32 Mineralizers in Ore Segregations [230 



4. The ores are introduced one after another in the fol- 

 lowing invariable sequence: (1) magnetite and ilmenite, (2) 

 pyrrhotite, (3) pentlandite, (4) chalcopyrite. There is a 

 certain amount of replacement of the earlier ore minerals by 

 the later ones. 



5. Hydrothermar alteration is distinctly later than the 

 period of ore deposition. 



These data of observation lead them to a theory of genesis 

 more nearly analogous to that of DeLaunay than any of the 

 others mentioned above. The fact that the ore minerals 

 replace the silicates without the formation of metallic sili- 

 cates by reaction is interpreted to mean that the ores were 

 not introduced in a molten state but that the same agency 

 that brought in the sulphides removed the dissolved silicates, 

 indicating the presence of active mineralizers. The altera- 

 tion of pyroxene to hornblende is further evidence of the 

 presence of mineralizers. Consequently they conclude that 

 mineralization took place at a temperature below the melting 

 point of the ores and that they were held in solution through 

 the agency of mineralizers. On the other hand, that ore de- 

 position took place under conditions different from those of 

 non-magmatic high temperature deposits is shown by the 

 absence of the secondary silicates characteristic of ordinary 

 pneumatolytic and hydrothermal processes, or that where 

 present they belong to a distinctly later period. They con- 

 clude, that the magmatic ores "have been introduced at a 

 late magmatic stage as a result of mineralizers." 



The direct evidence presented by Tolman and Eogers is 

 derived from the sulphide deposits, but the presence of a 

 greater or less quantity of titaniferous magnetite in these, and 

 numerous references in the literature to the silicates pre- 

 ceding the ores in order of crystallization in deposits of titan- 

 iferous magnetite, led them to infer that the same observa- 

 tions and same conclusions apply equally well to the oxidic 

 ores. My own experience with the titaniferous magnetites 

 corroborates the correctness of this inference. The relations 

 between ore minerals and silicates figured and described for the 



