102 THE ROYx^L SOCIETY OF CANADA 



felsitic equivalents), the phenocrysts being very markedly drawn out 

 in the direction of shearing." 



"The quartz veins lie in the feldspar and quartz porphyries north 

 and south of the Huronian (Temiskamian) sediments." 



From the above descriptions it is clear that the quartz veins were 

 formed about the period of the intrusion of the Algoman granite, to- 

 wards the close of the Pre-Huronian epoch. It is also interesting to 

 note that they occur in an area where quartz and feldspar porphyries 

 of Pre-Temiskamian age are abundant. 



Lake of the Woods. In the Lake of the Woods district rocks of 

 Temiskamian age have not been recognized, the series being confined 

 to the Keewatin schists, agglomerates, etc., into which are intruded 

 granites of either Laurentian or Algoman age. Near the Keewatin- 

 granite contact gold-bearing veins have been discovered in a number of 

 places. 



At the Mikado mine, where a very persistent quartz vein occurs, 

 the country rock is a chloritic calc schist cut by dykes or masses of fine- 

 grained biotite-granite-porphyry (felsite) doubtless offshoots from a 

 large granite mass to the North. 



The principal quartz vein carrying gold is approximately vertical 

 and is near the contact between the granite and greenstone. Down 

 to the greatest depth to which it has been followed it is very regular in 

 general character, being everywhere found to contain a little gold. 



In its deeper portions it is in the granite but higher up it crosses 

 the line of contact into the greenstone, and where it crosses the line 

 it becomes decidedly narrower. This line of constriction and entrance 

 of the vein into the greenstone is accompanied by a decided enrich- 

 ment for thirty feet or so beneath it, forming an ore-shoot with a Value 

 of from ten to twenty-five dollars in gold to the ton, in a vein with a 

 general tenor of less than one dollar to the ton. 



At the Sultana Mine the vein is also close to the Keewatin-granite 

 contact. 



At the Combined Mine ^Mr. Parsons gives the following descrip- 

 tion of the conditions. "The vein is nearly horizontal, though its 

 dip varies considerably. By some it has been looked upon as a blanket 

 vein which lies between overlying trap, exhibiting a pillow structure, 

 and a dark underlying felsite or fine-grained porphyry. With the 

 quartz, which in the principal vein varies from two to four feet in 

 thickness, is a large body of rusty carbonate rock which seems to be 

 derived from the alteration of porphyry or felsite and shows consider- 

 able sericite. In places this rock becomes a calcareous sericite schist. 



1 A. L. Parsons. Goldfields of Lake of the Woods, Manitou and Dryden. 21st 

 Ann. Rep. Ont. Bur. Min. 1912, pp. 190-1. 



