Browsing by Subject "Geochemistry"
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(2023)Northern peatlands are important carbon storing ecosystems, contributing to carbon cycle as sinks and sources. The two most important greenhouse gases in the carbon cycle are carbon dioxide (CO2) and methane (CH4). The study area of this work consists of two sloping fens in the Kuusamo area. from which the peat geochemistry and peat properties (peat stratigraphy, ash content, and bulk density) are studied. In addition, the chronology, carbon-nitrogen ratio, carbon content, and carbon accumulation are studied in the Puukkosuo from the three sampling sites. In the characterization of peat geochemistry, Puukkosuo in the dolomitic rock area and Suvisuo in the volcanic rock area were divided into different geochemical zones based on the cluster analysis. The paludification in the Puukkosuo area has started around 10 000 years ago, and the accumulation of peat have been ongoing in the whole peat basin after 1000 years. The geochemical zones in the Puukkosuo can be divided into five different groups, from which the deepest part of the peatland basin can be separated due to the high heavy metal concentrations in the oldest peat. Most of the bulk peat is differentiated into alternating groups, from which the changes in the peat nutrients are recorded. The margins of the Puukkosuo are separated based on the geochemical properties. The top part of the northwestern edge can be characterized as high concentrations of atmospheric origin elements, whereas the effect of the nearby road can be noted in the concentrations of the top part of the southeastern edge. The amount of carbon accumulated has varied throughout the development of Puukkosuo, and the highest rates are recorded in the lower part of the peat profiles in all study sites. Highest carbon-nitrogen -ratios are recorded near the basal peat samples especially in the deepest part of the Puukkosuo. The long-term carbon accumulation differs from the other long-term averages in the boreal zone. The largest differences were recorded in the deepest part of the basin in the long-term carbon accumulation rates during the Early Holocene. The respective value in the Puukkosuo is four times higher (60 g m-2 yr-1) in contrast to others. During the Late Holocene the long-term carbon accumulation rates correspond to the other average values in the boreal peatlands (25 g m-2 yr-1).
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Composition of chromite in the Sakatti Cu-Ni-PGE deposit, Central Lapland Greenstone Belt, Finland (2020)Chromite (Fe2+, Mg)(Cr, Al)2O4 contains in addition to the main elements a variety of minor and trace elements. It often occurs as an accessory mineral in cumulate rich olivine rocks. The melt composition is recorded into crystallised chromite. Due to these characteristics, the composition of chromite can be used as a proxy for the petrogenesis of the magma, providing vital information on how the sulphur saturation occurred, and, in particular, to record the conditions of the cooling cumulates. The Sakatti Cu-Ni-PGE orthomagmatic deposit is located in northern Finland in the CLGB. The deposit is hosted by an olivine cumulate body (the main body), where both disseminated and massive sulphides occur. In addition to the main body, the smaller satellite bodies, the NE and the SW bodies also host mineralisation. The upper barren olivine peridotite body occurs on top of the main body. Thin sections were selected from each of the olivine peridotite bodies (the main, the upper, the NE and the SW body). The chromites can be divided into two groups; unzoned chromites from the main body and the NE body, and zoned chromites from the upper body and the SW body. The chromite grains occur either as intercumulus positions relative to olivine grains or enclosed by unaltered olivine and pyroxene cumulus grains. The elemental compositions, including SiO2, TiO2, Al2O3, Fe2O3, FeO, V2O3, MnO, MgO, ZnO and NiO, of the chromites were analysed using EPMA. The trace element, Ru, was analysed using the LA-ICP-MS. The Sakatti chromites are characterised by variable content of Mg# (0.18 -0.56), moderately high Cr# (0.56 -0.92) and Fe3+# (0.11 -0.50). In addition to Mg# and Cr#, the Al2O3 and TiO2 compositions and textural features, the Sakatti chromites resemble more of those chromites which saturate from komatiitic magmas than chromites which are associated with picritic or basaltic melts. A subset from those chromites that are spatially associated with massive sulphides display high ZnO (> 0.5 wt.%), low Ni (as low as 225 ppm) and higher TiO2 (up to 3.22 wt.%). The source behind the elevated Zn-levels could be the assimilation of sulphide bearing sediments to the magma. The Ti enrichment could be explained by the magma being contaminated by iron-rich gabbro during its evolutional history. Nickel contents of the Sakatti chromites range from 225 ppm to 1731 ppm. The majority of the analysed chromite grains are Ni-depleted due to the separation of a sulphide liquid during the magmatic evolution of the Sakatti geological environment. Portion of the Sakatti chromites are Fe3+-rich, which is interpreted to reflect their crystallisation from a melt that have potentially assimilated a sulphur-rich evaporitic rocks, anhydrite. Fe3+-rich chromites together with high Zn, high Ti and low Ni contents represent primary magmatic features in the Sakatti olivine cumulate hosted chromite. Ru content in the Sakatti chromites are low (<2 pbb) and therefore, the low Ru values are an indication of mineralised geological environment.
