|Title||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|
|Author||Caté, A; Mercier-Langevin, P; Ross, P -S; Duff, S; Hannington, M D; Dubé, B; Gagné, S|
|Source||Geological Survey of Canada, Open File 7483, 2014, 19 pages, https://doi.org/10.4095/293116 (Open Access)|
|Publisher||Natural Resources Canada|
|Area||Snow Lake; Lalor|
|Lat/Long WENS||-102.0000 -98.0000 56.0000 54.0000|
|Subjects||economic 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|
|Illustrations||plots; photographs; tables|
Geoscience Initiative (TGI-4), Volcanogenic Massive Sulfide Ore Systems|
|Released||2014 03 02|
|Abstract||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
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.
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.