Digital Data 2023-0023
This digital data release contains georeferenced mosaic data from a preliminary analysis of WorldView-3 satellite imagery of the Leland Lakes area on the Canadian Shield (the Shield) in northeastern Alberta, described in AGS Special Report 2023-04. The area is characterized by extensive vegetation cover, and the objective of the analysis was to identify exposed outcrop, delineate lithological units, and detect and map potential mineral alteration. This initiative is part of an effort to identify potential metallic mineral occurrences in the Alberta Shield, where narrow belts surrounding several major shear zones have documented occurrences of gold, base metals, uranium, and rare-earth elements. These mineral occurrences are associated with surface exposures of alteration minerals such as weathered sulphide horizons, quartz-tourmaline metasediments, and pegmatites.
Due to the limited spectral dimensionality of the WorldView-3 data, the analysis focused on detecting iron oxides and clay alteration. Mineral indices were developed to detect and characterize mineral anomalies and guide fieldwork by identifying variations in rocks characterized by hydroxyl/white mica and mafic-felsic properties.
The high spatial resolution has enabled the creation of an outcrop distribution map, which can aid in planning fieldwork. To minimize the influence of vegetation and shadows, a significant amount of effort was invested in preprocessing the data to isolate the portions of the scene occupied by outcrop. As a result, the spectral data obtained from the resulting outcrop map could be analyzed to reveal regional variability in the strength of absorption features of iron and hydroxyl-bearing minerals. Lithological information is evident from several related index images (iron, hydroxyl, mafic-felsic) after carefully removing pixels occupied by water, clouds, shadows, and vegetation to retain only the "cleanest bedrock" pixels.
The digital data release comprises the following image data files:
'Leland-Rock-OH.tif' is the 'white mica index', where higher index values (red) represent the white mica absorption feature located nominally at 2200 nm. It is used with the intent of informing about the relative abundance of white mica.
'Leland-Rock-Fe.tif' is the 'iron index', where higher index values (red) indicate the strength of the iron absorption, nominally centered on band VNIR 7, located near 900 nm. It is used with the intent of gathering about the relative abundance of iron.
'Leland-RockMF.tif' is the 'mafic felsic index', where higher index values (red) indicate more mafic rocks, and lower index values (blue) indicate more felsic rocks.
'Leland-Outcrop.img' is the 'outcrop mask', which is used to identify outcrops, or exposed rock formations. This mask is a binary filter, with certain areas flagged as '1' for being an 'outcrop', and as '0' for being 'not an outcrop'.
This work was completed under the Mineral Grant provided by the Government of Alberta June 22, 2021.
Rivard, B. (2023): Analysis of WorldView-3 satellite imagery for the Leland Lakes area, Alberta (image data, TIFF and IMG formats); Alberta Energy Regulator / Alberta Geological Survey, AER/AGS Digital Data 2023-0023.