Geological and Explorational Characteristics of Jajarm Bauxite Deposit in the South West of Northern Khurasan- Northwest of Greate Khurasan

The Jajarm bauxite deposit is so far the biggest known bauxite deposit in Iran. This deposit is located in structural zone of Alburz. In this area two bauxite horizons, called A and B, with two stratigraphic gaps can be found. The A horizon is underlained by carbonate rocks of Mobarak Formation and covered by Nesen Formation. The B horizon that constitutes the Jajarm bauxite deposit overlies the dolomite of Elika Formation of the Upper Triassic age and covered by the Shemshak Formation. Sharp contact between bauxite deposit and overlaying as well as underlying units indicate an independent source for bauxite deposit. One of the most important characteristics of Jajarm bauxite deposit is its asymmetrical morphology along the tectonic structure of the area. The geologic setting is striking16 kilometers in E-W direction. In addition to major tectonic elements parallel to the strike, there are a number of minor north-south faults in the area that have tectonically divided the mine area into four regions. Based on these studies the tectonic activities have important role in mineralogy and improving the quality of bauxite deposit. Most of the karsts and sinkholes are along the fault planes and show a positive relationship with thickness and bauxite quality. Hard bauxite and diaspore formation instead of bohemite and gibbsite as well as the repetition of different bauxite layers are the result of these tectonic activities. Therefore, the hard diasporic bauxite has played very important role in the process of alumina production. Constant profiles of: Kaolinite clay-Hard bauxite- Clayey soft bauxite and Kaolinitic clay, from top to bottom can be seen in different karst and drill holes, respectively. But the nature of upper top kaolinite is different from the bottom one. Mineralogy and variation in chemical composition (Al2O3=30% to 60% and SiO2 between 5% to 39%) are other special characteristics of Jajarm bauxite deposit.Based on the exploration activities 22 million tones of diasporic bauxite, up to 250 meters of depth along the layer of ore deposit and Al2O3 content range between 47% to 48% with about 10% of SiO2, have been proved.