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The Paleoproterozoic Lalor VMS deposit, Snow Lake, Manitoba: Observations on the nature and architecture of the gold and base metal-rich ore zones and associated alterations.

Caté, Antoine; Mercier-Langevin, Patrick; Ross, Pierre-Simon; Duff, Shams; Hannington, Mark D.; Dubé, Benoît; Gagné, Simon (2013). The Paleoproterozoic Lalor VMS deposit, Snow Lake, Manitoba: Observations on the nature and architecture of the gold and base metal-rich ore zones and associated alterations. In: GAC/MAC Annual Meeting, 22-24 mai 2013, Winnipeg, Canada.

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Résumé

Lalor is a recently discovered Au-Zn-rich volcanogenic massive sulphide (VMS) deposit. It is located in the Paleoproterozoic Snow Lake arc assemblage, host to numerous past producing Cu-Zn and Zn-Cu VMS deposits. Lalor is the largest deposit of the Snow Lake camp and also the richest in gold with reserves of 14.4 Mt at 1.86 g/t Au, 24 g/t Ag, 0.6 wt.% Cu and 7 wt.% Zn and resources estimated at 12.6 Mt at 3.85 g/t Au, 27.3 g/t Ag, 0.9 wt.% Cu and 2.3 wt.% Zn, for a total size of approximately 27 Mt and potentially containing 75 t Au. It consists of distinct Zn-Cu-Pb±Au-Ag semi-massive to massive sulphide lenses and zones of Au-Ag-Pb-Cu disseminated sulphides. The ore zones are stratigraphically and/or structurally stacked in a complexly deformed and metamorphosed succession of intensely hydrothermally altered rocks attributed to the Chisel mature arc sequence that host other Zn-rich VMS deposits.Preliminary results indicate that the footwall is composed of at least three distinct but highly altered mafic to felsic volcanic (and perhaps sedimentary) units. The alteration of the footwall is both extensive and intense. At least 11 distinct alteration assemblages have been defined based on the distribution and relative abundance of specific metamorphic minerals such as amphiboles, chlorite, cordierite, biotite, muscovite, pyrite, staurolite, garnet, kyanite, sillimanite, diopside and epidote. The variations in alteration assemblages are possibly in part due to varying protolith composition, but also probably due to the superposition of several hydrothermal events. The hanging wall does not show any extensive alteration and could be in structural contact with the deposit as proposed earlier. At least five ore types can be defined. They include Zn±Cu-rich massive sulphide lenses and three distinct ore types that carry significant gold: (1) Cu-rich massive sulphides; (2) low sulphide calc-silicates zones with high Ag-Pb-Cu±As-Se-Te and; (3) anthophyllite-rich alteration zones with traces of finely disseminated pyrrhotite. These numerous alteration assemblages and the variety in ore styles result from a complex hydrothermal history and possible modifications during deformation and metamorphism. The important gold endowment of the deposit, its size and its distinctive features compared to known anomalous and gold-rich VMS deposits make Lalor an ideal site to document and better understand gold enrichment processes in the VMS environment, which is one of the main objectives of the current project.

Type de document: Document issu d'une conférence ou d'un atelier
Mots-clés libres: gisements paléoprotérozoïques; Manitoba; minerai; or; métaux communs
Centre: Centre Eau Terre Environnement
Date de dépôt: 19 nov. 2020 16:52
Dernière modification: 19 nov. 2020 16:52
URI: http://espace.inrs.ca/id/eprint/4037

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