The Rainy Day claim is underlain by a small mass of quartz diorite of the Middle Eocene Rainy Day pluton. It is named after the Crown-granted claim which covers the central part of the pluton. The pluton is in contact with Lower Jurassic Elise Formation (Rossland Group) hornfels, banded hornfels and siltstone and is intruded on the west by syenite and monzonite of the Middle Eocene Coryell Intru- sions. In 1983, a sample of the Rainy Day quartz diorite gave a potassium-argon age of 49.6 plus or minus 1.5 million years (Bulletin 74). The intrusive margins of the stock are sharp and irregular and underground mapping from the Le Roi mine (082FSW093) workings suggest the pluton may be tabular with a low to moderate dip.

Surface exposures are of light grey porphyritic and non-porphyritic quartz diorite. The non-porphyritic facies forms the central core and the porphyritic facies the marginal zone; both are truncated to the west by the Coryell syenite. The porphyritic, and to a lesser extent, the non-porphyritic quartz diorite are highly fractured with a network of intersecting veinlets containing fine-grained pyroxene, quartz, hornblende, biotite, chlorite, carbonates and sulphides com- prised mainly of pyrite and molybdenite. Accessory minerals are apatite, sphene, magnetite and zircon. Narrow pyroxene-quartz vein- lets host molybdenite and pyrrhotite.