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

Mineralium Deposita (Impact Factor: 2.15). 01/2011; 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

  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Uranium-bearing hematite (containing up to several wt.% U), also containing Al, Mo, W and radiogenic Pb, is described from Olympic Dam, South Australia. These elements are present in grains that display both oscillatory zonation and porous structures. Laser-ablation inductively coupled mass spectrometry (LA-ICP-MS) element mapping confirms oscillatory and sectorial zoned domains in hematite grains are enriched in 238U- and 206Pb, and are distinct from those of W and Mo. The crystal structure and absence of inclusions within zoned hematite was assessed by transmission electron microscopy on foils obtained by in situ slicing across zonation patterns using the scanning electron microscope-focused ion beam technique. Satellite reflections on the electron diffraction patterns obtained from banded zones in hematite are attributable to long-range superstructure ordering, that is inferred to assist metal incorporation via the substitution 2Fe3+ ↔ Me6+ + vacancy, where Me = U, W, Mo. The suitability of U-bearing hematite for Pb–Pb geochronology as a first pass was tested on both zoned and porous hematite grains via LA-ICP-MS, using the GJ-1 zircon as the primary external standard. Only Pb–Pb ages were considered and resulted in 207Pb–206Pb ages of 1590 ± 8 Ma and 1577 ± 5 Ma for oscillatory and sector zoned hematite from two samples. Although reconnaissance in nature, these ages potentially support the supposition that mineralization is coeval with emplacement of the Gawler Range Volcanics and associated Hiltaba Intrusive Suite. The geochronological application utilizing an abundant refractory mineral represents a new tool for dating iron-bearing ores.
    Precambrian Research 01/2013; 238:129–147. · 4.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The black shale-hosted selenide vein-type deposit at Tilkerode, eastern Harz, Germany, has specular hematite enclosed in clausthalite (PbSe). The specular hematite has Ti and V in amounts of up to ∼1 wt.% TiO2 and ∼3 wt.% V2O5, and subordinate, but important, contents of Mo (22–372 ppm) and B (up to 68 ppm). The Tilkerode hematite serves as a reference for hydrothermal hematite formed at relatively low temperatures (<150 °C). The composition of the Tilkerode hematite is compared with that of two generations of specular hematite from itabirite-hosted iron-ore deposits in the Quadrilátero Ferrífero of Minas Gerais, Brazil. The first generation of specular hematite represents an early tectonic hematitisation of dolomitic itabirite at Águas Claras and occurs as fine-grained crystals. Reconnaissance data indicate that the Águas Claras hematite is poorer in Ti and V, relative to the Tilkerode hematite, but has ∼5–10 ppm B and ∼7–11 ppm Li. The second generation of specular hematite defines the pervasive tectonic foliation of the Gongo Soco iron ore. This hematite has Ti contents of up to ∼2 wt.% TiO2 and subordinate amounts of V (62–367 ppm); its B and Li concentrations are mostly below <2 ppm B and <1 ppm Li. The presence of Ti and B in the Tilkerode hematite can be explained by highly saline, B-bearing fluids that were capable of mobilising otherwise immobile Ti. The Mo signature of the Tilkerode hematite suggests that Mo was derived from the host black shale. In Minas Gerais, B and Li were incorporated into the early tectonic hematite from saline fluids at relatively low temperatures (Águas Claras) and then released during metamorphic hematite growth at higher temperatures, as suggested by the foliation-defining hematite without B–Li signature (Gongo Soco).
    Mineralium Deposita 03/2013; · 2.15 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Eastern Tianshan Orogenic Belt of the Central Asian Orogenic Belt and the Beishan terrane of the Tarim Block, NW China, host numerous Fe deposits. The Cihai Fe deposit (>90 Mt at 45.6 % Fe) in the Beishan terrane is diabase-hosted and consists of the Cihai, Cinan, and Cixi ore clusters. Ore minerals are dominantly magnetite, pyrite, and pyrrhotite, with minor chalcopyrite, galena, and sphalerite. Gangue minerals include pyroxene, garnet, hornblende and minor plagioclase, biotite, chlorite, epidotite, quartz, and calcite. Pyrite from the Cihai and Cixi ore clusters has similar Re–Os isotope compositions, with ∼14 to 62 ppb Re and ≤10 ppt common Os. Pyrrhotite has ∼5 to 39 ppb Re and ∼0.6 ppb common Os. Pyrite has a mean Re–Os model age of 262.3 ± 5.6 Ma (n = 13), in agreement with the isochron regression of 187Os vs. 187Re. The Re–Os age (∼262 Ma) for the Cihai Fe deposit is within uncertainty in agreement with a previously reported Rb–Sr age (268 ± 25 Ma) of the hosting diabase, indicating a genetic relationship between magmatism and mineralization. Magnetite from the Cihai deposit has Mg, Al, Ti, V, Cr, Co, Ni, Mn, Zn, Ga, and Sn more elevated than that of typical skarn deposits, but both V and Ti contents lower than that of magmatic Fe–Ti–V deposits. Magnetite from these two ore clusters at Cihai has slightly different trace element concentrations. Magnetite from the Cihai ore cluster has relatively constant trace element compositions. Some magnetite grains from the Cixi ore cluster have higher V, Ti, and Cr than those from the Cihai ore cluster. The compositional variations of magnetite between the ore clusters are possibly due to different formation temperatures. Combined with regional tectonic evolution of the Beishan terrane, the Re–Os age of pyrite and the composition of magnetite indicate that the Cihai Fe deposit may have derived from magmatic–hydrothermal fluids related to mafic magmatism, probably in an extensional rift environment.
    Mineralium Deposita 03/2013; · 2.15 Impact Factor

Full-text (2 Sources)

Available from
May 16, 2014