Geochemistry and depositional environment of the Neoproterozoic Ereen and Dartsagt banded iron formation (BIF) deposits in the Idermeg terrane, eastern Mongolia

Abstract

This study aims to determine the depositional setting and deposit type of the Ereen deposit in the Bayanjargalan soum of Dundgovi province and the Dartsagt deposit in the Dalanjargalan soum of Dornogovi province, Mongolia. Both deposits are hosted within the sediments of the Neoproterozoic Oortsog Formation. The ore-hosted Oortsog Formation consists of shale with muscovite-sericite-magnetite-quartz and marbled limestone. The former is characterzid by gray to black shaly texture. Major, minor and trace elements composition of 16 ore samples of these two deposits were analyzed by XRF, ICP-MS and ICP-OES. The total iron (TFe) contents of the ore samples from the Ereen deposit range from 28.83 to 51.09 wt% with an average of 41.92 wt% whereas the TFe contents of the Dartsagt deposit from 37.61 to 49.78 wt% with an average of 43.15 wt%. In the Post-Archean Australian Shale (PAAS)-normalized REY diagram, the samples from the Ereen and the Dartsagt deposits show a weakly LREE depleted and HREE weakly enriched trend. Also, in the chondrite-normalized REY diagram, negative Eu anomaly Y-enriched trend are observed. The Eu/Eu*_SN values of the Ereen deposit (0.93 to 1.25, average 1.08) and the Dartsagt deposit range from 0.93 to 1.25 (avg. 1.08) and from 1.05 to 1.61 (avg. 1.22), respectively. These trace elements characteristics indicate that these two deposits belong to the Superior-type BIF deposit formed on the passive continental margin and are not likely to be associated with volcanogenic rocks.