Most of the rocks are of Archean age and consist of volcanic-sedimentary complexes containing abundant intrusive rocks of ultrabasic to acidic types. Almost all rock types contain some economic or potentially economic mineral deposits.

Base metal deposits, mainly massive sulphides, generally occur at contacts within a particular group of lavas. The rocks beneath the sulphide deposits are rhyolite breccia in most areas and are overlain by andesite or porphyritic rhyodacite. The sulphides and the enclosing rocks appear to exhibit a close relationship in time and space.

Ore bodies containing gold are related to dioritic and granitic intrusive rocks. The loci of deposition tend to be near the contacts of major groups of sedimentary and

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volcanic rocks. Economic deposits are within the competent members of any rock type.

Nickel-bearing sulphides are directly related to ultrabasic and basic intrusive rocks. The sulphide deposits occur at the bottom of sills or in structural traps in the underlying rocks.

Molybdenum, bismuth, and lithium mineralization is spatially related to late granites. Iron formations containing magnetite have potential economic value and are stratiform, sedimentary deposits.

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