Geochemistry, Petrology and Genesis Study of Baghoo Turquoise Deposit (Damghan)

The Baghoo turquoise deposit is hosted by Toroud-Chahshirin intrusive-volcanic belt (middle Eocene). Lithological units comprise andesite, rhyolite, granodiorite and dacite. The ore minerals occur as disseminated grains and veinlets in granodioritic to dacitic units. The ore minerals (Cu Al6 (PO4)4 (OH)8, 5H2O) range from 4mm to 1.2cm in thickness. The ore zone is limited by Anjiloo fault on the north and Toroud fault on the south. In order to achieve a genetic model for turquoise deposition in the area, this study focuses on the structural observation made in the field, microscopy and geochemical analysis of ore minerals and host rock. Different types of fractures were analysed and the results indicate a good correlation with standard R, R/, P, T وY type fractures. The turquoise mineralization correlates with the strike of P group fractures. Microscopic studies of polished and thin sections indicate the presence of hypogene and supergene mineralization (oxidation and enrichment zone) in the area. Paragenetic sequence shows that hypogene zone includs pyrite, chalcopyrite and galena and oxidation zone includs iron hydroxide (goethite, hematite, and limonite), angelesite, cuprite, marchasite, azurite and malachite and enrichment zone contains covelite and chalcosite minerals. In addition, textural evidences show that turquoise deposition has occurred in the waning stages of mineralization. Geochemical study confirms the results of IR, NAA, wet chemistry and SEM analysis and indicate that Alunite was gradually changed to turquoise. A genetic model is presented for the formation of Baghoo turquoise.