[TYRRELL] PRE-CAMBRIAN GOLDFIELDS OF CENTRAL CANADA 117 



turing, and left thin cracks between these layers to serve as channels 

 for mineral solutions. In other cases the layers broke across in many 

 places, giving rise to fractured and faulted zones through which the 

 solutions could rise in very irregular channels. 



The veins on the Hollinger and Mclntyre properties represent 

 different phases of this class. 



(b.) Where the rock was fairly massive. 



In this case the rock usually broke in a series of small irregular 

 fractures with a more or less linear arrangem.ent. 



2nd. Veins in small isolated fractures, without any evidence of 

 shearing or faulting, like fissures formed by contraction on cooling. 

 They are typical Gash Veins, and are usually short and disconnected. 



Wherever the age of these gold-bearing veins could be definitely 

 determined they appeared to be Algoman, and in conformity with 

 the idea of Metallogenetic Epochs suggested by Waldemar Lindgren 

 we may regard them as characterizing a strongly marked Chryso- 

 genetic Epoch which prevailed over the whole area of the Canadian 

 Shield. 



Conclusions. 



The following conclusions would seem to be justified from the 

 foregoing consideration of the Pre-Cambrian rocks of the Canadian 

 Shield. Whether these conclusions will apply to, or have any signifi- 

 cance in, Nova Scotia, southeastern Quebec and the Appalachian 

 region generally, I have not yet determined. 



1. The veins are Pre-Huronian in age, no gold-bearing veins 

 having been recorded in rocks of Huronian age in Central Canada. 



2. They frequently occur in both basic and acidic rocks of Kee- 

 watin age. 



3. Wherever the later Temiskamian rocks are present in associa- 

 tion with the Keewatin rocks the gold-bearing veins are clearly de- 

 terminable as being younger than the Temiskamian series. 



4. They are very generally associated with Albite-porphyries. 



5 . These porphyi ies, etc. , may reasonably be regarded as apophy- 

 ses from batholitic granitic intrusions of Laurentian and Algoman age. 



6. The gold quartz veins have not been found, and do not seem 

 to occur, in the body of the batholiths of granite or gneiss, whether 

 these are of Laurentian or Algoman age, as evidenced by their absence 

 in the vast areas of hundreds of thousands of square miles in northern 

 Canada, where such granites alone are well exposed. 



7. In the Algoman Period, in which most, if not all, of the gold- 

 bearing veins in the Pre-Cambrian rocks of Central Canada would 

 appear to have been formed, we have a Chrysogenetic Epoch, during 



Sec. IV. 1915—8 



