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Fritsch Emmanuel, Juillot Farid, Dublet G., Fonteneau L., Fandeur D., Martin E., Caner L., Auzende A. L., Beaufort D. (2019). An alternative model for the formation of hydrous Mg/Ni layer silicates ("deweylite"/"garnierite") in faulted peridotites of New Caledonia : II. Petrography and chemistry of white and green clay infillings. European Journal of Mineralogy, 31 (5-6), 945-962. ISSN 0935-1221

Lien direct chez l'éditeur doi:10.1127/ejm/2019/0031-2869

Titre
An alternative model for the formation of hydrous Mg/Ni layer silicates ("deweylite"/"garnierite") in faulted peridotites of New Caledonia : II. Petrography and chemistry of white and green clay infillings
Année de publication2019
Type de documentArticle référencé dans le Web of Science WOS:000505169400007
AuteursFritsch Emmanuel, Juillot Farid, Dublet G., Fonteneau L., Fandeur D., Martin E., Caner L., Auzende A. L., Beaufort D.
SourceEuropean Journal of Mineralogy, 2019, 31 (5-6), p. 945-962. ISSN 0935-1221
RésuméThis study, which complements a first mineralogical work, presents detailed petrographic and chemical data on the sequences of clay infillings commonly found in serpentine veins of reactivated faults from the New Caledonian peridotite formation. Chemical trends and transfers established from the outer serpentine fringe to the inner clay infilling, as well as from the white (deweylite) to the greenish (garnierite) parts of the veins, enable us to decipher the processes and conditions involved in the redistribution of Mg and Ni along reactivated faults. As commonly reported from studies of peridotite formations worldwide, two main chemical trends are distinguished. In New Caledonia, these trends belong to distinct periods of tectonic activities associated with the dislocation and early alteration of the ophiolite nappe. They result from two kinds of Ni-ore-forming processes and reveal a significant decrease in the mobility of Ni over time. The first process relates the step-by-step alteration of serpentine species into talclike (TL) minerals to the sequential leaching of Mg and Fe, together with their local replacement by Ni in octahedral sites of the newly formed TL minerals. The TL minerals are thus considered as the main Ni-bearing phases (pimelite) of the ore. The large-scale redistribution of Mg and Ni during a first period of tectonic activity and alteration leads to the differentiation of white (Ni-free) and olive-green (Ni-rich) clay infillings along the reactivated faults. The second process belongs to a second period of tectonic activity and alteration where most of the serpentine species have been converted into TL minerals without major Ni enrichment (formation of a second sequence of milky white and turquoise clay infillings). Redistribution of Mg and Ni occurs over shorter distances from the transition of Mg-rich to Ni-rich clay infillings (or breccias). It results from oscillatory phenomena and self-organised precipitation processes leading to cyclic and inverse Mg and Ni variations in alternating bands of contrasted optical anisotropy. The early redistribution of Ni and the significant decrease in the mobility of this element from the first to the second period of tectonic activity provide better constraints on an alternative model for the genesis of the Ni-silicate ore.
Plan de classementGéologie et formations superficielles [064]
Descr. géo.NOUVELLE CALEDONIE
LocalisationFonds IRD
Identifiant IRDPAR00020248
Lien permanenthttp://www.documentation.ird.fr/hor/PAR00020248

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