SECONDARY ENRICHMENT OF SILVER ORES 5 
phide, and Plattner’ obtained it by passing oxygen at 100° C— 
120° C. over the same substance. Stokes? found that the reactions 
Fe,(SO,);+2Ag=Ag,SO,+2FeSO, and 2CuSO,+2Ag=Cu,SO,+ 
Ag.SO, were reversible; silver was dissolved on heating, and 
reprecipitated on cooling. 
PREVIOUS WORK—FIELD DATA 
Field data bearing on this problem are abundant so far as the 
paragenesis is concerned but few attempts have been made to 
discuss the problems in the light of chemical principles. The most 
suggestive contribution to the literature of the subject is by Weed. 
He regards the presence of pyrite in silver lodes as prerequisite to 
the secondary enrichment of silver, and states that, in his experience, 
notable secondary enrichment has taken place only where there has 
- been pyrite in abundance; where pyrite has not occurred in con- 
siderable amount, secondary concentration has not taken place 
even though all other conditions were favorable. If this relation- 
ship is true, then the solution of primary silver sulphides in meteoric 
waters must depend either (a) on the action on the silver minerals of 
the oxidation products of the pyrite, which may form according to 
the equations FeS,+70+H,0=FeSO,+H,SO, and 2FeSO,+H,SO, 
+0O=Fe,(SO,);+H.0, or (6) on the direct oxidation of the silver 
minerals, due to the electrolytic action of the silver sulphide- 
pyrite couple, as recently described by Gottschalk and Buehler,‘ 
or (c) on a combination of these two actions. 
In addition to the work of Weed, we have the evidence afforded 
by analyses of mine waters. While the waters collected from a 
mine may differ slightly in composition from the ground-waters 
that seeped through the undisturbed deposit, in that they are 
probably more dilute on account of the freer circulation of the 
solutions, and are also more highly oxidized on account of greater 
access to the atmosphere, yet nevertheless their composition 
approaches fairly closely that of the original ground-waters. The 
following tables include most of the complete analyses that have 
t Plattner, C. F., Die Metallurgischen Rostprocesse. Freiberg, 1856. 
2 Stokes, Economic Geology, I (1906), 649. 
3 Weed, Trans. A.I.M.E., XXX, 431. 4 Op. cit. 
