The Darzi-Vali bauxite deposit, located 20 km east of Bukan, in northwestern Iran, occurs as discontinuous layers and lenses within the Upper Permian carbonate rocks of the Ruteh Formation. These layers extend laterally for over ∼1 km and vary in thickness ranging from 2 to 17 m. We studied the chemical variations in a selected stratigraphic section throughout the deposit, focusing in particular on numbers of selected special metals that make the deposit of potential economic importance.
The critical elements Co, Ga, Nb, Ta, LREEs, and HREEs, along with transition metal Ni, are variously depleted throughout the deposit with respect to Ti, which is assumed to be a less mobile element. Among the critical elements, Cr has only demonstrated conservative behavior. Factor analysis suggests that the factors controlling the distribution of LREEs and HREEs in the ore, which most likely depend on the local composition of groundwater during weathering, are different from those controlling the distribution of other critical elements. Further, the Darzi-Vali ore has ΣREE contents (773 ppm) much higher with respect to other deposits located in NW of Iran, making this deposit worthy of further investigations.
As for parental affinity, the Eu anomalies show negligible fluctuations (0.82–0.94) all along the deposit confirming that bauxitization does not affect the effectiveness of this provenance proxy. The average Eu/Eu* value (0.89) of the ore is relatively far afield from that of the average carbonate bedrock (1.3) and close to that of the average mafic protolith(0.94), and similar results are also obtained using the Sm/Nd and Tb/Tb* proxies. Bivariate plots of Eu anomaly versus Sm/Nd and Tb anomalies further support the idea that mafic rocks are probably related to the volcanic activities. These volcanic activities affected the Iranian platform during the Upper Permian as proposed for other bauxite deposits in northwestern Iran. These mafic rocks were the probable precursor of the Darzi-Vali bauxite ore.