Hydrothermal discharge on the seafloor results in significant accumulation of base- and precious-metal-rich sulfide material. Technological advances as well as elevated metal prices have led to a growing interest in the direct mining of these deposits from the modern ocean floor. The research presented in this thesis details an investigation of the size, grades, distribution, and accumulation rates of these deposits on the seafloor. A three-part resource assessment, originally designed for land-based ore deposits, was used to generate a predictive framework for the global seafloor sulfide resource. Using detailed descriptions of sizes, grades and locations for 92 known deposits, a resource estimate was generated that predicts a total of ~1,000 deposits and a total global abundance of 600 Mt of sulfide within the neovolcanic zones of the modern ocean floor. A detailed study of the hydrothermal sulfide deposits along the Endeavour Segment of the Juan de Fuca Ridge was carried out to investigate the processes of sulfide accumulation at the ridge-segment scale. Results of 226Ra/Ba dating of barite within the deposits indicate that hydrothermal activity has been ongoing for ~6,000 years and venting has been continuous at the Main Endeavour and High Rise vent fields for ~2,300 and 850 years, respectively. Abundant older sulfide samples from inactive sites outside of the main vent fields indicate a complex history of venting along the ridge segment. Analysis of high-resolution bathymetry of the Endeavour Segment, generated from eight autonomous underwater vehicle surveys, revealed the location of 581 individual hydrothermal sulfide edifices along 15 km of ridge length. Using GIS-based software, the volume of each edifice was calculated, and the total amount of sulfide at Endeavour is estimated to be 1.2 Mt. This estimate is the first comprehensive resource evaluation on the seafloor at this scale. Sulfide has been accumulating within the Endeavour axial valley at a rate of ~400 tonnes per year, which is similar to estimates for the TAG deposit on the Mid-Atlantic Ridge. Using endmember hydrothermal fluid chemistry data and estimates of fluid discharge rates, the mass accumulation rate calculated for Endeavour corresponds to a sulfide depositional efficiency of 6%.

A thesis project report submitted in partial fulfillment of the requirements for the degree Master of Fine Arts in Art.

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The reaction of monohalonaphthalenes with metal alkoxides and mercaptides in a solvent mixture of the corresponding alcohol and dimethyl sulfoxide (DMSO) has been studied. These reactions are convenient methods for the preparation of alkylnaphthyl ethers and sulfides. Only direct nucleophilic substitution was observed in the reactions of bromonaphthalenes with sodium methoxide and sodium nbutyl mercaptide. The reaction of fluoronaphthalene with potassium t-butoxide also proceeded by way of direct nucleophilic substitution rather than the 1,2-dehydronaphthalene intermediate as in the reactions of bromonaphthalene with potassium t-butoxide. The use of a base which is weaker than t-butoxide can change the apparent reaction mechanism from the dehydronaphthalene to direct nucleophilic substitution.

Because present data on free energy of formation and solubility product constants of the metal sulfides are both inconsistent and based on very old experimental data, a new study using modern techniques is amply justified. Because metal sulfide precipitates are often colloidal and becasue the solubility of these sulfides is so low, ordinary physical and analytical methods are not applicable to a direct determination fo the solubility product constant. Therefore, a more reliable thermodynamic approach was undertaken in this study. The standard free energy of formation of silver and mercury sulfide was determined from electromotive force measurements of suitable galvanic cells, and the solubility product constants calculated from the free energy measurements. This study is part of a large program extending to other metal sulfides and to other thermodynamic properties.

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E_h-pH diagrams were constructed from mass-balanced, computer calculations for the copper-sulfur-water system involving different Cu/S ratios that pertain to chalcocite, djurleite, anilite and covellite. Calculations were completed for cases where oxidation of the sulfur proceeded to i) elemental sulfur, ii) thiosulfate, iii) sulfate and iv) destabilized sulfate. Stability regions for each copper sulfide were shown to be dependent on both the Cu/S ratio in the system and the sulfur oxidation state. E_h-pH diagrams were also constructed for chalcocite oxidation to metastable copper sulfides, both with and without xanthate. Stability regions for copper xanthates were also shown to be dependent on the sulfur oxidation state. As oxidation proceeded from elemental sulfur to sulfate, the copper xanthate stability region extended to lower potentials, directly dependent on the sulfide ion concentration. IGP experiments at pH 1.1 suggested that chalcocite oxidation produced metastable nonstoichiometric copper sulfides while cyclic voltammetry indicated they formed at pH 1.1, 4.6, 6.8 and 9.2. XPS implied that copper sulfides may be solid solutions of chalcocite with variable amounts of copper disulfide: CU₂S·xCUS₂. The presence of djurleite in the chalcocite samples was confirmed by X-ray diffraction and may be responsible for the reduction reaction which occurred just prior to the reduction of chalcocite to metallic copper. Reinterpreting cyclic voltammograms from a previous study indicated chalcocite reacted with xanthate to form cuprous xanthate and a nonstoichiometric copper sulfide near 0 mV. Chemisorbed xanthate formed at -295 mV which correlated well with the lower flotation edge determined in this and other studies. The standard free energy of the chemisorbed xanthate was determined to be -13.08 kcal/mole. / Master of Science