Shale-normalized rare-earths and yttrium (REY(SN); Y inserted between Dy and Ho) patterns for detritus-free samples from both the Kuruman and Penge Iron-Formations (IFs) in the Late-Archaean to Early-Palaeoproterozoic Transvaal Supergroup display pronounced heavy rare-earth element (REE) enrichment, and positive anomalies of La-SN, Eu-SN, Gd-SN, Y-SN, and Er-SN, but neither positive nor negative Ce-SN anomalies. Excepting Ce-SN and Eu-SN anomalies, the Transvaal IFs yield all the features that are typical of the REY distribution in Modem seawater. (Eu/Eu*)(SN) ratios in the Kuruman IF correspond to ratios observed in other IFs of similar age, whereas the Penge IF is characterized by distinctly higher ratios. Within a sequence of eleven adjacent samples (each comprising less than ten microbands) from the Kuruman IF, (Eu/Eu*)(SN) ratios were found to vary significantly. Positive Eu-SN anomalies reveal the presence of a high-temperature hydrothermal component in Transvaal seawater. The absence of positive Ce-SN anomalies rules out the existence of an alkaline 'soda-ocean' with pH considerably above the Recent value of 8.2. Small-scale variation of (Eu/Eu*)(SN) ratios within the Kuruman IF as well as alternation of iron- and silica-dominated layers cannot be due to post-depositional modification of initially homogeneous material showing homogeneous REY distribution, because neither diagenetic nor metamorphic conditions were suitable for decoupling of Eu from the other REY. The observed small-scale variation may indicate short-term variability of (Eu/Eu*)(SN) ratios of Transvaal seawater, probably resulting from temporal variation of the activity of high-temperature venting at the seafloor. Preservation of this feature in IF microbands and the presence of positive Y-SN anomalies suggest that IF precipitation from upwelling marine bottom waters in an oxygenated shelf environment occurred very rapidly. Hence, REY adsorbed on the surface of iron-oxyhydroxide particles that eventually became Fe-rich IF microbands, were not in exchange equilibrium with REY dissolved in ambient seawater. Higher (Eu/Eu*)(SN) ratios in the Penge IF compared to the Kuruman IF suggest significantly more important REY input from high-temperature solutions to the REY budget of bottom waters in the Eastern Transvaal than in the Griqualand West sub-basin. The REY distribution in Penge and Kuruman IFs is compatible with a palaeogeographic setting which invokes the existence of a rather small basin in the northeast (the Eastern Transvaal sub-basin) in which spreading-related high-temperature fluid-rock interaction occurred. The basin widened towards the southwest (the Griqualand West sub-basin) where it was connected to the open ocean.
