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

The Timmins area and Kirkland Lake–Larder Lake area gold and intrusion subprojects utilized
detailed mapping and structural studies, lithogeochemistry and geochronology to provide an improved
understanding of the relationships between, and the ages of, the various assemblages, and the timing of
intrusions, structural, alteration and epigenetic gold mineralization episodes. The results of these studies
documented the existence of multiple gold mineralizing events at both Timmins and Kirkland Lake.
In the Timmins area, the main structural and gold mineralization events included D1 uplift and
excision of upper Tisdale assemblage stratigraphy with formation of an angular unconformity predating
deposition of Porcupine assemblage at 2690 Ma; an early, lower grade gold mineralizing event predating
the Timiskaming unconformity was probably synchronous with D2 thrusting and folding and early southover-north
dip-slip movement on the Porcupine–Destor deformation zone (PDDZ) between 2685 and
2676 Ma. Main stage gold mineralization was associated with a protracted D3 event which coincided with
the opening of the Timiskaming basin, but also overprinted the Timiskaming sediments. Rhenium–
osmium geochronology on molybdenite associated with main stage gold mineralization at the McIntyre
Mine provide an age of 2672±7 Ma and 2670±10 Ma at the Dome Mine. The D4 event included folding
and faulting that preserved the Timiskaming assemblage in synclines along the PDDZ and is associated
with a late stage gold mineralization event along the Pamour Mine trend.
In the Kirkland Lake–Larder Lake area, the main structural and gold mineralization events are post-
Timiskaming and include a D2 event corresponding with movement along the Larder Lake–Cadillac
deformation zone and the deposits spatially associated with this deformation zone (possibly correlative
with the D3 event in Timmins). The D3 event was related to the east-west shortening. The Kirkland Lake
gold deposits are associated with the brittle to brittle-ductile Kirkland Lake fault (Main Break) and its
subsidiary splays. The presence of open-space-filling textures in veins, and the association of veins with
brittle faults suggest relatively shallow crustal levels of mineralization. Distinct metal signature and
mineralization style suggest that the Kirkland Lake deposits probably represents a stand-alone
hydrothermal system that is unrelated to gold deposits along the Larder Lake–Cadillac deformation zone
and its splays. A deep magmatic fluid source appears most probable for the Kirkland Lake mineralization.
Gold-bearing veins could have formed early in the D4 event, synchronously with south over north
reverse-dextral to reverse movement along the Main Break. Alternatively, mineralization could have
predated the D4 event. Gold mineralization in the Narrows Break, north of the Kirkland Lake Main
Break, was synchronous with northwest-southeast shortening during the D4 event.
A new metamorphic framework has provided additional constraints on the setting of gold deposits
and a new tool for gold exploration. The metamorphic pattern in the study area is the result of
superposition of regional metamorphism on narrow higher grade contact metamorphic aureoles that
formed at different times immediately adjacent to granitic intrusions, indicating that most of the
granitoids are older than the regional metamorphic event. Pre-Timiskaming phases of deformation were
less penetrative and occurred at shallower depths in the crust and at lower temperatures than post-
Timiskaming deformation, whereas post-Timiskaming deformation, when peak regional metamorphic
conditions prevailed, was most conducive to formation of large synmetamorphic (orogenic) gold deposits.
There is a striking spatial relationship of the boundary between the lower and upper greenschist
metamorphic zones and a significant number of gold mines. Newly identified high priority targets are
defined by the coincidence of metamorphic anomalies with major structural features, specific rock
compositions, and moderate to intense deformation.
Regional structural patterns are now better understood, in part based upon improved knowledge of
the distribution of the stratigraphy and intrusions in conjunction with detailed and regional scale
geophysical surveys including magnetic, gravity and reflection seismic surveys. Major external intrusive
units such as the Round Lake and Kenogamissi batholiths include synvolcanic phases that occupy
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