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

Mineralization of Kirkland Lake camp (i.e., Toburn, Sylvanite, Wright–Hargreaves, Lake Shore,
Teck–Hughes, Kirkland Lake Gold and Macassa mines) consists of gold and telluride-bearing quartz
veins associated with brittle to brittle-ductile Kirkland Lake fault (Main Break) and the ’04 Break, as well
as with immediate splays of with these two faults. Presence of open-space-filling textures in veins, and
the association of veins with brittle faults suggest relatively shallow crustal levels of mineralization.
Relationships of gold-bearing veins, intra-mineral alkalic dikes and deformational fabrics, as well as
presence of S4-parallel syn-mineralization stylolites and cataclastic breccias in gold-bearing quartz veins
suggest that mineralization could have formed early in the D4 event synchronous with south-over-north
reverse-dextral to reverse movement along the Main Break. However, the presently available evidence
supporting temporal overlap of mineralization and D4 is relatively sparse, and it is possible that
mineralization predated the D4 event.
The positive correlation between high tellurium and gold content and the fact that the deposit is
hosted within an alkalic multiphase intrusive complex clearly indicate that the Kirkland Lake gold deposit
shares very strong analogies with gold deposits related to alkalic magmatism (e.g., Jensen and Barton
2000). The key geological parameters that support such an analogy include 1) location of the mineralized
system in an area characterized by protracted multi-stage alkalic magmatism (both volcanic and intrusive)
and its spatial association with a multi-phase alkalic stock; 2) gold- and telluride-rich high-grade
mineralization; 3) base metal-poor quartz-carbonate veins with high Au/Ag ratio; 4) carbonatization and
K metasomatism (sericite alteration); 5) enrichment in molybdenum; and 6) structurally focussed zones of
high-grade mineralization.
If the Kirkland Lake gold deposit is indeed related to alkalic magmatism, the parent intrusion is yet
to be identified. At present, it is impossible to establish a definite genetic link between gold
mineralization and any specific magmatic phase. Direct structural relationships imply that mineralization
postdated the emplacement and, most likely, complete crystallization of the syenite porphyry stock,
because the ore-controlling Main Break and subsidiary structures cut and displace the intrusion in a brittle
fashion. Moreover, the ≥2.5 km vertical extent of mineralization in the syenite porphyry, consistent
association of gold-bearing veins with discrete brittle faults throughout this vertical interval, and apparent
lack of zoning and features indicative of magmatic–hydrothermal transition within the intrusion, imply
that hydrothermal fluids probably were not derived directly from the syenite porphyry host. A deep
magmatic source (i.e., larger intrusion or magmatic chamber at depth) is more probable. Whether syenitic
intrusions exposed at present erosional level and mineralizing fluids of the Kirkland Lake gold deposit
were derived from a single deep magmatic source, or they instead represent two different magmatic
“events” within the Timiskaming-type, predominantly alkalic magmatic cycle, remains completely
unclear. This is mainly because the length of the time gap between emplacement of the syenite porphyry
and formation of gold-bearing veins is unknown, due to inconclusive nature of presently available
geochronological data. The occurrence of intra-mineral alkalic dikes is important. Even though these very
small dikes are unlikely to be genetically related to mineralization, their presence indicates that alkalic
magmatism overlapped in time with hydrothermal activity, and thus the existence of a deep magmatic
chamber (i.e., potential fluid source) is geologically feasible.
However, regardless of the timing of Kirkland Lake mineralization and many uncertain details of its
genesis, the distinct metal inventory (Te>Au, Mo, Pb, Ag, high Au/Ag, low As) of gold-bearing veins
indicates a distinct fluid source, that is, different from the source that contributed fluids for gold deposits
and occurrences clustering along the Larder Lake–Cadillac deformation zone and its splays. Based on
presently available data, a deep alkaline magmatic fluid source (magmatic chamber or intrusion at depth)
for Kirkland Lake gold mineralization appears most probable.
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