Back on Track GEOLOGY OF DETOUR LAKE

Most of the ore at Detour Lake lies adjacent to the contact between an ultramafic unit and a series of mafic volcanics. Gold is primarily localized in quartz- pyrrhotite/pyrite/ chalcopyrite structures within a wide variety of lithologies. The Main zone, which follows the contact, is spatially associated with a chert horizon accompanied by quartz veins and sulphide enrichment. The zone strikes east-west, dips steeply (50degrees to 70degrees) north and plunges about 45degrees to the west. Structurally, the ore is located on the nose of an open fold. The remainder of the ore is in narrow quartz veins which splay off the chert horizon at a strike of about 45 degrees and near vertical dip. Here the gold values are more erratic and have a lower-than-average grade. Styles of mineralization vary considerably within the deposit and are primarily a function of the host lithology’s competence and intensity of deformation. Lithologies north of, and including, the chert marker horizon mainly display brittle deformation and host planar quartz veins. These veins either occur adjacent to, or splay westerly from, the chert horizon. Units south of the chert have been dominantly affected by plastic deformation. Overall, the quartz vein mineralized structures appear to be developed in a wide shear zone that displays sinistral displacement. Vertical movement is reverse, with the north block moving up relative to the south.

The shearing event has been long- lived and appears to have intensified over two periods at slightly different locations. On the 11th level, shearing is dominantly subparallel to, or at a low angle to, the stratigraphy while on the seventh level it is mainly oblique. In the hangingwall volcanics, which have undergone brittle deformation, the quartz veins and the chert have been visibly folded on a small scale, with the folds having a westerly plunge. In the plastically deformed footwall units and along the western portion of the chloritic greenstone- mafic flow contact, on the 11th level, quartz occurs as prolate boudins that have a westerly plunge. The plunge of the fold axes is grossly conformable with the plunge of the deposit. Overall, the style of deformation suggests the deposit is localized within the noses of a series of S-folds in the north flank of a westerly plunging antiform. Stratigraphically, mineralization is localized near the chert horizon that marks the boundary between the brittle volcanics to the north and the ductile volcanics to the south. Gold-bearing quartz veins preferentially develop along fold noses.

Proceeding from north to south, the mappable units are: intermediate tuff-breccia, mafic flow, intermediate to felsic flow and hyaloclastite, chert, chloritic greenstone and talc chlorite. Intrusive dikes, which post-date all stratigraphic units and either post-date or are synchronous with the mineralized quartz veins, were identified as mafic, intermediate and felsic intrusive. Pre-intrusive units have been subjected to amphibolite grade metamorphism. Amphibolized hangingwall mafic flows have been variably overprinted by biotite-phlogopite- silica-sulphide alteration adjacent to mineralized quartz veins. The names “intermediate to felsic flows” and “hyaloclastite” have been assigned to these altered mafic flows. Chloritic greenstone is a chlorite altered mafic volcanic unit of unknown origin. Talc- chlorite units are ultramafic to mafic flows or intrusives that have undergone a variation of talc, chlorite, carbonate and sulphide alteration.