The giant Shilu Fe-Cu-Co deposit in Hainan Island, South China, which was structurally and hydrothermally superimposed, is mainly hosted in highly metasomatized dolostones/marbles of the- 900 Ma Shilu Group. This study confirmed that the ore bodies are originally strata-bound and epigenetic, but do not have spatial relations with any coeval intrusions. In this study, the paragenetic sequence of the pre-deformation mineralization is refined and consists of early Ca-silicate alteration (I), Fe (II), and Cu-Co (III) mineralization stages, followed by multiple overprints and/or undeformed veins (stage IV). Our new oxygen and in situ Pb-S isotopic results for stages Ito III show that the mineralizing fluids were initially magmatic-hydrothermal but have undergone variable degrees of interaction with country rocks during mineralization. On the other hand, stage IV fluids have in situ Pb-S isotopic compositions indicative of significant contributions of early-stage components through secondary re-mobilization. These features, in combination with chemical compositions of Fe oxides (e.g., elevated Ti in hematite), strongly argue that the Shilu deposit does not belong to BIF as previously considered, but is typical of magmatic-hydrothermal IOCG deposits. New sulfide Re-Os isotopic data show that the major Fe-Cu-Co mineralization formed at 780 +/- 24 Ma (MSWD =0.62). The deposit is confirmed to be broadly comparable to Neoproterozoic IOCG deposits in the Ailao Shan-Red River shear zone in terms of timing and nature of mineralization. Given that the shear zone likely extends to Hainan Island, the Shilu deposit is considered to be part of the same IOCG metallogenic belt and similar mineralization along the shear zone may be more widespread than previously thought.