The Otto vein strikes northeasterly and dips vertically. The narrow, discontinuous vein carries scattered bunches of argentiferous galena in a quartz gangue. Hostrocks belong to the Middle Aldridge Formation of the Middle Proterozoic Purcell Supergroup, intruded by gabbro sills of the Moyie intrusions (also of Middle Proterozoic age). The sedimentary rocks are described as quartzofeldspathic and quartz wacke with lesser argillite, mainly turbidites, by Brown and Stinson (Fieldwork 1994, page 115). Regional strike is 010 degrees with dips from 30 to 80 degrees west.