THE DEPOSITION OF COPPER BY SOLUTIONS OF 

 FERROUS SALTS 



INTRODUCTORY 



The genesis of the great deposits of native copper is a sub- 

 ject which has invited considerable speculation. From its occur- 

 rence in the cupriferous conglomerates and sandstones as a 

 cement, or replacer, of the constituent grains, the copper is 

 plainly of secondary origin. Its position here indicates that it 

 resulted as a deposition from aqueous solution.^ The metal, 

 doubtless, first dissolved as sulphate, an oxidation-product of an 

 original sulphide. Under the influence of solutions of calcium 

 bicarbonate, or alkaline silicates, the sulphate was speedily con- 

 verted into the carbonate, or silicate.^ From solutions of one, 

 or both, of these latter salts were probably derived the several 

 classes of copper deposits. 



In its paragenetic relations the position of the metallic copper 

 indicates, as Pumpelly shows, that it was deposited after the forma- 

 tion of the non-alkaline silicates and before that of the alkaline 

 silicates. As is further pointed out by the same writer, there is 

 an intimate connection between the native copper and such iron- 

 bearing minerals as delessite, epidote, and the green earth 

 silicates. So constant is their common occurrence that he is 

 led irresistibly to the conclusion that there is a close genetic 

 relation between the reduced copper and the ferric oxide con- 

 tained in the associated minerals ; that, indeed, the reduction of 

 the copper oxide to metallic copper was produced by the oxida- 

 tion of ferrous derivatives. Later Irving, in support of the same 

 view, called attention to the fact that many particles of copper 

 enclosed a central core of magnetite. ^ 



' R. D. Irving: Mon. U. S. Geol. Surv., No. 5 (1883), p. 420. 

 'Raphael Pumpelly: Am. Jour. Sci., Vol. II (1871), p. 353. 

 3 Mon. U. S. Geol. Surv., loc. cit. 



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