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TitleAlteration and ore assemblages of the LaRonde Zone 5 (LZ5) deposit and Ellison mineralized zones, Doyon-Bousquet-LaRonde mining camp, Abitibi, Quebec
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorBoily-Auclair, É; Mercier-Langevin, P; Ross, P -S; Pitre, D
SourceGeological Survey of Canada, Open File 8867, 2022, 48 pages, Open Access logo Open Access
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
RelatedNRCan photo(s) in this publication
File formatpdf
NTS32D/01; 32D/02; 32D/07; 32D/08
Lat/Long WENS -78.5833 -78.4000 48.2833 48.2333
Subjectseconomic geology; mineralogy; structural geology; stratigraphy; tectonics; geochronology; geochemistry; Nature and Environment; Science and Technology; mineral deposits; gold; silver; sulphide deposits; mineral exploration; ore mineral genesis; mineralization; ore controls; alteration; alteration halos; mineral assemblages; zoning; boudinage; inclusions; host rocks; bedrock geology; lithology; igneous rocks; volcanic rocks; volcaniclastics; rhyolites; basalts; andesites; dacites; intrusive rocks; sedimentary rocks; structural features; faults; fault zones; domes; tectonic setting; tectonic evolution; metamorphism; deformation; folding; foliation; hydrothermal systems; hydrothermal alteration; magmatism; volcanism; fluid flow; fluid dynamics; veins; veinlets; stockworks; lenses; emplacement; mineral enrichment; recrystallization; permeability; porosity; radiometric dating; uranium lead dating; geochemical analyses; major element analyses; stratigraphic analyses; stratigraphic correlations; modelling; metallogeny; petrogenesis; Archean; Abitibi Greenstone Belt; Doyon-Bousquet-LaRonde Mining Camp; LaRonde Zone 5 Deposit; LaRonde Zone 5 Mine; Ellison Property; Blake River Group; Bousquet Formation; Westwood Dome; Larder Lake-Cadillac Fault Zone; Lac Parfouru Fault; Lac Imau Fault; Destor-Porcupine Deformation Zone; Mooshla Intrusive Complex; Precambrian
Illustrationslocation maps; geoscientific sketch maps; correlation sections; geochemical plots; photographs; photomicrographs; schematic cross-sections; lithologic sections; geochemical profiles; plots; tables
ProgramTargeted Geoscience Initiative (TGI-6) Ore systems
Released2022 02 22
AbstractThe LaRonde Zone 5 (LZ5) mine is part of the Doyon-Bousquet-LaRonde mining camp and is located in the southern part of the Abitibi greenstone belt in northwestern Quebec. The LZ5 deposit consists of three stacked mineralized corridors: Zone 4, Zone 4.1, and Zone 5. Zones 4 and 4.1 are discontinuous satellite mineralized corridors, whereas Zone 5 represents the main mineralized body.
The mineralized zones of the LZ5 deposit and adjacent Ellison property (Ellison A and B zones) are hosted in the strongly-deformed, 2699-2695 Ma transitional to calcalkaline, intermediate to felsic, volcanic and volcaniclastic rocks of the Bousquet Formation upper member, which is part of the Blake River Group (2704-2695 Ma). Zones 4, 4.1, and 5 at the LZ5 mine are hosted in intermediate volcanic and volcaniclastic rocks of the Westwood andesitic to rhyodacitic unit (unit 5.1a), which forms the base of the upper member of the Bousquet Formation. The Ellison Zone A is hosted higher up in the stratigraphic sequence within a newly described intermediate volcanic unit. The Ellison Zone B is hosted in felsic volcanic and volcaniclastic rocks of the Westwood feldsparphyric rhyolite dome (subunit 5.3a-(b)).
Mineralization in all three zones of the LZ5 deposit consists of discordant networks of millimeter- to centimeter-thick pyrite ±chalcopyrite ±sphalerite ±pyrrhotite veins and veinlets (10-20 % of the volume of the rock) and, to a lesser extent, very finely disseminated pyrite and boudinaged veins (less than or equal to 5 vol. % each) in strongly altered host rocks. Gold commonly occurs as microscopic inclusions in granoblastic pyrite and at the triple junction between recrystallized grains. The veins, stockworks, and disseminations were intensely folded and transposed in the steeply south-dipping, east-west trending S2 foliation. The vein network is at least partly discordant to the stratigraphy. A distal alteration halo envelops the LZ5 mineralized corridors and consists of a sericite-carbonate-chlorite- feldspar ±biotite assemblage. A proximal sericite-carbonate-chlorite-pyrite-quartz- feldspar-biotite ±epidote alteration assemblage is present within the LZ5 mineralized zones.
A local proximal alteration assemblage of sericite-quartz-pyrite is also locally developed within Zone 4 and Zone 5 of the LZ5 deposit. Mass gains in Fe2O3 (t) and K2O, and mass losses in CaO, MgO, Na2O, and locally SiO2, are characteristic of the LZ5 alteration zones. The Ellison zone A and B are similar to LZ5 in terms of style of mineralization, but thin (10-20 cm) veins or bands of semi-massive to massive, finely recrystallized disseminated pyrite (0.1-1 mm) are distinctive. Chalcopyrite and sphalerite are also slightly more abundant in the mineralized corridors of the Ellison property and are usually associated with elevated gold grades. The zones are also slightly richer than at LZ5 in terms of gold and silver content, but narrower and less continuous in general. The Ellison Zone A is characterized by gains in Fe2O3 (t) and K2O and losses in CaO, MgO, Na2O, and SiO2. Gains in Fe2O3 (t) and local gains in K2O, MgO, and MnO, and losses in CO2, Na2O, P2O5, and SiO2, characterize the felsic host rocks of the Zone B corridor.
The style of mineralization at LZ5 (pyrite ±chalcopyrite veins and veinlets, ±disseminated pyrite with low base metal content), its setting (i.e. in rocks of intermediate composition at the base of the upper member of the Bousquet Formation), and the geometry of its ore zones (stacked lenses of sulfide veins and veinlets, without massive sulfide lenses) differ from the other major deposits of the Doyon-Bousquet-LaRonde mining camp.
Despite these differences, this study indicates that the LZ5 and Ellison mineralized corridors are of synvolcanic hydrothermal origin and have most likely been formed by convective circulation of seawater below the seafloor. An influx of magmatic fluids from the Mooshla synvolcanic intrusive complex or its parent magma chamber could explain the Au enrichment at LZ5, as has been suggested for other deposits of the camp. Evidence for a pre-deformation synvolcanic mineralization at LZ5 includes ductile deformation and recrystallization of the sulfides, the stacked nature of its ore zones, subconcordant alteration halos that envelop the mineralized corridors, evidence that the mineralized system was already active when the LZ5 lenses were deposited and control on mineralization by primary volcanic features such as the permeability and porosity of the volcanic rocks.
Summary(Plain Language Summary, not published)
This report presents the result of the study of the LaRonde Zone 5 and neighbouring Ellison property ore zones (Abitibi, Quebec), with a particular emphasis on the mineralogy and geochemical signature of the hydrothermal alteration zones associated with the ore, and presents a genetic model for this type of gold mineralization.

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