Frei, R., Dahl, P., Duke, E., Frei, K., Hansen, T., Frandsson, M., & Jensen, L. (2008). Trace element and isotopic characterization of Neoarchean and Paleoproterozoic iron formations in the Black Hills (South Dakota, USA): Assessment of chemical change during 2.9–1.9 Ga deposition bracketing the 2.4–2.2 Ga first rise of atmospheric oxygen. Precambrian Research. https://doi.org/10.1016/J.PRECAMRES.2007.10.005
Frei, Robert, Peter Dahl, Edward Duke, Karin Frei, Thomas Hansen, Mie Frandsson, and Lizette Jensen. 2008. “Trace Element and Isotopic Characterization of Neoarchean and Paleoproterozoic Iron Formations in the Black Hills (South Dakota, USA): Assessment of Chemical Change During 2.9–1.9 Ga Deposition Bracketing the 2.4–2.2 Ga First Rise of Atmospheric Oxygen”. Precambrian Research. https://doi.org/10.1016/J.PRECAMRES.2007.10.005.
Frei, R., P. Dahl, E. Duke, K. Frei, T. Hansen, M. Frandsson, and L. Jensen. Trace Element and Isotopic Characterization of Neoarchean and Paleoproterozoic Iron Formations in the Black Hills (South Dakota, USA): Assessment of Chemical Change During 2.9–1.9 Ga Deposition Bracketing the 2.4–2.2 Ga First Rise of Atmospheric Oxygen. Precambrian Research, 1 May 2008, doi:10.1016/J.PRECAMRES.2007.10.005.