Authors / CoAuthors
Mernagh, T.P. | Thomas, C.M. | Bastrakov, E.N. | Jaireth, S. | de Caritat, P.
Abstract
This study assessed the geochemical indicators for carbonatite-associated and alkaline igneous REE mineral systems based on state-scale ASTER data for Western Australia and the National Geochemical Survey of Australia. In the latter we applied discrete field models obtained by attributing catchment outlet sediment geochemical data to their catchment basins. The cerium data was found to be a suitable proxy for the main features of REE distribution across the continent. In general, this provided a well-expressed positive correlation between identified catchments with anomalous (elevated) Ce and the mineral occurrences and deposits that they contained but not all REE deposits were identified by these methods. The study also included more detailed mineral mapping using the recently released ASTER geoscience map of Western Australia (WA). A study of the relatively well exposed Yangibana 'ironstone' dykes in the Gascoyne Province of Western Australia showed relatively good correlations with known REE occurrences for the AlOH Group Composition, MgOH Group Composition and Ferrous Iron Content in MgOH/carbonate ASTER products. However, no well defined correlations were observed for Mt Weld, Ponton and Cummins Range all of which occur under cover. The ASTER SWIR products have difficulty detecting the types of minerals present in alteration zones surrounding these carbonatites. Some of these minerals may be detected with the ASTER thermal infrared geoscience products which were not available at the time of this study. These products will include a silica index (e.g. for quartz, feldspars, Al-clays), a carbonate index (e.g. for calcite, dolomite, magnesite, siderite, ankerite) and a mafic group index (e.g. for pyroxenes, garnets, olivine, epidote, chlorite, calcite, magnesite, dolomite). However, the lower resolution of the thermal infrared bands (~90 m) may still make it difficult to detect carbonatite-associated mineralisation. Finally, the ASTER data for the Brockman (Hastings) alkaline igneous REE deposit was also examined. The mineralised unit of this deposit only reaches a maximum width of 35 m and so, once again, proved difficult to detect with ASTER. However, the ASTER maps readily highlighted the contact between the Olympio Formation to the east with the Biscay Formation to the west and demonstrated the mapping capabilities of the ASTER products where the lithologies are relatively well exposed. In order to overcome the problem of only sampling the surface, we combined the ASTER data with the regional magnetic data because the magnetic signal is derived from a greater depth. As many carbonatite complexes are surrounded by mafic alkaline rocks, they often show up as a magnetic bull's eye combined with a gravity low and ringed by a gravity high.
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nonGeographicDataset
eCat Id
74261
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- GA PublicationRecord
- ( Theme )
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- geochemistry
- ( Theme )
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- mineral deposits
- ( Theme )
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- remote sensing
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2012-01-01T00:00:00
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