ORES PRODUCED BY IGNEOUS PROCESSES. 1049 



they also contain more water; so, when the stage of quartz veins is reached, the 

 magma is believed to be so attenuated that it may best be described as water highly 

 heated and heavily charged with mineral matter in solution." 



He further states that there is no great difference between veins 

 originating' in this manner and those having other origins. On this point 

 he says: "A quartz vein originating by magmatic segregation often might 

 not be distinguishable from one formed in the many other ways which are 

 possible." 6 The only difference which he suggests between gold-quartz 

 veins of magmatic origin and those deposited by aqueous solutions is that 

 the gold ores supposed to be produced by magmatic segregations are 

 "without the admixture of so great proportions of the commoner metals as 

 is usual in ore deposits." 6 Spurr, however, gives no reasons showing the 

 applicability of this criterion. From my own point of view, I should regard 

 it as applying in the reverse direction. That is to say, if the exceedingly 

 rare metal, gold, be segregated by magmatic processes to such an amazing 

 extent as to produce an ore deposit, it seems to me to be exceedingly likely 

 that other metals would be segregated in connection with the gold ores so 

 as to be present in greater amounts than usual. 



Since Spurr gives no certain criteria by which gold-quartz veins sup- 

 posed to be produced by magmatic segregation are to be discriminated from 

 those formed by solutions, I take the conservative view that gold-quartz veins 

 have their origin in solutions, and I ask for positive evidence from those who 

 assert that such quartz veins are produced by magmatic segregation alone. 



In general, concerning the production of ores of the metals other than 

 those of iron and aluminum by magmatic segregation alone, I repeat that it 

 seems to me that the enormous amount of segregation required should be 

 taken into account, and that it should be most conclusively shown that this 

 process alone produces the ores before the conclusion be accepted that during 

 the crystallization of the magma segregation took place to the necessary 

 extent. 



While Vogt, c Beck, ri Lindgren/ and others believe in a direct igneous 



ffl Spurr, J. E., A consideration of igneous rocks and their segregation or differentiation as related 

 to the occurrence of ores: Trans. Am. Inst. Min. Eng., vol. 33, 1903, p. 311. 



''Spurr, cit. , p. 311. 



c Vogt, J. H. L., Problems in the geology of ore deposits: Trans. Am. Inst. Min. Eng., vol. 31, 

 1902, pp. 131-147. 



tfBeck, R., Lehre von der Erzlagerstatten, Berlin, 1901, pp. 700. 



f Lindgren, Waldemar, Character and genesis of certain contact deposits: Trans. Am. Inst. Min. 

 Eng., vol. 31, 1902, pp. 242-244. 



