The first eight chapters of this thesis describe a study of the magnetic effects of drilling on bore cores of sedimentary rocks. Extensive rock and palaeo- magnetic methods were used to investigate such effects in three collections of bore cores from the North Sea and Sellafield, U.K., and Prudhoe Bay, Alaska. It is evident that a drilling imposed remanent magnetisation (DIRM) resides in the North Sea and Prudhoe Bay bore cores which is characterised by symmetries in its intensity and direction relative to the core axis. Such DIRM correlated well with the theoretically modelled magnetic field at one end of a steel drill barrel. The DIRM intensity distribution also appeared to be correlated with variation in the radial remanence susceptibility (i.e. the capacity of remanence acquisition) in the North Sea and Prudhoe Bay cores and magnetic susceptibility in the North Sea cores. Simulation experiments of shock impact conducted on bore core materials suggests that shock/vibration of the drill barrel is the major process that is responsible for the radial variation in core magnetic properties. Titanomagnetite (including magnetite) and pyrrhotite are the major carriers of DIRM but there is no DIRM identified in bore cores in which hematite is the only ferromagnetic mineral. Chapter 9 describes a novel attempt in using fractal geometry to statistically depict the geomagnetic field reversal sequence. A fractal distribution is shown to occur for longer geomagnetic polarity intervals (> 0.28 Ma) in terms of a power law relationship between interval length and cumulative number for the last 158 Ma. A simulation study indicates that the deviation from the power law at shorter intervals (< 0.28 Ma) is caused by missing of short intervals due to the limit of resolving power. This is strongly supported by a fractal model (i.e. a Cantor set) introduced for relating the shortest polarity interval, the transition time and the fractal dimension. Normal and reversed polarity intervals have similar fractal dimensions, suggesting that there is no, statistically, fundamental difference between the two magnetic polarity states.

<p> Magnetization associated with the emplacement or a rock body may be thermo-remanent magnetization (TRM) in an igneous body or detrital-remanent magnetization (ORM) in a sedimentary deposit. At the time or Formation the acquired remanence will tend to lie in the ambient field direction. This primary remanence may not remain unchanged through geologic time. Viscous demagnetization may progressively destroy the remanence in the primary direction or it may be reset as VRM in a later different ambient field direction. The amount or acquired VRM will depend on the temperature the rock is heated to and the length or time the heating lasts as well as the magnetic properties or the remanence carriers.</p> <p> The remanence may also be changed by chemical reactions taking place in the magnetic minerals. The remanence acquired during these chemical changes (CRM) is round, by this work, to be a determining factor in the stability or and initial NRM during thermal remagnetization. </p> <p> Synthetic samples were stored for up to 32 days at 400 C it is possible to access geologic time. To simulate viscous changes over geologic time elevated temperatures applied for laboratory times are related to longer times at lower temperatures using the thermal activation curves. Changes in remanence during the storage were observed at various times throughout the experiment. The remanence in samples with an initial NRM was diminished, remanece in samples with a weak initial NRM increased in intensity but the remanence direction lay in the Field direction after as little as l/2 a day storage time. </p> <p> Thermal demagnetization allows separation of the magnetization on the basis of blocking temperature spectra. During the storage the initial magnetite was oxidized to cation deficent magnetite with significantly higher blocking temperatures than those found in the magnetite. Hysteresis measurements, and thermomagnetic mesurements indicate that this change results primarily From the shirt in Tc due to cation deficency. Apparently the change in T did not significantly affect the mechanisms responsible for blocking remanence but merely shifted the blocking temperatures by a similar amount. In samples with a weak initial NRM the chemical change completely reset the magnetization and in samples stored for times as short as only 8 days the initial remanence direction could not be recovered. </p> / Thesis / Bachelor of Science (BSc)

