Hydrothermal Alteration Characteristics of the St Ives Gold Deposits, Kambalda

Honours Thesis Abstract

HYDROTHERMAL ALTERATION CHARACTERISTICS OF THE ST IVES GOLD DEPOSITS, KAMBALDA: A GEOCHEMICAL AND INFRARED SPECTRAL STUDY

Steven Whitehead UWA, WA

2005 AIG Honours Bursary Winner

The St Ives Gold Camp is located in the Norseman-Wiluna Greenstone Belt. It is defined by the Boulder-Lefroy Fault to the east and the Merougil Fault to the west, and comprises many gold deposits hosted by many different lithologies. The lithological and structural complexity of the St Ives Gold Camp has resulted in varying hydrothermal alteration characteristics for the different gold deposits within the camp. Little comparison can be made between the various deposits due to the differing nature of the deposits themselves. Geochemical and short wave infrared (SWIR) spectral techniques have been implemented at the St Ives Gold Camp to characterise the hydrothermal alteration halos surrounding the deposits. Infrared spectral analysis measured using a portable infrared mineral analyser (PIMA) is utilised to identify the changes in the mineral occurrence and chemistry of the deposits studied. Multi-element geochemical analysis identifies the pathfinder elements for the deposits studied and is used to back up the infrared spectral data. Tungsten has been identified as a stand-alone pathfinder element, with elevated tungsten halos extending 100 to 200 metres from gold mineralised structures. Bismuth and tellurium are seen to occur with one another, and occur either with or without gold mineralisation. Spectral characteristics of the St Ives Camp vary as a result of lithology. Mafic rocks display a good correlation of biotite and Mg-rich chlorite with gold mineralisation. Felsic rocks display a good correlation of phengitic mica with gold mineralisation. Gold mineralisation within the Black Flag Group is localised at the contact between high and low mica crystallinity values. Dolerite hosted gold mineralisation shows a gradation from shorter FeOH wavelengths to longer FeOH wavelengths, further from the mineralised structures. Little variation in the FeOH wavelength is identified in barren dolerite, with consistently longer wavelengths recorded. The SEM work identified the restrictions of infrared spectral analysis with respect to carbonates, with the carbonates identified via spectral analysis not matching the actual carbonate composition. The chlorites identified via spectral analysis, however, matched well with the composition identified via the SEM.