The MacLellan deposit is the central body of three stratiform, sub-concordant mineralized zones, with the Rainbow-Dot deposit located 300 m to the west and the Nisku 200 m to the east of the MacLellan deposit (Figure 8-1). All three deposits are located south of a major east-west trending NSZ fault, which strikes 065° and dips 75-85° to the north.
MACLELLAN MAIN AND EAST MAIN ZONE DEPOSIT
The MacLellan Main zone includes a number of grade-defined mineralized lenses with strike lengths ranging from 20 to more than 250 m, and widths averaging several metres, locally more than ten metres and fairly good overall grade continuity. Most of the individual mineralized lenses are in contact with the NSZ. Most of the previous production was taken from the Main and East Main zones. Mineralization is predominantly hosted in tuffaceous sediments within mafic volcanics and pyrite and pyrrhotite are the dominant sulphide minerals. Lesser amounts of arsenopyrite, sphalerite and galena are also present (Voisey 1990).
The mineralized lenses have been labelled as A, B, and C and there is also a small high-grade
shoot in the hang wall rocks about 8 m north of the NSZ, known as the HW lens. The lenses are
parallel are dip to the north at 82-85°. The A lens lies along the NSZ and the significant parts of
the B and C lenses are in en-echelon array to the south and east of the A lens. There are no obvious lithological or structural criteria by which the lenses can be recognised, other than the presence of disseminated and semi-massive sulphides. The NSZ cuts obliquely across the mineralization (Samson and Gagnon 1995) and there is a possibility of exploration potential to the north of NSZ.
Gold distribution in the Main zone is erratic and can occur in any rock type. Fedikow (1986) reports that the highest gold and silver values in the MacLellan deposit are associated with zones of silicification and mobilization adjacent to carbonate-quartz-sulphide veins. High assays are obtained where these veins cross-cut sulphidic siltstone.
The only geological feature of the Main and the East Main zones, which provides a fairly reliable anchor, is the persistent and relatively uniform NSZ. This east-northeasterly striking (070°) fault dips parallel to the foliation / stratigraphy at 82° north and extends laterally beyond the Nisku, East Main, Main and Rainbow zones. The NSZ marks the hanging wall of the Main and East Main zones.
The East Main zone is similar to the Main zone in that the NSZ forms the contact between the hanging wall andesite and the footwall tuffaceous sediments hosting the East Main zone. The mineralization consists of 30-40 % disseminated iron sulphides in addition to arsenopyrite, sphalerite and galena occur as tightly folded conformable lenses within siltstone and basalticultramafic komatiite and is accompanied by locally intense carbonatization. The nature and style of mineralization appears to be similar to the Main zone lenses, however the zone is composed of many small shoots with limited lateral and down-dip continuity (Samson and Gagnon 1995). The east end of the mineralized zone deteriorates into a 40 m wide belt of discontinuous stringers that are too narrow and far apart to form a significant body. The East Main zone between the 240 mL and the 370 mL is interpreted as a single mineralized zone dipping 85° north, adjacent to the NSZ. The mineralization has a maximum horizontal thickness of 12 m and a strike length of 20 m at the 240 mL increasing to 75 m at the 370 mL.
NISKU DEPOSIT
In contrast to the Main zone, mineralized zones at the Nisku can occur well south of the NSZ. There are NW-SE faults that bound the Nisku deposit and displacement along these faults could have moved the mineralization southward from its original position or moved the NSZ to the southeast.
Mineralization at the Nisku deposit is complex. Gold mineralization occurs in irregular sulphide concentrations and cherty zones within metasediments, and in veins with variable amounts of quartz, quartz-carbonate or massive sulphides. The veins of the Nisku zone are commonly narrow but quite high grade, with gold assays of up to 150 g/t reported. The various vein and vein systems at Nisku have a general east-west strike and dip nearly vertically.
The northernmost mineralization zone of the Nisku deposit, the Hangingwall zone, is situated just south of the NSZ and is comprised of two lenses, the HW1 and the HW2. These lenses are distinctive entities at their western limbs and are separated by approximately 10 m of unmineralized andesite. At the eastern limb, the two lenses coalesce to form a fold nose, with local thickening of higher grade mineralization of up to 12 m.
The Footwall zone is the more dominate zones of mineralization and is located approximately 30 m south of the Hangingwall zone. The zone is divided into four discrete bodies, the F1, F2, F3 and FN. The F1 is the largest and the most continuous structure of the Footwall zone.
The Ramp zone occurs between the Hangingwall and Footwall zones and occurs where the main access ramp cuts narrow zones of higher grade mineralization. Grade distribution is fairly erratic along strike whereas values are most consistent along plunge.
RAINBOW-DOT DEPOSIT
The Rainbow-Dot deposit consists of two en-echelon lenses of quartz and quartz-carbonate veins with < 10 % disseminated pyrite, pyrrhotite and lesser sphalerite and galena. Each lens is up to 15 m wide and approximately 150 m long. There are two significant zones, the Central and the Hanging Wall North which is thought to be the westerly strike extension of the Main zone (McMillan 1988). The veins are narrow and have sharp lateral cut-offs. McMillan (1988) has suggested a relationship between folding and mineralization.
The tenor of the gold mineralization is similar to that in the MacLellan Main zone (Fedikow 1986, Fedikow et al. 1991). Gold and gold-silver alloys occur as: (1) small, irregularly shaped grains or veinlets generally < 10 microns in gangue; (2) rims on, or fracture fillings in galena, arsenopyrite and pyrrhotite; (3) inclusions in arsenopyrite, pyrrhotite and galena; (4) anhedral grains associated with arsenopyrite and galena; and (5) sutured grains associated with galena (Augsten et al. 1986).
