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Composition and origin of hydrothermal ironstones from central Pacific seamounts

J.R. Hein·Y. Hsueh-Wen·S.H. Gunn·A. E. Gibbs·W. Chung-ho
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Abstract

Ironstones recovered from five Late Cretaceous seamounts in the central Pacific region probably formed during late-stage edifice-building volcanism. Ironstones are dense and compact with the appearance of brown chert. The ironstones are characterized by a goethite mineralogy with FeOOH contents up to 88%, extreme fractionation of Fe and Mn, low trace-element and rare earth element abundances, low Co Zn "> CoZn ratios, and isotopic equilibration temperatures of about 20–45 °C. These characteristics indicate that the ironstones formed from hydrothermal fluids. Ironstones probably formed below the seawater-seafloor interface, as indicated by their occurrence as a proximal hydrothermal deposit, presence of primary goethite cement, pervasive replacement of rocks by goethite, and absence of interbedded pyro-clastic beds.

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J.R. Hein, Y. Hsueh-Wen, S.H. Gunn, A. E. Gibbs, W. Chung-ho. 1994. Composition and origin of hydrothermal ironstones from central Pacific seamounts. https://doi.org/10.1016/0016-7037(94)90455-3

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