[TYRRELL] PRE-CAMBRIAN GOLDFIELDS OF CENTRAL CANADA 107 



Grace Mine the principal vein is at the contact of a massive feldspar- 

 porphyry and an old greenstone. At the Kitchigammi Claim the 

 vein is close to the contact of a coarse, gneissoid, hornblende granite, 

 typical of the Laurentian areas throughout the country, with a fine- 

 grained biotite granite which has been intruded into it. Narrow ton- 

 gues or dykes of the fine granite run out into the older coarse granite, 

 and in one place one of these narrow dykes may be clearly seen to ter- 

 minate in a quartz vein, indicating the essential unity in age between 

 the two. 



The exact age of the later granite or other intrusive rock associated 

 with the gold-bearing veins was not determined, but in view of the 

 fact that some of the granites of the district have been proved to be 

 newer than the Doré Conglomerate, and that the veins at some of the 

 mines, as at the Kitchigammi, are of the same age as the newer granite, 

 it would seem not improbable that the gold-bearing veins of this district 

 are of post-Temiskamian or Algoman Age. 



Whiskey Lake. One hundred and fifty miles south-east of Wawa 

 Lake, which lies about the centre of the gold-bearing portion of the 

 Michipicoten district, is Whiskey Lake, on and near the shores of 

 which quartz veins, carrying pyrite and gold occur in rocks included 

 by Dr. Coleman in his Sudburian series, which is equivalent to the 

 Temiskamian Series. These veins are therefore also of post-Temis- 

 kamian or Algoman age. 



West Shining Tree. Ninety miles north of Whiskey Lake is the 

 West Shining Tree District in which gold-bearing veins have been dis- 

 covered in considerable numbers. The prevailing rock is a green- 

 stone of Keewatin age, sometimes amygdaloidal, and often with 

 strongly marked ovoidal structure. Occasionally the angular masses 

 between the ovoids are replaced by quartz. The greenstone is cut 

 by dykes or bosses of much altered diorite, diabase and feldspar por- 

 phyry, the latter of which varies from a rock with abundant, but now 

 highly altered, phenocrysts of plagioclase and orthoclase in a medium 

 grained groundmass composed chiefly of grains of quartz, but without 

 quartz phenocrysts, to a schistose porphyry with squeezed pheno- 

 crysts of plagioclase, apparently Labradorite, and needles of horn- 

 blende, in a fine-grained groundmass of quartz, feldspar and iron oxide. 

 No evidence was seen in this district of the age of the gold-quartz 

 veins. 



Porcupine. From West Shining Tree the Keewatin greenstones, 

 etc., continue northward for 70 miles to Porcupine, which is now the 

 richest gold-producing district in the Province of Ontario, or in fact 

 in all Canada. 



