Browsing by Subject "geochemistry"
Now showing items 1-9 of 9
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(2019)Arsenic (As) is a metalloid naturally present in the environment. Arsenic species vary in toxicity. Metal mining has contributed to the anthropogenic input of arsenic to groundwaters and surface waters. In this study, water samples were collected from 20 sample points in three mining-impacted study areas in Finland: the former Ylöjärvi Cu–W–As and Haveri Au–Cu mines, and the active Pyhäsalmi Zn–Cu mine. Six groundwater well samples, eleven surface water samples and three tailings seepage collection ditch samples were analyzed for dissolved arsenic speciation by HPLC-ICP-MS and for geochemical composition by ICP-MS, titration, and ion chromatography. Dissolved arsenic concentrations ranged from 14.2 to 6649 µg L-1 in samples collected at the Ylöjärvi study area, from 0.5 to 6.2 µg L-1 in samples collected at the Haveri study area, and from 0.2 to 9.4 µg L-1 in samples collected at the Pyhäsalmi study area. In all study areas, measured dissolved arsenic concentrations showed a general decrease from the tailings to the surroundings. Speciation analysis showed that two of the samples collected at the Ylöjärvi study area had arsenite [As(III)] as the dominant form of dissolved inorganic arsenic (iAs), three had arsenate [As(V)] as the dominant form of dissolved iAs, and four had a mixture of both. In the water samples collected at the Haveri and Pyhäsalmi study areas, all concentrations of dissolved arsenic species were below method detection limits. Also, none of the 22 water samples analyzed for arsenic speciation had dissolved MMA or DMA concentrations above method detection limits. Identification of dissolved arsenic species in the sampled waters in Haveri and Pyhäsalmi, and of MMA and DMA in all sampled waters requires more detailed study. A significant 2-tailed Pearson correlation between dissolved arsenic and dissolved molybdenum (Mo) (r=0.80**, n=20), and dissolved arsenic and dissolved potassium (K) (0.68**, n=19) suggests that in these three study areas the distributions of dissolved arsenic and Mo, as well as dissolved arsenic and K may be controlled by the same environmental variables. Anomalously high maximum concentrations of dissolved Al, Ca, Co, Cu, Fe, Ni, and SO4 were measured in surface water samples collected at the Ylöjärvi and Haveri study areas, and in a seepage collection ditch sample collected at the Pyhäsalmi study area.
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(2020)The oldest rocks in Finland are the Archaean grey gneisses of eastern and northern Finland. The Archaean of the Karelian craton spans about 1000 Ma of crustal growth and evolution and forms the core of the Fennoscandian shield. The Karelian province is a complex patchwork of different rock types. The individual formations are of small territorial extent in accordance with often postulated small Archaean plates. Overall, the Karelian craton is a granitoid-greenstone terrain with prevailing TTGs and younger granites, which show increasing level of potassium. The craton also includes a distinct sodic variety of granites that combines features of classical Archaean TTGs and late Archaean high-K granites. A minor number of Mg-rich lithologic units, including adakites and sanukitoids, are reported as well. A small number of A-type granites, syenites and S-type granites are widely distributed and of local nature only. Peculiarly, a large number of TTGs is peraluminous. The formation of Karelian craton may be explained by accretion of small plates, perhaps during the late Archaean supercraton event in a process that at least in later stages included active plate marginal processes.
