoid intrusion is compared to other members of the Heinävesi suite to verify the hypothesis of their petrogenetic connection. The compositions of both Suvasvesi intrusion and Heinävesi suite are also compared to the potential proximal sources, the adjacent Paleoproterozoic metasedimentary rocks and Archean units in the area. In addition, the compositions of the Suvasvesi intrusion and Heinävesi suite rocks are compared to other granitoids from Eastern and Northern Finland with suggested Archean sources, and to regional granitoids of same age. Based on the similarity of major and trace element compositions, it is suggested that the Suvasvesi granitoid is part of the Heinävesi suite. The granites and granodiorites of the Suvasvesi granitoid and the Heinävesi suite are ferroan, calc-alkalic, and peraluminous with average ASI value of 1.08 (n = 73). Although the Heinävesi suite is postkinematic, it shows very few similarities to other rocks of same age. The εNd values of the Heinävesi suite and the paragneiss enclaves within the Suvasvesi intrusion indicate metasedimentary source component or assimilation. Conversely, the I-type mineralogy and geochemistry suggest igneous/meta-igneous source component for the Heinävesi suite. Potential infracrustal sources for the granitoid magma are the Archean TTGs and amphibolites. The conclusion for the magma source is ambiguous. For further studying additional isotope analyses and thermodynamic modelling of the Suvasvesi and Heinävesi magmas are suggested.
  • Lesch, Juho (2022)
    Continental flood basalts (CFBs) in the Karoo large igneous province were formed 189–178 Ma ago during the breakup of the Gondwana supercontinent. The flood basalts are found in the southern part of Africa, in Antarctica, and in the Falkland. The Karoo province can be divided into the North Karoo and South Karoo subprovinces on the basis of the geochemical compositions of the CFBs. The source of the South Karoo lavas has been interpreted to consist of pyroxenitic mantle and depleted upper mantle. The North Karoo lavas have been less well studied. The source of the North Karoo lavas at Luenha River, Mozambique, has been interpreted to be in a primitive part of the African LLSVP (Large Low Shear Velocity Province) in deep mantle. It is also believed that they have surfaced as part of a mantle plume. The results on the mantle source of the North Karoo CFBs have not been conclusive, however. In this study I analyze olivine crystals from the Luenha River picrites and utilize their mineral composition to address the mantle source of the North Karoo lavas. Four of the samples from Luenha River contain fresh olivine. They were analyzed using EPMA. All the analyzed olivine crystals are within Fo77–89. The compositional variation within the samples is relatively small and there is no evidence of multiple olivine populations. The olivine compositions support the proposed primitive peridotitic mantle source of the Luenha picrites. They are very similar to the olivines of the Etendeka CFBs that have been interpreted to be from peridotitic mantle source. The olivines from the Luenha picrites have high Mn/Fe ratios and low Ni, Ca, and Zn concentrations, which indicates a peridotitic source. The portions of pyroxenite and recycled oceanic crust were calculated to be less than 10 weight percent. In two samples, the crystallization temperatures were determined to be 1207–1368°C using an Al-in-olivine thermometer. Combined use of the Al-in olivine and the melt-olivine Mg-Fe equilibrium thermometers enabled the estimation of the temperatures of the primary melts (Fo92). The temperatures of the primary melts were 1300–1472°C, which supports the theory of Luenha picrites being derived from a mantle plume.
  • Karpoja, Anna (2019)
    Kaapelinkulma is an orogenic gold deposit located in the Paleoproterozoic Vammala Migmatite Belt (1.91 – 1.79 Ma) in Valkeakoski municipality in Southwestern Finland, and it is considered to have been formed in microcontinent collision during Svecofennian orogeny and has been classified as an orogenic gold deposit. Kaapelinkulma comprises a set of sub-parallel lodes in a tight array hosted within a sheared quartz-diorite unit inside a tonalitic intrusion. Gold occurrence is hosted by an en echelon type sheared quartz-dioritic dyke which forms a large xenolith inside synorogenic tonalite intrusion, surrounded by mica gneiss. It is estimated that Kaapelinkulma gold deposit contains at least, 168 Kt of ore containing 3.8 g/t Au. Textural setting, mineralogical association form and assemblage of gold, sulphides and telluride grains in Kaapelinkulma were studied with field-emission scanning electron microscopy, with electron probe microanalyzer and scanning electron microscopy. Ore minerals observed in Kaapelinkulma are: arsenopyrite, löllingite, pyrrhotite, pyrite and chalcopyrite. Other ore minerals identified are native bismuth, gold, scheelite, bismuth-tellurides and maldonite, which were all found in abundant amounts. Ore minerals occur as dissemination in intergranular spaces between silicate matrix, as polycrystal aggregates in quartz-veins and quartz clusters; and within shear zones. Gold in Kaapelinkulma is present as two generations: as single free native gold grains and as polycrystalline gold aggregates. Polycrystalline gold aggregates are grains formed from several mineral association and their combinations. Most common polycrystalline gold aggregates are formed from combination of: maldonite-native Au, Au-Bi alloys, Au-Ag grains and Au-hedleyite. Single free native gold grains are pure gold or gold-silver alloys. Free native gold grains can be found as intergranular, single grains in silicate matrix and adjacent or as a part of disseminated ore together with polycrystalline gold aggregates, bismuth and bismuth tellurides. Polycrystalline gold aggregates are found in disseminated ore, which are in close contact with quartz-veins and sulphide aggregates, or as inclusions in arsenopyrite-löllingite contact zones- or in other sulphides. Concentration of Au varies in native-gold grain from 76.83 to 97.87 wt% according to EPMA analyzes and from 50.03 to 100 wt% according to FE-SEM analyzes. Minor to moderate amounts of silver and copper were identified within the grains. Grain sizes of gold varies significantly from 7µm2 to 5mm2. Ore mineral paragenesis were observed to start when arsenopyrite and löllingite crystallized first, followed, partly simultaneously by pyrrhotite, pyrite and chalcopyrite. This was followed by crystallization of maldonite, first occurrence of native gold and bismuth, bismuth-tellurides, hedleyite and finally tellurides and main occurrence of gold. General ore forming process in Kaapelinkulma has been open space filling.