The COSC-1 borehole located in the Lower Seve nappe of the Central Scandinavian Caledonides is intended to study the tectonic evolution of the Paleozoic orogen. The drilling project reached a depth of 2495.8m and obtained samples from different lithologal units of mica schist, amphibolite, gneiss, and mylonitic gneisses.     To test if the samples are suitable for paleomagnetism, laboratory measurements of natural remanent magnetism are performed on sub-samples of the COSC-1 drill core in the paleomagnetic laboratory with alternating field demagnetization, IRM acquisition as well as the temperature dependence of susceptibility measurements. Important properties of the samples such as coercivity, Curie temperature, inclination, and declination are determined with the measurements.     Most of the samples carry a remanent magnetization that can be readily demagnetized with alternating field demagnetization up to 100 mT. Some of the samples may be suitable for paleomagnetism, with the major ferromagnetic mineral compositions of magnetite, hematite, and FeTi oxides. However, low coercivities and median destructive fields suggest that the magnetite-bearing samples will be prone to remagnetization, making them more challenging to use in terms of retrieving a primary magnetization originating from the Caledonian orogeny. The thermomagnetic results of some samples reflect the metamorphic conditions experienced by the rocks and the mineral assemblage changed irreversibly during step-wise heating experiments. These results can possibly be used as an indicator for the metamorphic temperature experienced by the different lithologal units. Although further measurements are needed to get a clearer understanding of the suitability of the COSC-1 sample for paleomagnetic reconstructions (including thermal demagnetization experiments), this thesis indicates that the COSC-1 rocks contain interesting paleo- and rock magnetic features that are worth further study.

Lake sediments can play an important role in understanding and reconstructing temporal characteristics of the geomagnetic field, as they potentially offer near continuous high-resolution archives of magnetic information extending throughout the Holocene. To date lake sediment geomagnetic data has typically been excluded from British archaeomagnetic secular variation curves (SVC) due to uncertainties with the acquisition of magnetisation by lake sediments. This paper presents the argument that, with regards to British datasets, the real problem lies with poor chronological control and sets out to illustrate that with British archaeomagnetic data some progress has been made. The results indicate that it is not currently possible to resolve secular variation on a time scale of ¿100 years from published British lake sediment data but more success has been made with data from archaeological sediments. This level of detail has been considered necessary for the incorporation of lake sediment data into the British archaeomagnetic dataset, as the ability to resolve short-term geomagnetic changes is critical for the integration of any dataset into the British SVC. As the latter is predominantly employed to date archaeological architecture and artefacts requires that it has the ability to resolve changes over timescales relevant to human lifetimes. Using currently available data this retrospective critique confirms that, in archaeological sediments, depositional and thermoremanent magnetisation can record the same direction over the same time interval.

O presente trabalho apresenta uma nova metodologia multidisciplinar que é capaz de estimar a idade de uma rocha-fonte a partir de sua anomalia magnética apenas, usando dados magnetométricos aéreos ou terrestres. Parte-se de anomalias magnéticas preferencialmente isoladas, e cuja componente remanescente seja provável em função do formato da anomalia. A partir dela calculamos a direção total da magnetização e estudamos as possíveis razões entre as componentes induzidas e remanescentes. Posteriormente, determinamos o segmento de reta que congrega todas os paleopólos virtuais possíveis, e finalmente relacionamos esse segmento de reta à curva de Deriva Polar Aparente da placa tectônica na qual a anomalia está hospedada. Aplicamos diversos testes de consistência na metodologia criada, usando exemplos sintéticos e reais, nas placas Sulamericana e Australiana. Finalmente, aplicamos a metodologia em cinco (5) conhecidas anomalias do território brasileiro, produzidas por complexos alcalinos de idade Mesozóica. As idades aparentes obtidas através da metodologia criada em três das anomalias cujas idades radiométricas são bem conhecidas Tapira, Araxá e Juquiá são similares às idades publicadas. As idades aparentes obtidas através das outras duas anomalias cuja idade radiométrica é desconhecida Registro e Pariqueraçu foram coerentes relativamente ao contexto geológico. Espera-se que a aplicação da metodologia ora criada possa contribuir para o conhecimento geológico das rochas fontes de anomalias magnéticas da Crosta Continental, especialmente nos casos em que as rochas sejam desconhecidas, cobertas por sedimentos ou não adequadamente amostradas. / The present work is a new multi-disciplinary methodology that estimates the age of a source rock from its magnetic anomaly only, taken directly from the airborne or ground magnetic data. The idea is to use those anomalies in which a strong remanent magnetic component is likely to occur, calculate from the magnetic anomaly the total magnetization and study the possible ratios between induced and remanence. Next, the line segment linking all virtual paleogeographic poles of this anomaly will be built, and finally this segment will be related with the position, on a paleogeographic projection, of the appropriate age fragment of the APWP curve. We ran several applications to test the efficiency of the methodology, both using synthetic and real examples. Tests were performed in two different tectonic plates, South American and Australian. Finally, we applied this procedure on five (5) well known magnetic anomalies of the South American plate, produced by alkaline complexes of Mesozoic age. The apparent ages obtained from the methodology application on three of the anomalies, where the radiometric age of the source rock is known Tapira, Araxá and Juquiá were reasonably close to the published ages. The apparent ages of the other two, obtained from anomalies in which the age of the source rock is not known Registro and Pariqueraçu magnetic anomalies were coherent relative to the geologic context. We expect that the application of the the developed methodology as a reconnaissance geochronological tool may contribute to geological knowledge over continental areas, especially when the source rocks of the magnetic anomalies are unknown or buried below superficial sediments.

