Summary:
The Red Lake operation is an underground mine, operating in three different historical mining complexes (Red Lake, Campbell and Cochenour) and the recently acquired Bateman Gold Project.
Red Lake mineralisation is hosted in the Red Lake greenstone belt. Mineralisation is associated with multiple episodes of volcanism, sedimentation, plutonism and deformation and is hosted in a variety of rock types within the Red Lake Greenstone belt. Economic zones of mineralisation are characterised by vein hosted gold systems accompanying sulphide replacement within sheared mafic to komatiitic basalts.
The Red Lake/Campbell, Cochenour, HG Young and McFinley deposits are hosted within significantly folded and sheared portions of the Balmer Assemblage dominated by tholeiitic basalt and komatiitic basalt intruded by felsic, mafic and lamprophyric intrusive rocks. Shear zones act as primary hydrothermal fluid corridors and host significant portions of the gold mineralisation in the area. Other significant mineralised structures occur within lower-strain areas of the stratigraphy.
Orebodies are generally steep dipping -50 to -60 degrees; lode geometry varies with relative position within the folded stratigraphy. Individual lenses of mineralisation vary considerably in thickness being mostly very narrow 0.3 – 1.0m but locally can contain multiple stacked lenses and stockworks and disseminations in excess of 10m in width. Gold appears as free milling gold, gold associated with sulphides, with magnetite as well as refractory, arsenopyrite-associated gold. It is common for zones to have multiple styles of mineralisation within the same host lithology.
The Red Lake/Campbell system has been defined to date to extend approximately 3,000m along strike and has drilling intercepts over a vertical extent of 3,000m. The Cochenour mine as modelled excludes the historically mined upper zones, commences approximately 750m below surface and has been defined along a strike length of 600m and extends 700m vertically. The updated McFinley model has been defined over a 1,350m strike length, 1,750m vertical extent and 800m across strike.
The majority of the mineralization in these types of deposits is intimately associated with quartz ± carbonate (calcite, ankerite, or siderite) veins with persistent sericite–carbonate alteration haloes in highly deformed, Archean host rocks that have been regionally metamorphosed to lower or middle greenschist facies. The host rocks are highly-altered, supracrustal rocks; most commonly tholeiitic basalts, komatiites or their volcaniclastic or subvolcanic equivalents. Mineralization also occurs in felsic volcanic rocks, porphyries, greywackes and conglomerates.
Mineralization is primarily localized within the tholeiitic mafic rocks and shows strong structural control along broad to discrete shear structures running along a 135° trend in the east, refracting to a 120° trend in the west. Other significant mineralized zones occur along discordant brittle structures which most commonly appear as a conjugates system generally oriented east-west (110° azimuth) and north–south (160° azimuth). Competency and permeability contrasts between adjacent lithologies is also important as seen by the strong association of higher-grade mineralization when basalt comes in contact with ultramafic rocks.
Mineralized zones in the Red Lake-Campbell deposit are distinguished first by spatial orientation relative to structural corridors and second by the style of mineralization. There are four types of mineralization in Red Lake-Campbell Deposit:
1) Vein style gold mineralization;
2) Vein and sulphide style gold mineralization;
3) Disseminated sulphide style mineralization (often referred to as replacement style mineralization), there are sub-styles within this group;
4) Free gold mineralization style.
The Cochenour can be accessed by the Cochenour Complex and is connected underground to the Campbell Complex. The Cochenour Deposit covers an area that is approximately 750 m by 500 m and remains open down-dip. Mine workings extend 1,800 m (5320 Level). The deposit remains open down-dip.
The Cochenour Deposit comprises the Main, Inco, Upper Main Zone (UMZ), Banded Iron Formation (BIF), Footwall and new exploration targets. The Main and Inco zones form part of the original Cochenour Mine. The Western Discovery exploration target is located on McKenzie Island, approximately 1.5 km due west of the Cochenour mine site and will be included in the Cochenour Deposit.
The Cochenour deposit appears folded about a southwest-trending antiform, plunging to the southwest at 50° immediately in the hanging wall of the East Bay deformational corridor. A series of massive, felsic tuffs, reworked tuffs and felsic intrusions occurs along the western flank of the former Cochenour mine, which makes up the base of the overlying Bruce Channel assemblage. At surface, these rocks define the location of a north–south running shear zone, referred to as the Gold Eagle Shear, which dips steeply due west at approximately 65° underneath the Bruce Channel of Red Lake.
Mineralization in the Cochenour deposit is made up of the same styles as the Red Lake-Campbell deposit. Mineralized zones in the Cochenour deposit are distinguished first by spatial orientation relative to major structural and by the style of mineralization.
Cochenour Main and West Zones
Mineralization is associated with discrete shear structures immediately in the footwall of the Cochenour Thrust structure. The geometries of this mineralization was complicated by numerous roughly north–south, steeply-oriented fault structures, as well as by numerous roughly east–west trending, steeply-dipping, very narrow (1 to 5 mm), brittle offset structures referred to as “black-line faults”.
This mineralization type occurs within sheared ankerite-altered iron-tholeiitic basalts and ankerite veins, with higher-grade mineralization located in close proximity to peridotitic rocks. Mineralization consists of intense late, vitreous silica replacement accompanied by a significant component (locally up to 30%) sulphide minerals. The most common sulphides include fine needle- like arsenopyrite, pyrite–pyrrhotite, with minor sphalerite, chalcopyrite and stibnite. Gold occurs as both free-milling gold as well as refractory grain coatings on fine arsenopyrite grains.
Bruce Channel Deposit (Upper Main and Footwall Zones)
Footwall Zone structures appear as a series of steeply-dipping, fault-hosted, ~160°-trending, sheared carbonate vein structures that are generally developed in the footwall to the UMZ. These Footwall Zone structures share many features in common with the north–south shear structures associated with the Inco Zone mineralization, and are probably directly related to the same suite of ~160°-trending narrow shears found higher up in the mine.
Upper Main Zone structures currently extend vertically for about 1,000 m and locally have strike lengths as long as 550 m. Mineralization is typically 2–5 m wide, but can occur as broader, structurally-stacked zones.
Bateman
Mineralisation at Bateman is primarily hosted within high-titanium basaltic units but also occurs within ultramafic and basaltic lithologies, and to a lesser extent within the felsic intrusive unit. Mineralisation is interpreted to have been deposited in two phases, with the first being a lower grade (<4g/t gold) phase associated with quartz-actinolite-sulphide veining, and as disseminated style of mineralisation associated with quartz-biotite-sulphide alteration within the host high-titanium basalt and felsic units. A higher-grade phase of mineralisation is associated with shear-related veining and localised shearing within the deposit. Gold occurs with disseminated sulphide mineralisation and within gold-bearing quartz veining. The Bateman deposit is approximately 1,200m along strike and has drilling over a vertical extent of 1,800m.