بررسي تركيب سنگ منشاء و دليل لايه بندي در كانسار بوكسيت جاجرم (شمال خاور ايران) با استفاده از داده هاي زمين شيميايي

Study of Sourc e Rock Composition and Reason of Layering in Jajarm Bauxite Deposit (North East of Iran) by using Geochemical Data

Abstract Study of source rock materials in Jajarm bam ite deposit is the main subject of this study to show its origin. From bottom to top, this deposit consists of lower argillaceous l iyer, argillaceous bauxite, hard bauxite and upper kaolinite units. Correlation coefficients and scatter diagrams of immobile elements in these four layers, demonstrate an early homogenous origin at the beginning ofthe bauxite formation, Accordingly, ~ ource materials were separated slowly due to the different conditions dominated in different parts of the deposit. Ditference in drainage conditions and leaching of some elements from upper part and their re-deposition in lower parts of the deposit are de main reasons for hard bauxite separation from argillaceous one. Formation of the lower argillaceous layer, located between argillaceous bauxite and carbonate footwall is due to the direct contact of the argillaceous bauxite and carbonate footwall and ilso difference in drainage rate in contact area of the two layers. Geochemica evidence also depicts that upper kaolinite formation is the result of the silica leaching from upper horizons and its re-deposition in hard bauxites. Compositional comparison of studied samples with chondrite and upper continental crust demonstrates the effect of both of the basic and sedimentary rocks in evolution of the Jajann bauxite. Formation of this deposit can be considered as a result of the alteration of the primitive laterite in an area close to the current location of the deposit. During alteration and transportation bauxite is deposited on the karstic topography and then some continental sediment was added to it.l