A. H. G. Mitchell
HMG/UNDP Mineral Exploration Project, Lainchaur, Kathmandu, Nepal
Granitic rocks occupying eight distinct tectonic settings can be recognized in the Himalayas and Transhimalayas. In the Lower Himalayas geographical belt a few plutons of two-mica granite intrude the lowest unit of the Nawakot Complex or Midland Group. More extensive are sheet-like bodies of augen gneiss intrusive within a possibly thrust-bounded succession of carbonates and graphitic schists beneath the Main Central Thrust to the north. The most abundant granites in the Lower Himalayas are the two-mica cordierite-bearing granites within klippen; minor tin and tungsten mineralization is associated with these plutons, which are of late Cambrian age. Within the Higher Himalayas above the Main Central Thrust, the `Central Crystallines’ or Central Gneisses include pegmatites and pegmatitic granites intrusive into gneisses of probable early Proterozoic age; these have same potential for ruby, sapphire, aquamarine and possibly spodumene. Further north within the Higher Himalayan succession a southern belt of anatectic two-mica granites and leucogranites of mid-Tertiary age is favourable for tin, tungsten and uranium mineralization; a northern belt of granites or gneisses is of uncertain age and origin. North of the Indus Suture in the Transhimalayas extensive batholiths of hornblende granodiorite representing the root zone of a late Mesozoic to early Eocene volcanic arc are associated with porphyry copper deposits. Further north in southern Tibet the tectonic setting for reported granitic bodies of Tertiary age is uncertain; their location suggests that they could be favourable host rocks for tin, uranium and porphyry molybdenum mineralization.
