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TitleFingerprinting iron oxide copper-gold mineralization in the Great Bear magmatic zone using indicator mineral and till geochemical methods: highlights from the IOCG-Great Bear GEM Project
AuthorMcMartin, I; Normandeau, P X; Paquette, J; Beaudoin, G; Corriveau, L
Source39th Annual Yellowknife Geoscience Forum, abstracts of talks and posters; by Fischer, B J; Watson, D M; Northwest Territories Geoscience Office, Yellowknife Geoscience Forum Abstracts Volume vol. 2011, 2011 p. 61-62 (Open Access)
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20110220
Meeting39th Annual Yellowknife Geoscience Forum; Yellowknife; CA; November 15-18, 2011
ProvinceNorthwest Territories
NTS85N; 86C; 86D; 86E; 86F; 86K; 86L
Lat/Long WENS-119.0000 -116.0000 67.0000 63.0000
Subjectsgeochemistry; surficial geology/geomorphology; economic geology; till geochemistry; tills; glacial deposits; copper; gold; mineralization; lithogeochemistry; Great Bear Magmatic Zone; Cenozoic; Quaternary
ProgramGEM: Geo-mapping for Energy and Minerals, Iron-oxide Copper-gold (IOCG) / Multiple Metals - Great Bear Lake (NWT)
AbstractAn applied Quaternary research activity was undertaken in the Great Bear magmatic zone (GBMZ) to evaluate whether iron oxide copper-gold (IOCG) deposits and other showings hosted within large IOCG-type alteration systems can be fingerprinted by drift prospecting methods. Bedrock (n=138) and till (n=111) samples were collected up-ice, proximal to, and down-ice from mineralization, host hydrothermal systems and least altered bedrock across the GBMZ. The till matrix geochemistry, combined with extensive lithogeochemical data collected as part of the IOCG-Great Bear Project, are used to assess the IOCG deposit mineralization or alteration signatures in glacial sediments. The abundance, physical characteristics and minor and trace element composition of sand-sized non-ferromagnetic and ferromagnetic minerals from bedrock and till samples are examined to develop an indicator mineral method for IOCG exploration.
Geochemical analysis of the clay and silt&clay size fractions of till reveal a list of potential IOCG deposit pathfinder elements, including Cu, Mo, Bi, Co, and Ti (depletion). A principal component analysis performed on combined till geochemistry and lithogeochemistry datasets shows that the combined datasets variability is largely explained by the variability in the lithogeochemistry, therefore enhancing the role of bedrock related geological processes within the till geochemical variability. Preliminary results show: 1) grouping of till samples according to their related IOCG showings; 2) simple differentiation of anomalous till samples based on multi-element enrichments, and 3) potential to identify the nature of bedrock IOCG alteration type in overlying till samples.
Results from an orientation study at the NICO Au-Co-Bi deposit, an atypical magnetite-group IOCG deposit with arsenopyrite mineralization, demonstrate one case where the non-ferromagnetic heavy minerals (0.25-2 mm; SG>3.2) are not particularly effective as indicator minerals of IOCG mineralization. However the abundance of pristine-shaped silt-sized gold grains in till collected immediately down-ice of NICO can be used to fingerprint the mineralization. In addition, the bulk of ferromagnetic grains from local tills collected over NICO shows similar elemental enrichments or depletions to those found in NICO bedrock grains. Indicator elements in iron oxides (magnetite dominant) from NICO are similar to pathfinder elements in bulk lithogeochemistry; this suggests that some elements substitute into magnetite, making it a potential IOCG indicator mineral.
Results from bedrock and till samples collected near the Sue Dianne Cu-Ag-Au magnetite to hematite-group IOCG deposit and near other mineral showings across the GBMZ indicate the presence of chalcopyrite, apatite, pyrrhotite, andradite, Mn-epidote, bornite, allanite, ferroactinolite, fluorite and gold in various concentrations within the heavy mineral fraction. SEM examination of grains revealed trace amounts of iron oxides in gahnite, apatite, tourmaline and andradite grains from till samples collected down-ice of Sue-Dianne and other showings. Some chalcopyrite grains are found in association with specular hematite and/or REE rich phases. Petrographic study of collected bedrock samples, clay mineralogy of till samples, additional electron microprobe and LA-ICP-MS analysis, as well as further examination of selected non-ferromagnetic and ferromagnetic grains will help to augment discrimination criteria for the different types of mineralization, alteration and host rocks in the GBMZ.