Geochemistry and gemology characteristics of corundum in the Khakoo pegmatites in the southeast of Alvand batholith (west Iran)

The Khakoo deposit is located in south and southeast of Hamedan city, near the Khakoo village, in western Iran. In this area, blue corundum formed inside the pegmatite veins and granite body. Geochronological data, using various radiometric methods, show that metamorphic rocks formed during the Jurassic to Cretaceous. Then during the Middle Jurassic to Early Cretaceous time, a massive intrusive masses as well as younger phases and pegmatite vines penetrated into this body. The hydrothermal activity of hot fluids driving from the granite mass has created specific paragenesis including corundum crystals. Aluminosilicate and corundum minerals are formed in the pegmatite filons and the margin of granite body. Based on recent studies, the metamorphic–metasomatic process and per-alumnus alkaline composition of intrusive body made a genetic model which based on the bimodal exchange of hot fluids at high temperature and medium pressure are the phenomenon of extensive desilicification and increases of the Al/Si ratio. Metasomatic progressive processes have changed aluminosilicate and plagioclase minerals to corundum in an open geochemical system. Therefore, the Khakoo deposit in a metasomatic magmatic model can be justified. According to the results obtained in this study, natural corundums have a large variation in most trace elements. The collected crystals are in the 6th- 7th rank in terms of tone, from the Saturation terms in the range of 2 and 3 cool colors and based on the Hue termsour samples fill in the Violet Blue (VB) and Blue (B) groups. The Khakoo corundum deposit contain less than 1% (Wt) Iron, 10 to 47 (ppm) Gallium, 83 to 690 (ppm) Titanium, and 30 (ppm) Vanadium. Finally, the Khakoo deposit has resembled associated deposits with the alkaline syenite in Tanzania mines.