ORES PRODUCED BY IGNEOUS PROCESSES. 1047 



of sulphide in passing from the center to the border of a norite area is just 

 what one would expect, even if the material had been segregated b} T circu- 

 lating solutions, since the trunk channels for circulation are frequently along 

 the borders of intrusive masses, and at such places solutions from the 

 igneous and adjacent rocks ' extensively mingle. At Sudbury almost con- 

 clusive evidence of segregations by solutions is furnished by distinct veins 

 of pure sulphides, evidently formed in openings in the norite. Both walls 

 of some of the veins are impregnated with ore in varying degrees. The 

 impregnation is greatest at the walls, and in passing from them the amount 

 of sulphide gradually lessens until none is visible." Tn short, the phe- 

 nomena are absolutely identical with those which Liudgren has described 

 as especially characteristic of metasomatic processes along the walls of 

 fissure veins. 



It may be suspected that a close study of some of the other nickel- 

 iferous deposits will show somewhat similar phenomena. To what extent 

 circulating' underground solutions have concentrated the nickeliferous 

 deposits of Norway and of Varallo in Piedmont I do not venture to say. 

 Nor do I express any opinion as to the part which magmatic segregation 

 has played in the production of the auriferous pyrites of Rossland, British 

 Columbia, and the high-grade copper ores described by Lotti; but Lind- 

 gren, as the result of careful studies by himself and previous studies by 

 King and Raymond, states that the Rossland deposits are metasomatic 

 replacements rather than magmatic differentiations b It is to be noted that 

 the copper ores described by Lotti and that chromite ores- described by 

 Pratt are in serpentinized peridotites. 



In those cases in which the ores are in much altered rocks the question 

 certainly should be asked as to what extent the ores have been modified 

 by the processes of alteration. In the other cases, in which no evidence of 

 secondary action is mentioned by Vogt, it certainly is a proper subject of 



a While this volume is going through the press a paper by Dickson on the ore deposits of Sudbury 

 has appeared (Ore deposits of Sudbury, by Charles W. Dickson: Trans. Am. Inst. Min. Eng., vol. 34), 

 -which gives a full summary of the views that others have held in reference to the genesis of the Sud- 

 bury ores and contains an elaborate discussion of the facts of occurrence of these ores. As a consequence 

 of his elaborate study, Dickson concludes that "while magmatic differentiation has gone on to some 

 extent, the sulphides are not the result of it." He says further: "It might be safely stated that at present 

 the whole weight of the evidence points to the secondary formation of the Sudbury ore bodies as 

 replacements along crushed and faulted zones, with only minor indications of open cavities." 



6 Genesis of ore-deposits: Am. Inst. Min. Eng., 2d ed., 1902, pp. 564-565. 



"Pratt, J. H., Occurrence, origin, and composition of chromite: Trans. Am. Inst. Min. Eng., vol. 

 29, 1900, pp. 22-24. 



