The area of the Ida May occurrence is underlain by Mississippian to Jurassic Bridge River Complex (Group) and Upper Triassic Cadwallader Group sediments and volcanics which are transected by a major north trending, steeply southwest dipping fault known as the Cadwallader break. The fault is a deep-seated crustal structure related to the Fraser fault system to the south. The fault is intruded by small granitic to ultramafic stocks and dykes. Diorite to gabbro of the Permian Bralorne Igneous Complex intrudes the Cadwallader break as an elongate body. Diorite also intrudes Pioneer Formation (Cadwallader Group) greenstones although at times the contact appears gradational. The diorite and greenstone are in turn "intruded" by sodic granite which may be an apophysis of the Cretaceous to Tertiary Bendor pluton. The sodic granite also appears gradational with the diorite and exhibits a migmatitic texture, which indicates that it may be a late differentiation of the same magma that formed the diorite. A 60-metre-wide belt of serpentinite (Bralorne Igneous Complex) borders the diorite on the southeast at the contact with the Noel Formation (Cadwallader Group). Finally, the intrusive belt is intruded by albitite dykes which often follow the chilled margin of the sodic granite and where associated with quartz veins, the dykes are altered to platy quartz-sericite schist. For details on areas geology refer to the Bralorne mine (092JNE001).

The Ida May (or Empire) vein, later known as the 51 Vein, strikes northwest and dips steeply northeast in the footwall of the Empire fault. It is irregular, commonly composed of ribboned quartz, sometimes 1 to 4 metres wide or much narrower and surrounded by one metre of sheared wall rock. Free gold is associated with arseno- pyrite and sylvanite intergrowths. Stibnite, pyrite and galena also occur, with the stibnite occurring as inclusions in calcite. Alteration is carbonaceous and hematitic. The vein cuts through soda granite and diorite, and also follows an albitite dyke which is altered to quartz sericite schist. The vein gradually decreases as it enters greenstone at the east end.

Earlier reports describe two parallel veins: an upper vein shallowly dipping with grades of 38.8 grams per tonne across 0.6 metre, and a vertically dipping lower vein grading 5.35 grams per tonne across 1 metre (Minister of Mines Annual Report 1913, page 258). The Blackbird or 55 vein is the faulted extension of the 51 Vein, occurring in the hanging wall of the Empire fault. It strikes northeast and dips steeply; the southwest end of the vein is cut off by serpentinite. The vein is well ribboned and wide, although it also occurs as a stringer in sheared diorite and along the southern side of a 38 metre wide altered albitite dyke. The western 60 metres of the vein occurs in talc rock on the edge of the serpentinite. Early production (1918-1919) on the Ida May before joining the Bralorne workings, yielded 145 tonnes of ore containing 2,353 grams of gold and 283 grams of silver.