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(2019)The Central Finland Granitoid Complex (CFGC) is a large (44,000 km2) plutonic core of a Svecofennian (Paleoproterozoic, 1.91–1.82 Ga) arc complex, formed from collisions of several volcanic arcs and their accretion over the Karelian craton. The CFGC consists mostly of granitic to granodioritic rock types. Mafic-ultramafic plutonic rock types are not common, and they consist of mostly small gabbro-diorite intrusions, which may have ultramafic parts. There are two distinct belts around the CFGC, where Ni-Cu potential mafic-ultramafic intrusions are situated – Vammala and Kotalahti. The intrusions within these belts were formed during the height of magmatism within the CFGC (1.89–1.87 Ga). They host Ni-Cu mineralizations, some of which have been economically exploited. The mineralizations are hosted by olivine-rich ultramafic cumulates. The intrusions formed from hydrous tholeiitic basalts (10–12 wt-% MgO) with arc-type trace element chemistry. The difference between Vammala and Kotalahti type intrusions (clinopyroxene and orthopyroxene-dominated, respectively) are attributed to the rock type of the assimilated country rock. In this thesis, three previously unknown or poorly studied mafic-ultramafic intrusions (Matokulma, Palojärvi, and Hongonniittu) within the CFGC are studied in detail. The petrology, similarity to Vammala-Kotalahti type intrusions, parental magma compositions, ore potential, and petrogenesis of the intrusions are described. Rock samples and field observations were gathered during the summer of 2017. Whole-rock geochemistry, mineral geochemistry, isotope geochemistry, and geophysics are used to describe the petrology of the intrusions. Matokulma and Palojärvi intrusions are studied in detail, compared to Hongonniittu intrusion, which was not studied as intricately. The Matokulma intrusion is the least evolved (whole-rock median Mg#=72) of the studied intrusions and consists of tholeiitic melagabbros where clinopyroxene±orthopyroxene and plagioclase are the main cumulus phases within interstitial, magmatic amphibole (magnesiohastingsite to pargasite in composition). Orthopyroxene and plagioclase are intercumulus phases in some samples. There are also mafic dikes that intrude the tonalitic country rock that surrounds the gabbro. The dikes are similar to the gabbros in geochemistry although they are generally more evolved. Trace element geochemistry suggests that the gabbros and dikes are genetically connected, and the dikes possibly represent the residual magmas of the gabbros. The Palojärvi intrusion is noticeably more evolved than the Matokulma intrusion (median Mg#=49), which is apparent in the iron and titanium rich mineral and whole-rock geochemistry. The strongly tholeiitic melagabbros are composed of both orthopyroxene and clinopyroxene as cumulus phases with plagioclase and common Fe-Ti oxide, often within interstitial magmatic amphibole (magnesio-hastingsite to magnesioferri-hornblende in composition). The Fe-Ti oxides are mostly ilmenomagnetite but both magnetite and ilmenite grains are present in same samples. Based on a few mineral analyzes, the ilmenomagnetite contains up to 1.4 wt-% V2O3. U-Pb age determination samples from a leucogabbro dike within the intrusion and granite that crosscuts the intrusion yielded weighted average 206Pb/207Pb ages of 1883.4±4.8 Ma and 1893.8±7.1 Ma, respectively. The age results are in contrast to the intrusive relationship observed in the field. However, considering the margin of error of the results, the granite can be younger than the gabbro, 1887 Ma and 1888 Ma, respectively. The age of ca. 1.89 Ga is at the early stage of the most voluminous mafic-ultramafic magmatism in the Svecofennian terrane. The parental magmas of the Matokulma and Palojärvi intrusions were evolved and contained approximately 5 wt-% and 2 wt-% MgO, respectively. The presence of magmatic amphiboles in most samples indicate that the parental magmas were hydrous. Samples from all intrusions plot similarly in primitive mantle normalized Rare Earth Element (REE) and Normal-Mid-Ocean Ridge Basalt (NMORB) normalized spider diagrams. Similar patterns indicate a similar source for the parental magmas. The trace element geochemistry has signatures of subduction related fluid metasomatism. The rocks are enriched in large ion lithophile elements (LILE) and depleted in High Field Strength Elements (HFSE). These geochemical characteristics indicate that the studied intrusions crystallized from a hydrous, NMORB-like evolved basaltic magma, which has experienced fluid metasomatism. The studied intrusions differ from olivine-rich ultramafic cumulates of Vammala and Kotalahti type intrusions based on their more evolved, gabbroic composition and because of this, they are not Ni-Cu ore potential. Palojärvi may host a Fe-Ti-V mineralization, if there are magnetite rich layers within the intrusion.
