Phosphorites

Phosphorite is a non-detrital sedimentary rock which contains high amounts of phosphate minerals. Phosphorite  and ferromanganese crust deposits are frequently associated, and widespread on the seafloor of continental shelves and slopes along the western continental margins of the Atlantic Ocean, also occurring on seamounts, banks and plateaus. They are especially abundant on the volcanic seamounts and ridges from the Macaronesia region (Canary-Madeira-Açores Islands).

Some thick Fe‐Mn crusts also contain carbonate fluorapatite (CFA), which was incorporated into the crusts during specific periods prior to middle Miocene (Baturin, 1982 ; Hein et al. 1985; Rao and Burnett, 1992). This type of mineralization seems to have occurred during two main Cenozoic episodes of phosphatization: the Eocene‐Oligocene (39–34 Ma) and Oligocene‐Miocene (27–21 Ma) with potentially other minor phosphogenic events, especially the middle Miocene, about 15 Ma ago (Hein et al. 1993).

Figure 1
Figure 1

Exploration of phosphorites and ferromanganese deposits, multichannel seismic profile southern Galicia Bank, NE Atlantic). Source: González et al. 2016 https://doi.org/10.1002/2015GC005861.

Figure 2
Figure 2

Phosphorite and ferromanganese crust, sample from Galicia Bank (Galicia margin, NE Atlantic Ocean). Photo: IGME.

Figure 3
Figure 3

Thin and polished-section photomicrograph of phosphorite. Sample from Sancho seamount (Galicia margin, NE Atlantic Ocean). Source: González et al. 2016 https://doi.org/10.1002/2015GC005861.

Figure 1
Figure 1

Exploration of phosphorites and ferromanganese deposits, multichannel seismic profile southern Galicia Bank, NE Atlantic). Source: González et al. 2016 https://doi.org/10.1002/2015GC005861.

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These deposits are related to strong upwelling along the continental margins and seamounts. Marine phosphorites are known to concentrate rare earth elements (REEs) and yttrium (REY) during early diagenetic formation (Hein et al. 1993; 2016; González et al. 2016).