REPORT OF THE DIRECTOR IQII l8l 



led to more pronounced concentration than was effected by 

 primary sedimentation. In both processes organic matter, the 

 residue of which appears as graphite, would be an active agent. 

 Deposits of either origin would of course during metamorphism 

 undergo recrystallization, together with the other constituents of 

 the sediments, accompanied by little if any concentration. Pyritifer- 

 cus gneisses and schists would result, but obviously the pyrite would 

 not bear to the other minerals the relations that it has been seen to 

 bear in the ores. True enough, some sections, as already described, 

 have pyrite that appears to be an essential part of the gneiss, and this 

 is doubtless of the earlier origin and metamorphosed, but it is so 

 rare that an extensive postmetamorphic recrystallization in situ is 

 demanded unless much of the pyrite is, as here argued, of this later 

 period of formation. Between the two hypotheses, the latter is 

 deemed more probable. 



While the suggestion of four periods of concentration of pyrite, 

 under diverse conditions, may be thought to indicate a degree of 

 complexity not demanded by the facts, and perhaps even improbable, 

 it must be remembered that the ore deposits belong to a type that is 

 essentially complex and occur in a region that is complex. 

 These are facts to be reckoned with, and it is believed that no 

 simple explanation will meet the existing situation. Indeed, the 

 writer is convinced that what is here presented constitutes the barest 

 outline of the actual series of processes involved in the genesis of the 

 ores, a series which, if it could be worked out in complete detail, 

 would doubtless afford a bewildering assemblage of phenomena. 



Pyrite is a mineral capable of forming and existing under a great 

 variety of conditions. Its constituents are abundant and circulate 

 freely, favoring much diversity and complexity in methods of con- 

 centration. Granted the primary deposition of some pyrite in the 

 original sediments (and such an assumption is conservative) the 

 general geological relations of the region, together with the details 

 of the ore bodies, point very clearly to the various stages of con- 

 centration stated, with the exception of the second, which is assumed 

 on the grounds of probability based upon the known properties of 

 pyrite as a rock constituent. In other words, some of the pyrite is 

 regarded as probably of sedimentary origin, and must of course have 

 passed through all the many and complex conditions to which the 

 Grenville sediments have been subjected, involving its circulation in 

 ground waters, recrystallization during metamorphism under con- 

 ditions of stress, and finally another recrystallization under static 



