| 1. |
- Butler, Aodhán D., 1986-
(författare)
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Exceptionally Preserved Cambrian Lophotrochozoa : Taxonomy, Systematics and Taphonomy of Chengjiang and Indian Springs Lophophorates
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The origin and evolution of Lophotrochozoa can be traced to the plethora of lower Cambrian scleritome taxa. We aim to determine the character suites linking these stem-Lophotrochozoa to their extant crown relatives, in particular the small shelly tommotiids and the stem-group brachiopods. Tracing the origin of morphological characters from these fossils informs the evolution and construction of lophotrochozoan body plans associated with the Cambrian Explosion. This is achieved by comparing records of exceptional preservation, most conspicuously Burgess Shale type Lagerstätten with more widespread Cambrian stem-brachiopods and small shelly fossils with their purported extant relatives, for example. Determining morphological character homologies is crucial to reconstructing the brachiopod stem-group and in polarising character changes associated with the putative transition from scleritome organisms to crown-group brachiopods. In this thesis arguments for a common origin of specific shell structures and exceptionally preserved soft-tissues are investigated. New records of enigmatic stem-group lophotrochozoans are described from two localities, the Indian Springs and Chengjiang Lagerstätte. Comprising the stem-brachiopod Mickwitzia cf. occidens, a putative stem-group entoproct Cotyledion tylodes and an enigmatic agglutinated tubular lophophorate possessing an unusual combination of phoronid, brachiopod and tommotiid characters, Yuganotheca elegans gen. et sp. nov. The interplay of bauplan, microbial activity and environmental factors resulting in such incidences of exceptional soft tissue preservation is also examined critically. Consequently, the evolution of through-gut bearing bilaterians is suggested as the reason for why the Cambrian hosts such a plethora of Lagerstätten. The closure of this taphonomic window is then associated with increased bioturbation following the Cambrian substrate revolution.
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| 2. |
- Nzulu, Gabriel Kofi
(författare)
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Characterization of Gold Pathfinder Minerals
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this Thesis, I investigate the properties of artisanal small-scale gold mining concentrate samples from the Kubi Gold Project of the Asante Gold Corporation near Dunkwa-on-Offin in the Central Region of Ghana with a material science perspective.X-ray diffraction (XRD) is used to identify SiO2 (quartz), Fe3O4 (magnetite), and Fe2O3 (hematite) as the main indicator minerals in the mining site while contributions from pyrite, arsenopyrites, iridosmine, scheelite, tetradymite, garnet, gypsum, and other sulfate minerals were insignificant.Furthermore, the X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) results indicate elements like Fe, Ag, Al, N, O, Si, Hg, and Ti as the important host elements that either form alloy with Au or inherent elements in the soil at the site. The result also indicate that Si and Ag are in strong co-occurrence with Au due to their eutectic qualities, while N, C, and O follow alongside because of their attraction to Si. These findings indicate that primary geochemical dispersion evolving from crystallization of magma and hydrothermal liquids are the main attributes and this constitute a confirmative identification of Au indicator and pathfinding minerals in this mineralogical area. Furthermore, the findings suggest that XRD, XPS, and EDX could also be applied in other mineralogical laboratories to aid in identifying indicator minerals of Au and location of ore bodies at reduced environmental and exploration costs.
