Geochemical analyses, sequential leaching and X-ray diffraction (XRD) results of Fe-oxyhydroxide and massive sulphide samples from the Semenov Hydrothermal Field, Mid-Atlantic Ridge, during RRS James Cook cruise JC224 (March-April 2022)

Discrete samples of Fe-oxyhydroxide and seafloor massive sulphide were collected on the RRS James Cook cruise JC224 (March - April 2022) from the Semenov Hydrothermal Field, a seafloor massive sulphide (SMS) system located within the Mid Atlantic Ridge. Samples were collected using the ROV HyBIS (Murton et al., 2012). The samples were analysed onshore at the National Oceanography Centre, the University of Southampton and the British Geological survey for: (1) scanning electron microscope energy dispersive x-ray spectroscopy (SEM-EDS), (2) laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICP-MS) to obtain geochemical data of specific minerals, (3) geochemical composition analysis of sequential leaching by ICP-MS and ICP optical emission spectroscopy (OES) and (4) mineralogical quantification by using previously obtained X-ray diffraction (XRD) datasets after Bishop et al. (2025) and processed by Siroquant v5.2 (supplied by Sietronics Pty Ltd). This dataset aims to improve understanding regarding the mobilisation, distribution and retention of metals during the oxidation of sulphide minerals and subsequent alteration to their secondary products. The data were collected as part of a PhD project funded under NERC's Ultramafic-hosted mineral Resource Assessment (ULTRA) project, grant reference NE/S004068/1, and the samples are stored at the National Oceanography Centre, Southampton, UK.