The Study On Gemological And Mineralogical Characteristics Of Emerald In Swat,Pakistan

Emerald deposits in Swat are important for yielding of the world's finest gemstone-quality emerald in recent decades.Although previous studies in long time span have presented comprehensive information and results on the mining areas,there is a lack of studies on the characteristics of gemology,fluid inclusion and multiple spectroscopy.The present study uses FTIR spectrometer,UV/VIS spectrometer,Laser Raman spectrometer and EPMA to make systematically research on gemological and mineralogical characteristics of Swat emerald.Emerald from Swat is pure green with small intact crystal form.Associated matrix consist of quartz,talc and magnesite.Relative density of Swat emerald is affected by metasomatism of associated mineral between 2.71 and 2.86.Swat emerald show relatively high refractive index between 1.572 and 1.600.Fluid inclusion include sickle shaped,tadpole shaped,drizzle shaped gas-liquid two phase inclusion and gas-liquid-solid three phase inclusion.Solid inclusion includes but not limited to pyrite,limonite,muscovite,quartz,talc and magnesite.The chemical components are rich in Mg and Na.Fe and Cr as major color causing elements vary in different individuals with low V.From the evidence we can deduced that the samples are probably derived from Charbagh and Makhad areas in Swat,Pakistan.Compared with emeralds from Gandao and Mohmand areas in Pakistan,samples are high Cr and low V.Emeralds from Panjshir Valley in Afghanistan,Dabdar in Xinjiang Province of China and Khaltaro in Pakistan are similar in chemical components,but compared with the samples are low in Fe?Mg and Na content which probably ascribe to the host rock.There is almost no difference in infrared spectroscopy fingerprint region between parallel C-axis and vertical C-axis.UV/VIS spectroscopy indicates Fe³⁺?Fe²⁺?V³⁺and Cr³⁺are major color-causing ions.Type?water molecules are far more than Type?which indicates high-alkali emeralds.Most fluid inclusions belong to H₂O-Na Cl-CO₂type and the gas section is consist of CO₂?N₂and CH₄.According to previous studies bodies of magnesite-rich rocks likely formed due to carbonate alteration of previously serpentinized ultramafic rocks by CO₂-bearing fluids released as result of metamorphism of spatially associated,originally sedimentary rocks of the Indo-Pakistan plate.Late-stage hydrothermal activity affected these highly fissile magnesite-rich rocks to produce veins and stockworks of quartz as well as emerald,Cr-rich tourmaline and Cr-rich muscovite.The host carbonate-altered ultramafic rocks most likely supplied Cr for the formation of the emerald.The most likely source of Be is the association of tourmaline±fluorite with felsic pegmatites and the S-type granitoids exposed along the Malakand Pass,about 45km southwest of the Mingora emerald mine area.