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| 3. |
- Sjöqvist, Axel S.L. 1990
(författare)
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Agpaitic Rocks of the Norra Kärr Alkaline Complex: Chemistry, Origin, and Age of Eudialyte-hosted Zirconium and Rare-earth Element Ore
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Agpaites are peralkaline nepheline syenites that are denominated by rock-forming complex silicate minerals such as eudialyte. The exotic mineralogy and chemistry of these rocks are not only interesting for research, but globally these rocks also have potential as polymetallic resources of elements such as zirconium, niobium, rare-earth elements, zinc, and uranium. The Norra Kärr alkaline complex is a small agpaitic intrusion in southern Sweden, which in recent years has become recognised as a major zirconium and rare-earth element resource. These rocks have been known for over a century, but have been researched sparingly with the modern petrologist’s toolkit, including in situ analysis techniques and isotope geochemistry. This thesis work focuses on two aspects of Norra Kärr. Firstly, a systematic investigation of the major element composition of a large selection of eudi- alyte samples established an overview of eudialyte geochemistry. Analyses by SEM-EDS and EMP-WDS were compared. Eudialytes from different rock units cluster according to their Mn/(Fe+Mn) ratios, which distinguish- es three groups. Two of these groups, which are the most common types, are rich in rare-earth elements. This broad overview provides a necessary context for more detailed investigations of eudialyte’s complex zoning. Secondly, the age of intrusion and magma source were not precisely determined before this work. We indirectly determined the age of magmatic emplacement by precisely dating the syn-magmatic alkali metasomatic alteration (fenitisation) of the hanging-wall granite. Here, the U–Pb geochronometer in reset and newly-formed zircon records the time of feni- tisation at 1.49 ± 0.01 Ga. Lu–Hf isotope systematics of these zircons and eudialyte from Norra Kärr support the petrographic link between fenitisation and the emplacement of Norra Kärr. Hf isotopes suggest a liquid line of descent from subcontinental lithospheric mantle, which has a significantly higher εHf signature than the Svecofennian and TIB crust.
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| 4. |
- Sjöström, Jenny, 1978-
(författare)
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Reconstruction of Holocene atmospheric mineral dust deposition from raised peat bogs in south–central Sweden
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Atmospheric mineral dust plays a dynamic role in the climate system acting both as a forcing and a feedback mechanism. To date, the majority of paleodust studies have been conducted on marine sediments or polar ice cores, while terrestrial deposition has been less studied. As such, it is important to produce new terrestrial Holocene paleo–dust records and fill existing regional gaps. Ombrotrophic (atmospherically–fed) peat bogs can be used to reconstruct dust deposition through elemental chemistry analysis. Multi–elemental data sets are commonly used infer net dust deposition rates, source changes, grain size, and mineral composition. Mineralogical identification of dust particles is particularly important because it allows both provenance tracing and increased understanding in climate and ecosystem feedbacks. Establishing mineralogy from elemental data of mixed mineral matrixes can however be challenging. X–ray diffraction analysis (XRD) is a standard technique for mineral identification which ideally requires removal of organic matter (OM). Therefore, a test procedure was undertaken where common OM removal methods were evaluated on bulk peat samples was therefore undertaken. The results showed that combustion at 500°C was most efficient in removing OM, while leaving the majority of minerals intact, but not all. In this Licenciate thesis, early result of a paleodust study from Draftinge Mosse, southern Sweden, are also outlined. Here, the method development mentioned above was applied, enabling a combination of elemental data with mineralogy. Future work includes minor and trace element analysis by ICP–AES and ICP–MS, evaluation of the reproducibility of single core reconstructions, tests of some of the methodological assumptions used in previous paleodust studies, source tracing and paleodust reconstruction from a second site (Gällsered Mosse).
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| 5. |
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| 6. |
- Andersson, Joel, 1981-
(författare)
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Structural evolution of two ore-bearing Palaeoproterozoic metasupracrustal belts in the Kiruna area, Northwestern Fennoscandian Shield
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this project, two key study areas in the northwestern Fennoscandian Shield are under investigation. The “Western supracrustal belt” and “Central Kiruna area” are both located along lithotectonically comparable Rhyacian-Orosirian metasupracrustal belts and both areas are characterized by iron oxide-apatite (IOA) and iron oxide-copper-gold (IOCG)-style mineralizations and related hydrothermal alterations. The area is in general well studied but the structural evolution remains unresolved. In order to build a structural framework for the Kiruna area, the number of deformation events, kinematics, geometries, mineralogy and interrelationships of the dominant structures are under focus in this study. The paired structural-alteration configuration is targeted in order to constrain the relative timing of dominant structures and mineral alteration parageneses in order to use these systems as structural vectors of mineralized systems. Furthermore, the Orosirian stratigraphy is re-evaluated in order to constrain the pre-compressional geological history of the study areas. This is important as it controls the character of the structural development during subsequent compression forming the sub-surface architecture as we see today.The Orosirian stratigraphy suggests the development of a syn-extensional basin in Kiruna where iron oxide-apatite deposits were emplaced. This basin was subsequently inverted accompanied by shearing, folding, and faulting during D1 and D2, refolded during D3, and further fractured during D4. The shortening directions inferred during the deformation events suggest a clockwise rotation of the stress field from NE-SW (D1) to E-W (D2) and finally NNW-SSE (D3). Regional scapolite ± albite alteration is interpreted to be coeval with regional amphibole + magnetite alteration during D1. Mineral alteration parageneses linked to D2 is more potassic in character and often structurally controlled by shear zones. As a regional generalization, the potassic dominated D2-alteration is characterized by sericite ± epidote ± biotite ± chlorite ± magnetite ± sulphide ± K-feldspar. Fe- and Cu-sulphides are concentrated into brittle D2-structures suggesting that a IOCG-style of mineralization can be linked to the potassic D2 event. This implies that iron oxide-apatite emplacement can be linked to the basin development phase, whereas epigenetic Fe- and Cu-sulphides are linked to the basin inversion-phase of the geological evolution, and hence, separated in time and probably not directly genetically linked in Kiruna.
