The Nkonko Ni-Cr bearing regolith in DRC: a study of petrography and geochemistry to understand serpentinization and weathering processes of mantle rock
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引用次数: 0
Abstract
Regolith-hosted Ni-Cr prospects in the Nkonko serpentinized massif are located near Kananga city in the Democratic Republic of Congo (DRC). This serpentinized massif displays an underground regolith profile divided into three main layers: (1) unweathered serpentinite bedrock, (2) saprolite serpentinites, and (3) the pedozone top layer. The bedrock serpentinites consist of serpentine (including lizardite and antigorite “garnierite”) as a major phase, with Cr-spinel and magnetite as a subsidiary phase. The rock contains rare pseudo-olivine relicts. Saprolite serpentinites contain serpentines (e.g., lizardite, chrysotile, antigorite “garnierite”) and subordinate ferrochromite and Cr-magnetite. These saprolite serpentinites are crosscut by veins of “garnierite” phase, talc, brucite, magnetite, magnesite, and chlorite. The pedozone primarily consists of lateritic soils with red and yellow limonite. Saprolite serpentinites exhibit relatively higher Al2O3, FeO, Fe2O3, and volatiles (LOI: loss on ignition) compared to bedrock serpentinites, while maintaining similar SiO2 contents. For trace elements, saprolite serpentinites contain elevated Cr (up to 5.4 wt%) and Ni (up to 2.0 wt%) compared to bedrock samples (Cr up to 0.9 and Ni up to 0.3 wt%). The REE concentrations are low (total REE of about 2.0 ppm) and remain unchanged between the saprolites and bedrocks. Spinel is identified as the main host mineral for Cr, while secondary serpentine “garnierite” is the primary host phase for Ni. Plots of Al2O3/SiO2 versus MgO/SiO2 for bedrock and saprolite serpentinites, along with the REE patterns, suggest that the serpentine regolith originated from the alteration and weathering of harzburgite.
期刊介绍:
Geosciences Journal opens a new era for the publication of geoscientific research articles in English, covering geology, geophysics, geochemistry, paleontology, structural geology, mineralogy, petrology, stratigraphy, sedimentology, environmental geology, economic geology, petroleum geology, hydrogeology, remote sensing and planetary geology.