O presente trabalho apresenta uma nova metodologia multidisciplinar que é capaz de estimar a idade de uma rocha-fonte a partir de sua anomalia magnética apenas, usando dados magnetométricos aéreos ou terrestres. Parte-se de anomalias magnéticas preferencialmente isoladas, e cuja componente remanescente seja provável em função do formato da anomalia. A partir dela calculamos a direção total da magnetização e estudamos as possíveis razões entre as componentes induzidas e remanescentes. Posteriormente, determinamos o segmento de reta que congrega todas os paleopólos virtuais possíveis, e finalmente relacionamos esse segmento de reta à curva de Deriva Polar Aparente da placa tectônica na qual a anomalia está hospedada. Aplicamos diversos testes de consistência na metodologia criada, usando exemplos sintéticos e reais, nas placas Sulamericana e Australiana. Finalmente, aplicamos a metodologia em cinco (5) conhecidas anomalias do território brasileiro, produzidas por complexos alcalinos de idade Mesozóica. As idades aparentes obtidas através da metodologia criada em três das anomalias cujas idades radiométricas são bem conhecidas Tapira, Araxá e Juquiá são similares às idades publicadas. As idades aparentes obtidas através das outras duas anomalias cuja idade radiométrica é desconhecida Registro e Pariqueraçu foram coerentes relativamente ao contexto geológico. Espera-se que a aplicação da metodologia ora criada possa contribuir para o conhecimento geológico das rochas fontes de anomalias magnéticas da Crosta Continental, especialmente nos casos em que as rochas sejam desconhecidas, cobertas por sedimentos ou não adequadamente amostradas. / The present work is a new multi-disciplinary methodology that estimates the age of a source rock from its magnetic anomaly only, taken directly from the airborne or ground magnetic data. The idea is to use those anomalies in which a strong remanent magnetic component is likely to occur, calculate from the magnetic anomaly the total magnetization and study the possible ratios between induced and remanence. Next, the line segment linking all virtual paleogeographic poles of this anomaly will be built, and finally this segment will be related with the position, on a paleogeographic projection, of the appropriate age fragment of the APWP curve. We ran several applications to test the efficiency of the methodology, both using synthetic and real examples. Tests were performed in two different tectonic plates, South American and Australian. Finally, we applied this procedure on five (5) well known magnetic anomalies of the South American plate, produced by alkaline complexes of Mesozoic age. The apparent ages obtained from the methodology application on three of the anomalies, where the radiometric age of the source rock is known Tapira, Araxá and Juquiá were reasonably close to the published ages. The apparent ages of the other two, obtained from anomalies in which the age of the source rock is not known Registro and Pariqueraçu magnetic anomalies were coherent relative to the geologic context. We expect that the application of the the developed methodology as a reconnaissance geochronological tool may contribute to geological knowledge over continental areas, especially when the source rocks of the magnetic anomalies are unknown or buried below superficial sediments.