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| 7. |
- Andersson, Thommy
(författare)
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Geology of Lagoa das Furnas, a crater lake on São Miguel, Azores archipelago
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, the results from a geophysical mapping and coring campaign of Lagoa das Furnas are presented. Specific focus is placed on the origin of a subaqueous volcanic cone mapped in the southern part of the lake. Lagoa das Furnas is a crater lake within the Furnas volcanic centre which is located on the island of São Miguel in the Azores archipelago. The Furnas volcanic centre has a long history of earthquakes and volcanic activity. The area is relatively well-studied, except for the lake floor. Therefore, a high resolution geophysical and geological mapping survey was conducted at Lagoa das Furnas. Sidescan sonar was used to map the surface of the lake floor and single beam sonar was used to acquire sub-bottom profiles. In addition to the geophysical mapping, sediment surface sampling and core drilling were carried out followed by geochemical analyses of the retrieved material. The mapped data permitted a characterisation of the floor of Lagoa das Furnas and revealed several volcanic features including fumarole activity and a volcanic cone in the southern part of the lake. In order to unravel the origin of this cone several methods were applied, including analyses of tephra and minerals collected from the cone itself and from nearby deposits of two known eruptions Furnas I and Furnas 1630. Sedimentological, petrological, geochemical and geochronological studies of pyroclastic deposits from the cone suggest a subaqueous eruption linked to the Furnas 1630 eruption. The chemistry of glass and crystal fragments sampled from the cone suggests that it is composed of more evolved magma than that of the main Furnas 1630 implying that the lake cone is likely a product of the last eruptional phase. Historical documents reveal three lakes in Furnas valley before the 1630 eruption. Two of these lakes were lost due the eruption and the remaining lake is most likely Lagoa das Furnas and consequently did exist before the 1630 eruption.
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| 8. |
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| 9. |
- Bark, Glenn
(författare)
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Genesis and tectonic setting of the hypozonal Fäboliden orogenic gold deposit, northern Sweden
- 2005
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The well-known Skellefte Ore District, northern Sweden, hosts a large number of massive sulphide deposits, a few porphyry-type-deposits and a number of gold deposits in different geological settings. Southwest of this district a new ore province, the so called Gold Line, is presently being uncovered. During the past decade a number of gold occurrences have been discovered in this area. Only one deposit is in production, the Svartliden gold deposit (2 Mton at 4.3 ppm Au). However, with regards to tonnage the Fäboliden gold deposit stands out with a known mineral resource of c. 16 Mton with 1.33 ppm Au. Additional 24.5 Mton with 1.5 ppm Au is indicated down to a depth of 350 m. The late- to post-orogenic, c. 1.81-1.77 Ga, Revsund granite constitutes the main rock type in the Fäboliden area and surrounds a narrow belt of metavolcanic rocks and metagreywackes. The metasedimentary rocks are strongly deformed, within a roughly N-S trending subvertical shear zone, with boudinaged competent horizons that indicate E-W shortening and a suggested dextral sense of shear within the shear zone. The mineralization at Fäboliden constitutes a 30-50 m wide, N-S striking, steeply dipping ore zone. The mineralization is commonly hosted in arsenopyrite-bearing quartz-veins, which parallel the main foliation, within the metagreywackes in the shear zone. The fine-grained (2-40 µm) gold is closely associated with arsenopyrite-löllingite and stibnite and found in fissures and as intergrowths in the arsenopyrite-löllingite. Gold is also seen as free grains in the silicate matrix of the metagreywacke host rock. Microprobe analysis shows that the gold occurs as electrum (Au:Ag 2:1). The proximal