528 brown. SEDIMENTARY HOSTS FOR ORE DEPOSITS [Ch. 29 



vein structures and values over a good vertical extent. Some examples 

 of the two classes are listed below. It will be noted that the veins 



Veins Generally Across Bedding Veins More or Less Along Bedding 



Kentucky-Illinois, fluorspar Coeur d'Alene, lead-zinc-silver veins, 

 S.E. Ontario, post-Cambrian lead-zinc Idaho 



veins Mother Lode gold veins, California 



Park City, Utah, in Weber quartzite Homestake gold veins, South Dakota 



Cobalt, Ontario, silver veins Southern Appalachian gold veins, in 

 Barite and fluorite veins of England part 



Chanarcillo silver, Chile Spanish lead veins (Linares) 



along bedding are generally of a deeper-seated type than those formed 

 across bedding and are apt to combine features of both fissure filling 

 and replacement in varying degrees. 



There seem to be no good general references on the subject of the 

 contrasts between veins in sedimentary rocks and other types, a topic 

 that might be worthy of summation. Much detail will be found in the 

 literature of individual districts where both types are present, particu- 

 larly in the western United States and Canada. 



REPLACEMENT DEPOSITS 



General Survey 



From the standpoint of number, importance, and scientific problems 

 presented, the replacement deposits are the chief focus of our atten- 

 tion. Replacement of sedimentary rocks or of sedimentary rocks that 

 subsequently have been metamorphosed is found in many mining dis- 

 tricts. A similarly important group of replacement deposits, however, 

 shows little or no relation to sedimentary rocks. Well-known repre- 

 sentatives of each group are listed below. An inspection of this rather 

 impressive list of deposits in sedimentary rocks makes it apparent at 

 once that it includes a large proportion of the world's great lead-zinc 

 districts. There are a few clear exceptions such as the Buchans mine 

 and Bawdwin in igneous rock. Some districts, such as the Coeur 

 d'Alenes district, are hard to classify. In the Coeur d'Alenes area 

 sedimentary rocks have been cut by fissure veins, though in places they 

 have been replaced, chiefly however as a result of previous vein filling. 

 The Linares district of Spain is somewhat similar. The Tennessee- 

 Virginia zinc deposits may be questionable in that they involve prob- 

 ably more filling of breccia spaces than actual replacement, but they 

 are commonly accepted as replacements. The Joplin district, likewise, 



