The Biddy occurrence is located near the headwaters of Big Creek, approximately 7 kilometres north-northeast of Nina Lake and approximately 3 kilometres south-southwest of Razorback Mountain. It lies within 1 kilometre to the west of the Otter Lakes, near an old exploration gravel road that connects to the Germansen Landing road south of Nina Lake.
Regionally, the general area is divided by a major, layer parallel, thrust fault that separates para-autochthonous North American rocks of the Cassiar Terrane from rocks belonging to the Intermontane Superterrane represented by the Slide Mountain and Quesnel terranes (Ferri and Melville, in prep). This fault boundary roughly corresponds to the Omineca-Intermontane belts boundary. This regional stratigraphy forms part of a southwest-dipping homoclinal sequence that is cut by a series of northwest-striking normal faults to the north of the Biddy occurrence and northeast-striking normal faults to the south. With the exception of the easternmost portions of the pericratonic strata, all other rocks have been weakly metamorphosed up to chlorite grade (Ferri and Melville, in prep. and Exploration in British Columbia 1989, pages 193-196).
The Cassiar Terrane is represented by a Proterozoic to Mississippian carbonate and siliciclastic miogeoclinal wedge. These sequences of miogeoclinal rocks include the Proterozoic Ingenika Group, the Lower Cambrian Atan Group, the Cambrian (?) to Ordovician Razorback Mountain Group, the Silurian to Lower Devonian Echo Lake Group, the Middle Devonian Otter Lakes Group, the Upper (?) Devonian to Mississippian Big Creek Group and the Mississippian to Permian Cooper Ridge Group (Ferri and Melville, in prep.).
The Slide Mountain Terrane is represented by Upper Paleozoic oceanic rocks of the Nina Creek Group. The Pennsylvanian to Permian Nina Creek Group consists of a lower argillite-dominated sedimentary package and an upper pillowed to massive basalt-dominated sequence. Rocks belonging to the Quesnel Terrane lie to the west of the Nina Creek Group, across the Manson fault zone, and are represented by the Middle Triassic to Lower Jurassic Takla Group.
The Biddy occurrence is hosted within the Middle Devonian Otter Lakes Group and the Silurian to Lower Devonian Echo Lake Group. The Otter Lakes Group is characterized by approximately 150 to 200 metres of grey to black limestones and dolostones that are direct correlatives of the carbonates of the McDame Group in the Cassiar area (Ferri and Melville, in prep.). The Echo Lake Group is a thick succession of approximately 100 metres of limestone, dolomite, sandy dolomite and minor quartzite. It is divided into two units with the lower unit consisting primarily of carbonate and the upper unit, sandy dolomites and quartzites. Overlying these two groups is the Upper (?) Devonian to Lower Mississippian Big Creek Group that is approximately a 500 metre thick succession of blue-grey to dark grey shales, argillites and minor sandstones.
Mineralization is stratabound within a stratigraphic interval from the Otter Lakes-Big Creek contact downwards to the uppermost sandy dolomites of the Echo Lake Group. The sulphides occur as semimassive irregular-shaped pods in solution breccias (dolomitic breccias), as massive sulphides in localized shear zones and as disseminated blebs in arenaceous dolomites. Where brecciated, the mineralization is found towards the top of the Otter Lakes Group, near the Big Creek shale contact. The sulphides within the breccias may replace clasts, matrix or a combination of both suggesting multiphase fluid influx and deposition (Exploration in British Columbia 1989, pages 193-196). Mineralization consists of sphalerite and galena with associated barite and minor pyrite. Lead-lead dates from the galena have a Cambrian shale curve model age (Ferri and Melville, in prep.). The sphalerite is on average 0.05 per cent germanium (Assessment Report 16946). A grab sample from this occurrence analysed 4.11 per cent zinc, 28 grams per tonne silver and 0.120 per cent germanium (Exploration in British Columbia 1989, page 195). One of the best drillhole intersections analysed 1.3 per cent zinc and 1 per cent lead over a 2-metre interval (Assessment Report 20492).