Frank, Mark R.
M.S. (Master of Science)
Department of Geology and Environmental Geosciences
Lead and zinc mineralization has been documented in low-temperature Mississippi Valley Type (MVT) deposits and high-temperature porphyry systems. These deposits are characterized by the presence of galena (PbS) and sphalerite (ZnS) that formed from a salt-bearing hydrothermal fluid. The lead and zinc are most likely transported as PbCl₂ and ZnCl₂ before precipitating as galena and sphalerite through a decrease in temperature, an increase in pH, or the addition of reduced sulfur. The HCl concentration (pH) of the hydrothermal fluid plays a major role in the concentration of lead and zinc carried in the fluid; however, there are few data detailing the solubility of galena and zinc in acidic hydrothermal fluids at temperatures applicable to MVT and porphyry systems. Experiments were conducted in Rene 41 cold-seal pressure vessels from 200 to 500°C and 100 MPa to determine the concentrations of lead and zinc in hydrothermal fluids as a function of HCl. Platinum capsules were loaded with natural galena and sphalerite and an aqueous fluid of 13 to 15 wt.% NaCleq. containing HCl + NaCl + H₂O. The aqueous fluids were captured at the conclusion of the experiment and lead and zinc concentrations were determined by using AA and ICP-OES. Lead concentrations were 1.1(±0.1)x10¹ [mu]g/g (HCl = 4.68x10³ [mu]g/g), 1.6(±0.2)x10¹ (HCl = 5.35x10⁴ [mu]g/g), and 7.9(±0.5)x10³ [mu]g/g (HCl = 5.35x10⁴ [mu]g/g) at 200, 300, and 500°C, respectively. Zinc concentrations were found to be 1.3(±0.1)x10³ [mu]g/g (HCl = 9.36x10³ [mu]g/g), 2.4(±0.3)x10³ [mu]g/g (HCl = 5.35x10⁴ [mu]g/g), and 2.6(±0.3)x10³ [mu]g/g (HCl = 5.35x10⁴ [mu]g/g), respectively. The data demonstrate that the concentration of lead and zinc in the fluid increased directly with temperature and HCl concentration. Therefore, decreasing temperature and HCl (increase pH) are efficient at inducing the precipitation of galena and/or sphalerite in MVT and porphyry systems. The variable Pb:Zn ratios observed in some ore-bearing systems are possibly the result of differences in the rate of change of temperature, acidity, and/or reduced sulfur.
Rock, Marlena Joyce, "An experimental study of lead and zinc solubility in a hydrothermal fluid" (2018). Graduate Research Theses & Dissertations. 1286.
Northern Illinois University
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