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Banded iron formation (BIF) is the most commonly mined source of iron ore, but the details of its genesis are poorly defined. Algoma-Type BIF is a predominantly chemical sedimentary rock comprising iron-rich phases (hematite, magnetite, chlorite) and chert as distinct laminae associated with deep marine lithologies, especially volcanic rocks and black shales. The iron minerals are thought to be direct chemical precipitates from Fe-enriched bottom waters or formation waters, most probably related to proximal volcanic activity. Key questions examined in this study are the paragenetic relationships and origins of mineralogically distinct layers in the Temagami BIF and the possible mechanism of replacement of primary hematitic layers by magnetite. The latter is a fundamental process in generating ore-grade BIF. The mineralogical and geochemical fingerprints of the different components of the BIF are also examined as clues to their likely sources (i.e., from upflowing hydrothermal fluids, contemporaneous volcaniclastic material, or precipitation from the local bottom water). Field observations indicate three separate depositional horizons for BIF in the area and exclude previous suggestions of fold repetition. Documented relationships between different types of layers and different facies of BIF in outcrop and in samples of the ore material, including petrographic features and aspects of the mineral chemistry and whole rock geochemistry, were used to construct a detailed paragenesis of the Temagami BIF. Two paragenetically distinct types of hematite and three types of magnetite are distinguished by different habits, grain size, cross-cutting relationships and growth features. Whole rock geochemical data confirm that the different facies of BIF were mainly products of redox-driven precipitation, combined with local hydrothermal and clastic input.