Overview of Results from the Greenstone ... - Geology Ontario

The Kirkland Lake giant gold deposit is clearly a structurally controlled syn-deformation gold- and
telluride-rich high-grade hydrothermal system characterized by steeply to moderately dipping fault-fill
veins hosted by brittle to brittle-ductile faults (primarily the Main Break and the 04 Break). The goldbearing
veins were formed at relatively shallow crustal levels, probably simultaneously with reversedextral
to reverse movement on the Main Break. The deposit shares strong analogies with high-grade
gold-telluride deposits linked to alkalic magmatic systems (Jensen and Barton 2000). Because the exact
timing of hydrothermal activity and gold mineralization and development of the Main Break and 04
Break structures relative to alkaline magmatism remain speculative, it is impossible to establish a definite
genetic link between gold mineralization and any known magmatic phase. In a structural sense, goldbearing
veins postdate the Timiskaming assemblage clastic-volcanic sequence and the syenite porphyry
stock as both are cut by the gold-bearing Main Break, 04 Break and associated structures. The structural
timing of Kirkland Lake mineralization is not entirely clear. Using the relative chronology between the
intra-mineral dikes, the quartz veins and the foliations, we propose that the mineralization could be syn-
D4 (D5 in Timmins?), however, we recognize that evidence supporting this timing is not 100%
conclusive and additional work is needed to provide more reliable constraints. It is possible that
mineralization entirely predated D4. The distinct metal inventory (Te>Au, Mo, Pb, Ag, high Au/Ag, low
As) of Kirkland Lake mineralization indicates a separate fluid source, different from gold deposits and
occurrences clustering along the Larder Lake–Cadillac deformation zone and its splays. A deep alkaline
magmatic fluid source (magmatic chamber or intrusion at depth) appears most probable.
As reported by Sillitoe (2002), several giant gold deposits related to alkaline rocks may be
considered unique in term of combination of geological characteristics and, as shown by its geological
parameters, the Kirkland Lake gold deposit fits such a statement. The interpretation of Kirkland Lake as a
stand-alone hydrothermal system related to alkalic magmatism and unrelated to gold mineralization along
the Larder Lake–Cadillac deformation zone agrees with the interpretation of Robert (2003).
Conclusions
The objective of this project was to improve knowledge of the stratigraphy, volcanology, geochemistry,
metamorphic petrology, and structural geology to better understand the metallogeny and architecture of
the Abitibi greenstone belt in the Timmins–Kirkland Lake study area. We have, thus, considerably
changed and improved our knowledge of Abitibi stratigraphy and belt-scale architecture by
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utilizing 34 new TIMS and 11 SHRIMP U/Pb zircon ages to further subdivide and refine the
distribution and age ranges for the volcanic and sedimentary assemblages, the intrusions and the
timing of metallogenic and structural events.
providing new evidence in the form of xenocrystic zircons that the Pacaud and Deloro assemblages
were widespread basal units, but are now restricted to units only found wrapped around the margins
of external batholiths and in the cores of domes. The data also provide evidence for pre-Abitibi-age
inheritance in volcanic assemblage samples, proving early (pre-D1) interaction with an older
(>2.85 Ga) crustal precursor to the Abitibi greenstone belt.
documenting a series of interformational unconformities in the volcanic “Keewatin” stratigraphic
assemblages. Submarine unconformities are preserved locally at the top of Pacaud, Deloro,
Stoughton–Roquemaure and Kidd–Munro assemblages.
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