Deformational and Metamorphic Imprint upon Lesser Himalayan Sulphide Ores: Examples from the Nepal-Sikkim Belt

Ore textures in the stratabound Zn-Pb deposit of Ganesh Himal (Nepal) and the Cu-Zn deposit of Dikchu (Sikkim, India) from amphibolite-facies environment of the Lesser Himalaya arc described and discussed in relation to deformation and metamorphism. Primary are depositional fabric is almost completely obliterated in the ores, except for the rare presence of some framboids and polyframboids at Ganesh Himal. Both deposits show features characteristic of intense deformation and high-grade metamorphism. A variety of fracture, overgrowth and rotational fabric followed by recrystallization textures are recorded. The majority of the fabric characteristics are syn- to post tectonic with respect to the strongest deformational episode and associated metamorphism related to the Tertiary Himalayan orogeny. However, the meta-carbonate hosted Zn-Pb ore of Ganesh Himal is strongly recrystallized, whereas the metapelite hosted Cu-Zn ore of Dikchu is characterised by a more noticeable deformational imprint. The textural characteristics of ores in the two deposits, with respect to the contrasting host lithologies, indicate that the variations in are compositions and in host rock rheologies in different tectonic settings of the deposits might have influenced the resultant ore textures.