Sedimentary and igneous rocks of several ages are represented in the Dundas area.
The oldest rocks are represented by Proterozoic schists. Next is a series of grey and black slates, sandstones and conglomerates. The ore-bodies occur in these sediments. The upper part of the Cambrian is represented by the Dundas series. The youngest rocks in the district are represented by intrusive sills and dykes of Jurassic dolerite ( diabase).
Dundas Series
This series consists of tuffs, breccias and lavas, slates and conglomerates. There was a cycle of vulcanism, in which tuffs, pyroclastics and lavas were poured into a sedimentary basin, followed by periods of normal sedimentation.
During the Cambrian a long period of quiescence of vulcanism is represented by thick fossiliferous slate formations. Inter-bedded in this are numerous layers of tuff, indicating that vulcanism still persisted.
During the late Cambrian this succession was intruded by the olivine rich rock, peridotite.
During the Devonian mountain building phase, these rocks were folded and intensely faulted and sheared, allowing channels for mineralizing fluids to penetrate. Hydrothermal activity associated with the intrusive dolerites is responsible for the deep weathering of the serpentine.
Red Lead Mine
The surface gossans at the Red Lead Mine lie on the contact of the serpentinites with the Dundas series rocks. Beds of conglomerate are evident in the creek bed running through the lease, while slates and tuffs are evident in various parts of the open cut. It appears that the rocks are altered to a great depth, perhaps over 150 metres from the top of the mine.