Mineralogy and composition of manganese crusts and nodules and sediments from the Manihiki plateau and adjacent areas: Results of HMNZS Tui Cruises

Abstract

Forty‐four sediment samples and 23 Mn crusts and Mn nodules have been analyzed for several elements in order to characterize their geochemical nature. Most of the Mn crusts and Mn nodules are of hydrogenous origin, although one crust (U375) from the flanks of the Rarotonga volcano is thought to be of hydrothermal origin. δ‐MnO₂ is the principal Mn mineral in the crusts, whereas todorokite and birnessite occur in addition to δ‐MnO₂ in the nodules. The sediments can be divided into carbonates, with calcite as the dominant phase, and deep‐sea clay, consisting mainly of illite and smectite.

Keywords:

• manganese crusts
• manganese nodules
• Manihiki Plateau
• sediments