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The early Precambrian rock sequences at both localities consist of three major types, metabasalt, acidic welded tuff, and sediments. At Red Lake the Keewatin sediments are graywacke and argillite with conglomerate beds high in the sequence. In the Porcupine area the Keewatin sediments are mainly argillite which is unconformably overlain by Timiskaming conglomerate, graywacke, quartzite and argillite. The intrusive rock suites are also generally similar and range in composition from early basic and ultrabasic rock to later intermediate and acid rocks.
New information has been added on the type, thickness, persistence and relative ages of the major units of country rocks. Similar rock types in a similar sequence indicate a rhythmic volcanic-sedimentary cycle.
Known copper mineralization of economic grade is restricted to the Pearl Lake porphyry in the Porcupine area. Gold orebodies occur in a variety of rock types but some particular types are restricted to individual beds.
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