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Stratigraphic and structural setting of the Hemlo gold deposit, Ontario, Canada

Shoufa Lin
Stratigraphic and structural setting of the Hemlo gold deposit, Ontario, Canada
Economic Geology and the Bulletin of the Society of Economic Geologists (June 2001) 96 (3): 477-507

Abstract

Results of detailed surface and underground mapping and a compilation of data from the three gold mines in the Hemlo area, Ontario, are presented. In particular, the lithostratigraphy of the area is established, the nature of the lithologic units spatially closely associated with the ore and the protolith of the ore are determined, and the deformation history and the three-dimensional geometry of the area are elucidated. The genesis of the gold deposit is discussed in context of these results. Four generations (G (sub 1) to G (sub 4) ) of ductile structures, as well as brittle faulting, are recognized. G (sub 2) deformation is the strongest and the geometry of the Hemlo camp is dominated by macroscopic (camp-scale) "S"-shaped F (sub 2) folds. The two ore zones at Hemlo, the main and lower ore zones, are spatially associated with the two limbs of a newly recognized camp-scale F (sub 2) fold, the Moose Lake fold, and the orebody is folded by F (sub 2) at outcrop scale, mine scale, and possibly camp scale. G (sub 2) deformation is most intense in the Hemlo shear zone, interpreted to be a sinistral transpressional zone. The Hemlo gold deposit is hosted in the shear zone, mainly in the segment that trends east-southeasterly where deformation is stronger. The main gold mineralization at Hemlo occurred before G (sub 2) or early during G (sub 2) deformation and before peak metamorphism. The latter took place during late G (sub 2) to after G (sub 2) deformation. The ore and alteration zones are dominantly, but not exclusively, spatially associated with the stratigraphically lower contact of a volcanic quartz+ or -feldspar porphyry (the Moose Lake porphyry). A "mafic fragmental" unit (altered felsic fragmental rock) and a barite horizon are spatially closely associated with the ore zones. The protolith of the ore is mainly the fragmental rock and the barite. The stratigraphically lower contact of the Moose Lake porphyry and the fragmental rock at the contact probably served as mechanical traps and the barite horizon as a chemical trap.


ISSN: 0361-0128
EISSN: 1554-0774
Coden: ECGLAL
Serial Title: Economic Geology and the Bulletin of the Society of Economic Geologists
Serial Volume: 96
Serial Issue: 3
Title: Stratigraphic and structural setting of the Hemlo gold deposit, Ontario, Canada
Author(s): Lin, Shoufa
Affiliation: Geological Survey of Canada, Ottawa, ON, Canada
Pages: 477-507
Published: 200106
Text Language: English
Publisher: Economic Geology Publishing Company, Lancaster, PA, United States
References: 41
Accession Number: 2001-051099
Categories: Economic geology, geology of ore deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. block diags., sects., strat. col., geol. sketch maps
N46°19'60" - N49°40'00", W87°49'60" - W82°40'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200116
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