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TitleUse of Landsat TM Data for the Mapping of Limonitic and Altered Rocks in the Sulphurets area, Central British Columbia
AuthorMe, J; Slaney, V R; Harris, J R; Graham, D F; Ballantyne, S B; Harris, D C
SourceCanadian Symposium on Remote Sensing, Proceedings, 14th, Calgary, Alta., May 6-10; 1991 p. 419-422
Alt SeriesEarth Sciences Sector, Contribution Series 20041006
Alt SeriesRESORS 1085674
AbstractThe Sulphurates area is located in central British Columbia within map sheets 104A and 104B. The study area occupies 200 km2 centred on latitude 56°-30'N, longitude 130°30'W. While the geology of the region is poorly known, the study area itself includes extensive exposures of rock showing limonitic and phyllic alteration. Recent mapping and mineralogical studies by Geological Survey geologists and recent drilling by mining exploration companies indicates that this alteration is a surface indicator of hydrothermal alteration zones that are associated with potentially economic deposits of gold, silver and copper. A very distinct circular structure 20 km in diameter seen on a Thematic Mapper (TM) image appears to be related spatially to the limonitic rocks and the hydrothermally altered rocks in the region. Digital processing techniques that are commonly applied to TM images to recognise limonitic and altered rocks in arid areas (Buckingham et al., 1983) are less effective in this region because of the many glaciers, and the dense forest cover at lower elevations. This problem was largely solved by creating separate themes for areas of ice and snow, for vegetated areas, and for areas associated with water and deep shadow. These themes were used to exclude ice, snow, vegetation, water and shadow from the classification routines. Most of the unmasked pixels that remain, represent exposed rock, rock with a thin cover of ice of a mix of rock and vegetation. A principal component analysis applied to the unmasked pixels provided good discrimination between areas of limonitic rock, hydrothermally altered rock and unaltered rock. A supervised maximum-likelihood classification of the TM data using eleven training sets, was used to produce a thematic map. The rock units identified on this thematic map correspond quite well with those portrayed on the published geological map and with the results of field work.

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