REE Distribution during Diagenetic Processes of Sedimentary Copper Deposit in Nahand‐ Ivand Area, NW Iran

NahandIvand area, NW Iran contain disseminated copper sulfides along a redox boundary within gray sandstone and microconglomerate in contact red sandstones, siltstones and shaly-marly sediments. Over forty samples were studied in the north of Tabriz, where organic rich sandstones are exposed in the lower part of the Upper Red Formation (M2), and formed reduced zones in contacts with underlying and overlying oxidized zones. Mineralogy investigation along with geochemical analysis show that the highly mineralized samples are organic-rich sandstones with 0.14 wt.% TOC (Table 1) and the main ore minerals are Cu-sulfides (digenite, covellite) and Cu– Fe sulfides (bornite, chalcopyrite), and pyrite. Typical variations in TOC content could influence the REE contents. For example, Byrne and Kim (1990) found that the affinity of REE for surfaces can be strongly affected by organic coatings. The present content and distribution of rare earth elements is probably due to mineralogical composition, depositional environment and later diagenesis. Geochemical analyses show that the nonmineralized red sandstone are depleted in REE in comparison to NASC (Gromet et al., 1984) probably because of the greater dilution by SiO2, as a result of coarser grain size (Laux et al., 2005), and show rather flat REE patterns and depletion in LREE and enrichment in MREE relative to HREE (Fig. 1a). Mineralized unit usually occurs in the gray sandstones with the similar trend of REE pattern. The REE patterns of average gray sandstones in Khaje are more convex than those in the red and gray zone and relatively enriched in Eu and Tm anomalies (Fig. 1b). The high mineralized sandstone in this unit is characterized by a flat pattern, no positive Eu anomaly, and the lowest ∑REE (88ppm) (Table 1, Fig. 1b). Some mineralized sandstones in this unit are more oxidized in comparison to other samples, the REE patterns of them are more convex and much higher (av. 134 ppm) than those in the high mineralized sandstone and show possitive Eu anomaly (Fig. 1b). Oxidation of sandstone in the M2 unit is a secondary feature. Comparisons between mineralized and oxidized sandstones show that they differ significantly in REE contents, REE distributions and anomalies. Relatively higher abundances of REE within these sandstones compared to the mineralized samples were found in this study. Roberts et al., 2009 suggested that during early diagenesis REE are released to pore waters and during late diagenesis scavenged and precipitated. So strong enrichment in REE of the M2 unit might be due to their desorption from large volumes of oxidizing, probably mineralizing, solutions which emerged from the underlying red sediment into the M2 unit. Also there is highly significant positive relationship between Cu and ∑REE contents in sandtone from M2 unit in upper Red formation spetially in the mineralized SADATI Seyedeh Narges, MAO Jingwen, YAZDI Mohammad, BEHZADI Mehrdad, ADABI Mohammad Hossein , XU Lingang and MOKHTARI Mir Ali Asghar, 2014. REE Distribution during Diagenetic Processes of Sedimentary Copper Deposit in NahandIvand Area, NW Iran. Acta Geologica Sinica (English Edition), 88(supp. 2): 460-462.