Multiple sulfur isotopes from the Neoarchaean Serra Sul black shale, Carajas mineral province, northern Brazil

摘要

In-situ laser ablation and multicollector-inductively coupled plasma-mass spectrometry were combined to analyse for sulfur isotopes in sulfide minerals that occur in the 2.7-billion-year-old black shale of Serra Sul, Carajas mineral province, Brazil. The black shale is part of a banded-iron-formation unit - the Carajas Formation - that hosts world-class iron-ore deposits. An obvious signal of mass-independent fractionation of sulfur isotopes (MIF-S) is not present in the black-shale sulfide minerals. Any significant MIF-S signal, above the analytical error of similar to 0.5 parts per thousand Delta S-33, was likely obscured by endogenic S. This explanation should also apply to the missing MIF-S signal in the clastic rocks of the overlying Aguas Claras Formation. The absence of MIF-S in the latter was interpreted to indicate a depositional age younger than 2.45 Ga. However, Palaeoproterozoic hydrothermal pyrite can reconcile the non-MIF-S signature with the Neoarchaean Aguas Claras Formation. (C) 2017 Elsevier Ltd. All rights reserved.