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TitreApatite as an indicator mineral to IOCG deposits in the Great Bear magmatic zone, Northwest Territories, Canada
AuteurNormandeau, P X; Corriveau, L; Paquette, J; McMartin, I
SourceNorthwest Territories Geoscience Office, Yellowknife Geoscience Forum Abstracts Volume 2014, 2014 p. 53-54
Année2014
Séries alt.Secteur des sciences de la Terre, Contribution externe 20140294
ÉditeurNWT&Nunavut Chamber of Mines
Réunion42nd Annual Yellowknife Geoscience Forum; Yellowknife; CA; Novembre 25-27, 2014
Documentpublication en série
Lang.anglais
Mediapapier
Formatspdf
ProvinceTerritoires du Nord-Ouest
SNRC86
Lat/Long OENS-120.0000 -112.0000 67.0000 64.0000
Sujetsgisements minéraux; gîtes minéralogiques; oxydes de fer; cuivre; or; argent; altération; roches ignées; apatite; éléments d'indice; géochimie des éléments en trace; géologie économique; géochimie
ProgrammeÉtude des gîtes d'uranium, Initiative géoscientifique ciblée (IGC-4)
LiensOnline - En ligne
Résumé(disponible en anglais seulement)
Apatite is a diagnostic mineral of amphibole-magnetite alteration in iron oxide alkali-alteration systems that host IOCG deposits. Considering how much apatite chemistry can evolve within such systems and be distinct in composition from common rocks, apatite has potential as an indicator mineral to IOCG deposits in glaciated terrains. As part of the GEM-1 IOCG-Great Bear Project, mineral chemistry of apatite picked from till samples and crushed bedrock samples from the GBmz, as well as from thin sections from the Sue Dianne and Fab Lake systems were analysed. A variety of possible substitutions within the apatite structure (e.g. Na+, Sr2+, Mn2+ or a Rare Earth Element (REE)3+ for Ca2+, and Si4+ for P5+) are here being investigated in light of the major and trace element budget of alteration types of the studied systems . REE-rich apatite forms during high temperature alkali metasomatism and as temperature declines and fluid chemistry evolves. REE leaching takes place within apatite and leads to secondary REE-bearing minerals. Such apatite characteristics have been observed both experimentally and in several iron oxide-apatite deposits (e.g., Kiruna district in Sweden, Baqf district in Iran).

Dark irregular zones observed under SEM backscatter images are related to lower REE content measured through electron dispersive spectroscopy (EDX) and laser ablation inductively coupled plasma mass spectrometry (La-ICP-MS), as well as dissolution pits, and in some rare cases, the presence of secondary REE-rich mineral inclusions. Some apatite crystals from IOCG systems have a contrasting blue or blue and green zoned cathodoluminescence (CL) response associated with irregular zonation in REE. Apatite crystals from the GBmz least altered host rocks and other apatite crystals from the studied IOCG systems have green or green and yellow CL response.

Apatite is commonly present in till from the GBmz in amounts typically ranging from traces to over 2 wt% of the non-paramagnetic ( 1>amp) heavy mineral concentrate within the 0.25 to 0.5 mm as well as in the 0.5 to 1 mm fraction but in minor amounts (separated at SG>3.2). Coarser grains (1-2 mm) are locally present as well. While dissolution pits and irregular zonation (visible in shades of green and yellow CL response) are widespread, blue CL response and the REE-rich mineral inclusions are generally associated with grains collected either down-ice (< 1 km) or directly over the Sue Dianne deposit. These characteristics can be observed in picked grains under CL before or after the grains are mounted in epoxy stubs providing promising potential to discriminate apatite related to IOCG systems from background apatite. Further work is currently ongoing to develop this method. However, the picking process was shown to induce an artefact: the apatite grains, both from till and disaggregated bedrock samples were commonly coated by Ca-rich mineral rosettes, likely produced by a surface reaction during oxalic acid wash prior to hand picking. This surface reaction did not modify the CL response of apatite or its REE-rich mineral inclusions.
Résumé(Résumé en langage clair et simple, non publié)
L'Initiative géoscientifique ciblée (IGC-4) est un programme géoscientifique fédéral de collaboration qui fournit à l'industrie les connaissances géoscientifiques et les techniques novatrices de prochaine génération dont elle a besoin pour mieux détecter les gîtes minéraux enfouis, réduisant ainsi certains risques liés à l'exploration. Cette étude examine la composition et la nature du minéral apatite et peut aider à retracer les roches minéralisées en oxyde de fer cuivre-or (IOCG) dans les sédiments glaciaires non consolidés laissés au cours de la dernière glaciation dans la région du Grand Lac de l'Ours. Ces travaux aideront à fournir les connaissances géoscientifiques nécessaires pour développer des méthodes d'exploration minérale efficaces en terrain anciennement englacés. Ce travail fait partie d'un projet de recherche de 3e cycle à l'Université McGill, effectué d'abord dans le cadre du Programme en géocartographie de l'énergie et des minéraux (GEM-1) et poursuivit sous l'Initiative Géoscientifique Ciblée 4.
GEOSCAN ID295508