THE SOLUTION OF GOLD IN THE SURFACE ALTERA- 

 TIONS OF ORE BODIES 



ALBERT D. BROKAW 



The leaching of gold from the outcrop of auriferous lodes has 

 been the subject of much discussion, and many contradictory state- 

 ments regarding the chemistry involved have arisen in the literature. 

 Frequently these statements are based on experimental evidence, 

 and the contradictions may be explained, in part at least, by a 

 lack of uniformity in the conditions under which the experiments 

 were carried out, and a tendency to ignore the conditions of tempera- 

 ture and concentration of solution that we are justified in supposing 

 to be operative in the surface alteration of such deposits. 



Clarke' has summarized the natural solvents for gold as reported 

 by various observers. Their experiments, however, have been made 

 under such a diversity of conditions that the results are not an ade- 

 quate basis for comparisons, and it seemed desirable to ascertain 

 where the emphasis should be placed in discussing this phase of the 

 natural solution of gold. 



At the suggestion of Professor W. H. Emmons, the writer under- 

 took a series of experiments with a view of determining which of the 

 various solvents noted are most effective in the solution of gold. By 

 limiting the problem to alteration many substances are eliminated; 

 only such as are known to occur in mine waters or in the gossan were 

 studied, and the concentrations used are comparable to those shown 

 by mine waters. The experiments were carried on at room tempera- 

 ture (i8° to 25°), as Stokes^" has shown that elevated temperatures 

 have a very marked influence on the solubility of gold in ferric salt 

 solutions. 



A few of the solvents suggested by Don, Rickard, Lenher, and 

 others were made the subject of a comparative study, the conditions 

 of temperature and concentration being practically uniform for the 



I Clarke, U.S.G.S. Bull. 330, 557. 

 a Stokes, Econ. Geol., I, 650. 



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