126 



THE GOLD DEPOSITS. 

 Origin. 



It has been suggested, in the notes accompanying the 

 editions of the Porcupine map, that the quartz veins of 

 the area are the result of a granitic intrusion, the immense 

 quantity of quartz present in the veins having been supplied 

 by the acid magma as a differentiation product. The 

 primary quartz of the veins shows evidence of having been 

 deposited under pressure, as it contains numerous cavities 

 of gas and liquid inclusions. The quartz has filled the 

 fissures rapidly, as there is generally an absence of well- 

 defined walls, except where there has been secondary 

 movements. Quartz and rock are often cemented, forming 

 a contact like that of an intrusive. 



Mr. C. W. Knight noted the occurence of feldspar in a 

 quartz vein on the Miller-Middleton, one of the Timmins 

 locations, and suggested the relationship of the deposit to 

 granite or pegmatite dikes. The feldspar which is an acid 

 plagioclase has also been noted in other veins, including the 

 No. i vein of the Hollinger, the Rea vein, and in many of 

 the narrow veins in the vicinity of Three Nations lake. 

 The feldspar is most abundant near the margins of the veins. 

 The extinction angle of the feldspar in the veins on the 

 Three Nations Lake Mining Company's claim shows it to 

 be very near albite. A chemical analysis of this feldspar 

 gave : Soda, 10.37 P er cent. ; potash, 0.90 per cent. 



The mineral scheelite, calcium tungstate, occurs in some 

 of the veins around Pearl lake as one of the earliest con- 

 stituents. It has been found in the Jupiter, Plenaurum, 

 Mclntyre and Hollinger, but only in very minor quantity. 

 It is interesting to note that scheelite generally occurs with 

 minerals like topaz, cassiterite, tourmaline, and arsenopyrite 

 in pegmatitic veins, which are considered to have a genetic 

 relationship with granites. The presence of scheelite in 

 the Porcupine veins may point to the pegmatitic origin 

 of the veins in this area. 



Tourmaline occurs quite frequently, not only as a later 

 mineral in the veins but with the original quartz, as at the 

 Dome Extension, West Dome and other properties. 



Arsenical pyrites is abundant in the quartz veinlets on 

 the McAuley-Brydges claim in Bristol township. 



