IOWA ACADEMY OF SCIENCE 



97 



The circulation of ore-matter seems to he very much more complex 

 than this and the immediate sources of the ore-materials are widely dif- 

 ferent from a mere settling down along a vein. The ordinary circula- 

 tion of metalliferous groundwaters is graphically indicated by the sub- 

 joined cut (Fig. 1). 



In the diagram the courses of the various circulations are represented 

 as merging at a single point or along a given line. The latter may be 

 an old mineral vein or it may be a recently formed fault-plane. In either 

 case the currents reach ground-water-level where their burdens of oxidic 

 ores are mainly reduced to sulphidie form, and dropped, forming the 

 bonanza zone or layer of secondary sulphide enrichment. A minor part 

 goes on downward into the profound zone. The proportions of metallic 

 substances derived from each source are not easy at this time to accur- 



