The BIF record underpins our understanding of the global rise in atmospheric oxygen and the geochemical evolution of the oceans. Through the application of geochemical proxies, changes in their chemical, mineralogical and isotopic compositions have provided a record of the physiochemical conditions in the Earth’s hydrosphere-atmosphere system at the time of their deposition (Bau and Möller, 1993). Given that their precursor minerals are resistant to diagenetic processes, BIFs are likely to faithfully reflect the chemical composition of seawater (Robbins et al., 2015). In particular, rare-earth element (REE) systematics and Nd isotope compositions have been widely used to understand the origin of BIFs and the relative proportions of terrigenous and hydrothermal inputs to the ancient oceans (Alexander et al., 2009). In this contribution the trace element systematics of a collection of BIF from the Hamersley Basin, Western Australia will be discussed. The sample suite includes 40 samples which range in age from 2.60 to 2.44 Ga and includes samples from the Marra Mamba, Brockman, Weeli Wolli and Boolgeeda Iron Formations. All of the samples come from drill core and have been selected to avoid regions of secondary hypogene enrichment or supergene alteration. However, in an endeavour to eliminate preferential sampling biases samples were collected at a relatively even spacing throughout the formations. High precision trace element analyses of 45 elements from across the periodic table has been conducted, including quantifying several bioavailable elements (e.g. Cd, Mo, Zn) that will form the foundation of future isotopic studies. Systematic variations in specific trace elements hint a significant change in the local depositional environment including increasing terrigenous input during the late Archean in the Hamersley basin. This work will be supplement by sequential leaching experiments (after Oonk et al., 2017) which will be conducted to separate the carbonate, oxide and silicate phases and interrogate their trace element compositions independently.

Reference(s)

Alexander, B.W., Bau, M. and Andersson, P. (2009) Neodymium isotopes in Archean seawater and implications for the marine Nd cycle in Earth's early oceans. Earth and Planetary Science Letters v. 283, p. 144-155.

Bau, M. and Möller, P. (1993) Rare earth element systematics of the chemically precipitated component in early precambrian iron formations and the evolution of the terrestrial atmosphere-hydrosphere-lithosphere system. Geochimica et Cosmochimica Acta v. 57, p. 2239-2249.

Oonk, P.B.H., Tsikos, H., Mason, P.R.D., Henkel, S., Staubwasser, M., Fryer, L., Poulton, S.W. and Williams, H.M. (2017) Fraction-specific controls on the trace element distribution in iron formations: Implications for trace metal stable isotope proxies. Chemical Geology v. 474, p. 17-32

Robbins, L.J., Swanner, E.D., Lalonde, S.V., Eickhoff, M., Paranich, M.L., Reinhard, C.T., Peacock, C.L., Kappler, A. and Konhauser, K.O. (2015) Limited Zn and Ni mobility during simulated iron formation diagenesis. Chemical Geology v. 402, p. 30-39.