University of Twente Student Theses


Hydrothermal alteration events in the Archaean Coongan greenstone belt

Rubaba, Tendai (2022) Hydrothermal alteration events in the Archaean Coongan greenstone belt.

[img] PDF
Abstract:Hyperspectral data of the 3-3.5Ga Coongan greenstone belt in the Pilbara craton Western Australia shows the presence of fossiliferous chert horizons and indications of hydrothermal alteration not present in published regional geological maps. These maps show stratigraphic and structural interpretations of geologic events within the volcanic-sedimentary greenstone sequence; however, little detail exists about the hydrothermal events and the extent of hydrothermal alteration within the greenstone belt. This study seeks to map the hydrothermal alteration patterns and related paleosurfaces to predict the relative timing of geologic events and possible linkages with early life in this context. This research employs an integrated analysis informed by remote sensing hyperspectral imagery, aerial photos and airborne geophysics for a detailed mapping of the hydrothermal systems and paleo-surfaces. Geophysical data were used to form the framework of the study, showing the mineral zonation and general division of the nCGB. Potential paleosurfaces were identified through the nature of the contacts. Subsequently, mineral mapping techniques were applied to the airborne hyperspectral data, and a mineral map was produced. Interpretations of the occurrence and spatial distribution of hydrothermal minerals were done to see how they related to the general division of the study area. Research findings identified seven potential paleosurfaces. Mineral mapping results indicate that the volcano-sedimentary sequence has been altered to various alteration assemblages ranging from chloritecarbonate to different types of white micas and pyrophyllite. The spatial distribution of alteration minerals indicates episodes of hydrothermal alteration connected to paleo-layers within the volcano-sedimentary sequence. The classified hydrothermal alteration minerals showed white micas (muscovite, paragonite, phengite, illite), clay minerals (pyrophyllite, kaolinite, dickite), silicates (amphibole, biotite epidote, chlorite, talc), carbonate minerals (dolomite), sulfate minerals (alunite) and iron oxides (hematite, goethite). The occurrence of pyrophyllite indicates reducing acidic conditions, silica-rich and low-intermediate temperature hydrothermal fluids. Variations in pyrophyllite and muscovite up the stratigraphy towards the paleosurface suggest a connected hydrothermal system with changing temperature, acidity and redox conditions. The identification of paleosurfaces stands as evidence of paleoclimates paleoenvironments and conditions. The spatial distribution of these hydrothermal alteration minerals and rock unit characteristics were summarised and organised into a relative chronology of events for the nCGB. The overall sequence of events shows a younging direction up the stratigraphy towards the east. The findings show a correlation between the potential paleosurfaces, formation, interpreted hydrothermal alteration, and inferred changes in paleoenvironment across the study area, indicating that there have been temporal changes in the northern Coongan Greenstone Belt with part of the field indicating a connected hydrothermal system with changing temperature, acidity and redox conditions.
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:
Export this item as:BibTeX
HTML Citation
Reference Manager


Repository Staff Only: item control page