Main findings:

      Mineralization in the Eastern Kumaon Himalaya appears to have made no distinction with regard to the stratigraphic horizon, lithology, mineralogy or age of the host rocks.  It occurs in virtually all rock formations throughout the district.

  There is, however, a significant association of known mineral deposits in space.  They occur in clusters and are confined to known fracture systems, or lineaments identified on the basis of various criteria and through processing of multispectral satellite data.

  There appears to be a tectonic and structural control on the main elements of metallogeny. Linear zones of wallrock alteration were developed by hot fluids ascending and reacting with hostrocks along deep fracture systems.

  There is a conspicuous zone of altered wallrock overlying the sulfide orebody at Barigaon near Askot.  The alteration mineral assemblages in the sheared, fine grained, schistose host rocks consist predominantly of sericite, chlorite, feldspars and clays.

  The spectral signatures of the altered zone of Askot were characterized by a statistical analysis of hyperspectral data provided by the Advanced Spaceborne Thermal Emission and Reflection Radiometer on board the TERRA satellite launched in December 1999 as part of NASA's Earth Observing System (EOS).

  Based on this characterization, zones of similarly altered wallrock were identified throughout the district by a supervised classification of Landsat ETM+ data.  About one hundred localities, where similar alteration is prevalent, have been identified.  Many of these are small occurrences, but at least thirty of them are sizeable and therefore merit further exploration.

  All rock formations throughout the district are marked by a high density of lineaments.  These have been identified, mapped and analyzed by processing of Landsat ETM+ data.  The rocks are dislocated by a high density, but just a few sets of fractures.  The dominant lineament trends are WNW-ESE and NNE-SSW.

  Known mineral occurrences and wallrock alteration zones identified through satellite data processing trend in a WNW-ESE to NW-SE direction.  Orebodies, viz., the ones at Askot and Rain Agar, also trend in this direction, suggesting a strong lineament control.

  Spatial analysis of lineaments, altered zones and known mineral occurrence in the Eastern Kumaon region suggests a strong lineament control over metallogeny.  Digital terrain modeling of the region suggests that lineaments have played a significant role in the geomorphic evolution of the area.

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Wallrock Alteration



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S. Farooq

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