|Résumé||(disponible en anglais seulement)|
As part of Canada's Geomapping for Energy and Minerals (GEM) Program, an applied Quaternary research activity under the IOCG-Great Bear Project was undertaken
in the Great Bear magmatic zone (GBMZ) to provide a practical guide to geochemical and indicator mineral exploration for iron oxide copper-gold (IOCG) deposits in glaciated terrain. Detailed till sampling (n=111) was completed in the vicinity of the
NICO Co-Au-Bi magnetite-group IOCG deposit and the Sue-Dianne Cu-Ag-Au magnetite to hematite-group IOCG deposit, and near showings hosted within other IOCG-type alteration systems. Samples were collected up-ice, proximal to, and down-ice from
mineralization, hydrothermally altered host rocks and least altered bedrock. Extensive lithogeochemical data of all studied showings and deposits are available through collaborations within the project.
Glacial sediments over the GBMZ consist of
a single, thin till unit (< 2 m), characterized by a silty sand matrix (40 to 60 % sand) and a local provenance (5 to 40 % of locally derived clasts). Glaciolacustrine reworking is common but winnowed and modified tills were avoided during sampling.
The predominant ice-flow direction was towards the west-southwest yet 4 distinct phases were observed. Phase 1 represents a flow towards 210°. Phases 2 (252°) and 3 (280°), respectively in the southern and northern parts of the GBMZ are the dominant
directions. Phase 4 represents a late reorientation towards 215° in the southern half of the GBMZ. Transport distances are short. For example, at the Sue Dianne deposit, the dispersal of heavily metasomatized clasts is less than 800 m. The Sue Dianne
geochemical dispersal train may be less than 500 m, as shown by a Cu anomaly in the clay-sized fraction. Dispersal train orientations are coherent with the dominant flow directions.
Lithogeochemical signatures of mineralization and/or alteration
are reflected in tills (K, Na, Ca, Mg, Ti, Cu, Ba, Cr, Co, Th, Bi, Mo, U, As) despite variable degrees of post-glacial weathering and textural variability. Possible IOCG deposit pathfinder elements in till include Cu, Mo, Bi, Co, and Ti (depletion).
However, the high variability of IOCG mineralization calls for a multivariate statistical approach based on their signature alterations. A principal component analysis was performed on combined till geochemistry and lithogeochemistry datasets. The
combined datasets¿ variability is largely explained by the variable lithogeochemistry. This approach helps to isolate the role of geological processes that influenced the bedrock from later processes that led to internal variability of the till
geochemistry. Results so far show: 1) grouping of till samples according to their related IOCG showings; 2) simple differentiation of anomalous till samples based on multi-element enrichments, therefore decreasing the effect of the IOCG
mineralization variation, and 3) potential to identify the nature of bedrock IOCG alteration type in overlying till samples. Petrographic study of collected bedrock samples and clay mineralogy of till samples will allow to test the correlation of
geochemical signatures to their mineralogical sources, shed light on processes responsible for alteration related elements (K, Na, Ca) behaviour as well as provide textural data relevant to the ongoing study of indicator minerals.