  • Lehtovuori, Aki (2023)
    The Bjurböle meteorite, which fell near Porvoo in 1899, is categorised as a fall. The Bjurböle meteorite is classified as an L/LL4 ordinary chondrite. Chondrites are undifferentiated meteorites that contain notable amounts of non-volatile elements of the early solar system. Chondrites usually contain small spherical igneous chondrules and they are classified into three groups: carbonaceous (C), enstatite (E) and ordinary chondrites (O). Ordinary chondrites are further classified into groups H, L and LL according to their metallic iron content. Chondrites are classified into petrologic types 1 – 6 based on their metamorphic grade so that Type 3 is the least metamorphosed and Type 6 is the most strongly metamorphosed, whereas Type 1 and Type 2, on the other hand correspond to meteorites that are, respectively, strongly and mildly affected by low-temperature aqueous alteration processes. The chemical equilibration of chondrites is controlled by the degree of metamorphism they go through. The more equilibrated a chondrite is, the more simplified its mineral assemble is and the more homogenised compositions the minerals have. Chondrules contain mostly olivine, pyroxene and interchondrule matrix. They are classified into Type I and Type II by the compositions of their olivine and pyroxene. Chondrule types can be further divided into A, B and AB by their olivine content. In addition, chondrules can be classified according to their texture into porphyritic, barred, radial, granular, cryptocrystalline, and metallic chondrules. The aim of this thesis is to inspect the variation in olivine composition in Bjurböle meteorite chondrules, to document the petrography of the Bjurböle meteorite and to find connections between petrographic discoveries and olivine composition. Furthermore, in this study I will discuss about the classification of the Bjurböle meteorite and the formation of chondrules in the Bjurböle meteorite. For this study, I examined 11 thin sections and three epoxy buttons that have 34 chondrules in total. Thin sections were inspected by microscope and six of the uncoated thin sections were also inspected under cold-cathode luminescence. The epoxy buttons were inspected with a scanning electron microscope, scanning electron microscope cathodoluminescence and scanning electron microscope energy-dispersive X-ray spectroscopy. Most of the inspected chondrules in the Bjurböle meteorite samples have very uniform olivine composition, as reported in earlier studies. Most of the olivines are Fo75–78, but there is also a bimodal peak at Fo89–92. The E1 chondrules (small) have very uniform olivine compositions of approximately Fo76–77. The E2 chondrules (medium) have also olivines of approximately Fo76–77, but some of the olivines reach Fo80–83. The E3 chondrules (large) have the broadest olivine composition variation at Fo74–93. However, most of the E3 olivines are Fo76–79. The E3-2 chondrule, in particular, has a broad olivine composition variation and its Fo-value increases up to 93 in the core of the chondrule. All chondrules with broader olivine variation have barred texture and are relatively large. Cathodoluminescence did not provide substantial data for the study. Other links between olivine compositions and petrography were not observed and, for example, proximity to metallic phases did not seem to have any effect on the olivine composition, and the exceptionally Mg-rich (Fo90) olivines may represent primary compositions. E3-6 and E3-7 chondrules are abundant in sulphide and metallic phases. The E3-7 chondrule resembles something that might be called micropallasite. Based on porosity, magnetic susceptibility, metamorphic signs, and the Fe variation in olivine and mineral assemblages, the Bjurböle meteorite fits the classification of an L/LL4 ordinary chondrite. Chondrules of the Bjurböle meteorite also have diverse forming histories.
