Ragi Ramesh HBSc Thesis Abstract

Archean precipitates such as crystal fans can be used to investigate the difference between Archean ocean and modern-day seawater chemistry. The globose radiating masses of crystal fans in the Hogarth Member of Steep Rock, the crystal fan fabric in the Elbow Point member of Steep Rock, and the vertically stacked acicular crystal fans from Red Lake carbonates were included in this study. These vertical crystals which grew off the substrates precipitating from anoxic Archean seawater are suggested to be primarily aragonite or gypsum. By analyzing Sr and Ba in the Steep Rock and Red Lake samples and comparing them with gathered literature data of old and modern-day carbonates, the primary mineralogy of these crystal fans is investigated. Sr and Ba show preferential substitution in aragonite, calcite and dolomite with high preservation of Sr concentrations in aragonite. Steep Rock fans have significantly higher Sr concentrations relative to older and dolomitized Red Lake fans representing tidal flats, while the Red Lake atikokania showed a relatively higher Sr value representative of deeper waters. Dolomite samples from both study areas showed a notable distinction in their Sr value from calcite samples. However, Sr concentrations for Steep Rock and Red Lake are significantly lower when compared to modern aragonites. This result concurs with the Sr loss that happens during recrystallization over time, i.e., as the mineral transforms from aragonite to calcite to dolomite. The primary mineralogy of these crystal fans is inconclusive due to this significant Sr loss, however, it is most likely that they were carbonates than gypsum or anhydrite.