Abstract The main metallic mineral resources of New Caledonia are hosted by the obducted Peridotite Nappe. Ni, Co, Cr and the Pt group elements (PGEs) are specific to this ultramafic terrane. Cr, as podiform chromitite in the uppermost mantle, is the only hypogene metal mined economically in the past. The largest chromitite deposits are located in the lherzolitic Tiébaghi Massif. Supergene Ni and Co deposits are concentrated by the tropical climate that has prevailed since the Miocene. New Caledonian lateritic Ni deposits account for 10% of the global Ni resources. Hydrous Mg silicate and oxide types coexist in a single deposit. A local genetic model based on geomorphological evolution is proposed. Sc is a prospective resource associated with these supergene deposits. The PGEs are a prospective resource associated with chromite, with potential in the hypogene, supergene and fluvio-littoral domains. Pt and Pd are the most significant elements. The transition zone between the upper mantle and crustal cumulates constitutes a regional Pt–Pd-enriched horizon. The concentrations are related to small disseminated chromite lenses in a pyroxene-rich lithology. The PGEs are concentrated in weathering profiles. The value of chromite-rich sands as placers or sand beach deposits might be enhanced by the occurrences of PGEs.

Abstract This review presents an objective account of metamorphic, microstructural and geochronological studies in the Greater Himalayan Sequence (GHS) and adjacent units in Nepal in the light of recent research. The importance of integrated, multidisciplinary studies is highlighted. A personal view is presented of strategies for determining pressure–temperature evolution, and of petrological processes at the micro scale, particularly in relation to departures from equilibrium and the behaviour of partially-melted rock systems. Evidence has accumulated for the existence within the GHS of a High Himalayan Discontinuity, marked by differences in timing of peak metamorphism in the hanging wall and footwall, and changes in P–T gradients and paths. Whether or not this is a single continuous horizon, it forms at each location the lower boundary to a migmatitic zone capable of ductile flow, and separates the GHS into an upper division in which channel flow may have operated in the interval 25–18 Ma, and a lower division characterized by an inverted metamorphic gradient, and by metamorphic ages that decrease downsection and are best explained by sequential accretion of footwall slices between 20 and 6 Ma. An overall model for extrusion of the GHS is still not resolved.

Abstract Crystalline klippen over the Lesser Himalayan Metasedimentary Sequence (LHMS) zone in the NW Himalaya have specific syn- and post-emplacement histories. These tectonics also provide a means to understand the driving factors responsible for the exhumation of the rocks of crystalline klippen during the Himalayan Orogeny. New meso- and microscale structural analyses, and thermochronological studies across the LHMS zone, Ramgarh Thrust (RT) sheet and Almora klippe in the eastern Kumaun region, NW Himalaya, indicate that the RT sheet and Almora klippe were a part of the Higher Himalayan Crystalline (HHC) of the Indian Plate which underwent at least one episode of pre-Himalayan deformation and polyepisodic Himalayan deformation in ductile and brittle–ductile regimes. The deformation temperature pattern within the Almora klippe records a normal thermal profile from its base to top but an inverted thermal profile from the base of Almora klippe down towards the LHMS zone. New fission-track data collected across the RT sheet and Almora klippe along Chalthi–Champawat–Pithoragarh traverse in the east Kumaun region document the exhumation of both units since Eocene times. Zircon fission-track (ZFT) ages from the Almora klippe range between 28.7 ± 2.4 and 17.6 ± 1.1 Ma, and from the RT sheet between 29.8 ± 1.6 and 22.6 ± 1.9 Ma; and the apatite fission-track (AFT) ages from the Almora klippe range between 15.1 ± 1.7 and 3.4 ± 0.5 Ma, and from the RT sheet between 8.7 ± 1.2 and 4.6 ± 0.6 Ma. The age pattern and diverse patterns of the exhumation rates reflect a clear tectonic signal in the RT sheet and the Almora klippe which acknowledge that the Cenozoic tectonics influenced the exhumation pattern in the Himalaya.