The roll of sinkholes refill in formation of abnormal bauxite deposits, case study: Beyglar bauxite deposit, Ab-e-Garm district, Qazvin Province

Bauxite deposits in the Ab-e-Garm area, Qazvin Province occur in karst sinkholes, considered to be allochthonous originating from neighboring volcanic rocks, which are mainly intermediary rocks. The underlying rock is composed of dolomite. The bauxite orebody is underlain by Retian-Liassic shales and sandstones. A selected profile in the Beyglar area was sampled. The weathering profile reaches a thickness of 25m. The Beyglar section contains mainly Al2O3 (14.78-44.1 wt.%), Fe2O3 (0.99-48.54 wt.%), SiO2 (14.78-50.31 wt.%) and TiO2 (2-6.91 wt.%). Diaspore is accompanied by anatase in the ore. Kaolinite, hematite and minor illite, quartz and chlorite are also observed. In contrast with other karst bauxite deposits, the Beyglar bauxite profile does not indicate significant zonation. In addition, two diaspore-bearing horizons through the profile show abnormal pattern. The lower horizon is thicker than the upper. It seems that the sinkhole, in which the Beyglar profile has been formed, filled in two different stages.