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(2020)Geochemical ore exploration with geogases is based, like the MMI method, on the movement of mobile metal ions. The assumption is that the buried mineralization is possible to locate using the samples collected from the surface sediment. In this study, the detection of gold-copper anomalies by geogases was tested in three different regions of the West Lapland ice divide zone. Geogas samples were collected using an active gas collector at 25 cm below the lowest visible soil horizon. The samples were bubbled into nitric acid and analysed with ICP-MS. The elements studied were As, Co, Cr, Cu, Fe, Hg, Ni, Pb, U and Zn. Only few elevated levels of arsenic, cobalt, mercury and nickel were found in the gas samples In the Hannukainen mining area, geogases were collected at known ore settlement, in which gas concentrations showed a clear anomaly in soil directly above the outcropping ore. At Kelontekemä, the concentrations of geogases were compared with MMI results from soil samples collected nearby. There appears to be a connection between concentrations of gases and soil samples, but the concentrations of soil samples are often a thousandfold higher. In this study, the Jolhikko region served as a background area, which allowed to conduct a comparison between the area containing mineralization and the background area of precious metals. In light of this research, geogases are a working tool for geochemical ore exploration. However, and in order to understand the complexity of this phenomenon, it is necessary to conduct further studies. The use of geogases also requires special care from samplers to minimize contamination risks.
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(2020)Siilinjärvi carbonatite in the eastern Finland is an Archaean intrusion. It is mined for the phosphorus bearing apatite used in fertilizers. Saarinen open pit is a satellite mine of the main Särkijärvi open pit. Siilinjärvi carbonatite is the lowest grade apatite ore in the world being excavated and the largest industrial mineral mine in Finland with approx. 11 Mt ore mined yearly making up almost 70 percent of the industrial minerals mined in Finland. The Siilinjärvi carbonatite is a north-south trending and nearly vertical intrusion within basement gneisses. The complex consists of a continuous rock series between end members of nearly pure glimmerite and carbonatite. During the intrusion, the glimmerite-dcarbonatite has metasomatically altered the adjacent country rocks resulting a fenite halo of varying thickness. The purpose of this M. Sc. thesis was to produce a geological map and study the petrography and geochemistry of the rock types of the complex in the Saarinen area. The bedrock surface of Saarinen open pit area was mapped in detail with a GNSS receiver and data was edited with LeapFrog, ArcMap and QGIS. 24 rock samples were collected and thin sections were prepared for petrographic analysis. ICP-MS analysis was made of 20 rock samples to obtain whole rock geochemical data. Sludge sampling was carried out which produced 299 samples from 51 drill holes down to maximum 24 metres from the surface. Sludge samples were analysed with ICP-OES. Geological mapping showed that the most carbonate rich rock types of the complex are located in the middle of the complex. The different rock types of the complex are oriented along the main direction of the formation. Fenite occurs on the edge of the complex and as xenoliths within the glimmerite-carbonatite series rocks. Petrography studies showed that nearly all of the samples shared the same mineral constitution, only the modal proportions of different minerals vary. The main minerals are phlogopite, calcite, richterite and apatite. Geochemical whole rock analysis indicated that the phosphorus content of the rocks studied is highest in the rock types containing 10-50% carbonates. The trace element and REE compositions of the samples differ from average carbonatite, especially Nb, La, Ce and Y contents are lower. The geochemical analysis of sludge samples showed that the rock types are not continuous across long depths.
