Geochemical characteristics of the karst-type bauxites: an example from the Kanirash deposit, NW Iran

The Kanirash bauxite deposit belongs to the Iran-Himalayan karst-type bauxite belt, which is situated about 30km southeast of Mahabad city, northwestern Iran. The bauxite ores are embedded by the Late Permian carbonate rocks intercalated with shale of the Ruteh Formation and occurred as layer and lens-shaped patches. The bauxite ores contain diaspore, clinochlore, hematite, pyrophyllite, illite, rutile, and lesser amounts of zircon, pyrite, and barite. This mineral assemblage indicates that this deposit was formed in a transitional zone between the vadose and the phreatic environments. The presence of pyrite in the bauxite ores demonstrates that organic matters were present in the uppermost parts of the profile and the depositional diagenetic/epigenetic environment was reducing. Ti and Fe together with a suite of trace elements, including Ni, Cr, Co, Ga, Ta, and V, were leached from the upper parts of the weathered profile and concentrated in the bottom parts with respect to Hf, chosen as the least mobile element. Some factors, such as pH variations in weathering solutions, buffering nature of the carbonate bedrock, mineral control, the existence of organic materials, and fluctuations of groundwater table played important roles in distribution of trace and rare earth elements.