|Title||Hyperspectral remote sensing detection of hydrothermal alteration associated with the Izok Lake base-metal deposit, Nunavut, Canada|
|Author||Laakso, K; Rivard, B; Peter, J M; White, H P; Maloley, M|
|Source||8th EARSeL (European Association of Remote Sensing Laboratories) SIG-Imaging Spectroscopy Workshop, abstracts; by Canadian Symposium on Remote Sensing; 2012 p. 67|
|Links||Online - En ligne|
|Alt Series||Earth Sciences Sector, Contribution Series 20130511|
|Meeting||8th EARSeL (European Association of Remote Sensing Laboratories) SIG-Imaging Spectroscopy Workshop; Nantes; FR; April 8-10, 2013|
|Lat/Long WENS||-112.5000 -112.0000 65.7500 65.5000|
|Subjects||geophysics; metallic minerals; remote sensing; satellite imagery; hydrothermal alteration; analytical methods; mineral deposits; volcanogenic deposits; sulphide deposits; hyperspectral imagery;
Geoscience Initiative (TGI-4), Volcanogenic Massive Sulfide Ore Systems|
|Abstract||Volcanogenic massive sulfide (VMS) deposits are a globally important source of Cu, Zn and other trace metals. Convective hydrothermal circulation of metalliferous fluids that forms these deposits
through the host rocks alters their mineralogical and chemical compositions to form so-called "hydrothermal alteration zones" comprised of chlorite, white mica, and other minerals (e.g., quartz, carbonates). Hyperspectral remote sensing methods are
potentially useful in delineating these hydrothermally altered rocks in high latitude regions with little or no vegetative cover and may be a potentially useful exploration vectoring tool. We have investigated the application of ground and airborne
remote sensing methods to the detection of hydrothermal alteration associated with the Archean (2.5 Ga) Izok Lake Zn-Cu-Pb-Ag VMS deposit in Nunavut, northern Canada. Here, hydrothermally altered rocks contain muscovite and chlorite as alteration
minerals, and there is a classic Na-depleted alteration halo that extends several kilometers around the deposit. |
Airborne hyperspectral imagery was obtained for the deposit and surrounding area that is comprised of outcrops of felsic and mafic
volcanic, volcaniclastic, and sedimentary rocks. These data were supplemented by field hyperspectral data collected in-situ from outcrops, drillcores from 8 drillholes comprising a cross-section through a mineralized zone, and hand specimens in the
laboratory. The objective was to delineate the extent and intensity of hydrothermal alteration using the absorption band positions of AlOH and FeOH in micas and chlorite group minerals. These band positions shift as a result of hydrothermal
alteration-induced mineral chemical changes. We developed a band position search algorithm for obtaining the continuum-removed AlOH and FeOH band positions of the phyllosilicate minerals. The algorithm was applied to our hyperspectral data sets,
which range in scale from millimeters to kilometers. The resulting band position maps were compared with standard whole rock geochemical alteration indices (Ishikawa, chlorite-carbonate-pyrite, sericite and Spitz-Darling).
Our data indicate a
shift to shorter wavelengths both in mica and chlorite group minerals with increasing alteration intensity. Based on AlOH band position results, mica group minerals display considerable compositional variability and range from paragonite to phengite.
In order to optimize the predictive capability of the hyperspectral data, alteration indices were correlated with the spectral data. The correlation coefficients for the alteration indices and the AlOH band positions from the airborne data are weak.
However, there is a statistically significant moderate correlation between the AlOH band positions of the ground data and the airborne data, thus validating the band position extraction process. The mineralogy and mineral chemistry of the 26 hand
specimens as determined by the band position search algorithm, will be validated by petrographic microscopy and electron microprobe analysis. Spectral shifts in the samples will be compared to their chemical composition. After the spectral results
have been validated, they will be used to construct a three-dimensional model of the hydrothermal alteration around the VMS deposit, hence gaining new insights into its geometry.