Abstract
Mineralogy of phosphatized and zeolitized hydrogenous cobalt-rich ferromanganese crusts from Dirck Hartog Ridge (DHR), the Perth Abyssal Plain (PAP), formed on an altered basaltic substrate, is described. Detail studies of crusts were conducted using optical transmitted light microscopy, X-ray Powder Diffraction (XRD) and Energy Dispersive X-ray Fluorescence (EDXRF), Differential Thermal Analysis (DTA) and Electron Probe Microanalysis (EPMA). The major Fe-Mn mineral phases that form DHR crusts are low-crystalline vernadite, asbolane and a feroxyhyte-ferrihydrite mixture. Accessory minerals are Ca-hydroxyapatite, zeolites (Na-phillipsite, chabazite, heulandite-clinoptilolite), glauconite and several clay minerals (Fe-smectite, nontronite, celadonite) are identified in the basalt-crust border zone. The highest Ni, Cu and Co contents are observed in asbolane and Mn-(Fe) vernadite. There is significant enrichment of Ti in feroxyhyte−ferrihydrite and vernadite. The highest rare earth element (REE) content is measured in the phosphate minerals, less in phyllosilicates and Na-phillipsite. The geochemical composition of minerals in the DHR crusts supports the formation of crusts by initial alteration, phosphatization and zeolitization of the substrate basalts followed by oscillatory Fe-Mn oxyhydroxides precipitation of hydrogenous vernadite (oxic conditions) and diagenous asbolane (suboxic conditions).
Highlights
Co-rich ferromanganese crusts formation and mineral composition have been the subject of several scientific works [1,2,3,4,5,6,7,8]
Cobalt-rich ferromanganese crusts consist of layered Fe-Mn oxyhydroxide deposits found on rock substrates at depths between 400 and 7000 m below sea level, where ocean bottom currents clear rocks of sediment cover [13]
The major aim of this paper is to present mineralogical description of cobalt-rich ferromanganese crusts from Dirck Hartog Ridge (DHR) located central Perth Abyssal Plain (PAP), Indian Ocean
Summary
Co-rich ferromanganese crusts formation and mineral composition have been the subject of several scientific works [1,2,3,4,5,6,7,8]. Recent discoveries from previously unstudied locations, mainly due to increase of marine research, provide new data on crusts chemistry, mineralogy, formation conditions and economic importance [9,10,11,12]. Cobalt-rich ferromanganese crusts consist of layered Fe-Mn oxyhydroxide deposits found on rock substrates at depths between 400 and 7000 m below sea level (mbsl), where ocean bottom currents clear rocks of sediment cover [13]. According to the cobalt-rich ferromanganese crusts classification based on types of fluids and seawater sources of elements
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