The Lily May mine is underlain by siltstone and hornfelsic siltstone of the Lower Jurassic Elise Formation, Rossland Group. The occurrence is located 400 metres south of the southern edge of the Early Jurassic Rossland Monzonite and lies within the zone of thermal metamorphism associated with the monzonite intrusive. The grey to black siltstone and argillite grades to hornfels. Ammonites of Early Jurassic age were reported to occur in the siltstone on Ivanhoe Ridge.

Mineralization consists of veins, crosscutting the siltstone, hosting pyrite, pyrrhotite, magnetite, chalcopyrite, sphalerite, galena and minor stibnite. The vein system is considered part of the South belt of mineralization in the Rossland Camp. The ore is composed of fine-grained, disseminated, or crudely banded, massive sulphides in a gangue consisting of thoroughly sericitized rock with carbonate and quartz. The gangue consists mainly of quartz with altered wallrock. The deposit strikes 135 degrees, dipping 85 degrees north. Minor magnetite skarns also occur.

In 1910 and 1935, a total of 37 tonnes of ore were mined from the vein system with the resulting recovery of 124 grams of gold, 18,506 grams of silver, 549 kilograms of copper, 407 kilograms of lead and 578 kilograms zinc.

At the Lily May mine, considerable galena occurs in massive form showing cleavage cubes 0.6 centimetres in diameter. The galena is argentiferous and is associated with the sphalerite, chalcopyrite, pyrrhotite and minor stibnite. Boulangerite occurs in the ore. Also, a small amount of galena occurs as narrow bands and irregular masses interstitial to bladed and tabular crystals of boulangerite.