[TYRRELL] PRE-CAM BRIAN GOLDFIELDS OF CENTRAL CANADA 101 



been metasomatically altered to vein matter through the influence of 

 the solutions rising through the established, though often interrupted, 

 channels. 



Veins often occur near the contact of intrusive acid dykes with 

 other rocks, usually more basic than the dykes. In some cases these 

 dykes have been shown to be connected with batholiths of granite or 

 similar rock, while in many other cases the origins of the dykes are 

 unknown. 



Rice Lake District. Beginning with the records of the presence 

 of gold in the localities farthest west and coming eastward we will first 

 consider the Rice Lake district, near the eastern border of Manitoba. 



Gold here occurs in quartz veins associated with pyrite, with a 

 small amount of chalcopyrite and siderite. 



^Dr. Moore states that the rocks of the district belong to the 



Rice Lake Series or Keewalii "made up of acid igneous rocks, 

 including quartz-porphyry, rhyolite and orthoclase-porphyry," with 

 altered diabase and elypsoidal greenstone. 



Wanipigow Series {Lower Huronian ? or Temiskamian) consisting 

 of conglomerate, arkose, graywacke, chert, jasper, grey gneiss and 

 schist in a closely-folded syncline. 



Manigotagan series of granite, pegmatite and gneiss, mostly 

 newer than and cutting the sediments of the Wanipigow series and 

 thus probably of Algoman age. 



Speaking of the gold-bearing veins ^Dr. Moore says: 



"The Rice Lake rocks contain more of the large quartz veins than 

 the Wanipigow," and again, "the granites and pegmatites are believed 

 to be the source of the quartz veins, and the gold ore of this region." 



In describing this district ^Dr. Wallace gives the following in- 

 teresting information about the character and age of the rocks in 

 which the gold veins occur. 



"The feldspar porphyry which is the dominant rock in the Kee- 

 watin in this area, and in which the quartz veins as a rule lie, is even 

 in its altered condition remarkably poor in quartz, and was originally 

 a plagioclase feldspar rock probably to be classified among the tra- 

 chytes." 



"The Keewatin eruptives of this area are noteworthy in that the 

 more basic phases, elsewhere so pronounced, are here very imperfectly 

 represented. The rocks are either acid quartz-porphyries or inter- 

 mediate feldspar-porphyries very poor in quartz (with fine-grained 



1 Sum. Rep. G.S.C. 1912, pp. 262-270 and map. 



2 Op. cit. p. 264-265. 



3 R. C. Wallace. The Rice Lake Gold District of Manitoba. Trans. C.M.I. 

 Vol. 16 pp. 538-544, 1913. 



Sec. IV, 1915—7 



