Slowly adjusting and incising river network in a Ni-bearing landscape, SE New Caledonia

Constraining the evolution of river networks under external forcings is critical because drainage evolution and landscape dissection control the redistribution of regolith, which has implications for mining resources. In this study, several Neogene geomorphic evolution stages of the Southern Massif of New Caledonia, where supergene nickel ore is exploited, are reconstructed by combining Digital Elevation Model (DEM) analysis with field mapping of abandoned lateritic paleo-landsurfaces. Results show that the drainage has been mostly exorheic, and that stream capture and piracy have slowly modified the landscape over the past 20 million years. The river long profiles are still adjusting to ongoing uplift, as demonstrated by southward island tilting and the uplift of quaternary reefs to the North of the study area. Ranges of drainage area changes and river incisions are assessed. Neogene incision rates are very low in the vicinity of the Goro pit (i.e., 1–15 m.Myr −1 ), the classic basin-type Nickel deposit of New Caledonia, compared to other places (i.e., up to 15–30 m.Myr −1 ). We propose that such low incision rates can explain the singularly high thickness of oxide Ni deposits in the area due to enhanced polygenetic weathering on lateritic profiles during the Neogene.