GEOSCAN Search Results: Fastlink


TitleApatite as an indicator mineral to IOCG deposits in the Great Bear magmatic zone, Northwest Territories, Canada
AuthorNormandeau, P X; Corriveau, L; Paquette, J; McMartin, I
SourceNorthwest Territories Geoscience Office, Yellowknife Geoscience Forum Abstracts Volume 2014, 2014 p. 53-54 (Open Access)
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20140294
PublisherNWT&Nunavut Chamber of Mines
Meeting42nd Annual Yellowknife Geoscience Forum; Yellowknife; CA; November 25-27, 2014
File formatpdf
ProvinceNorthwest Territories
AreaGreat Bear Lake
Lat/Long WENS-120.0000 -112.0000 67.0000 64.0000
Subjectseconomic geology; geochemistry; mineral deposits; mineral occurrences; iron oxides; copper; gold; silver; alteration; igneous rocks; apatite; indicator elements; trace element geochemistry; indicator minerals; IOCG deposits
ProgramTargeted Geoscience Initiative (TGI-4), Uranium Ore Systems
AbstractApatite 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.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. This study examines the composition and nature of the mineral apatite which can help to trace mineralized rocks of iron oxide copper-gold (IOCG) deposits in the unconsolidated glacial sediments left during the last glaciation in the Great Bear Lake area. The work will help provide the geoscience knowledge required to develop effective mineral exploration methods in formerly glaciated terrain. It is part a graduate research project from McGill University, conducted first under the Geo-mapping for Energy and Minerals (GEM-1) Program and continued as part of the Targeted Geoscience Initiative 4.