The Mac occurrence is located in the south western headwaters of Butler Creek, approximately 3.5 kilometres east of Bluff Lake.
The occurrence consists of precious and base metal mineralization associated with quartz veins in hydrothermally altered volcanics and intrusive bodies. The occurrence lies between two major northwest-striking faults along the northeastern margin of the Jurassic to Tertiary Coast Plutonic Complex: the Yalakom fault and the Tchaikazan fault (Geological Survey of Canada Open File 1163). A splay of the latter fault, called the Niut Fault, runs through the area of interest.
The area around the Mac occurrence is underlain in part by Lower Cretaceous volcanics and minor sedimentary rocks of the Gambier overlap assemblage (Geological Survey of Canada Map 1713A). The volcanics are mainly andesitic tuffs, with minor breccia and porphyritic flows. These are interbedded with rhyodacitic flows and tuffs. The other main host rock is medium-grained, porphyritic quartz diorite to diorite, probably related to the Coast Plutonic Complex. The volcanics are also intruded by dikes, including monzonite porphyry and quartz-feldspar porphyry.
The rocks have extensive alteration: silicification, propylitic, argillic, sericitic and limonitic alteration are all reported. Pyrite and pyrrhotite are generally present, at up to about 10 per cent. Alteration is strongest in fracture zones where significant quartz veining is developed.
Mineralized quartz veins and stockworks have been related mainly to the dioritic intrusions (Assessment Reports 13780, 17080).
The largest and most significant vein, the Cow Trail vein, is mostly hosted in intensely altered (argillic-sericitic) quartz diorite, the remainder being volcanics. The Cow Trail vein can be traced for at least 200 metres, and has an average strike of 080 degrees, dipping 70 degrees south; it varies between 0.3 and 1.5 metres in thickness. Locally, banded and vuggy textures are present suggesting an epithermal origin, at least in part (Assessment Report 13780). The vein is mineralized with pyrite, chalcopyrite, up to 2 per cent galena, black sphalerite, and tetrahedrite.
In 1985, vein samples assayed up to 3.74 per cent zinc, up to 2.0 per cent lead, and up to 0.24 per cent copper (Assessment Report 13780). Significant gold and silver values are sporadic, but grab samples have reached assay values of 12.2 grams per tonne gold and 1138 grams per tonne silver (Assessment Report 13780). Other surface values between 1.4 and 2.75 grams per tonne gold, and between 100 and 240 grams per tonne silver, are not uncommon (Assessment Report 13780).
In 1987, a trench in the Cow Trail vein yielded a channel sample with 48 grams per tonne silver averaged over 7 metres (Assessment Report 17080).
Another interesting quartz vein, the Goat Trail zone, outcrops 150 metres southwest of the Cow Trail vein. The vein is up to 1 metre thick, and is mineralized with up to 0.9 gram per tonne gold and 396 grams per tonne silver, with 6.8 per cent zinc and 2.0 per cent lead (Assessment Report 17080).
In 1984 and 1985, Imperial Metal completed programs of soil and rock sampling, trenching and geological mapping on the area as the Mac claims. In 1987 and 1988, Jacqueline Gold completed programs of rock and soil sampling, geological mapping and an induced polarization survey on the area as the Newmac 1-3 claims. In 1990 and 1991, Noranda completed programs of rock and soil sampling, geological mapping and ground and airborne geophysical surveys on the area as the Newmac claims. In 1998, Ascot Resources Ltd. and Canevex Resources explored the area. In 2004, Scott Geophysical completed a program of ground magnetic and induced polarization surveys on the area. In 2006, Newmac Resources completed a 6 hole diamond drill program, totalling 1134 metres, on the area.