Interpretation of Pb and S isotope data for the Ganesh Himal metamorphosed stratiform Zn-Pb deposit, Central Nepal Himalaya

摘要

The Ganesh Himal Zn-Pb deposit in central Nepal has been highly deformed and metamorphosed together with its host rocks. Pb isotope data for the deposit are interpreted to define an age of about 875 to 785 Ma, which is permissive of age equivalence to the upper Vindhyan Supergroup of the north-central and northwestern Indian Shield. The slightly positive to slightly negative sulphur isotope values for the Ganesh Himal deposit are in accord with coeval seawater sulphate delta(34)S values in the range +15 to +20 parts per thousand, and thus with an age greater than about 650 Ma. Apparent equilibrium sulphur isotope fractionation temperatures for sulphide pairs are generally 500 degrees C to 750 degrees C, a range that agrees with kyanite-staurolite and biotite-staurolite assemblages.The 875 to 785 Ma age for Ganesh Himal has been calculated on the basis of Pb isotope ratios and age data for other Neoproterozoic and Cambrian sediment-hosted deposits. These Ganesh Himal results and those for the Genekha deposit, Bhutan, help confirm the previously postulated widespread distribution of Vindhyan rocks in Himalayan metasedimentary belts. The available Pb isotope and age data for the Amjhor deposit, in Upper Vindhyan rocks in Bihar State, India, are suggestive but not confirmatory of a tentative conclusion that the Ganesh Himal deposit is its age equivalent.