Mineralogical and geological significance of hydrothermal products: A case from the Chihu hydrothermal field, South Mid-Atlantic Ridge

The Chihu hydrothermal field is a mineral occurrence related to a detachment fault structure. It was discovered in 2019 at 23.7°S of the southern mid-Atlantic ridge. The detachment fault is believed having important influences on the hydrothermal activity and mineral deposition of the field. In this paper, mineralogy and mineralogy chemistry studies are conducted for the hydrothermal products by means of transmission-reflection microscope, Terraspec Halo mineral discriminator and X-ray diffraction (XRD). The results suggest that the hydrothermal products are mainly composed of siliceous sulfides, siliceous mineralized and carbonate mineralized breccias consisting of altered rock fragments, massive sulfide breccia, fine-grained disseminated sulfide, and siliceous and carbonate cemented matrix. The difference in mineral composition, structure and mineral composition between massive sulfide and fine-grained disseminated sulfide indicates that the hydrothermal area may have experienced multiple times of eruption cycles. The complexity and diversity of altered rock fragments suggest that in addition to basic source rocks, this hydrothermal field may also be affected by ultrabasic source rocks.