University of Twente Student Theses
Estimating lithology, metamorphic grade & intensity of hydrothermal alteration using remote sensing and geophysical datasets: Applied to the meta-volcanic rocks in the eastern Pilbara Craton, W. Australia
Mosazghi, Ghidey Zeresenay (2013) Estimating lithology, metamorphic grade & intensity of hydrothermal alteration using remote sensing and geophysical datasets: Applied to the meta-volcanic rocks in the eastern Pilbara Craton, W. Australia.
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| Abstract: | In this research ASTER satellite imagery, geochemical, airborne gamma-ray and magnetic datasets were used to estimate lithology, grade of metamorphism and intensity of hydrothermal alteration in three areas in the Eastern Pilbara Craton, W. Australia. The study areas consist mainly of mafic volcanic rocks of the East Pilbara Granite-Greenstone terrane in the Western Australia. From the ASTER imagery band ratio values were extracted from each pixel along the traverses of the selected transects to check their variability. ASTER band combination, band 4, 6 and band 8 and the ASTER band combination of band ratio (4+6)/5 with band ratio (5+7)/6 and band ratio (7+9)/8 were found useful in determining lithology, the grade of metamorphism and intensity of hydrothermal alteration. Different band ratios gave different results depending on the mineralogical composition of individual rock units. Specific band ratios are sensitive to a specific alteration mineral present in the lithological unit. ASTER band ratio (5+7)/6 for example was sensitive muscovite and ASTER band ratio (7+9)/8 was sensitive to minerals such as hornblende, actinolite and Mg-chlorite which are present in the studied areas. Gamma-ray Ternary image technique, potassium in red, thorium in green and uranium in blue was found useful in estimating lithology. Moreover different lithologies at different grades of metamorphism and intensity of hydrothermal alteration have different radioelement contents depending on their mineral compositon. Airborne magnetic data was analysed using techniques such as analytical signal, and the 1st vertical derivative of the total magnetic field data. The 1st vertical derivative was found suitable in detecting and mapping ultramafic rock units and banded iron formations which have relatively high magnetic mineral contents and therefore cause high amplitude magnetic anomalies. Different lithologies at different grades of metamorphism and intensity of hydrothermal alteration show different magnetic strength. Intensely hydrothermally altered rocks responded by causing long wavelength magnetic anomalies since the magnetic characteristics of these rocks and their mineral content is destroyed under intense, high temperature hydrothermal alteration processes (metasomatism). Field data such as whole rock and trace element XRF data on 88 rock samples from the three areas, spectral mineralogy, legacy geological maps and reports associated to them as well as literature was used to compare, evaluate and validate the results found from the remote sensing and geophysical datasets. The integration of all this data allowed the successful delineation of geological units, to distinguish greenschist or amphibolitic metamorphic grade and to determine if serious hydrothermal alteration had affected the rocks in the three study areas. |
| Item Type: | Essay (Master) |
| Faculty: | ITC: Faculty of Geo-information Science and Earth Observation |
| Programme: | Geoinformation Science and Earth Observation MSc (75014) |
| Link to this item: | https://purl.utwente.nl/essays/93733 |
| Export this item as: | BibTeX EndNote HTML Citation Reference Manager |
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