Geochemistry of rare earth elements of Darzi-vali bauxite deposit, east of Bukan, West-Azarbaidjan province, NW of Iran

Darzi-vali bauxite deposit of the Bukan (south of West-Azarbaidjan province, NW of Iran) developed as semi-continous stratiform layers and lenses within carbonatic rocks of the Ruteh Formation (Upper Permian). Based on physical characteristics, in one of layers considered, four bauxite types were recognized which are, from bottom to the top, (1) brownish red ore, (2) greenish cream ore, (3) greyish geen ore, and (4) dark green ore. Based on petrographical considerations, the ores of this deposit contain pelitomorphic, pseudo-breccia, fluidalcollomorphic, pisoidic, nodular, ooidic textures, and allogenic clasts. Mineralogical data indicate that the major rock-forming minerals of bauxitic ores include diaspore, boehmite, pyrophyllite, illite, goethite, hematite, chamosite, kaolinite, rutile, anatase, muscovite, calcite, dolomite, chlorite, corundum, and quartz. The presence of high quantities of silicate minerals indicates immaturity and poor draining system during development of this deposit. Thedistribution pattern of REEs (normalized to chondrite) display differentiation and enrichment of LREEs relative to HREEs and Eu weak negative anomalies during bauxitization processes. Calculations of absolute weathering index (AWI) with assumption of Th as an immobile monitor element and the upper continental crust (UCC) as parent rock along with pattern of changes of Ce anomaly and (LREEs/HREEs)N and (La/Yb)N ratios in studied profile indicate that changes of pH, mineralogical control, adsorbtion, scavenging, and protolith heterogenity played important role in distribution of REEs in the ore of this deposit. Correlation coefficients between elements suggest that concentration and distribution of REEs were controlled by illite, muscovite, and secondary phosphates.