spencer: chalcocite deposition 73 



CU2S + 2Fe(S04)3 = 4FeS04 +S+ 2CUSO4 



Group in. Intermediate equations and final equation indi- 

 cating the last stage of pyrite oxidation where cupric sulfate is 

 the reagent, and chalcocite a side product : 



2FeS.2 + 2CUSO4 = CU2S + 2FeS04 + 3S (9) 



3S + 2CUSO4 = Cu^S + 4SOo (10) 



5SOo + 6H0O + 2CUSO4 = CU2S + 6H0SO4 (11) 



5FeSo + I4CUSO4 + I2H0O = TCu.S + 5FeS04 + I2H2SO4 (12)^ 



Equations analogous to (12) but involving chalcopyrite and 

 sphalerite in place of pyrite are the following: 



SCuFeS. + IICUSO4 + 8H2O =8Cu2S + 5FeS04 + 8H2SO4 (13) 

 5ZnS + 8CUSO4 + 4H2O = 4CU2S + 5ZnS04 + 4H2SO4 (14) 



Here, in the interest of completeness, may be introduced the 

 Stokes equation representing the change pyrite to covellite, and 

 the analogous equation involving chalcopyrite: 



4FeS2 + 7CUSO4 + 4H2O = 7CuS + 4FeS04 + 4H2SO4 (15) « 

 CuFeS2 + CUSO4 = 2CuS + FeS04 (16) 



It is to be noted that equation (5) which is given by Stokes^" 

 is stated by him to conform with the observation that on expo- 

 sure to the air, pyrite yields free sulfur which may be detected 

 by extraction with ether. Also equation (6) conforms with the 

 results of experimental oxidation of pyrite by H, N. WinchelP^ 

 and is in accord with observation as recorded by Gottschalk and 

 Buehler.i2 



Of the expressions under Group III, equations (9) and (10) are 

 seen to be analogous to equations (5) and (6), and if the latter 

 are real it may be thought likely that the former are. In any 

 event it is almost obvious that equations (9) to (11) were used 



* Derived from the foregoing equations. This expression, which is to be cred- 

 ited to Stokes, was first printed in the work of Lindgren already cited (p. 183.) 

 where the reader is led to infer that the equation was tested by quantitative de- 

 termination of the H2SO4 formed. See also Stokes, Economic Geology, 2: 22, 

 1907. 



9 Stokes, H. N., loc. cit. 



10 U. S. Geol. Survey Bull. 186, pp. 15 and 19, 1901. 



11 Loc. cit. 



12 Economic Geology 7: 16, 1912. 



