138 ECONOMIC GEOLOGY OF SILVERTON QUADRANGLE, [bull. 182. 
pyrite carrying a little gold, silver, and copper. The lead may have 
originally been sparingly deposited as galena with the pj^rite. It is 
into such low-grade auriferous and argentiferous pyrite, carrying 2 or 
3 per cent of copper and containing an occasional bunch of galena, 
that the rich ore bodies passed in the Guston, National Belle, Silver 
Bell, Hudson, and Yankee Girl mines when the ore became too poor 
to work. 
Subsequently, as the surface of the region was reduced by erosion, 
descending waters, which found ready passage through the fissured 
and mineralized rocks of the region and through the upper portions of 
the lean primary ore bodies, effected a second concentration, which 
produced the rich ore formerly mined. The penetration of this water 
into the primary pyritic ore must have been aided by the porous, 
crumbling character of much of the latter. These waters are known 
to have been heavily laden with the sulphates of iron and copper and 
other salts, resulting from oxidation of the upper portions of the ore 
bodies. As these solutions penetrated downward they probably acted 
upon the low-grade pyritic ore, replacing part of the iron sulphide by 
sulphides of copper and silver. Apparently much experimental work 
remains to be done before all the details of the chemical processes 
involved will be actually known, but the probability of the transfor- 
mations outlined is shown by the following chemical equations taken 
from Van Hise's suggestive paper. 1 
By taking solutions containing merely the sulphates of copper the 
production of chalcopyrite from iron sulphides may be written as 
follows: 
Cupric sulphate -f ferrous sulphide=chalcopyrite+ferrous sulphate. 
OuS0 4 + '2 FeS = CuFeS 2 + FeS0 4 
Or, 
Cupric sulphate+ pyrite +oxygen = chalcopyrite+ferrous sulphate +sulphurous anhydride. 
CuS0 4 -f 2 FeS 2 + C) 4 = CuFeS 2 + FeS0 4 + 2 S0 3 
Bornite may be produced as follows : 
Cuprous sulphate + cupric sulphate + ferrous sulphide = bornite + ferrous sulphate. 
Cu 2 S0 4 + CuS0 4 + 3 FeS =Cu 3 FeS 3 + 2 FeS0 4 
Or, 
Cuprous sulphate + cupric sulphate + pyrite + oxygen = bornite + ferrous sulphate + 
Cu 2 S0 4 + CuS0 4 +3 FeS 2 + 6 O =Cu 3 FeS 3 + 2 FeS0 4 + 
sulphurous anhydride. 
3 SO, 
But bornite may also be formed by direct action of the copper sul- 
phates on chalcopyrite, as follows : 
Chalcopyrite +cupric sulphate + oxygen = bornite + ferrous sulphate+sulphurous anhydride. 
2 CuFeS 2 + CuS0 4 + 2 = Cu 3 FeS 3 + FeS0 4 + S0 2 
'Some principles controlling the deposition of ores: Trans. Am. Inst. Min. Eng., Vol. XXX, 
1900, pp. 111-112. 
