Abstract
Abstract Iron‐formation and associated chert and jasper are subordinate to, but commonly intercalated within the upper, dominantly terriginous clastic sequences in the early Archaean Barberton Mountain Land (South Africa) and Pilbara Block (Western Australia). The iron‐formation, jaspillite and chert are exclusively lutitic and occur in a variety of palaeoenvironmental settings, namely: (1) at the base of prograda‐tional submarine fan sequences; (2) within interchannel mudstones enclosing inner and mid‐fan channel deposits; (3) capping Bouma turbidite beds; (4) intercalated within outer‐fan to basin‐plain mudstones; (5) at the base of progradational offshore shelf‐beach sequences; and (6) in lacustrine deposits intercalated within thick, braided, alluvial sequences. These associations suggest that the iron‐formations and associated orthochemical sediments define diastems and that precipitation took place in any environments basinwards of or between events of terrigenous influx. Recognition of such diverse environments of deposition places constraints on existing models for the origin of iron‐formations. Insofar as being removed from terrigenous dilution at the time of accumulation, any of the iron‐formations, cherts or jaspilites are potential precious and base‐metal targets.
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