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TitleMapping hydrothermal footprints: case studies from the Meliadine Gold District, Nunavut
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AuthorLawley, C J M; Dubé, B; Mercier-Langevin, P; Vaillancourt, D
SourceGeological Survey of Canada, Open File 7744, 2015, 22 pages, https://doi.org/10.4095/295920 (Open Access)
Image
Year2015
PublisherNatural Resources Canada
Documentopen file
Lang.English
Mediaon-line; digital
File formatpdf
ProvinceNunavut
NTS55J/13; 55K/16; 55N/01; 55O/04
AreaRankin Inlet
Lat/Long WENS -92.5833 -91.4167 63.7500 63.1250
Subjectsgeochemistry; mineralogy; economic geology; hydrothermal deposits; hydrothermal alteration; alteration; sulphides; sulphide deposits; arsenopyrite; iron formations; gold; mineral deposits; mineral occurrences; Archean; Churchill Province; Meliadine gold district; Tiriganiaq Deposit; Pyke Break; Precambrian
Illustrationslocation maps; plots; photographs; histograms; tables
ProgramGold Ore Systems, Targeted Geoscience Initiative (TGI-4)
Released2015 02 27
AbstractThe geochemical and mineralogic signature, or hydrothermal footprint, of ore deposits has great potential as an exploration tool. In some cases, hydrothermal footprints can be mapped up to several kilometers beyond the economically viable portion of the deposit and thus offers the potential to vector from sub-economic mineralization towards higher-grade ore from district- to deposit-scales. Conventionally, hydrothermal footprints are mapped using some preferred threshold concentration for each pathfinder element, or ratio, of interest. The results are then generally portrayed as stacked geochemical traverses adjacent to known ore bodies. However, the conventional approach inadequately accounts for the multivariate nature of ore processes and the inherently imprecise boundary between barren and mineralized rock. In this contribution we explore alternative methods to define and map the hydrothermal footprint at six gold deposits and ore zones within the Meliadine Gold District (MGD), Nunavut.
MGD host rocks are variably altered (silicified ± sericitized ± sulphidized ± carbonatized ± chloritized) adjacent to BIF-hosted replacement-style gold mineralization and auriferous greenstone-hosted quartz (± ankerite) veins cutting mafic volcanic, interflow sediments and turbiditic successions. Robust principle component analysis defines key element assemblages (Au-Ag-As-S-Te-Bi-W-Sb) that are associated with gold and are enriched from 10s to 100s of meters adjacent to ore zones. We integrate and map pathfinder element enrichment and quantified measures of hydrothermal alteration intensity using a hybrid fuzzy- and conditional probability-based model (weights of evidence) in an effort to further highlight the complementary nature of multivariate datasets and to define fuzzy footprints. The available whole-rock data suggests that multi-element anomalies are, in some instances, better suited for defining broader geochemical anomalies than was apparent from analysis of individual pathfinder elements. We emphasize that samples containing pathfinder element concentrations in excess of some preferred threshold are akin to conventional definitions of geochemical anomalies, but in this case occur primarily in the ore zone and are thus of limited use for vectoring. In contrast, fuzzy footprints delineate the simultaneous occurrence of favourable pathfinder element enrichment and hydrothermal alteration for samples that would have been excluded following the conventional approach. These samples occur in hanging wall and footwall rocks devoid of gold (< 5 ppb), and thus provide a possible vector to high-grade gold ore.
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 presentation was given at the 42nd Yellowknife Geoscience Forum (November 25 to 27 2014) and summarizes one aspect of the TGI-4 research project at the Meliadine Gold District. Hydrothermal footprints are key tools for vectoring towards undiscovered ore deposits in the subsurface. However, they are difficult to map. In this contribution, we explore the advantages of hydrothermal footprint mapping following a probabilistic approach and delineate fuzzy footprints at six gold deposits within the Meliadine Gold District.
GEOSCAN ID295920