  • Karampelas, Nikolaos (2022)
    Archean cratons hold information of the early crustal development of the Earth, in conditions much different than the ones that exist today. Archean cratons consist of felsic plutonic rocks and greenstone belts. These belts are a useful tool for the understanding of the development of the early geological processes that shaped the Earth. There has been a variety of suggestions regarding the origin and geodynamic conditions that formed the Archean greenstone belts and there are several possible geotectonic scenarios that could form them. This thesis focuses on the Takanen greenstone belt found in the Karelia province in the Fennoscandian shield. The main objective of this study is to constrain the age of the greenstone belt, as well as to classify and group the formations found in it and compare it with its neighbouring, and much larger, Suomussalmi-Kuhmo-Tipasjärvi greenstone belt system - the biggest complex of its kind in the Karelian craton. A diamond drilling profile across the Takanen belt has been sampled. The various rocks found in the belt are divided into 5 groups based on their thin-section petrography and major and trace element geochemistry, outlining the general stratigraphy of the belt. There are also whole rock analyses that help to obtain major and trace element geochemical data for multiple samples from different locations throughout the belt. There are 3 calc-alkaline units (CALC1, CALC2, CALC3, named after their predominantly calc-alkaline nature) that include felsic, to intermediate volcanic/volcanosedimentary rocks and 2 units that consist of channelized komatiitic lavas and tholeiitic basalts (KOMBAS, named after the komatiites and basalts of the unit), olivine/olivine-pyroxene cumulates and high-Mg to tholeiitic basalts (OLIAD, named after the abundance of olivine adcumulates). The CALC1 unit is found lowest in the stratigraphy of the area and bares the oldest age of 2.95 Ga, while CALC3, which is the youngest formation of the belt, gives an age of 2.7 Ga. There is a direct correlation with the lowest CALC1 unit and the Luoma group in the Suomussalmi greenstone belt in terms of petrography, geochemistry and age, indicating that Takanen is the continuation of the Suomussalmi-Kuhmo-Tipasjärvi system to the north. Based on the initial Lu-Hf isotope composition of the dated samples, and the stratigraphic layering of Takanen, the oldest units in the belt originate from a process of continental rifting, while the youngest ones were most likely formed by a combination of continental rifting and some interaction of the continental crust with oceanic lithosphere. The Takanen greenstone belt lies on top of a large positive gravimetric and magnetic anomaly in the Koillismaa area called the ‘‘hidden dyke’’, composed of mafic-ultramafic cumulates and hypothesized to be related to the Paleoproterozoic Koillismaa-Näränkävaara Layered Intrusion Complex. The dyke and Takanen may not be genetically related, yet their overlapping existence points to a large crustal structure that served as a magma pathway throughout the Archean and the Paleoproterozoic. The potential of an economic orthomagmatic nickel deposit related to Takanen should not be completely overlooked, as there are some favorable indications in the geochemistry of the komatiitic units, as well as their possible interaction of these units with older sulphur rich units of the belt.
  • Markkanen, Minna (2021)
    The orbicular quartz monzonite from Kuohenmaa, Southwest Finland, is one of the most beautiful and well-known orbicular rocks in the world. The cores of the orbicules are peraluminous in composition, most likely of xenolithic metasedimentary origin. The cores are surrounded by orbicule mantles, which consist of several alternating biotite- and plagioclase-rich shells. There are three types of orbicules in Kuohenmaa orbicular rock: proto-, small-, and large-orbicular types. Proto-orbicules have only a few shells, small orbicules ~ 50 shells in average, and large orbicules over 250 distinct shells. In addition to shells, one sample was observed to be associated with comb layering in the contact of proto-orbicular and large orbicular types. Structures and textures of the comb layer resembles those of the outer shells of large orbicules. The orbicules are embedded in interstitial coarse-grained groundmass that forms locally almost pegmatitic patches. The petrographic observations were acquired from eight samples or sample photographs gathered from different collections. A mineral chemistry dataset was measured from a single large orbicule from the University of Helsinki collections. The main minerals of the Kuohenmaa orbicular rock are plagioclase, biotite, microcline, muscovite, and chlorite. The shell textures vary from branching plagioclase-rich shells to fine-grained plagioclase- or biotite-rich shells. Branching shells are mainly oligoclase, but a few granular andesine crystals were detected in the core. Peculiar interstitial fibrous allanite masses were found in the inner branching plagioclase-rich shells. The plagioclase compositions generally follow a regular fractional crystallization trend from core to groundmass, but some changes towards more primary compositions are observed in the orbicule mantle. Plagioclase crystals display only minor compositional zoning, suggesting rather quick crystallization. Biotite is very aluminous (Al2O3 17.63–18.53) in composition, and the compositional changes seem to have somewhat positive correlation with plagioclase compositions, suggesting changes in their crystallization conditions. Injections of primary melt from a deeper source most likely caused the observed changes to more primitive composition in plagioclase and biotite composition. Through the detailed petrographic and geochemical studies, a model of undercooling caused by decompression driven fluid saturation is proposed as a mechanism for orbicule formation in the Kuohenmaa orbicular rock. Branching plagioclase with interstitial fibrous allanite masses and several fluid inclusions in plagioclase indicates separate aqueous REE-enriched melt and rapid crystallization. Further studies of fluid inclusions and REE-enriched phases could provide information of the fluid origin and crystallization conditions.