Pakistan Emerald: Gemstone Information
Pakistan Emerald is found in deposits which occur along or close to the suture zones in which two plates meet, in this case the Indus suture zone characterized by the Main Mantle Thrust and the Karakoram suture zone characterized by the Main Karakoram thrust (Kazmi and O’Donoghue, Gemstones of Pakistan 1990). Emerald showings have been reported from a number of sites. The finest emerald crystals have been found east of Mingora town, where the Indian subcontinent sequence is composed of Precambrian crystalline schist, which is overlain by Alpurai talc-mica-garnet schist and the Saidu calc-graphitic schist possibly of Palaeozoic to early Mesozoic age. These rocks comprise an antiform in the core of which the Swat granite gneiss has been intruded. The Indus suture Melange Group (an assemblage of rocks from various origins) has been thrust over these crystalline schists and gneisses. One of the thrust sheets of the Melange Group is the Mingora ophiolitic melange and is composed of blocks of talc-dolomite schist, serpentinite and other rocks, all in a matrix of talc-chlorite-dolomite schist and calcquartz-mica-chlorite schist. Emerald mineralization in the suture zone is confined to the talc-chlorite-dolomite schist. Considerable work on the mineralization of emerald has been carried out by the Geological Survey of Pakistan and by the University of Peshawar. The most exhaustive study is A.H. Kazmi and L.W. Snee, Emeralds of Pakistan, Geology, Gemology and Genesis, New York, 1989.
Primary and secondary fluid inclusions are characteristic of Pakistan emeralds whose colour can equal that shown by the best Colombian stones. However, crystals are almost always small in the finest qualities. Inclusions of dolomite have been found as rhombohedra. The Khaltaro emerald deposits are reported to be in pegmatites (and at high altitude) in the Gilgit Agency of the Northern areas of Pakistan. The best description is by Kazmi and Snee (1989).