Section IV., 1915. [89] Trans. R.S.C. 



* 

 Pre-Camhrian Goldfields of Central Canada. 



By J. B. Tyrrell, F.R.S.C. 

 (Read May Meeting, 1915). 



For almost fifty years gold has been known to occur in the Pre- 

 Cambrian rocks of Central and Northern Canada. First discovered 

 at what was afterwards known as the Richardson Mine in Hastings 

 County, Ontario, it has since been found to be widely distributed wher- 

 ever the greenstones, porphyries and conglomerates of the Pre-Huron- 

 ian Complex occur from northern Quebec westward to the Province of 

 Saskatchewan. 



Production has been confined to the Province of Ontario, and until 

 recently the quantity obtained from any one locality has not been large. 

 Up till the 31st December, 1914, the total production of gold from the 

 Pre-Cambrian rocks of the Canadian Shield was 718.500 fine ounces. 



However desirable it might be for the material welfare of the 

 community that gold should occur in sufficient abundance to be 

 extracted at a profit in all of the places where its presence is known, 

 the facts are that it occurs in many places where, either on account 

 of being too sparsely scattered, or for other reasons, it cannot be mined 

 at a profit, to the one place where the value of the gold won is greater 

 than the cost of winning it. Nevertheless we will here set aside the 

 question of profit or value for a short time, and consider it as a geo- 

 logical unit, regardless of whether the vein matter or rock in which it 

 occurs contains 2 dwts. or 2 oz. or 200 oz. to the ton. The determin- 

 ation of the presence of the quantity of gold contained in rock (or 

 vein matter, etc.) may be the question of greatest immediate economic 

 importance in regard to it, but a thorough knowledge of the rocks 

 with which it is associated, and of its mode of occurrence in those 

 rocks may be of inestimable service in assisting to ascertain the ex- 

 tent of known goldfields, and in discovering and developing new ones. 



In addition to the above considerations it would appear not 

 unlikely that the gold-bearing veins in the Pre-Cambrian rocks of 

 Central Canada are all of about the same age, in which case their pres- 

 ence should be of material assistance in helping to define the age of 

 the rocks with which they are associated. 



In order to understand clearly what is here meant by the Pre- 

 Cambrian rocks of the Canadian Shield, and the particular sub- 

 divisions of those rocks with which we are now more particularly con- 



