Mineralogy, geochemistry and genesis of the Shirinabad clay-bauxite deposit, south-east of Gorgan

The Shirinabad clay-bauxite deposit with more than 1 km long and about 8 m in thickness is located in 60 km south-east of Gorgan. The Shirinabad deposit has been developed as a stratiform horizon along the contact zone of Triassic dolomitic limestones and Jurassic shales and sandstones. The basal contact zone of the horizon is mainly undulatory¡ whereas the upper contact zone is concordant with the hanging-wall shales and sandstones. The rocks within the horizon show pelitomorphic¡ microgranular¡ oolitic and pisolitic textures. Textural analysis indicates both allochthonous and autochtonous origins for the Shirinabad deposit. Based on textural and mineralogical evidences the deposit can be divided into four distinct units. Kaolinite¡ anatase¡ routile¡ bohemite¡ hematite¡ goethite and berthierine are the principal constituents. From geochemical data¡ it is concluded that the Shirinabad deposit probably originated from basaltic volcanic rocks. Combination of mineralogical and geochemical data shows that the Shirinabad deposit formed in two stages. First¡ bauxite materials and clay minerals were developed as authigenic bauxitization processes of alkaline basaltic parent rock. Then¡ these materials were transported to karst depressions and formed the Shirinabad clay-bauxite deposit.