University of Twente Student Theses
Data integration for reconstructing of volcano-sedimentary sequences in the Coongan greenstone belt, Eastern Pilbara Craton
Bogale, Meaza Girmay (2020) Data integration for reconstructing of volcano-sedimentary sequences in the Coongan greenstone belt, Eastern Pilbara Craton.
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| Abstract: | Archean greenstone belts are known for their ore deposits, diverse lithostratigraphy, and well-preserved evidence of the early earth. The Coongan greenstone belt, located in Western Australia, is one of the Archean greenstone belts, which is part of the Eastern Pilbara Craton. Rock units of the Coongan greenstone belt might be a host of economic ore deposits. Several studies have been done in the Coongan greenstone belt, mostly using geological field methods and geophysical interpretations. However, remote sensing methods for mapping mineral indices were not used in this area. Remote sensing data can provide information on abundances of different mineral groups, their relationship to the lithological units, and indications of hydrothermal alterations. Moreover, a data integration approach is useful in assessing the various geological aspects of an area and improving the quality of interpretation. Still, it is not well-known how the integration of gamma-ray and remote sensing data with geological field studies can improve the lithostratigraphic interpretation of the northern Coongan greenstone belt. Therefore this study aims at 1) providing surface mineral distribution maps, 2) determine the contribution of each dataset in the lithostratigraphic interpretations, 3) delineate the possible indications of hydrothermal alterations Stratigraphic sequences of the study area were defined from the previous works (literature works and geological data). In this study, an integrated data analysis approach was used, including a quantitative and qualitative analysis of gamma-ray, ASTER, Sentinel-2, aerial photograph, and field observation datasets, as well as a geological map. Relationships were established based on the properties of the lithologic units in different datasets. A surface mineral distribution mapping and lithological interpretations were made using band ratio, visual interpretation, and image classification methods. Training and validation areas were selected for detailed lithological interpretations. The approach was a step-wise interpretation starting from interpretation of the broad lithological boundaries and going to a more detailed analysis. This approach was accomplished by starting from the 90-meter resolution gamma-ray data followed by a 30-meter resolution ASTER data, then Sentinel-2, and an aerial photograph. The gamma-ray and remote sensing images were classified based on the visual interpretations in the training and validation areas. After estimating the classification accuracies of the training and validation areas, the classifications were extrapolated to the whole study area. In this study, the validation area was used as an “uncommon” kind of validation that is to see the variations in radiometric/spectral characteristics of the lithologic units throughout the study area (i.e., not to assess the quality of classification). The results of this interpretation were able to provide information on the surface distribution of minerals in the northern Coongan greenstone belt, to show the contribution of each dataset in reconstructing of the volcano-sedimentary stratigraphy, and to locate the possible indications of hydrothermal alterations. Ferrous iron, aluminum hydroxyl, kaolin group minerals, and iron oxides were the dominant minerals which were able to be mapped using ASTER-SWIR and Sentinel-2-VNIR images. In all datasets, visual interpretations were able to provide more accurate lithological boundaries compared to image classifications. Accuracy estimations in the training area show a partial decrease as more lithologic units were interpreted within the predefined boundaries. This partial decrease might be due to low spectral/radiometric contrast between the newly interpreted units. Classification accuracies in the training area were much higher than those in the validation area, which implies compositional variations in the stratigraphic units of the study area. Integration of remote sensing and gamma-ray data with geological field studies was able to improve the lithostratigraphic interpretation of the northern Coongan greenstone belt by adding more details, delineating accurate lithological boundaries, and determining the prominent areas of hydrothermal alteration. The chert units and gossans are examples of the new units delineated in this study but not in the previous studies. The Duffer formation, which is part of the Warrawoona group rocks, was delineated as a hydrothermally altered unit. |
| 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/85172 |
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