The geochemistry of gold, arsenic, and antimony in the Carlin-type gold deposits and the mechanics of geologic fractures

Because geologic fractures often control the location and grade of an orebody, the ability to understand their occurrence and mineralogy is a significant step in assessing the economic viability of a deposit. In Part I of this dissertation, the geochemistry of gold, arsenic, and antimony in the fractured, Carlin-type gold deposits of Nevada is investigated. In Part II, a tribute to the late Dr. Neville G. W. Cook is paid with three independent geomechanics studies designed to understand the conditions leading to fracture, as well as develop methods to detect their presence.; Part I of this dissertation begins with a review of the geology and geochemistry of the Carlin-type gold deposits necessary to constrain the geochemical model developed in the study (Chapter 1). Following this introduction, the HKF equation of state is shown to inadequately describe the derivative thermodynamic properties of neutral aqueous species (Chapter 2). Despite these reservations, the HKF equation of state parameters for aqueous gold, arsenic, and antimony species are calculated in Chapter 3. Given the available geologic data for the Carlin-type gold deposits, antimony and arsenic solubility in the system are found to be controlled by their hydroxide species, and gold by its sulfide complexes (Chapter 4). These results imply that sulfidation of host rock iron is a process which could selectively precipitate gold, pyrite, and arsenian pyrite; however, phase and solubility diagrams also suggest that the oxidation state of the system is a key variable, and additional research is required.; After a brief prologue to Part II (Chapter 5), far field compressive stresses are shown to be responsible for jointing at a field site on Vancouver Island, British Columbia (Chapter 6). Despite the prevalence given to "tensile" mechanisms in the geologic literature, these are found to be secondary effects. In the next geomechanics study (Chapter 7), a method to predict the occurrence of fractures in rock using seismic amplitude measurements at various orientations to bedding is investigated. Finally, in Chapter 8, a new, nondilatational fracturing mechanism which likely contributes to sand production in oil and natural gas reservoirs is identified.