Low-temperature magnetic behavior of isocubanite from seafloor hydrothermal deposits in the Okinawa Trough

The characteristic behavior of magnetic remanence correlated with mineralogical textures and composition was observed using low-temperature magnetometry, microscopy, and chemical analysis of three isocubanite samples collected from hydrothermal deposits in the Okinawa Trough and a sample transformed from natural cubanite via heating. Both zero-field remanence acquired at 5 K and field cooling remanence acquired at 300–5 K of all samples sharply decreased with increasing temperature at approximately 100 K. In addition, low-temperature cycling of isothermal remanence at 300 K exhibited a transition at approximately 100 K; remanence increased with decreasing temperature and vice versa. The intensity of remanence at low temperature and sharpness of the transition varied across samples with different compositions and microscopic textures, that is, the presence or absence of chalcopyrite lamellae and their widths. The sample obtained from a hydrothermal chimney, in which the magnetic transition was most clearly observed, was also subjected to X-ray diffraction, Mössbauer spectroscopy, electrical resistivity, and magnetic hysteresis measurements. The obtained results were generally consistent with those reported previously for unnamed mineral CuFe₃S₄ with an ordered cation arrangement. The low-temperature magnetic behavior of isocubanite possibly depends on the degree of cation ordering and can be regarded as an indicator of chemical composition and cooling history. Therefore, low-temperature magnetometry is useful for the detection of isocubanite and a potentially powerful technique for the prompt estimation of its composition and texture, contributing to our understanding of the formation process of hydrothermal deposits.