The Big Andy prospect is described as being located on the east side of Bute Inlet, 6.4 kilometres east-southeast of Purcell Point, at approximately 1219 metres elevation.
The earliest record of mineral exploration in the Upper Bute Inlet area was in 1967 by Rio Tinto Canadian Exploration Ltd. who explored a porphyry-style copper occurrence northeast of the confluence of Bishop Creek with Southgate River. Swiss Aluminum Mining Co. of Canada Ltd. explored the same area in 1971. Low-grade copper mineralization related to a felsic granitoid plug was outlined in the area but the claims were allowed to lapse. Hecla Operating Company explored a stratiform polymetallic target on the east side of Bute Inlet in 1973. In 1989, Slumach Jackson Mines Ltd. staked a claim group north of Southgate River on what Mustang Resources Inc. reported was staked on a high grade gold mine in the 1700s and 1800s. In 1991 and 1992, Galleon Mining Limited conducted sampling, geological mapping, geophysical surveys and trenching.
The area is regionally underlain by the Jurassic to Cretaceous Coast Plutonic Complex, composed of foliated and non-foliated granodiorite, granite and quartz diorite intrusions. These intrusions are flanked by older Paleozoic and/or Triassic age sedimentary and volcanic strata, largely as roof pendants composed of amphibolite, gneiss, schist, quartzite, limestone and andesite. The regional structural trend is northwest.
The oldest rocks in the area is a complex of Paleozoic or older garnetiferous amphibolite, schlieren gneiss, biotite hornblende schist, medium-grained diorite and rare hornblendite, which are preserved in northwest trending belts in the Coast Plutonic Complex. Foliations usually parallel contacts. Metavolcanic and metasedimentary rocks consist of porphyritic andesite, micaceous quartzite, biotite schist, phyllite, siltstone, argillite and minor impure limestone of the Cretaceous Gambier Group. These rocks are contained within diorite and granodiorite of the Coast Plutonic Complex.
The Big Andy zone consists of a single, known, enclosed sulphide lens within structurally complex phyllite, argillite and minor chert of the Gambier Group. Exposed mineralization is confined to a variably sheared and silicified bedding plane dipping 70 to 85 degrees northeast. The sulphide lens was exposed by five trenches in 1990.
Pyrite, chalcopyrite, pyrrhotite, sphalerite and galena occur in a gangue of quartz, clay, carbonate, chlorite and rare barite. The sulphides are massive in appearance. Wallrock alteration consists of variable silicification and pyritization, extending up to 5 metres and are deeply weathered forming gossans. The sulphides have been traced for 100 metres along a strike of 120 degrees.
In 1990, weighted averages of continuous chip sampling across the sulphide lens yielded up to 1.80 per cent copper, 0.30 per cent zinc, 0.04 per cent lead and 0.58 gram per tonne gold across a true width of 1.1 metres (Assessment Report 21236). Individual samples yielded up to 7.40 per cent copper, 0.90 per cent zinc, 0.09 per cent lead and 1.83 grams per tonne gold across 0.20 metre (Assessment Report 21236). In 1991, the best weighted averages of continuous chip sampling across the sulphide lens yielded up to 3.38 per cent copper, 0.89 per cent zinc, 0.03 per cent lead and 1.51 grams per tonne gold across a true width of 1.48 metres (Assessment Report 22178). From this weighted average, sample 915731113 yielded up to 5.31 per cent copper, 1.40 per cent zinc, 0.06 per cent lead and 2.30 grams per tonne gold across 64 centimetres (Assessment Report 22178).
