[tyerell] PRE-CAM BRIAN GOLDFIELDS OF CENTRAL CANADA 99 



or township of the same name. The feldspar, which is labradorite, is 

 partly decomposed to saussurite and other secondary materials. The 

 other chief constituent is pyroxene, and it is frequently altered to 

 chlorite and green hornblende. Pyrite, apatite and titaniferous magne- 

 tite or ilmenite are present in the usual subordinate quantities." 



"The gabbro-diabase series is important from the economic point 

 of view, as in it at Cordova are the auriferous veins of the Cordova 

 Mine." 



"Deloro Mine. The ore bodies at the Deloro Mine and adjacent 

 properties lie near the contact of the intrusive granite of the western 

 edge of Huckleberry hills, with dark Keewatin schists and associated 

 crystalline limestone of Grenville age." 



"The ore bodies consist essentially of quartz lenses in the schist 

 which contain visible gold and mispickel. The lenses conform to the 

 strike of the schist and cut across dykes of granite which intrude the 

 latter." 



"The ore of the Deloro mine and of adjacent properties appears to 

 be genetically connected with the Moira granite intrusion. The 

 openings occupied by the ore bodies were probably formed by the con- 

 traction of the granite mass on cooling, and the ores came from the 

 waters that followed the intrusion." 



The Keewatin, Grenville and Hastings Series are all portions of 

 the Pre-Huronian Complex, and the gabbro-diabase and Moira granite 

 are near the top of this Complex, and are of Algoman age. 



Of the occurrence of gold associated with arsenopyrite here re- 

 corded from three widely separated localities, one is genetically asso- 

 ciated with a granite, another with a diabase, while the source of the 

 third was not determined. All are of Pre-Huronian age, and two, 

 namely those at Long Lake, and in Hastings County belong to the 

 terminal portion of that Period, namely the Algoman, while the third, 

 at Beaver Lake, is probably of the same age. 



VEINS CONTAINING PYRITE AND GOLD. 



The three cases described above have been taken as typical 

 examples of the occurrence of gold in association with arsenopyrite in 

 quartz veins in the Pre-Cambrian rocks of Canada. 



Now we will turn to the larger class of veins in which gold is 

 associated with pyrite while arsenopyrite is generally absent. 



These veins occur in rocks of Pre-Huronian age which immediately 

 overlie or adjoin granitic batholiths by which these rocks are intruded, 

 and they are found more especially in places where the rocks have 

 been sheared or otherwise rendered schistose, so that ore-bearing 

 solutions were able to find their way readily through them. 



