Abstract Laterite deposit at Sheikh‐Marut (NW Mahabad, West‐Azarbaidjan province, Iran) occurred within middle–upper Permian carbonate rocks. It consists of seven stratiform and/or discontinuous lenticular layers extending over 4.2 km in length and having thicknesses ranging from 3 to 14 m. Mineralogical data show that the ores contain kaolinite and hematite as major and boehmite, diaspore, halloysite, amesite, anatase, and muscovite‐illite as minor mineral phases. The computed Ce anomaly values in the ores range from 0.05 to 20.84. Conservative index (e.g., Eu/Eu*) suggests that this deposit is a product of alteration and weathering of basaltic rocks. Rhythmic increment of ΣREE values of the ores with approaching to the carbonate bedrocks shows an in‐situ occurrence of lateritization processes. Mass change calculations of elements indicate that two competing processes namely leaching and fixation were the major regulating factors in concentration variation of REEs (La–Lu) in this deposit The obtained results show that pH increase of weathering solutions by carbonate bedrocks, existence of organic matters, and the degree of comlexation with organic ligands played remarkable role in distribution of REEs during lateritization. Further geochemical considerations revealed that secondary phosphates, Mn‐oxides and ‐hydroxides, diaspore, and anatase were the potential hosts for REEs in this deposit.
Mehredjan bentonite deposit is located ~33 km southeast of Khoor in Isfehan province. It includes 15 discrete outcrops and occurs as layered and massive forms within a volcano-clastic sequence. Bentonitization process was accompanied with development of minerals such as montmorillonite, quartz, cristobalite, calcite, kaolinite, halite, albite, orthoclase, and muscovite. The collected field and laboratory data indicate that this deposit was developed by authigenic alteration of tuffs ranging in composition from trachyandesite, through andesite to basaltic andesite in a shallow marine environment. The distribution patterns of REEs normalized to chondrite in both bentonite and enclosing tuffs illustrate similar trend indicating the fractionation and enrichment of LREEs relative to HREEs and negative anomalies for Eu. Geochemical data revealed that transformation of tuffs into bentonite took place in an open system where leaching and fixation processes were two basic regulating factors in concentrating of common trace and rare earth elements. By pointing to the obtained results, factors such as differences of alteration intensity of protolith, physico-chemical conditions of alteration environment, adsorbing mechanism, structural incorporation, existing of organic matters, effects of diagenesis, carbonate complexation, ionic exchange, physical concentrations, and existing of resistant minerals played important roles in development of Mehredjan bentonite. .
Mn-bearing veins of Jonub -ESehchangi are located 200 km southwest of Birjand, Southern Khorasan province (east of Iran). These veins are hosted by andesitic rocks of Eocene to Oligocene ages. Ore minerals identified by XRD method and mineralographic studies and are Pyrolusite, cryptomelane, psilomelane, hollandite, hematite and goethite, displaying colloform and open-space filling textures. Gypsum, halite, barite, carbonate and silica are the gangue minerals. Alteration zones, specifically argillic alteration zone, are developed along the vein within the andesitic wall rocks. Based on the mineralogical and geochemical data, the primary manganese minerals were Mn oxides and hydroxides, which have gradually been converted to psilomelane and hollandite, and finally pyrolusite. The average grade of Mn within the veins is 38.61%. Considering the average Mn/Fe ratio (about 48.55) in the Mn-bearing veins, as well as the positive correlation of Sr, U and Ba with Mn mineralization in this area show hydrothermal origin.
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