Article

Discriminant diagrams for iron oxide trace element fingerprinting of mineral deposit types

Mineralium Deposita (Impact Factor: 2.67). 04/2011; 46(4):319-335. DOI: 10.1007/s00126-011-0334-y

ABSTRACT Magnetite and hematite are common minerals in a range of mineral deposit types. These minerals form partial to complete solid
solutions with magnetite, chromite, and spinel series, and ulvospinel as a result of divalent, trivalent, and tetravalent
cation substitutions. Electron microprobe analyses of minor and trace elements in magnetite and hematite from a range of mineral
deposit types (iron oxide-copper-gold (IOCG), Kiruna apatite–magnetite, banded iron formation (BIF), porphyry Cu, Fe-Cu skarn,
Fe-Ti, V, Cr, Ni-Cu-PGE, Cu-Zn-Pb volcanogenic massive sulfide (VMS) and Archean Au-Cu porphyry and Opemiska Cu veins) show
compositional differences that can be related to deposit types, and are used to construct discriminant diagrams that separate
different styles of mineralization. The Ni + Cr vs. Si + Mg diagram can be used to isolate Ni-Cu-PGE, and Cr deposits from
other deposit types. Similarly, the Al/(Zn + Ca) vs. Cu/(Si + Ca) diagram can be used to separate Cu-Zn-Pb VMS deposits from
other deposit types. Samples plotting outside the Ni-Cu-PGE and Cu-Zn-Pb VMS fields are discriminated using the Ni/(Cr + Mn)
vs. Ti + V or Ca + Al + Mn vs. Ti + V diagrams that discriminate for IOCG, Kiruna, porphyry Cu, BIF, skarn, Fe-Ti, and V deposits.

KeywordsMagnetite–Hematite–Mineral deposit–Electron microprobe–Mineral chemistry–Discriminant diagram

