Summary:
The Westwood complex includes the Westwood underground mine, the Grand Duc open pit mine, and the Fayolle open pit mine.
Westwood and Grand Duc Deposits
The Westwood underground mine and the Grand Duc open pit are part of the Doyon-Bousquet-LaRonde (“DBL”) mining camp, which is located within the Southern Volcanic Zone of the Abitibi subprovince.
At the Westwood Mine, the Zone 2 Extension share similarities with the Doyon Mine intrusion-related veins system while the Westwood Corridor is related with the VMS-type lenses of the LaRonde Penna and Bousquet 2-Dumagami mines. The North Corridor mineralization represent the base of the Westwood Corridor.
Fayolle Deposit
The Fayolle deposit is characterized by the komatiite flows of the Lanaudiere Formation (Goutier, 1997) intruded by a swarm of quartz-feldspar porphyry and/or feldspar porphyry dykes. A post-intrusive brecciation event seems to control gold deposition.
Mineralization Westwood and Grand Duc
VMS-type mineralized zones of the DBL camp are mainly associated with units #5.1.4 and #5.2.1 of the Bousquet Formation upper member. These units host gold-rich VMS-type semi-massive to massive sulphide lenses as well as stringer zones such as the Bousquet 1, Bousquet 2-Dumagami and LaRonde Penna deposits as well as the Westwood and North corridors. Intrusion-related mineralized zones composed of gold sulphide veins are mostly hosted in units #4.2.1, #4.3.0 and #4.4.0 as well as in the apex portion of the MIC such as zones 1, 2, and West at the Doyon Mine and Zone 2 Extension at Westwood.
The Zone 2 Extension: Mineralized zones consisting of quartz-pyrite veins and veinlets with variable but usually minor amounts of chalcopyrite and rare sphalerite. They are generally less than 15 cm thick and are hosted in strongly sericitized wall rock containing 2% to 10% disseminated pyrite. The alteration corridor is weaker at depth and towards to eastern part of the property, but the veins and the gold grade remain. The vein system is roughly oriented N85-105° with a dip varying between 60-70°S and is slightly discordant to the regional foliation and S0 planes (direction and dip). Remobilized free gold, at the origin of high-grade values, is frequently observed in these veins which are located within units #4.3.0 and #4.4.0, which are, felsic and mafic volcanic respectively.
The North Corridor: Mineralization characterized by quartz-pyrite veins and concentrations with locally abundant sphalerite-chalcopyrite±pyrrhotite-galena. The amount of sulphide is variable within centimetres to decimate wide veins and veinlets. The system is generally parallel to the Zone 2 Extension with a dip ranging from 70-80°S and is weakly discordant to the regional foliation. Occasional free gold is also present in the veins. Mafic to intermediate volcanic rocks (units #5.1.1 and #5.1.2) host the North Corridor.
The Westwood Corridor: Auriferous semi-massive to massive sulphide lenses, veins and dissemination containing variable but significant amounts of Cu, Zn and Ag. The mineralization is characterized by pyrite sphalerite-chalcopyrite-pyrrhotite±galena veins, stringers and massive sulphides associated with variable amounts of quartz and rare visible gold. The sulphides are also enriched in the epithermal suite of elements (i.e., As, Sb, Bi, Pb, Se, Te, and Hg). These mineralized zones are a few centimetres to more than 50 cm thick in a disseminated pyrite halo and in some places reach thicknesses of up to 10 m. Local massive to semi-massive sulphide lenses ranging from 1 to 14 m are also present within the corridor.
The Grand Duc mineralization is at the late stage of the Moushla pluton. The late stage includes the injection of plagioclases-amphibole porphyry dykes and sills, plagioclase-quartz porphyry, aphyric and phenocrystalline quartz trondhjemite located south of the other two intrusive stage. Mineralization in the West zone of Doyon Mine (Savoie e al., 1991) as well as the Mooshla A and Grand Duc pit gold showings are hosted in rocks of this late stage. The trondhjémite is massive, homogeneous and competent, and little deformed by the main foliation that systematically affects the volcanic rocks of the mining camp. Locally, the rock contains up to 15% miarolitic cavities filled with chlorite, amphibole, epidote, quartz and/or pyrite (Galley et Lafrance, 2007).
A gold mineralizing episode of Grand Duc is closely associated with the miarolitic facies. This facies host low-grade mineralization forming a long corridor oriented N105-N110 south dipping (50-70°). Gold mineralization occurs as either disseminated pyrite in shears zone, quartz-pyrite-carbonate-chlorite veins and veinlets, as fill in fractures or in centimetric pyritic band parallel to foliation. The pyrite is fine to coarse, but the grade is higher in the presence of coarse pyrite.
The second gold mineralizing element is associated by a series of veins and fractures oriented N175 and N045. The veins are generally centimetric and rarely exceed 10 cm. At this time, two north-south corridors are recognized in the Grand Duc pit and they are 60 m apart. Mineralization in these corridors consists mainly of quartz-pyrite-chalcopyrite high-grade remobilization veins.
Mineralization Fayolle
The Fayolle deposit comprises wide alteration zones that contain brecciated mineralized zones. Gold mineralization is hosted in porphyritic dykes of intermediate composition and in volcanic rocks (Gaudreault and Beauregard, 2009).
Most of the ankerite and quartz-ankerite veins occur in brecciated rocks. Several ankerite and quartz ankerite veins, 0.5 to 2 cm wide, as well as chlorite-filled fractures and gouge with irregular orientations, have been observed within and near the mineralized zones. Vein density increases from 5% to 80% in the mineralized zone, and fuchsite alteration is locally observed.
Mineralization is characterized by disseminated pyrite (generally 1-5%) spatially associated with or contained within veinlets of quartz and/or carbonate minerals. Gold is present in the pyrite or as grains of free gold in quartz veinlets. Pyrite is generally found as pods and fine-grained disseminations along schistosity planes and chloritized fractures which are variably deformed at dyke contacts. Pyrite also occurs as barren cubic grains (up to 12%) in the host rocks, and pyrite content is therefore not a direct indicator of gold mineralization in the Fayolle deposit (Carrier, 2007).
Gold is directly associated with ankeritized and pyritized deformation zones (brittle ductile shears) displaying variable degrees of potassic alteration (fuchsite-sericite) and albitization.