ore zone display enrichment in Ca, total S, As, Ag, Au, Sb, Sn, W, Pb, Bi, Cd, Se, and Hg, whereas K and Na are slightly depleted. The hydrothermal alteration assemblage in the proximal ore zone is diopside, calcic amphibole, biotite, and minor andalusite and tourmaline. This type of assemblage is commonly recognized in hypozonal orogenic gold deposits worldwide. The c. 1.3 km long ore body (lode) is steeply dipping and known to a depth of 150 m, with a few deeper boreholes indicating a continuation of the mineralization towards depth. The mineralization is also open towards north and south. The fabric that hosts the mineralization is also found in the outer margin of the surrounding Revsund granite. It is therefore suggested that at least the final stages of the gold mineralization are late- or post-orogenic in age, and the maximum age for the mineralization is constrained at c. 1.80 Ga (Revsund age). The mineralizing fluids were composed of CO2-CH4-H2S. Gold, arsenopyrite- löllingite, and graphite were precipitated from this fluid. The crystal structure of the graphite, enclosed in the gold related quartz veins, indicates a maximum temperature of 520-560ºC for the mineralizing event, temperature conditions equal to mid-amphibolite facies. These temperatures indicate pressure conditions of c. 4 kbar for the mineralizing event. During deformation mineralizing fluids are often concentrated into deformation zones. Therefore, the potential for economic mineralization in the Lycksele-Storuman region is regarded as very high since the initial results from this project have indicated the existence of several larger ductile to semi-ductile shear zones and accompanied silica alteration in the studied area. During 2004 the project strongly assisted in locating a new gold target in the Gold Line area. For more effective future exploration in this area a better understanding of the structural conditions and evolution is a key factor.
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| 10. |
- Bassett-Butt, Lewis, 1990-
(författare)
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The Cambrian lophotrochozoans of the Transantarctic Mountains, Antarctica
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The origin of many lophotrochozoan groups can be traced to “small shelly fossil” (SSF) faunas of the Early Cambrian. Antarctica is a key region of study, due to the continent’s known close geographical proximity to well-studied Australian and Indian basins in in the Cambrian. Few studies have focused on this region however, due to a paucity of data. Re-examination of camenellan sclerites from the Early Cambrian Shackleton Limestone of the Churchill Mountains of Antarctica has revealed a previously unidentified species of Dailyatia in the formation, co-occurring alongside previously described Dailyatia odyssei Evans and Rowell, 1990, as in the Arrowie Basin of Australia. Re-examination of material previously described as Kennardia sp. A and Kennardia sp. B has indicated that these taxa can likely be synonymized as a second species of Dailyatia. Dailyatia sclerites were also found in the temporally equivalent “Schneider Hills Limestone” formation, which cropsout in the Argentina Range of Antarctica. These specimens appear to belongto a third species of Dailyatia, suggesting that the spatial distribution of tommotiids in the Early Cambrian was more complex than previously recognized, and that the group may be useful in future biostratigraphic studies. A study ofthe Middle Cambrian (Drumian Stage) Nelson Limestone Formation of the Neptune Range, Antarctica has revealed a moderately diverse brachiopod and trilobite fauna. The brachiopods have strong faunal links to taxa from South Australia and India, as well as other parts of the Antarctic province, fitting independent strong evidence for a united East Gondwanan region in the Middle Cambrian. An unidentified camenellan tommotiid sclerite is also described from the Nelson Limestone. This extends the worldwide temporal range of the tommotiid clade into the Drumian Stage, and suggests that more basal members of the brachiopod stem-group survived to form part of a more diverse Middle Cambrian fauna.
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