Rare Earth Element Tracing for Bamsar, Revesht and Nezam-Abad Tungsten Deposits in Central Iran

Bamsar, Revesht and Nezam-Abad tungsten deposits are located southwest of Shazand in central Iran. Rare Earth Element (REE) and other trace elements in samples of scheelite (CaWO₄) from these deposits have been determined by Neutron Activation Analysis in order to constrain the composition and sources of the mineralizing fluids. Paleozoic and Triassic volcano-sedimentary rocks and upper Triassic-Jurassic detrital-chemical and volcanic units outcrop in the Shazand region. The intrusives in the region have granitic and granodioritic compositions that have caused metamorphic haloes in the upper Triassic-Jurassic units. Six ore-bearing skarn horizons have been identified at Bamsar, while granodioritic intrusives host vein-type mineralization at Revesht and Nezam-Abad. Revesht and Nezam-Abad scheelites have higher total REE and Na concentrations than Bamsar samples. Bamsar scheelites show flat chondrite-normalized REE (REE_N) patterns, whereas scheelites from Revesht and Nezam-Abad exhibit hump-shaped REE_N patterns with maximum REE_N concentrations displaced towards Dy. Following the findings of Ghaderi et al. (1999) on scheelites from Western Australian gold deposits, it is suggested that Bamsar scheelites have variable Eu anomalies and trivalent REE concentrations and thus appear to contain mostly Eu²⁺ and to have formed under reduced conditions. Revesht and Nezam-Abad scheelites, on the other hand, exhibit no changes in the size of the Eu anomaly with REE concentration, implying a predominance of Eu³⁺ and crystallization under relatively oxidized conditions. Bamsar scheelites have (Ce/Lu)_N > 1 and are interpreted to have crystallized from LREE-enriched fluids, whereas Revesht and Nezam-Abad scheelites with (Ce/Lu)_N < 1 formed from LREE-depleted fluids. The elevated Na contents of Revesht and Nezam-Abad scheelites compared with Bamsar samples, suggest crystallization from hydrothermal fluids with higher Na activities. Reference: Ghaderi, M., Palin, J.M., Campbell, I.H., & Sylvester, P.J. (1999): Rare earth element systematics in scheelite from hydrothermal gold deposits in the Kalgoorlie-Norseman region, Western Australia. Economic Geology, v. 94, p. 423-437.