240 University of California Publications in Geology [Vol. 13 



The writer has concluded that in the case of the Friday Mine 

 deposit the preponderance of evidence points to a syngenetic origin. 

 The almost complete lack of veining effects, either of silicate minerals 

 by ore minerals or of one ore mineral by another, is noteworthy in 

 this deposit. 



Even had such veining effects as are described by the proponents 

 of replacement theories been noted in the Friday Mine ore, still the 

 writer would have held to the syngenetic theory on account of the 

 evidence of the larger scale geologic relationships. 



The reason for this statement is that he questions the validity of 

 the criteria employed by Campbell, Knight, and Tolman and Rogers 

 to establish the order of arrival of the various minerals at the partic- 

 ular point studied. In the first place, it should be noted that both 

 Howe and Dresser, who made careful petrographic studies of Sudbury 

 materia/1, deny the definite order in the relations between the sulphide 

 minerals that has been affirmed by the other workers. 



Even if the various sulphides should cut one another in a definite 

 order, and granting as a fact that the sulphides sometimes cut the 

 silicates in veinlets, no evidence has been offered that this proves the 

 relative time of arrival of the minerals from some source outside the 

 rock in which they are now found. Many examples might be cited 

 of veins that without any doubt grew in their present positions with- 

 out accession of any material from without, e.g., quartz veinlets in 

 radiolarian chert, calcite veinlets in limestone, etc. 



Objection may be raised to such examples as being not pertinent 

 to the present discussion. As offering almost perfect analogies to the 

 nickel ores, we may turn to the evidence furnished by metallurgical 

 products, e.g., mattes and alloys. 



Plate 4, figure 6 is reproduced from Fulton's "Metallurgy." 75 It 

 is a photograph of a polished surface of copper matte. The light 

 portion is substance "D" (CiuS, -f- Cu) with dissolved FeS - Fe. 

 The dark portion is metallic copper. 



The textural relations between the metal and sulphide here are 

 much like those between pentlandite and pyrrhotite in plate 13, fig- 

 ure 1. Now substance "D" melts at something less than 1150° C, 

 while metallic copper melts at 1084° C. The temperature of matte 

 smelting generally exceeds 1200° C. It is evident, then, that the 

 matte was entirely molten when poured from the furnace and that 

 all of the solidification took place within the matte pot. The textural 

 relations between the metal and the sulphide are the result of one 



75 Pulton, C. H., Principles of metallurgy (New York, 1910), p. 305. 



