Abstract

Calculations and experiments have been performed to delineate the natural conditions under which native gold can be dissolved as the auric chloride complex. It is shown that above (i.e., at higher Eh or Cl (super -) ) the line Eh = 0.90 -- 0.08 log(Cl (super -) ) the solubility of gold theoretically exceeds 10 (super -5) moles/liter, or 2 ppm; it is dissolved as the auric chloride complex, AuCl 4 (super -) . Only part of the region above this line lies below the upper stability limit for water.Experiments produced clear etching on smooth gold plates. A solution, 1 N in H 2 SO 4 and 0.1 M in NaCl, was passed over crushed pyrolusite and a gold plate; this dissolved 0.8 mg of gold in 51 ml of solution in one week. Another portion of this solution, in passing over crushed goethite and gold dissolved 0.2 mg in 209 ml in ten days.Comparison of the experimental conditions with natural environments indicates that this mode of transport is to be expected in some, but not all, oxidizing ore bodies.This study was intended only to delineate more precisely the limits of gold solubility under inorganic conditions. No attempt is made to assess the importance of organic compounds.

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