The clay mineralogy data and K-Ar ages of I/S measured in this study agree with previous work conducted within the Disturbed Belt (Hoffman, 1976) and show that diagenetic I/S formed quickly at several different places in response to thrust sheet burial during the Laramide orogeny. The averages of concordant age values for clay sub-fractions separated from three bentonites of Cretaceous and Jurassic depositional age increase from southeast (53.6 Ma) to northwest (56.7 Ma) along the trend of the Disturbed Belt. This northwestward increase of mean ages of I/S is consistent with a thrust sheet emplacement model for the Disturbed Belt (Mudge and Earhart, 1980). The rate of the eastward advancement of the Lewis Thrust Sheet derived from the concordant K-Ar dates of I/S was about 1 cm/year in the Marias River area. The absence of the 2M1 illite polytype in most bentonitic shales does not permit the derivation of the age of diagenetic I/S by Illite Age Analysis and yet constrains the estimate of maximum burial temperature to 250°C.

The Bergslagen region has three base-metal mines operating today, and one of them is the Lovisa mine, which host a Zn-Pb-Ag deposit. The Lovisa mine is located in the Guldsmedshyttan area north of Lindesberg. The mine is part of in the X-Mine H2020 project that includes four different mines with the aim of an improved environmental resource management. The project aims at reducing the environmental impact from transport, ore processing and chemical handling as well as result in lowering the costs per produced amount of metal. The purpose for this thesis is to determine the petrophysical characteristics of the host rocks to the thin tabular mineralised units in the Lovisa mine with petrophysics. Petrophysics is used to obtain information about the physical properties of rocks, which is then is integrated with geophysics and the geology, to obtain an improved understanding about the different geophysical anomalies. The petrophysic methods used here, reviled three different physical properties of the rocks: density, magnetic volume susceptibility and natural remanent magnetization. These properties were measured on five different drill cores and correlated with the literature data and lithologies of the core. The lithologies close to the ore correspond to literature data for volcanic siltstone, volcanic sandstone, massive rhyolite, skarn (calc-silicates) and dolomite. Dolomite is not present in the cores and corresponds to breccia, volcanic sandstone and skarn. My conclusion for this method, is that in order to do a lithological interpretation based on the measured petrophysical properties, is that a good knowledge of the lithologies as well as a good understanding of the geological processes that have affected the rocks in the investigated area are required. / I Bergslagen finns det idag tre aktiva gruvor som bryter sulfidmalm, och en av dem är Lovisagruva som är en malmkropp Zn-Pb-(Ag)-malm. Lovisagruvan ligger i Guldsmedshytteområdet, norr om Lindesberg. Gruvan är en del av X-Mine-projektet som bl.a. undersöker små, komplexa malmkroppar i syfte att reducera miljöpåverkan och effektivisera produktionen. Syftet med detta kandidatarbete är att bestämma petrofysiska egenskaper hos lithologin i det malmnära sidoberget vid Lovisagruva. Petrofysik används för att ta reda på bergets fysikaliska egenskaper, och dessa egenskaper används sedan inom geofysik, för att få en förståelse för de olika avvikelser som visas i andra geofysiska mätningar. De petrofysiska mätningarna som utfördes, gav tre fysikaliska egenskaper hos varje prov, densitet, magnetisk susceptibilitet och den naturliga magnetiska remanensen. Resultaten från varje prov korrelerades sedan med litteraturdata och jämfördes med borrkärneloggar från Lovisa. De petrofysiska mätningarna utfördes på prover från fem olika borrhål. Resultatet visar att det malmnära sidoberget korrelerar med litteraturdata på vulkanisk siltsten, vulkanisk sandsten, kalksilikat, ryolit, skarn och dolomit. Dolomit finns inte i kärnorna utan representeras av bl.a. breccia, vulkanisk sandsten och skarn. Min slutsats är att det går att bestämma lithologin med dessa fysikaliska egenskaper, men man måste ha en god kännedom om vilka bergarter som förväntas att förekomma i området samt vilka geologiska processer som påverkat dem. / H2020 X-mine

The master thesis is focused on a remanent magnetism of electromagnets of DC contactors. In the first part of the thesis deals with the formation of a magnetic field in different kinds of materials, description of their magnetization and sorting. The next part is focused on the principle and history of an electromagnet. Negative effects and remanent induction of the contactor are described in the end of the theoretical part. The second part is a practical part. First, the reaction times were measured on a pair of DC contactors. Using the obtained data, an electronic circuit was designed to minimize the difference in switching times of the given DC contactors.

