Sphalerite and galena solubilities have been determined in NaCl-rich (1-3 m) acidic solutions at temperatures up to 95 degrees C under H 2 S saturation. The solubility (moles/Kg H 2 O) of sphalerite over this range of conditions is consistently greater than that of galena by factors of 40 to 80. Some representative solubilities at pH 2, based on the best fit solubility isotherms, are: 1 m NaCl, 80 degrees C: [Zn] = 10 (super -4 51) , [Pb] = 10 (super -6 51) ; 3 m NaCl, 80 degrees C: [Zn] = 10 (super -3 28) , [Pb] = 10 (super -4 92) ; 3 m NaCl, 95 degrees C: [Zn] = 10 (super -2 12) , [Pb] = 10 (super -3 76) .The experimental results are compared with solubilities calculated using thermodynamic data and are found to agree quite well for sphalerite. Calculations for galena agree well at 1 m NaCl but give high results at 3 m NaCl. Galena and sphalerite stoichiometric solubilities were calculated for 3 m NaCl solutions up to 150 degrees C, i.e., over the range of temperatures of Mississippi Valley-type ore deposits. They indicate that if chloride complexes are the dominant form of Pb and Zn in ore-forming solutions, it is unlikely that 3 m NaCl solutions below 150 degrees C could carry sufficient quantities of metal(s) and reduced sulfur to form an ore deposit.

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