Composition of iron oxides in Archean and Paleoproterozoic mafic-ultramafic hosted Ni-Cu-PGE deposits in northern Fennos
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ARTICLE
Composition of iron oxides in Archean and Paleoproterozoic mafic-ultramafic hosted Ni-Cu-PGE deposits in northern Fennoscandia: application to mineral exploration M. Moilanen 1 & E. Hanski 1 & J. Konnunaho 2 & T. Törmänen 2 & S.-H. Yang 1 & Y. Lahaye 3 & H. O’Brien 3 & J. Illikainen 4 Received: 19 March 2019 / Accepted: 1 January 2020 # The Author(s) 2020
Abstract Using electron probe microanalyzer (EPMA) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), we analyzed major and trace element compositions of iron oxides from Ni-Cu-PGE sulfide deposits hosted by mafic-ultramafic rocks in northern Fennoscandia, mostly focusing on Finland. The main research targets were the Archean Ruossakero Ni-(Cu) deposit; Tulppio dunite and related Ni-PGE mineralization; Hietaharju, Vaara, and Tainiovaara Ni-(Cu-PGE) deposits; and Paleoproterozoic Lomalampi PGE-(Ni-Cu) deposit. In addition, some reference samples from the Pechenga (Russia), Jinchuan (China), and Kevitsa (Finland) Ni-Cu-PGE sulfide deposits, and a barren komatiite sequence in the Kovero area (Finland) were studied. Magnetite and Crmagnetite show a wide range of trace element compositions as a result of the variation of silicate and sulfide melt compositions and their post-magmatic modification history. Most importantly, the Ni content in oxide shows a positive correlation with the Ni tenor of the sulfide phase in equilibrium with magnetite, regardless of whether the sulfide assemblage is magmatic or post-magmatic in origin. The massive sulfide samples contain an oxide phase varying in composition from Cr-magnetite to magnetite, indicating that Crmagnetite can crystallize directly from sulfide liquid. The Mg concentration of magnetites in massive sulfide samples is lowest among the samples analyzed, and this can be regarded as a diagnostic feature of an oxide phase crystallized together with primitive Fe-rich MSS (monosulfide solid solution). Our results show that magnetite geochemistry, plotted in appropriate discrimination diagrams, together with petrographical observations could be used as an indicator of potential Ni-(Cu-PGE) mineralization. Keywords Fe oxide . Magnetite . Trace element . Ni-Cu-PGE sulfide deposit . Fennoscandian Shield
Introduction Orthomagmatic sulfide deposits are important sources for base- and precious metals, such as Ni, Cu, Co, and PGE. Editorial handling: P. Eilu Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00126-020-00953-1) contains supplementary material, which is available to authorized users. * M. Moilanen [email protected] 1
Oulu Mining School, University of Oulu, P.O. Box 3000, FI-90014 Oulu, Finland
2
Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland
3
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
4
Mawson Oy, Ahjotie 7, 96320 Rovaniemi, Finland
Experimental studies and empirical observations have shown that sulfides in these deposits are products of segregation of an immiscible sulfide liqui
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