The Big G occurrence is located on Greenstone Creek, approximately 4.8 kilometres south west of the creek mouth.
The area is underlain by Karmutsen Formation volcanics overlain by Quatsino Formation limestone, both of the Upper Triassic Vancouver Group. These in turn are overlain by volcanic flows and breccias of the Lower Jurassic Bonanza Group. Intruding the stratigraphy are plutonic rocks of the Lower to Middle Jurassic Island Plutonic Suite. These plutonic rocks on Vancouver Island vary in composition from gabbro to quartz monzonite but are mainly granodiorite and quartz diorite.
The volcanics, probably Karmutsen, consist of a dark green, amygdaloidal, basic volcanic flow overlain by tuffaceous andesitic rock, the contact dipping gently to the north. The tuffs contain several bands of limestone and limy argillaceous beds in which most of the economic mineralization occurs. These rocks are all cut by mafic porphyry dykes. Intrusive rocks are not found at the showing but a dioritic belt does occur to the east of the showing.
The main skarn showing seems to form a lens or lens-like body about 3 metres thick and 46 metres long, dipping about 20 degrees to the north. Minerals present in the skarn include fibrous greenish amphiboles, garnet, possibly vesuvianite, calcite, chlorite, magnetite, pyrrhotite, pyrite, chalcopyrite, and minor sphalerite. The magnetite and pyrrhotite are massive and most abundant. The chalcopyrite is more erratic and patchy but, at one location, does occur massively, over a width of 30 centimetres.
In 1965, sixteen samples taken along a 45 metres strike length of the main showing yielded from 0.15 to 4.6 per cent copper with an average of 1.18 per cent copper (Assessment Report 699). In 1996, sampling of a mineralized vein exposed in an adit assayed 2.53 per cent copper, 4.0 grams per tonne silver, 0.160 grams per tonne gold, 0.046 per cent cobalt, 0.047 per cent cadmium and greater than 5.0 per cent zinc over 0.6 metre (Assessment Report 24571). In 1998, sampling of the No.2 adit yielded values up to 6.17 per cent copper, 17.8 grams per tonne silver and 0.969 per cent zinc (Sample A7; Assessment Report 25809).
The mine workings are on the north side of a deep precipitous canyon, through which Greenstone Creek flows, and about 30 metres above the river bed. As of 1916, the workings consisted of several large open cuts and two adits, the latter 18 and 9 metres in length. In 1917, 83 tonnes of ore was mined from which 14,018 kilograms of copper, 4,074 grams of silver and 31 grams of gold were produced (Mineral Policy data).
The South Side showing is located on the south side of Greenstone Creek across from the main workings. Locally, disseminated chalcopyrite is hosted by a volcanic breccia. In 1998, grab sampling yielding up to 10.0 grams per tonne silver and 0.818 per cent copper ; previous sampling of the zone has reportedly yielded up to 1.0 per cent copper (Assessment Report 25809).
The Canyon showing is located approximately 100 metres down stream of the main workings and consists of chalcopyrite filling fractures in a porphyritic basalt.
In 1965, Gunnex Limited completed a program of geochemical sampling, geological mapping and ground magnetic and electromagnetic surveys on the area as the M and Thelma claims. In 1969, Georgia Mines completed an airborne magnetic survey on the area. This work identified four areas of anomalously high response and three areas of anomalously low response to the north of the former workings (Assessment Report 2507). In 1996 and 1998, A. Doiron completed programs of geological mapping and rock and soil sampling on the area as the Allana claims.