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Mineral supply in Viiankiaapa mire during the Holocene : evidenced by geochemistry and ash content (2021)In 2011 Anglo American published a promising multi metal ore deposit in Sodankylä, Northern Finland. The ore is named Sakatti, after a small pond in the vicinity of the discovering place. The ore is under the Viiankiaapa mire, which is part of national mire protecting program and Natura 2000 program. Viinkiaapa is at the eastern side of river Kitinen, which is known to have flooded, bringing mineral material to the mire. To prevent the possibly environment effects in the future, it is essential to know present conditions of the mire. The study area is at the southern part of the Viiankiaapa mire and consist of eight sampling sites for peat. The basal sediment of the study area was determined with ground penetrating radar profiles that pass the sampling sites. To study the mineral supply of the mire, nine elements (Na, Mg, Al, S, P, K, Ca, Mn, and Fe) were chosen for geochemical analyses and the ash content of the peat profiles was determined. The basal sediment is highly affected by the vicinity of the river Kitinen. Fluvial channels have eroded till, which was deposited during the last glacial period. At the eastern side of the study area possibly aeolian sand is detected. Depressions eroded by fluvial channels are filled by gyttja, typically below 179 m a.s.l. The geochemistry of the peat indicates that the early phase of the mire was characterized with higher mineral supply. At the eastern part of Viiankiaapa the mineral supply has decreased after the early phase of the mire. The mineral supply has been higher at the middle parts of the mire throughout the Holocene. The floods of the river Kitinen are the main source of the mineral supply. The decrease in the mineral supply indicates that the flooding events have reduced, and the normal floods inundate smaller area than the early floods.
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(2020)Geological Survey of Finland conducted bedrock mapping in the eastern parts of Central Finland Granitoid Complex (CFGC) and the area next to the Archean craton in the 1990s. The area consists mainly of Paleo-proterozoic paragneisses, with minor volcanic rocks present. The granitoids belonging to the Central Finland Granitoid Complex make up part of the bedrock in the area. The granitoids of CFGC are divided into a 1.89-1.88 Ga syn-kinematic group, and a crosscutting, 1.88-1.87 Ga post-kinematic group. In this Master’s thesis, three post-kinematic granitoid intrusions of Löytölamminvuori, Sorsakoski and Karvalevä are studied, covering their lithological, petrographical and geochemical features. The intrusions are non-foliated, porphyritic granites and quartz-monzonites, with a minor mafic phase of mostly dioritic composition in the Karvalevä intrusion. The main mafic silicates in the granite phase are biotite and hornblende, in the quartz-monzonite and mafic phases also clino- and orthopyroxene are present. Resembling the other post-kinematic plutons of the CFGC, the studied intrusions are geochemically high in Al2O3, FeO and K2O, and low in MgO, CaO and Sr. One U-Pb age of 1876+6 Ma has been measured for the Löytölamminvuori intrusion, which places the intrusion at the same time frame as the other post-kinematic plutons. Geochemically the intrusions show A-type affinity and close similarities to the post-kinematic pluton Types 2 and 3, fitting best with the Type 3a, which is transitional between the two. The magmas forming Löytölamminvuori, Sorsakoski and Karvalevä were derived from partial melting of mantle derived basalts, which underwent crustal contamination by partial melts from the lower crust. Slight deviation in composition from the strictly A-type magma and the volcanic arc affinity can be explained by the crustal component. The mafic phases show more primitive geochemistry, and thus present the mantle-derived source component with less crustal assimilation in the source. The intrusions show signs of bimodal mafic-felsic magmatism, the dioritic phases in Karvalevä intrusion and one syn-plutonic dyke in Sorsakoski intrusion representing the mafic component. The mafic magmatism was cogenetic with the felsic phases, but not comagmatic, the diorites intruding simultaneously but slightly after the felsic phases. The mafic phases show a continuum in chemical composition to the granites and quartz-monzonites, but with a slight compositional gap.
Now showing items 1-4 of 4