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TitreThe Ni-Cr-Cu content of biotite as pathfinder elements for magmatic sulfide exploration associated with mafic units of the Sudbury Igneous Complex, Ontario, Canada
AuteurWarren, M; Hanley, J; Ames, D E; Jackson, S
SourceJournal of Geochemical Exploration vol. 153, 2015 p. 11-29,
Séries alt.Secteur des sciences de la Terre, Contribution externe 20140552
Mediapapier; en ligne; numérique
Lat/Long OENS -81.5000 -80.5000 46.7500 46.2500
Sujetsbiotite; sulfures; gîtes magmatiques; nickel; cuivre; platine; enrichissement des minéraux; Huronien; sediments; Complexe de Sudbury Igneous ; Discrimination; géologie générale
Illustrationslocation maps; geological sketch maps; tables; photomicrographs; plots; graphs; histograms
ProgrammeÉtude des gîtes magmatiques de Ni-Cu-EPG, Initiative géoscientifique ciblée (IGC-4)
Résumé(disponible en anglais seulement)
Laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) was used to evaluate the dissolved Ni-Cr-Cu content of biotite as an exploration pathfinder for magmatic Ni - Cu - platinum-group element (PGE) sulfide deposits associated with mafic igneous units of the Worthington quartz diorite offset dyke and their host rocks at the Totten Mine (Vale Canada Ltd), Sudbury Igneous Complex (SIC), Ontario, Canada. Enrichment in Cu in biotite (up to two orders of magnitude higher than background) occurs within barren to weakly
mineralized, sublayer quartz diorite and adjacent Huronian metasediments within ~200 m of massive sulfide. With respect to Ni and Cr, three distinct populations of biotitewere distinguished based on textural and chemical criteria: (i) type I - isolated, euhedral laths within only inclusion-rich sublayer quartz diorite (IQD; the main mineralized host lithology), and high Ni (~1400 ppm b [Ni]Bt b ~2700 ppm), low to moderate Cr (~50 ppm b [Cr]Bt b ~2450 ppm) and variable Ni/Cr ratios (always N2). (ii) Type II - coarse-grained poikiloblasts (enclosing amphibole, chlorite, and type III biotite) within country rocks, and having moderate to high Ni (~500 ppm b [Ni]Bt b ~1400 ppm), moderate to very high Cr (~1750 ppm b [Cr]Bt b ~6000 ppm) but consistently low Ni/Cr ratios (always b0.5); and (iii) type III - subhedral to euhedral laths, intergrown with amphibole in dense, foliated aggregates and having low Ni ([Ni]Bt b ~300 ppm), very low to moderate
Cr (~4 ppm b [Cr]Bt b ~1200 ppm), and variable Ni/Cr ratios (b20), found within Huronian country rocks, sublayer quartz diorite (QD), and cross-cutting diabase dykes (Sudbury dyke swarm). Type I biotite within IQD is compositionally distinct from those observed in all other lithologies associated with the Sudbury Igneous Complex and its footwall rocks, and can be most readily discriminated in a Ni/Cr vs. Ni binary diagram or in a Ni-Cr-Cu ternary diagram by anomalously high Ni content and Ni/Cr ratio N2. Application of biotite chemistry to routine exploration requires establishing local "background" metal-in-biotite concentrations for each potential host lithology, and scrutiny of anomalous or heterogeneous metal contents in biotite resulting fromdiscrete sulfide microinclusions that contaminate the analytical volume, and chloritization or coeval sulfide minerals in direct contact with biotite causing localized modifications to primary biotite metal
abundance. In the Sudbury environment, the Ni-Cr-Cu chemistry of biotite can be used (i) in drill core to identify proximity to mineralization, and to differentiate QD (hosting minimal sulfides) from IQD (primary host to sulfide ore bodies), rock types for which bulk textural and compositional discrimination is problematic; and (ii) in soils and tills through the analysis of biotite and its weathering products to locate buried or surface-exposed IQD. The results may be extended to other mafic-ultramafic systems where sulfide-saturated or metal-enriched
intrusive phases grew metal-enriched biotite during primary crystallization, or through secondary processes of metasomatic enrichment involving remobilization of base metals by magmatic-hydrothermal fluids.