Ferromanganese precipitates from the Jiawang Seamount, Bransfield Strait, Antarctica

Abstract

The Jiawang Seamount is a young volcanic edifice in the central Bransfield Basin, Antarctica. Ferromanganese precipitates were collected from its top during the R/V “Xianghong 01” cruise during the austral summer season of 2017/2018. The mineralogical and chemical compositions of typical species were analyzed to decipher their origin. These ferromanganese fragments were very light in weight and characterized by channel/cavity structures. Their mineralogy was mainly amorphous Fe-Si oxyhydroxide, with minor amounts of pyrite, arsenopyrite and metal compounds. Geochemically, they were enriched in Fe and Si and depleted of Mn, with Mn/Fe ratios of approximately 0.009. Most trace elements were depleted in these species, but Mo and Ge were enriched relative to the elemental contents of the upper continental crust. Additionally, these samples were depleted in rare earth elements, with an average of 77.64 μg/g. The post-Archean Australian shale (PAAS)-normalized rare earth element (REE) patterns showed negative Eu anomalies but no Ce anomalies. Biomorphic-like structures were present in the samples, probably indicating that bacteria such as Leptothrix ochracea, Gallionella ferruginea and Mariprofundus ferrooxydans had, to some extent, affected sample formation. All of these facts also indicated that one mixing process (hydrothermal process and biological process) affected the ferromanganese deposits in the Bransfield Basin.