VIMP Report 89 - The regolith of the Rupanyup 1:100 000 map area
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Product description:AbstractRegional regolith mapping in the Rupanyup 1:100 000 map area (RUPANYUP) of western Victoria was completed to define the major regolith–landform units and to aid interpretation of hyperspectral data collected over a smaller survey area that included the Kingston gold mine. RUPANYUP straddles the margin between the West Victorian Uplands and the Murray Basin. Mapping identified twenty regolith–landform units that fall broadly within either saprolite-dominated hills and rises, or transported cover. Bedrock consists predominantly of low-grade sandstone, siltstone and mudstone of the St Arnaud and Nargoon groups. Higher-grade amphibolite, quartz–mica schist and metapsammite also crop out, but are confined to a thin zone of polydeformed rock in the hanging wall of the Moyston Fault. The area lies along strike from the Stawell gold mine and is prospective for exploration, hosting a number of small orogenic gold deposits and minor placer deposits. A hyperspectral survey of a 300 km² area covering the southeastern portion of RUPANYUP and part of the adjacent St Arnaud 1:100 000 sheet (ST ARNAUD), was carried out using HyMapTM hyperspectral data complimented by soil, rock and drill hole PIMA data. The hyperspectral data showed differences related to lithology, metamorphic grade, regolith and possibly mineralisation. RGB and de-correlation stretches of the HyMapTM data helped show the major image components and their spectral characteristics. De-correlation stretches of bands in the Short Wave Infrared Region emphasised variations in the clay compositions between different geology and regolith–landform units. Spectral edge member mapping showed that the clay mineralogy of the Warrak and Pyrenees formations of the St Arnaud Group are different. Portable Infrared Mineral Analyser (PIMA) data from rock and soil samples confirmed that the differences in clay mineralogy relate to variations in muscovite composition. We suggest that these variations reflect changes in metamorphic grade across the Landsborough Fault. At the Kingston gold deposit, both HyMapTM and PIMA data show increases in the relative abundance of kaolinite towards and over the zone of brecciated metasediment that hosts mineralisation. As this area also coincides with a distinctive regolith–landform unit (SVel1), increases in kaolinite are attributed to intense weathering. Over the zone of brecciation, trends relating to muscovite composition were seen in the PIMA analysis of A horizon soil samples dominated by kaolinite. The PIMA data appears to show an increase in the Al content of muscovite/illite towards the breccia zone, which may represent a vector to mineralisation. Although the survey area was mostly over abundant (>50%) vegetation and spectrally indistinct, quartz-rich lithologies, this trial has shown that with an integrated approach, spectral surveying can still be a useful tool in apparently difficult terrains. Other exploration areas with comparable vegetation density, host rocks and mineralisation may also benefit from hyperspectral remote sensing, regolith and mineral determination studies. Bibliographic reference Williams, B. & House, E.R., 2006. The regolith of the Rupanyup 1:100 000 map area. Victorian Initiative for Minerals and Petroleum Report 89. Department of Primary Industries, Victoria. Download The downloadable version of this report is supplied in PDF format: 34468 VIMP89 Report (PDF 104.9MB) Please be patient when downloading large files as this might take some time depending on your internet connection. Related products:
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