Numerous techniques are used to study the magnetic history and properties of rocks, which provides important data on the Earth’s interior. In this study we conducted a series of experiments on two different sample sets, comprising pure magnetite (Set1) and a mixture of magnetite-hemoilmenite-bearing quartzite (Set2), in order to gather information about their magnetic susceptibility and remanent magnetization. A miniature diamond anvil cell (mDAC) constructed from hardened non-magnetic alloy (40HNU) was used for high pressure experiments. With the help of high sensitivity susceptibility bridge (MFK1-FA Kappabridge, AGICO), we measured the susceptibility of three samples and of the mDAC. Consequently, we loaded one of the samples in the mDAC and acquired susceptibility measurements during the compression and decompression of the system. For remanence measurements we used a 2G Enterprises SQUID magnetometer. We measured the natural remanent magnetization (NRM) and performed alternating field (AF) demagnetization on ten samples and on the mDAC. Additionally, isothermal and anhysteretic remanent magnetization (IRM and ARM) acquisition were performed on nine and one samples, respectively and demagnetization on three and one samples, respectively. Results showed that Set1 samples consist of both SD and MD magnetite grains. Regarding Set2 samples, the main magnetic carriers are SD and MD magnetite or titanium bearing magnetite grains, while there are indications that hematite and ferrimagnetic titanohematite might be present as well. The presence of eddy currents, due to the conducting materials of the mDAC, resulted in masking the signal of the sample making it difficult to draw any safe conclusions regarding how the susceptibility of the sample changes with pressure. All in all, there was a satisfactory response of the instruments working with very small amounts of material and an adequate signal stability of both the samples and the mDAC. Our study provided us with an insight into high pressure experiments and showed possible directions for future studies. / Många metoder används för att studera magnetiska egenskaper i berg, vilket ger viktig information om Jordens inre. I denna studie genomförde vi en rad experiment på två olika uppsättningar prov, innefattande ren magnetit (Set1) och en blandning av magnetit-hemoilmenit-bärande kvartsit (Set2), för att samla information om deras magnetisk susceptibilitet och magnetiska remanens. En miniatyr diamantstädcell (mDAC) konstruerad av en härdad icke-magnetisk legering (40HNU) användes för högtrycksexperiment. Susceptibilitetet av tre prover och av mDAC mättes en MFK1-FA Kappabridge, AGICO. Följaktligen monterade vi ett av proverna i mDAC och vi genomförde susceptibilitetsmätningar under kompression och dekompression. Vi använde en 2G Enterprises SQUID magnetometer för remanensmätningar. Den naturlig remanentmagnetiseringen (NRM) mättes och vi utförde alternerande fält (AF) demagnetisering på tio prover och på mDAC. Dessutom genomfördes isotermisk och anhysteretisk remanentmagnetisering (IRM och ARM) på nio respektive ett prover, och demagnetisering på tre respektive ett prover. Resultaten visade att Set1-prover består av både enkeldomän (SD) och multidomän (MD) magnetit. SD och MD magnetit- och titanomagnetitkorn är de viktigaste magnetiska mineral av Set2-prover, medan finns det indikationer på att hematit och ferrimagnetisk titanohematit också bidrar till signal. Virvelströmmar, som skapats av mDACs ledande material, maskerade provets magnetiska susceptibilitet och det var svårt att kommentera på hur provets susceptibilitet förändras med tryck. Sammantaget var instrumentens prestanda tillfredsställande, även vid små mängder material. Prov och mDACs signalstabilitet var också adekvat. Vår studie gav oss en inblick i högtrycksexperiment och magnetiska egenskaper och den visade möjliga riktningar för framtida studier.