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TitleThe 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
AuthorCaté, A; Mercier-Langevin, P; Ross, P -S; Duff, S; Hannington, M D; Dubé, B; Gagné, S
SourceGeological Survey of Canada, Open File 7483, 2014, 19 pages, (Open Access)
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
File formatpdf
AreaSnow Lake; Lalor
Lat/Long WENS-102.0000 -98.0000 56.0000 54.0000
Subjectseconomic geology; mineral deposits; mineral assemblages; mineralization; gold; volcanogenic deposits; sulphides; deformation; metamorphism; alteration; hydrothermal alteration; volcanic rocks; igneous rocks; paragenesis; geochemical interpretations; Flin Flon Greenstone Belt; Lalor Deposit; Precambrian; Proterozoic
Illustrationsplots; photographs; tables
ProgramTargeted Geoscience Initiative (TGI-4), Volcanogenic Massive Sulfide Ore Systems
Released2014 03 02
AbstractLalor 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 grading 1.86 g/t Au, 24 g/t Ag, 0.6 wt.% Cu and 7 wt.% Zn and resources estimated at 12.6 Mt grading 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. The deposit consists of distinct Zn-Cu-Pb±Au-Ag semi-massive to massive
sulphide lenses and zones of disseminated Au-Ag-Pb-Cu sulphides. The ore zones are stratigraphically and/or structurally stacked in a complexly deformed and metamorphosed succession of intensely hydrothermally altered rocks of the Chisel mature arc sequence that hosts other Zn-rich VMS deposits.
Preliminary mapping and lithogeochemistry results indicate that the stratigraphic 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 various alteration assemblages may be in part due to varying protolith compositions, together with the superposition of several hydrothermal events. The hanging wall does not show any extensive alteration and may be in structural contact with the deposit. Five ore types can be defined. They include Zn±Cu-rich massive sulphide lenses and three distinct ore types that contain significant gold: (1) Cu-rich massive sulphides; (2) low sulphide calc-silicate zones with high Ag-Pb-Cu±As-Se-Te and; (3) anthophylliterich alteration zones with trace of finely disseminated pyrrhotite.
The numerous alteration assemblages and the various ore styles result from a complex hydrothermal history and possible modifications during subsequent deformation and metamorphism. The 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.
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. The Lalor deposit was recently discovered in the Snow Lake region of northern Manitoba. It consists of a large zinc, copper, gold, silver and lead deposit, the largest of the area. The concentration of gold in that deposit is exceptional when compared with similar deposits of the same type and the this report summarizes the local geologic setting and some of the principal characteristics indicating the presence of the deposit and possibly explaining the auriferous nature of the ore.