SOME ASPECTS OF THE PHYSICAL CHEMISTRY OF HYDROTHERMAL ORE-FORMING SOLUTIONS (DEPOSITS, SOLUBILITIES, STABILITY CONSTANTS, ACTIVITY COEFFICIENTS)

This thesis is comprised of four individual, yet related studies of the thermodynamics and chemistry of hydrothermal solutions as applied to ore deposits. In the central study I measured the solubility of the assemblage pyrite-pyrrhotite-magnetite-galena-sphalerite-stibnite-argentite-bismuthinite-molybdenite-gold in H(,2)O-NaCl-CO(,2) solutions from 200(DEGREES) to 350(DEGREES)C. Fe, Zn, Pb, Au, and Ag all form chloride complexes in these solutions, but Sb and Mo appear to be unique. The exact identity of the Sb and Mo species in hydrothermal solution is uncertain. However, it is suggested that Sb forms bisulfide- and hydroxy-complexes while Mo exists as an oxyacid. For the chloro-complexes, metal valences, ligation numbers and equilibrium constants were derived.; In order to quantitatively analyze the results of the above experiment, the activity coefficients of NaCl were required. This led to the measurement of the vapor pressures of NaCl solutions at 325(DEGREES) and 350(DEGREES) and of KCl and CaCl(,2) solutions at 200-350(DEGREES)C from which osmotic and activity coefficients were derived using both the Lietzke-Stoughton and the Pitzer formulations. A critical evaluation of vapor pressure data in the literature above 200(DEGREES)C was undertaken for related electrolytes and a model for non-ideal electrolyte behavior was developed.; To extend the solubility measurements to higher temperatures, a new autoclave was designed and tested. This autoclave, made of Hastelloy C and Incoloy 901 alloys and lined with titanium, is capable of external sampling at up to 550(DEGREES)C and 2 KB. It is based on the Barnes-type pressure vessel and is sealed with a simple ring gasket. The internal volume of the autoclave is 140 ml (approximately).; Finally, the Joule-Thompson coefficient for NaCl-CO(,2)-H(,2)O solutions was calculated at a variety of temperatures (50-500(DEGREES)C) and pressures (sat. to 2 KB). Instead of cooling upon throttling, a salt-rich aqueous fluid at 150(DEGREES)C may heat up on the order of tens of degrees. This phenomenon may help explain the origin of Mississippi-Valley-Type ore deposits.