Controls on metal enrichment in ferromanganese crusts: Temporal changes in oceanic metal flux or phosphatisation?

Oceanic hydrogenetic ferromanganese (Fe-Mn) crusts are a major repository for many metals, such as Co, Ni, Cu, Pt, Te and REE, which essential decarbonisation of transport energy systems. Secondary mineralisation processes, occurring during phosphatisation episodes, commonly impregnate the shallower deposits with carbonate fluorapatite (CFA). The suboxic oceanic conditions events frequently invoked to explain lower Co content unusually high Zn Pt older phosphatised crusts. Here, hypothesis diagenetic recrystallization induced by episodes driving mechanism enrichment depletion is evaluated. Accurately dated geochemical profiles, spanning 75 Ma depositional history, shallow (1100 mbsl) sample deeper (3100 unphosphatised from Tropic Seamount in north-east Atlantic, compared. An isocon analysis, allows quantitively evaluate chemical gains losses mass transfer therefore permits compensation dilution effect addition CFA Fe-Mn crusts, demonstrates that no loss has occurred crust, whilst Te, Ni enriched relative younger, crust. Both profiles show sympathetic trends similar amplitudes variation concentration. This excludes metal depletion. Systematic differences between two samples, higher Cu sample, consistent depth profile dissolved concentrations water column. variability observed temporal changes fluxes ocean, result evolving climate oceanographic configuration Atlantic Ocean through Cenozoic. It concluded changing fluxes, rather than secondary process associated phosphatisation, dominant control on primary crust at Seamount.