Abedini and Calagari reported in early 2013 that a Laterite deposit at Sheikh-Marut (NW Mahabad, West-Azarbaidjan province, Iran) occurs 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 presumed 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 l Eu*) suggests that this deposit is a product of alteration and weathering of basaltic rocks. Rhythmic increment of ~REE values of the ores with approaching to the carbonate bedrocks shows an in-situ occurrence of laterization 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 complexation with organic ligands played remarkable role in distribution of REEs during laterization. Further geochemical considerations revealed that secondary phosphates, Mn-oxides and -hydroxides, diaspore, and anatase were the potential hosts for REEs in this deposit.
The authors concluded that:
1) Incremental trend of ~REEs values from top to bottom of the profile indicate in-situ laterization during the evolution of this deposit.
2) Distribution pattern of REEs and index values of Eu | Eu* in the ores provide evidence concerning discrepancy in degree of mobility of REEs during laterization and a mafic origin (basaltic rocks) for this deposit.
3) Values obtained from mass change calculations of REEs (by taking Sc as immobile monitor element) implicate the dual role of carbonate bedrocks in
distribution of REEs in the studied deposit. It appears that the carbonate bedrocks owing to buffering of groundwater weathering solutions and hence destruction of REEs organic complexes caused the deposition of LREEs, Th, and Dy in the lower parts of the deposit. Formation of HREEs-carbonate complexes led to the leaching of Ho, Er, Tm, Yb, and Lu from the weathered system.
4) The strong and positive anomalies of Ce in the lower parts of the profile may indicate the preferential deposition of Ce in the form of cerianite in the deposit. This may be reasoned by the change of chemistry (oxidation potential) of the ore-forming solutions and increase of pH in groundwater, and
5) Interpretation of correlation coefficients among major oxides and REEs attest to the controlling role of scavengers such as oxides and hydroxides of manganese along with secondary phosphates, diaspore, and anatase in distribution of REEs in the studied deposit.
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