%0 Journal Article
%A Merinero Palomares, Raúl
%A Lunar Hernández, Rosario
%A Martínez Frías, Jesús
%A Somoza Losada, Luis
%A Díaz del Río, Víctor
%T Iron oxyhydroxide and sulphide mineralization in hydrocarbon seep-relatedcarbonate submarine chimneys, Gulf of Cadiz (SW Iberian Peninsula)
%D 2008
%@ 0264-8172
%U https://hdl.handle.net/20.500.14352/49572
%X This paper aims to investigate the iron mineralization hosted in the submarine hydrocarbon seep-relatedcarbonate chimneys, from the Gulf of Cadiz continental slope (SW Iberia). Chimneys are made ofa general fine groundmass of major Fe-rich dolomite, ankerite and calcite, small grains of quartz andphyllosilicates, and some foraminifer tests and ostracod shells. Primary porosity is frequently generatedinside foraminifer chambers and ostracod shells, and is filled with closely packed microcrystals of ironoxyhydroxide and sulphide minerals forming framboids. Some extremely peculiar multiframboidaltextures are also detected, corresponding to microcrystal groups, spherical framboids and euhedralcrystals without framboidal texture. The mineralogy observed is mainly goethite (pyrite pseudomorphs);traces of tiny grains of pyrite were also observed. Cubic, octahedral and pyritohedral are the habitsobserved in both minerals. Chemical analyses of framboids and euhedral crystals display high (oftenerratic) amounts of As, Co, Ni and Mo in oxyhydroxides and Mo, Pb, V and Co in sulphides versus almostalways negligible concentrations of Cu and Zn. A textural, geochemical and mineralogical evolution isproposed to explain the coexistence of different morphologies in the multiframboidal texture: (a) growthand aggregation of microcrystals as typical framboidal-type mineralogical associations; (b) developmentof euhedral habits; (c) coalescence and homogenization of the microcrystal into large size (euhedral toanhedral) crystals, and (d) formation of euhedral crystals or polycrystalline masses, with complete loss offramboidal texture. Along this process, an increase of the concentration of Fe, S, Mn and Ti, linked toa decrease in Mg, Si, Al, As, P, Ca and V was observed. The study of the iron mineralization in the Gulf ofCadiz is a first, and can give clues to understand the complex geobiological interactions in this and othersimilar extreme hydrocarbon-bearing submarine ecosystems.
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