New Caledonia holds one of the largest supergene nickel ore deposits worldwide. Two main ore types are recognized: oxide and hydrous Mg-Ni silicate types. Our study focuses on the latter type, usually located in elevated parts of the Peridotite Nappe, forming the so-called plateau and slope deposits. Understanding the controls of these nickel ore deposits is important in order to optimize the resource exploitation; however, to date there are only a few models to refer to, and structural aspects are rarely documented.
From its formation at an oceanic ridge to Eocene obduction, the Peridotite Nappe of New Caledonia underwent several episodes of brittle fracture that mostly preceded weathering. We suggest that inherited fractures coated with serpentine polymorphs play a major role in the Ni enrichment process. Fracture analysis shows that this early fracture network shares the same orientations with lineaments of peridotite massifs and controlled erosion and plateau dissection during uplift events. The subsequent steep slopes together with circulating waters within serpentine-filled fractures parallel to underlying valleys led to slope failure. The collapse of plateau edges provoked plateau decompression and hence multidirectional extension. Gravity-driven faulting caused preferential opening of joints within the hanging walls of faults. The lateral permeability contrast favored weathering and eventually resulted in an increase of Ni content in the saprock. The controlling faults have a specific polyphase infill, which could be a metallotect and a potential guide for nickel exploration.