Abstract The Larder Lake-Cadillac Break is a gold metallotect, which extends for more than 250 km from Matachewan in Ontario to Val-d’Or in Quebec. For much of its length it juxtaposes older komatiitic rocks against younger sedimentary units. Among the adjacent sedimentary rocks are distinctive intervals of polymict conglomerate and crossbedded sandstone, which make up part of the Timiskaming Group that unconformably overlies previously folded volcanic strata. Rocks in the vicinity of the break are commonly strongly carbonatized, with the type and abundance of carbonate minerals being controlled largely by protolith composition. Shoshonitic to alkalic igneous rocks occur along the break as volcanic units within the Timiskaming, as plutonic rocks in syn-Timiskaming stocks and plugs, and as local arrays of albitite dikes of intermediate composition. High-strain dislocative deformation is variably developed along the break but its intensity is in part a reflection of metasomatic phyllosilicates in the affected rocks. Gold deposits tend to form clusters along the break and their relationship to it is two-fold: a subset of geologically similar deposits are localized in direct proximity to the break but the majority of gold in the region is found in diverse settings away from it with no clear genetic connection.