Phosphorites, Co‐rich Mn nodules, and Fe‐Mn crusts from Galicia Bank, NE Atlantic: Reflections of Cenozoic tectonics and paleoceanography

Abstract

A wide variety of marine mineral deposits were recovered from 750 to 1400 m water depths on Galicia Bank, Iberian margin. Mineral deposits include: (1) carbonate fluorapatite phosphorite slabs and nodules that replaced limestone and preserved original protolith fabric. (2) Ferromanganese vernadite crusts with high Mn and Fe (Mn/Fe = 1) contents, and thick stratabound layers consisting mainly of Mn (up to 27% MnO) and Fe (15% Fe2O3), which impregnated and replaced the phosphorite. (3) Co‐rich Mn nodules are composed of romanechite and todorokite laminae. Mn‐rich layers (up to 58% MnO) contain up to 1.8% Co. (4) Goethite nodules with Fe up to 67% Fe2O3 have low Mn and trace metals. We interpret this mineralization paragenesis to be related to major changes in oceanographic and tectonic regimes. Three phosphatization generations formed hardgrounds dated by 87Sr/86Sr isotopes as late Oligocene, early Miocene, and latest early Miocene. During the latest early Miocene, the hardground was fractured and breached due to regional intraplate tectonism, which was coeval with a widespread regional erosional unconformity. The stratabound layers and Co‐rich manganese nodules were derived from low‐temperature geothermally driven hydrothermal fluids, with fluid conduits along reactivated faults. During middle and late Miocene, the introduction of vigorous deep water flow from the Arctic generated growth of hydrogenetic ferromanganese crusts. Finally, growth of diagenetic Fe‐rich nodules (late Pliocene) was promoted by the introduction of hypersaline Mediterranean Outflow Water into the Atlantic Ocean.

Hydrogenetic, Diagenetic and Hydrothermal Processes Forming Ferromanganese Crusts in the Canary Island Seamounts and Their Influence in the Metal Recovery Rate with Hydrometallurgical Methods

“…Comparing our results with previous work, it can be deduced that the diagenetic laminae in the hydrogenetic crusts are similar to diagenetic layers in nodules for instance from the CCZ. In [24] and then in [30], authors have conducted similar high resolution studies on a set of diagenetic nodules Figure 12. (A) EPMA spots analysis plotted in the ternary diagram from [27] to differentiate genetic processes of the Fe-Mn oxides, light grey field hydrogenetic, medium grey hydrothermal and dark grey diagenetic, modified according [6,33], discontinuous red lines, to better differentiate the genetic fields; (B) the same EPMA analysis plotted in the binary diagram according [28] to differentiate diagenetic or suboxic diagenetic fields.…”

“…% and 1800 and 2000 µg/g) [2]. Finally, Fe-Mn hydrothermal deposits show large fractionation between Fe and Mn, and the oxide minerals can be enriched in one or more of Li, Mo, Zn, Pb, Cu, or Cr [23] and in scarce cases in Co, Cu, Ni, Hg and Ag [24][25][26]. These three genetic processes are usually discriminated by the use of the concentration of Fe, Mn, Ni, Cu and Co of the samples and plotted in a ternary diagram [27][28][29].…”

Composition and genesis of ferromanganese deposits from the northern South China Sea

“…The terminology is based on the type of fluid from which the Fe-Mn oxide precipitate. In general, marine Fe-Mn oxide precipitates are defined as purely hydrogenetic when all constituents are derived from cold seawater, as diagenetic when all constituents are derived from cold oxic or suboxic sediment porewaters, and as hydrothermal when they precipitate in the vicinity of vent sites from fluids with temperatures higher than ambient bottom waters (Bau et al, 2014;González et al, 2016). However, in many places, Fe-Mn nodules and crusts form through a combination of fluid sources thereby exhibiting a mixed origin, primarily either hydrogeneticdiagenetic or hydrothermal-hydrogenetic Baturin et al, 2014;González et al, 2016).…”

“…Much of the research on Fe-Mn oxides has focused on openocean oxides from areas such as the Clarion-Clipperton Fracture Zone (CCFZ) in the central Pacific Ocean, the Central Indian Ocean Basin and the Peru Basin in the southeastern Pacific Ocean (Rona, 2008;Kuhn et al, 2012). Only a few studies focused solely on continental margin Fe-Mn nodules and crusts, such as from Galicia Bank (NW Atlantic Iberia margin) (González et al, 2016), Gulf of Cadiz , California continental-margin (Hein et al, 2005;Conrad et al, in press), Canary Island Seamount Province (Marino et al, in press) and the Philippine Sea (Xu et al, 2006).…”

Mineralogy of Cobalt-Rich Ferromanganese Crusts from the Perth Abyssal Plain (E Indian Ocean)

“…Hydrothermal crusts that precipitate directly from low temperature hydrothermal fluids (few tens of degrees up to 200 • C), usually grow significantly faster, even up to 1600-1800 mm/Ma [19]. Ferromanganese crusts in some locations form through a combination of fluid sources and thereby exhibit a mixed origin, primarily either hydrogenetic, diagenetic or hydrothermal-hydrogenetic [15,18,20,21].Co-rich ferromanganese crusts formation is dominated by hydrogenetic processes. The precipitation from bottom waters is extremely slow, with growth rates of 1-5 mm/Ma.…”