A model for the formation of hydrothermal manganese crusts from the Pitcairn Island hotspot

The distribution of elements in the hydrothermal Mn crusts from the Pitcairn Island hotspot can be explained by considering processes occurring within the hotspot volcano. These include the role of boiling of the ascending hydrothermal fluid which leads to sulphide deposition and seawater intrusion into the upper part of the volcano. This in turn results in the development of an oxycline above which FeOOH can precipitate. The high Mn/Fe ratios and low contents of Ni and Zn in the massive crusts are thought to reflect the rapid incorporation of the ore elements into sulphide minerals such that only a small proportion of these elements are available for incorporation in the crusts. The small positive Eu anomaly in the crusts on a NASC-normalized basis reflects the lower temperatures in the hydrothermal fluids at the Pitcairn Island hotspot (