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Article Dans Une Revue Chemical Geology Année : 2012

Parental melt of the Nadezhdinsky Formation: Geochemistry, petrology and connection with Cu-Ni deposits (Noril'sk area, Russia)

Résumé

The paper addresses genetic relationship between volcanic rocks and ore-bearing intrusions of the Noril'sk area, Siberian Trap Province. Mg-rich rocks were found inside layered the Mikchangdinsky and Ikensky flows at the highest level of the vertical section of a tuff-lava pile in the Nadezhdinsky Formation in the east- ern part of the Noril'sk area. The high La/Sm, Th/U ratios, depletion in Cu, highly radiogenic Sr and unradio- genic Nd isotope compositions suggest their affiliation with the Lower Nadezhdinsky Formation and distinguish them from the Sunduksky layered flow, which has similar internal structure but belongs to the Tuklonsky Formation. The composition of layered Mg-rich basalt flow (the Mikchangdinsky flow) indicates that these rocks likely represent previously unknown parental melt of Nadezhdinsky lavas which are thought to play a crucial role in the genesis of ore mineralisation. Compositionally this melt was significantly different from the parental melt, which formed lavas of the Tuklonsky Formation and this precludes their direct genetic relationship. Olivine composition of the Mikchangdinsky flow indicates rapid depletion of melt by Ni and Cu suggesting early precipitation and fractionation of sulphide melt. Chemical composition and Sr and Nd isotope compositions of rocks from the Mikchangdinsky flow are similar to the Low Talnakh intrusion, while composi- tion of olivine and coexisting spinels manifest significant differences. The compositional differences between the olivine (contents Mn and V) and coexisting spinel (Fe2+/Fe3+ ratios) from the picrite gabbro-dolerites of the Low Talnakh intrusion and picrite of the Mikchangdinsky flow suggest that they may have crystallised from magma of similar composition but at different oxygen fugacity (intrusions being unusually oxidised). The substantial differences in contents of Ca, HREE and Y in olivines from these objects, however, leave open the question of genetic relationship between Nadezhdinsky parental melt and the Low Talnakh intrusion. Although some rocks of the Nadezhdinsky Formation contain unusually low concentrations of chalcophile elements, their role in the ore-forming processes of the Noril'sk district still remains largely uncertain.

Dates et versions

hal-01517783 , version 1 (27-02-2018)

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Citer

N.A. Krivolutskaya, A.V. Sobolev, V.N. Mikhailov, A.A. Plechova, Yu.A. Kostitsyn, et al.. Parental melt of the Nadezhdinsky Formation: Geochemistry, petrology and connection with Cu-Ni deposits (Noril'sk area, Russia). Chemical Geology, 2012, 302-303, pp.87 - 105. ⟨10.1016/j.chemgeo.2011.11.022⟩. ⟨hal-01517783⟩
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