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(2010)Object of this reseach is geochemical characterization of Häme diabase dyke swarm. The analysed dyke (n=42) samples were collected using a hammer. The chemical analysis were performed at Helsinki University for major and some trace elements using XRF analyser and at GeoLab, Washington University for lanthanides and trace elements using ICPMS analyser. The reseach area is situated in the east 35 km north from Tampere and in the west the area of Heinola city. The age of Häme dike swarm is ~1.6 Ga, which is also the age of nearby rapakivi inturions in the area. The Häme dike swarm cuts sharply 1.9 Ga svecofennian bedrock. The Häme swarm has been divided into two sets of dykes based on different strikes, compositional features and in age. One of the sets strikes WNW and the other one NW. Häme dyke swarm resembles continental flood basalts. They are relatively alkaline ironrich continental quartz and olivine tholeiites. Main minerals are olivine, pyroxenes and plagioclase. Their TiO2 (1,4–3,3 p. %), P2O5 (0,4–1,1 p. %), Fe2O3 (12,3–16,6 p. %) and Al2O3 (12,9–18,6 p. %) contents are relatively high and MgO (3,4–5,9 p. %) and CaO (6,2–8,7 p. %) contents are relatively low. The abundances of incompatible trace elements are high and they show LREEenriched REEpatterns, also their Ni and Cr contents are relatively low. In Spider diagram you can see negative Eu, Nb and Ti anomalies in and positive Pb anomaly. Geochemical data doesn’t correlate with two different strike sets and dykes have no correlation with their geographical settings.
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(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.
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(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.
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(2021)A NW–SE trending dike swarm cuts Miocene volcanic rocks in the Ibex Hills and Precambrian to Cambrian cratonic rocks and sedimentary strata in the Saddlepeak Hills and Salt Spring Hills in southern Death Valley, California. These dikes are aligned with Jurassic and Cretaceous dike swarms of eastern California that are linked to the Mesozoic North American Cordilleran magmatism. The Ibex Hills dikes have been previously dated and yield K-Ar date of 12.7 Ma and are coeval with the early stage of the Miocene Basin and Range crustal extension in Death Valley. This Master’s thesis examines in detail the geology, petrography and geochemistry of the previously unstudied dikes of Ibex Hills, Saddlepeak Hills and Salt Spring Hills of southern Death Valley and a ~90 Ma dike of Mojave Desert to discuss (1) their petrogenetic link to each other and (2) their geologic significance. The samples and field observations were obtained in 2019. The Ibex Hills samples are relatively fresh compared to the dikes of Saddlepeak Hills and Salt Spring Hills which are pervasively altered by secondary minerals and have been subject to low-grade metamorphism. The sub-solidus processes that have modified the mineral assemblages of the metamorphic dikes are also reflected in various degrees of major element mobility and LOI. The whole-rock geochemical composition of the Ibex Hills and Mojave Desert samples is trachyandesite to trachyte, the Saddlepeak Hills and Salt Spring Hills samples are andesites. One Saddlepeak Hills sample is basaltic and, based on mineralogy, texture and composition, represents a 1.1 Ga diabase intrusion. All studied samples are enriched in LREEs and LILEs and have negative Ta-Nb anomaly, representing magmas with typical subduction zone characteristics with enriched lithospheric mantle component in source. EPMA and in situ LA-MC-ICP-MS analysis of plagioclase phenocrysts of two Miocene samples of Ibex Hills shows variation in anorthite content and 87Sr/86Sr ratios across phenocryst profiles indicating open-system magma chamber evolution with episodes of recharge, hybridization and assimilation during the crystallization. Variation in anorthite content and 87Sr/86Sr ratios between samples suggest heterogeneities in the source magmas. The studied dikes represent multiple episodes of dike emplacements in southern Death Valley. The Miocene dikes of Ibex Hills, coeval with the Basin and Range crustal extension, indicate an early period of southwest directed extension in the southern Death Valley. The metamorphosed dikes of Saddlepeak Hills and Salt Spring Hills represent one or more episodes of older dike emplacement and could be coeval with the Mesozoic magmatism of North American Cordilleran orogeny and the Cretaceous dike of Mojave Desert. However, geochronological analysis is needed to verify the exact ages of these dikes.
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