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Trace elements in magnetite as petrogenetic indicators

Dare Sarah A.S., Barnes Sarah-Jane, Beaudoin Georges, Méric Julien, Boutroy Emilie et Potvin-Doucet Christophe. (2014). Trace elements in magnetite as petrogenetic indicators. Mineralium Deposita, 49, (7), p. 785-796.

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Résumé

We have characterized the distribution of 25 trace elements in magnetite (Mg, Al, Si, P, Ca, Sc, Ti, V, Cr, Mn, Co,Ni, Cu, Zn, Ga,Ge,Y, Zr,Nb,Mo, Sn, Hf, Ta,W, and Pb), using laser ablation ICP-MS and electron microprobe, from a variety of magmatic and hydrothermal ore-forming environments and compared them with data from the literature. We propose a new multielement diagram, normalized to bulk continental crust, designed to emphasize the partitioning behavior of trace elements between magnetite, the melt/fluid, and co-crystallizing phases. The normalized pattern of magnetite reflects the composition of themelt/fluid, which in both magmatic and hydrothermal systems varies with temperature. Thus, it is possible to distinguish magnetite formed at different degrees of crystal fractionation in both silicate and sulfide melts. The crystallization of ilmenite or sulfide beforemagnetite is recorded as amarked depletion in Ti or Cu, respectively. The chemical signature of hydrothermal magnetite is distinct being depleted in elements that are relatively immobile during alteration and commonly enriched in elements that are highly incompatible into magnetite (e.g., Si and Ca). Magnetite formed from low-temperature fluids has the lowest overall abundance of trace elements due to their lower solubility. Chemical zonation of magnetite is rare but occurs in some hydrothermal deposits where laser mapping reveals oscillatory zoning, which records the changing conditions and composition of the fluid during magnetite growth. This new way of plotting all 25 trace elements on 1 diagram, normalized to bulk continental crust and elements in order of compatibility into magnetite, provides a tool to help understand the processes that control partitioning of a full suit of trace elements in magnetite and aid discrimination of magnetite formed in different environments. It has applications in both petrogenetic and provenance studies, such as in the exploration of ore deposits and in sedimentology.

Type de document:Article publié dans une revue avec comité d'évaluation
ISSN:0026-4598
Volume:49
Numéro:7
Pages:p. 785-796
Version évaluée par les pairs:Oui
Date:2014
Sujets:Sciences naturelles et génie > Sciences naturelles > Sciences de la terre (géologie, géographie)
Département, module, service et unité de recherche:Départements et modules > Département des sciences appliquées > Unité d'enseignement en sciences de la Terre
Mots-clés:magnetite, trace elements, mineral deposits, magmatic Hydrothermal, petrogenesis
Déposé le:07 juill. 2016 16:04
Dernière modification:09 déc. 2016 16:08
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