SOURCE OF THE METALS. 1035 



rocks, from ancient igneous rocks, from sediments, from metamorphosed 

 rocks, or from any combination of the above. When the important eco- 

 nomic districts of the world are inductively studied, and certain knowledge 

 obtained, I believe that it will be discovered that a great number, if not the 

 majority, of ore deposits are not the result of a single segregation, but are 

 the accumulated fruits of a great interrupted process of segregation, a part 

 of the metals for the deposits having been worked over many times by the 

 metamorphic processes. 



According to this view, it has been shown in Chapter XI, on the 

 redistribution of the elements, that a general result of metamorphism and 

 accompanying processes is that many of the secondary rocks are depleted 

 in reference to each metal, and that correlative with such depletion other 

 deposits are formed in which each metal is segregated. Since these 

 processes result in deposits in which each of the common metals is 

 segregated, why should we hold that the metal of a present deposit of 

 gold or silver or copper is derived solely from an immediately adjacent 

 igneous rock unless evidence for this be conclusive? The natural view is 

 that the metallic ore deposits of the world are, broadly, the accumulated 

 results of the processes of segregation carried on throughout geological 

 time. 



While it is held that the metals for very numerous and important ore 

 deposits do not have their immediate source in igneous rocks, it is recog - - 

 nized, as stated at the outset, that ultimately the metals for all ore deposits 

 are probably to be traced back to igneous rocks. Since leaving- their 

 original positions the metals for many ore deposits have been transferred 

 and segregated here and there until they reached the places where they 

 are now found. 



It is recognized that this general statement as to the sources of metals 

 for ore deposits will be unsatisfactory to many persons, as every one is more 

 or less influenced in his view by his own personal experience and by the 

 particular metals which he has studied, but it is not the purpose of this 

 chapter to consider individual districts, except as they illustrate principles. 

 It is properly the part of the g-eologist or mining engineer who studies an 

 individual district to find the source of the metals. In many cases careful 

 investigations can undoubtedly determine this point, as, for instance, in the 

 Lake Superior iron region. In other districts, however, the most exhaustive 



