@article{fdi:010071071,
  title = {{U}nusual massive magnetite veins and highly altered {C}r-spinels as relics of a {C}l-rich acidic hydrothermal event in {N}eoproterozoic serpentinites ({B}ou {A}zzer ophiolite, {A}nti-{A}tlas, {M}orocco)},
  author = {{H}odel, {F}. and {M}acouin, {M}. and {T}riantafyllou, {A}. and {C}arlut, {J}. and {B}erger, {J}. and {R}ousse, {S}onia and {E}nnih, {N}. and {T}rindade, {R}. {I}. {F}.},
  editor = {},
  language = {{ENG}},
  abstract = {{I}f magnetite is a common serpentinization product, centimetric, massive and pure magnetite veins are rarely observed in serpentinites. {U}nique example, in the {A}it {A}hmane ultramafic unit ({B}ou {A}zzer {N}eoproterozoic ophiolite, {A}nti-{A}tlas, {M}orocco) allows to assess the hydrothermal processes that prevailed at the ending {P}recambrian. {I}n this study, rock magnetism, petrography, mineral and bulk chemistry are combined to assess iron behavior in these meta-ultramafics, in order to constrain the serpentinites alteration and magnetite veins formation processes. {V}ery high {C}r#, low {M}g$, high {F}e3+# and low {T}i content of {C}r-spinels cores reflect a supra-subduction zone origin for the {A}lt {A}hmane serpentinites precursor. {T}ypical lizardite/chrysotile pseudomorphic texture in fresh serpentinites reveals an initial oceanic-like serpentinization, involving temperature < 350 degrees {C} while the abundance of magnetite (up to 10.14 wt%) in these unaltered serpentinites attests of a relatively high serpentinization temperature > 200 degrees {C}. {M}agnetic measurements reveal a lower magnetite content in hydrothermalized serpentinites hosting the magnetite veins, with lowest values (down to 0.58 wt%) for bleached serpentinites constituting the wall rock of the veins. {T}hese magnetic data are consistent with bulk rock chemistry showing a lower total iron content in hydrothermalized serpentinites. {H}ysteresis parameters and thermomagnetic measurements denote a magnetic grains size that increases with the alteration, associated with the emergence of a new magnetic phase ({C}r-magnetite) produced by {C}r-spinels alteration. {A} new proxy, based on thermomagnetic measurements, the {C}r{M}/{M} ratio, provides a quantification of its contribution to the magnetic susceptibility. {M}ineral chemistry allowed to identify the {C}r-spinels alteration sequence and reveals an important chlorine enrichment in serpentine phases from hydrothermalized serpentinites. {T}hese results suggest that a {C}l-rich acidic hydrothermal event involving temperatures below 350 degrees {C} produced an intense magnetite leaching in the host serpentinite and an advanced {C}r-spinels alteration to ferritchromite and {C}r-magnetite. {I}ron provided by this leaching have led to the formation of unique magnetite veins in the {A}lt {A}hmane ultramafic unit. {T}wo different settings are proposed for the hydrothermal event: (1) a continental hydrothermal system as advanced for the {C}o-{N}i-{A}s ores in the {B}ou {A}zzer inlier or (2) an oceanic black smoker type hydrothermal vent field on the {N}eoproterozoic seafloor.},
  keywords = {{N}eoproterozoic ; {S}erpentinite ; {H}ydrothermalism ; {M}agnetite ; {C}r-{S}pinel ; {O}phiolite ; {MAROC}},
  booktitle = {},
  journal = {{P}recambrian {R}esearch},
  volume = {300},
  numero = {},
  pages = {151--167},
  ISSN = {0301-9268},
  year = {2017},
  DOI = {10.1016/j.precamres.2017.08.005},
  URL = {https://www.documentation.ird.fr/hor/fdi:010071071},
}