Date of Award

Spring 5-15-2020

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Geosciences

First Advisor

Prof. Daniel Deocampo

Second Advisor

Prof. W. Crawford Elliott

Third Advisor

Prof. Nadine Kabengi

Abstract

Mineral reduction simulations imitating various geochemical environments were conducted over 1 – 30 hours. Ferrihydrite was prepared from solid phases using a solvent-deficient method. In each experiment, ferrihydrite was abiotically reduced with sodium dithionite solution in 1 Molar buffered Na-carbonate and Na-sulfate/sulfide brine at 70°C under nitrogen atmosphere. Six (n=6) and ten (n=10) samples of resultant sulfate/sulfide and carbonate precipitates were collected, respectively. X-Ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM) analytical methods were used to characterize the experimental products. Diagenetic siderite and goethite in carbonate simulations were identified with XRD. Siderite was observed as spherules and platy structures possibly of chukanovite. Calculations using PHREEQ software predicted siderite and pyrite forming in carbonate and sulfate/sulfide brines respectively. The expected pyrite did not precipitate. Rather magnetite, which was unexpected, was formed by either partial reduction of ferrihydrite or partial oxidation of an intermediate reduced phase such as wüstite. Understanding the diagenetic pathways and water-mineral interactions of these systems is necessary for paleoenvironmental reconstruction and for the fidelity of paleomagnetic records.

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