Rare earth element geochemistry of the Upper Permian limestone: the Kanigorgeh mining district, NW Iran

The limestone of the Ruteh Formation of Upper Permian age in the Kanigorgeh district (northeast of Bukan, NW Iran) contains several layers and lenses of bauxitic ores. Mineralogical data show that this limestone consists of calcite and quartz as major and plagioclase, kaolinite, and hematite as minor mineral phases. Geochemical analyses reveal that the proportions of Sigma REEs (La-Lu) in this limestone vary from 35.28 to 160.78 ppm. The values of Eu and Ce anomalies (normalized to PAAS) of the limestone have ranges of 1.11-1.68 and 0.89-1.16, respectively. The high values of Sigma REEs; low values of Y/Ho; strong and positive correlations between Sigma REEs and elements such as Si, Al, Ti, V, Co, Ni, Rb, Cu, and Nb; and negative correlations between CaO and Sigma REEs suggest that the observed variations in values of Sigma REEs in the limestone were controlled principally by the quantity of detrital materials. Geochemical data also illustrate that the observed positive Eu anomalies in the limestone may be due to the presence of plagioclase and also a function of diagenetic processes. Furthermore, the variations in Ce anomalies may be due to the detrital input. The distribution of REEs (normalized to chondrite) illustrates different patterns in both rocks (the limestone and the bauxitic ores) in light of differentiation degree of LREEs from HREEs and values of conservative indexes such as Eu anomaly. Considering these pronounced discrepancies, it appears that the limestone, despite having relatively high concentration of Sigma REEs, did not play a significant role in supplying lanthanides for the bauxitic ores.