The geology and origin of the Precambrian Goe Range iron formation and associated metasediments

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Abstract
The Goe Range area comprises two rock units — a mainly syenite-banded gneiss complex with amphibolite intercalations and a metasedimentary Goe Range Series, consisting of para-gneisses and para-amphibolites, argillaceous schists, metacherts and iron formation. Upper amphibolite-lower granulite facies-metamorphic conditions prevail in the syenite gneiss complex, while epidote-amphibolite-amphibolite conditions prevail in the Goe Range Series. The area was most recently recrystallized during the Pan-African thermotectonic event (550± m.y.). However, metasediments were most probably deposited prior to the Liberian thermo-tectonic event (±2700 m.y.). The upper segment of the Goe Range Series consists of argillaceous schists, metacherts, and iron formation. Within the iron formation, aluminum and phosphorus have coincidental variation. The iron formation and the metacherts originate as chemical sediments, which are products of deep chemical weathering of the adjacent landmass. Iron formations are deposited when the landmass is characterized by swampy and poorly drained conditions, resulting in kaolinitic rather than a bauxitic or lateritic residuum. Cherts are deposited when the weathered profiles are uplifted, with resulting complete leaching of silica and hence lateritization. Iron is leached due to either a CO2-rich or reducing atmosphere.