[TYRRELL] PRE-CAMBRIAN GOLDFIELDS OF CENTRAL CANADA 113 



"While the gold-bearing veins were formed subsequent to the in- 

 trusion of the porphyry, it is hkely that they are genetically connected 

 with this intrusive rock which occurs as dykes and boss-like masses. 

 The cooling of the intrusive was apparently accompanied by shrinkage, 

 faulting and displacement in the porphyry itself and in the adjacent 

 rocks. The gold-bearing, silicious solutions that deposited their bur- 

 dens in the fissures and other fractures in all probability represented 

 the end product of the intrusion of the acid rocks that have been 

 mentioned."^ 



Quartz Veins. Quartz veins occur in the greenstone, diorite- 

 porphyry and conglomerate or greywacke, and some veins have also 

 been observed in the albite-diorite. 



Most of them dip at a high angle, usually not more than a few 

 degrees from vertical, though the dip may vary to some extent at 

 different depths. Thus, at one place a vein may dip at an angle of 

 70°, while above or below it may be vertical, or even dip in the opposite 

 direction. 



In the greenstone and porphyry the veins are of quartz of a white 

 or light blueish colour, often enclosing inegular masses of country 

 rock. Very often the vein matter is distinctly banded, and in such 

 cases the bands may be of green chloritic material, or they may con- 

 tain a considerable percentage of dark tourmaline. 



In the conglomerate the veins may contain a considerable pro- 

 portion of specular iron ore, or, as in the case of the Tough-Oakes vein, 

 they may contain a very large quantity of molybdenite. In almost 

 every vein in which gold is found pyrite is more or less freely dissemin- 

 ated through the quartz, and also through the country rock adjoining 

 the vein. Some of the gold is intimately associated with this py- 

 rite, while other portions of it are scattered through the quartz quite 

 independently of the pyrite. 



Many of the quartz veins are at or near the contact of the diorite- 

 porphyry and greenstone or conglomerate. The contact zone is not 

 usually very sharply defined, for the rocks were very much disturbed, 

 crushed and faulted by dynamic agencies as they assumed their present 

 condition. The veins may run parallel to the general trend of the 

 contact or they may branch off at angles from it along subsidiary 

 fissures which have extended out into one rock or the other. 



Faults. In the tremendous disturbances to which these old rocks 

 have been subjected, numerous slips have occurred, and faults have 

 been formed of greater or less displacement. 



1 A. G. Burrows and P. E. Hopkins. "The Kirkland Lake and Swastika Gold 

 Areas." 23rd Rep. Ont. Bur. Min. 1914. Pt. II, p. 18. 



See also J. B. Tyrrell. "The Occurrence of Gold in Ontario." Trans. I.M.M. 

 Vol. 23 pp. 143-162. London, 1914. 