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Available from: Georges Beaudoin, Aug 04, 2015
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    • "Magnetite composition from a wide variety of iron deposit types has been the focus of many recent studies (e.g., Dupuis and Beaudoin, 2011; Huang et al., 2013; McQueen and Cross, 1998). Those studies have demonstrated that trace elemental compositions of iron oxides are important for the understanding of the origin of different mineralization styles (Müller et al., 2003; Carew, 2004; Singoyi et al., 2006; Anderson et al., 2008; Dupuis and Beaudoin, 2011; Dare et al., 2012; Nadoll et al., 2014; Chen et al., 2015; Huang et al., 2015; Liu et al., 2015; Zhao Ore Geology Reviews 65 (2015) 917–928 ⁎ Corresponding author. "
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    ABSTRACT: Keywords: Magnetite Trace elements LA–ICP-MS Late Palaeoproterozoic Iron formation Labrador Trough Sokoman Formation Canada The Sokoman Iron Formation in the Labrador Trough, Canada, a typical granular iron formation (GIF), is coeval with the ~1.88 Ga Nimish volcanic suites in the same region. It is composed of the Lower, Middle and Upper Iron Formations. In addition to primary and altered magnetite in iron formations of the Hayot Lake, Rainy Lake and Wishart Lake areas, magnetite in volcanic breccia associated with the iron formation is identified for the first time in the stratigraphy. Trace elemental compositions of the most primary, altered and volcanic brecciated magnetite of the Sokoman Iron Formation were obtained by LA–ICP-MS. Commonly detected trace elements of magnetite include Ti, Al, Mg, Mn, V, Cr, Co and Zn. These three types of magnetite have different trace elemental compositions. Primary magnetite in the iron formation has a relatively narrow range of compositions with the depletion of Ti, Pb, Mg and Al. Magnetite from volcanic breccia is rich in Ti, Al, V, Mn, Mg, Zn, Cu and Pb, indicative of crystallization from mantle-derived magmas. Altered magnetite in the iron formation shows a relatively wide range of trace elemental compositions. Mineralizing fluids associated with magmas that generated the ~1.88 Ga Nimish volcanic suites circulated through the sedimentary piles to further enrich the iron formations and to form magnetite with variable compositions. The comparisons of different types of primary and altered magnetite in the iron formation in the region show distinct provenance discrimination. Our findings also support the origin of iron formations in association with multiple stages of exhalative volcanic and hydrothermal processes.
    Ore Geology Reviews 11/2015; 65. DOI:10.1016/j.oregeorev.2014.09.030 · 3.38 Impact Factor
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    • "Magnetite contains numerous trace elements, such as Al, Ti, Mg, Mn, Zn, Cr, V, Ni, Co and Ga, and can form in a variety of physico-chemical environments. Chemical composition of magnetite thus can be used to fingerprint the types of mineral deposits and to distinguish different ore forming processes (Beaudoin and Dupuis, 2009; Carew, 2004; Chen et al., 2015-in this issue; Dare et al., 2012; Dupuis and Beaudoin, 2011; Hu et al., 2013; Huang et al., 2013, 2014, 2015-in this issue; Müller et al., 2003; Nadoll et al., 2012, 2014; Rusk et al., 2009; Singoyi et al., 2006). Previous studies of Fe oxides in Bayan Obo have dealt with the paragenesis and chemical compositions of magnetite (IGCAS (Institute of Geochemistry, Chinese Academy of Sciences), 1988; Wei and Shangguan, 1983; Zeng et al., 1981) . "
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    ABSTRACT: Keywords: Trace element LA-ICP-MS Magnetite Hematite Bayan Obo North China The Bayan Obo Fe-REE-Nb deposit in northern China is the world's largest light REE deposit, and also contains considerable amounts of iron and niobium metals. Although there are numerous studies on the REE mineraliza-tion, the origin of the Fe mineralization is not well known. Laser ablation (LA) ICP-MS is used to obtain trace elements of Fe oxides in order to better understand the process involved in the formation of magnetite and hematite associated with the formation of the giant REE deposit. There are banded, disseminated and massive Fe ores with variable amounts of magnetite and hematite at Bayan Obo. Magnetite and hematite from the same ores show similar REE patterns and have similar Mg, Ti, V, Mn, Co, Ni, Zn, Ga, Sn, and Ba contents, indicating a similar origin. Magnetite grains from the banded ores have Al + Mn and Ti + V contents similar to those of banded iron formations (BIF), whereas those from the disseminated and massive ores have Al + Mn and Ti + V contents similar to those of skarn deposits and other types of magmatic-hydrothermal deposits. Magnetite grains from the banded ores with a major gangue mineral of barite have the highest REE contents and show slight moderate REE enrichment, whereas those from other types of ores show light REE enrichment, indicating two stages of REE mineralization associated with Fe mineralization. The Bayan Obo deposit had multiple sources for Fe and REEs. It is likely that sedimentary carbonates provided original REEs and were metasomatized by REE-rich hydrothermal fluids to form the giant REE deposit.
    Ore Geology Reviews 10/2015; 65. DOI:10.1016/j.oregeorev.2014.09.010 · 3.38 Impact Factor
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    • "Aitchison, 1986; Gilliom and Helsel, 1986; Helsel and Gilliom, 1986; Helsel and Cohn, 1988; Helsel, 1990; Glass and Gray, 2001; Martin-Fernandez et al., 2003; Succop et al., 2004; Gochfeld et al., 2005; Helsel, 2005; Helsel and Lee, 2006; Smith et al., 2006; Martin-Fernandez et al., 2012; Verbovsek, 2011; Filzmoser et al., 2009; Hron et al., 2010; Grunsky, 2010; Grunsky et al., 2013; de Caritat and Grunsky, 2013). Excluding censored data, or arbitrary substitutions are most often used, but are not ideal as they produce biased estimates of summary statistics (Gilliom and Helsel, 1986; Helsel, 2005; Beaudoin and Dupuis, 2009), although Verbovsek (2011) showed that the statistical mean of censored data substituted with DL/√2 (Croghan and Egeghy, 2003) is close to the mean of the population. In this study, the robCompositions package implemented in the software environment R, has been used to investigate censored data (Filzmoser et al., 2009; Hron et al., 2010; Bacon-Shone, 2011; Grunsky "
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    ABSTRACT: Magnetite grains from the Izok Lake (Nunavut, Canada) and the Halfmile Lake (New Brunswick, Canada) volcanogenic massive sulfide deposits, and from till covering the nearby areas were investigated using the scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and optical microscopy. The method of robust estimation for compositional data (rob-composition) was applied to censored geochemical data, and the results were analyzed by principal component analysis (PCA). Textural relationships and mineral association of magnetite reveal the history of formation, and contribute to the explanation of characteristic compositional differences of magnetite from different geological settings. The integration of petrography and mineral chemistry allows discriminating magmatic, metamorphic and hydrothermal magnetite grains in the VMS deposits bedrock samples. Magmatic magnetite is found in Izok Lake gabbro, and Halfmile Lake syenite, felsic ash tuff and gossan samples, whereas magnetite in Izok Lake massive sulfides, gahnite-rich dacite and iron formations formed during the amphibolite facies metamorphism. In Halfmile Lake andesite, magnetite recrystallized during greenschist facies metamorphism. In the magnetite alteration zone associated to the Halfmile Lake deposit, hydrothermal magnetite has been overprinted by metamorphic magnetite. Halfmile Lake massive sulfides in chloritic argillite contain hydrothermal magnetite. PCA identifies discriminator elements and their contributions to magnetite composition from different Izok Lake Lake and Halfmile Lake bedrock samples. The results suggest that Si, Ca, Zr, Al, Ga, Mn, Mg, Ti, Zn, Co, Ni and Cr are discriminator elements for VMS deposits and their host bedrocks. The distinct chemical signatures for magnetite from various bedrock lithologies demonstrate that magnetite grains of the same origin share more similarities in chemistry, as high Ti indicates magmatic sources for magnetite, whereas high Si, Ca and Mg are indicative of hydrothermal settings. Variable compositions of metamorphic magnetite suggest that the chemistry of this type of magnetite is controlled by the composition of host rocks, the grade of metamorphism and oxygen fugacity. PCA of EPMA and LA-ICP-MS data of magnetite from the Izok Lake and Halfmile Lake bedrock samples yield discrimination models for classification of magnetite grains from till. Decreases in the proportion of magnetite grains with the chemical signature of the Izok Lake massive sulfides and gahnite-rich dacite down-ice from the Izok Lake deposit show the use of magnetite chemistry in geochemical exploration. In the Halfmile Lake area, till magnetite grains with the signature of VMS mineralization make a glacial dispersal train more than 2 km down-ice from the deposit.
    Ore Geology Reviews 07/2015; DOI:10.1016/j.oregeorev.2015.06.023 · 3.38 Impact Factor
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