Algoma-type banded iron formation is common in Neoarchean greenstone belts, and many of its distinctive features such as the banding of iron-rich and silica-rich material and deposition in volcanic terranes have been ascribed to their deposition related to volcanic-hydrothermal activity and cyclic variability in depositional pathways. The work presented in this thesis tests these assumptions and presents a model for the deposition and post-depositional processes now represented by the petrography and geochemistry of a 2.73 Ga type-locality of Algoma-type BIF in Temagami, ON. Adsorption of components onto the surface of Fe-oxyhydroxides forming in the anoxic Neoarchean water column is the most likely process capable of transferring silica, as well as trace quantities of transition metals, rare earth elements, Ge, P, U and other components to the sediment. The petrogenesis of the Temagami BIF lithologies suggests ongoing recrystallization processes and volume loss reactions leading to the formation of magnetite layers, while jasper is identified as the most pristine lithology best representative of the initially deposited Fe-oxyhydroxide-silica gel. Recrystallization and volume loss reactions are controlled by the ongoing dewatering during compaction and diagenesis, without the influence of external hydrothermal or metamorphic fluids. When corrected for the volume loss and small amounts of clastic contamination, little residual variability can be observed in the composition of jasper and magnetite layers, indicative of an originally homogenous primary precipitate instead of sorted and layered material deposited on the seafloor. This model is in stark contrast to previous interpretations of seasonal variability in biologic activity, cyclical seasonal or hydrothermal events responsible for primary layering in BIF. Instead, very little direct input of hydrothermal components is recorded in the chemistry of the Temagami BIF, and elements abundant in high-temperature hydrothermal fluids such as sulfur are instead sourced from atmospheric sources and deposited by bacterial pathways. Lack of primary chemical variability and non-hydrothermally sourced components captured in BIF argue against a genetic link to local hydrothermal venting, but rather an open ocean depositional setting. As such, the Temagami BIF does not represent a marker horizon related to local or regional hydrothermal venting and potential formation of associated massive sulfide deposits but reflects processes and the chemistry of the open Neoarchean ocean.

Underlying all applications of sulfur isotope analyses is our understanding of isotope systematics. This dissertation tests some fundamental assumptions and assertions, drawn from equilibrium theory and a diverse body of empirical work on biochemical kinetics, as applied to the multiple sulfur isotope systematics of microbial sulfate reduction. I take a reductionist approach, both in the questions addressed and experimental approaches employed. This allows for a mechanistic, physically consistent interpretation of geological and biological sulfur isotope records. The goal of my work here is to allow interpreters a more biologically, chemically and physically parsimonious framework to decipher the signals coded in modern and ancient sulfur isotope records. / Earth and Planetary Sciences