Summary:
The Kiena Complex project lies within the Abitibi Subprovince of the Archean Superior craton,
eastern Canada. The Kiena Complex project straddles the limit between the southern part of the Abitibi Subprovince and the northern part of the Pontiac Subprovince. In this region, the Cadillac Tectonic Zone (CTZ) marks the separation between the two. Fromsouth to north, the Project is underlain by the lithologies of the Pontiac Group (PO), the Piché Group (PG), the Héva Formation (HF), the Val-d’Or Formation (VDF), the Jacola Formation (JF) and the La Motte-Vassan Formation (LVF).
The region has several large-scale strike faults and/or shear zones, trending W to WNW and dipping steeply to the north. They are, from south to north: the Cadillac Tectonic Zone (CTZ), the Parfouru Fault (PF), the Marbenite Fault (MF), the Norbenite Fault (NF), the Callahan Fault (CF), the K Shear Zone (KSZ), and the Rivière Héva Fault (RHF). The Quebec Wesdome Project is cut by all of them. These major structures contain dykes or stocks of monzonitic or tonalitic composition with highly variable ages (pre, syn- or post-tectonic) that are spatially associated with several gold mines (Norlartic, Marban, Kiena, Sullivan, Goldex, Siscoe, Joubi, Sigma and Lamaque). The observed diversity in the styles and ages of gold mineralization related to these large-scale strike faults and/orshearzones demonstratesthatseveral distinct episodes of mineralization occur.
Significant mineralized quartz veins are commonly hosted in second- and third-order shear zones. Structurally, these shear zones vary from brittle–ductile to ductile, depending on their depth of formation. At depths greater than 10 km, quartz veins are seldom located within shear zones whereas gold mineralization is mostly associated with disseminated sulfides. A widely accepted model for orogenic gold deposit is the continuum model, which involves the migration of hydrothermal fluids from a deep- seated reservoir to mid-crustal level along a crustal-scale fault. This model allows for gold deposits to be formed over a range of crustal depths of more than 15 km. The timing of gold mineralization relative to metamorphism in higher metamorphic grade rocks has been contentious. In the past two decades, complex gold depositional sequences have been documented in several gold deposits that support the concept that gold deposits form by accumulation during several hydrothermalepisodes.
The most important feature of the deformation from the perspective of gold mineralization was the development of shear zones. The timing of the shear zones is controversial, but there is general consensus that a significant component of the vertical elongation and thrusting along these fault zones occurred during the Kenoran orogeny. Gold deposits in the Val-d’Or district are hosted or spatially associated with shearzones. The deposits occur in all rock types present in the district, except forthe late-tectonic Archean granitic batholiths and the Proterozoic diabasedikes.
Gold mineralization in the property occurs in all rock types except Proterozoic dykes but is more common in intrusive bodies and basalt as these acted as competent rock units that promoted fracturing during deformation. Gold mineralization concentrated where there is a marked competency contrast between these competent units and the adjacent deformed komatiite and/or chlorite-talc schists.
There are at least two main gold mineralizing events in the region: young deposits in which the gold mineralization did not experience much deformation after its emplacement; and early mineralization in which ore bodies are commonly affected by D1 asymmetric folds, are highly strained and are locally dismembered. In a few deposits, both generations are present. Precise U-Pb zircon dating of an intermineral granodiorite dyke assigns a minimum age of 2686 ± 2 Ma to the gold mineralization at the Kiena mine (Morasse et al., 1995). This age reveals that gold mineralization postdates volcanism and the Snowshoe plutonism but predates regional synmetamorphic deformation (ca. 2677-2645 Ma).
Gold-bearing veins in the region exhibit a great variety of orientations, mineralogy and crosscutting relationships. For the purposes of this report, they are classified into the following three main types:
Type 1: early quartz-carbonate veins cut by various dykes;
• Type 2: deformed veins within a shear zone; and
• Type 3: relatively weak deformed late quartz± tourmaline veins cutting all intrusive types and previous gold-bearing vein systems.
In general, mineralized zones on the property occur near a large-scale fault. They are often associated with a subsidiary shear zone that may be proximal, adjacent or host to the mineralization. Alteration minerals are dominantly albite, carbonates and pyrite with lesser chlorite and silica.
The gold occurrences found in shear zone settings are mainly restricted to competent units, and thus the size and shape of the mineralized zones often depend upon the size, shape and concentration of the competent intrusive or basalt. In zones of structural dislocation, two settings for gold mineralization have been recognized:
• Shattered intrusive bodies, such as diorite or feldspar porphyry dykes, enclosed in talcchlorite schist; and
• Zones of fracturing and brecciation in large bodies, such as basalt.
In large bodies of basalt, fracturing was generally restricted to narrow zones, and subsequent mineralization resulted in narrow and often closely spaced mineralized zones. In narrower dykes, the whole body is affected by fracturing, and subsequent mineralization was able to spread throughout the dyke, forming large mineralized zones. Two factors, the size of individual dykes and the density of the swarms, control the size and shape of mineralized zones associated with dykes in shear zone settings.