Sm-Nd and Sr isotope fingerprinting of iron mining tailing deposits spilled from the failed SAMARCO Fundao dam 2015 accident at Mariana, SE-Brazil

摘要

This work presents the first Sm-Nd and Sr isotope TIMS data on the fine-grained fraction (< 74 mu m) of iron-rich deposits related to the November 5th, 2015 Mariana accident, caused by the rupture of the Fundao dam, an iron tailings pond operated by SAMARCO Mining. The failure of the Fundao dam provoked the gravitational flow of approximately 62 Mi m(3) of a quartz and iron oxide-rich slurry composed of water, fine sand and silt, that flowed into the Gualaxo do Norte and Carmo rivers, and eventually along the whole Doce River. Samples were collected between 5 and 80 km downstream from the Fundao Dam, along the Santarem creek and the Gualaxo do Norte and Carmo rivers. XRD analyses show that samples are > 90% composed of quartz and iron oxides (hematite, goethite and magnetite), with minor phyllosilicates (kaolinite and mica). Owing to sediment transport processes, heavy (hematite, goethite, magnetite) to light (quartz, phyllosilicates) mineral fractionation is observed. As with XRD data, major and trace element compositions also closely match those of the original Paleoproterozoic Caue Formation BIF iron ore. The studied samples yielded delta(Nd) between -17.0 and -19.7 pptt (part per ten thousand), with the exception of one sample, with delta(Nd) of - 23.2 pptt. Strontium Sr-87/Sr-86 ratios show variability between 0.7351 and 0.7729. The T-DM ages scatter between 1.94 Ga and 2.75 Ga, with a negative correlation with phyllosilicate contents, indicating that the latter has preferential provenance from younger, more juvenile sources than the Caue Fm itabirites. This interpretation is corroborated by two component mixing models of Nd and Sr isotope ratios, where the Nd-Sr isotopic signatures of the studied samples are compatible with > 98% of the Caue Fm itabirite component, mixed with a Neoproterozoic juvenile mafic rocks component, such as those from the ophiolitic assemblages of the distal Macaubas Group, or tholeiitic mafic rocks of the Pedro Lessa suite. The report