120 



The extinction angle of some of the feldspar phenocrysts is 

 near that of oligoclase-albite. Sericite scales are often 

 grouped around the crushed feldspar crystals and have pene- 

 trated them. Cubes of iron pyrites are abundant. 



In addition to the quartz-porphyry there are numerous 

 dikes of a grey feldspar-porphyry. These are generally 

 less than ioo feet in width, and south of Porcupine lake 

 on the Edwards claim intrude the schistose quartz-porphyry. 

 One such dike of feldspar-porphyry, on H. R. 1,043 i n 

 Deloro townhip, has been prospected for gold. The dike is 

 intersected with minute stringers of quartz in which most 

 of the gold occurs. A thin section of the rock shows the 

 phenocrysts to be an acid plagioclase which is fairly fresh, 

 but is partly invaded by scales of sericite. Plagioclase is 

 also prominent in the groundmass. 



At times the Keewatin has been much crushed and 

 broken, so that the rock has the appearance of a conglom- 

 erate ; so much so that in the vicinity of the Dome mine, 

 where greywacke and conglomerate occur, it is impossible 

 to draw a close line of distinction between the autoclastic 

 rock and the true conglomerate. 



Iron-Formation. Banded iron-formation, grouped with 

 the Keewatin, has an extensive development in parts of the 

 area. It outcrops frequently in the southwest part of 

 Whitney township, in the first and second concessions. The 

 disturbance in the formation here has not been so great as 

 in other areas. Often the bands are lying almost hori- 

 zontally. In places they have been somewhat brecciated, 

 but are otherwise little disturbed. The bands are alternate 

 reddish or greyish sugary quartz and magnetite or hematite. 

 Sometimes the narrow bands of magnetite, one-eighth inch 

 thick, carrv a merchantable percentage of iron, but these are 

 relatively subordinate in comparison with the main mass of 

 rock. It is unlikely that merchantable iron ore will be 

 found in quantity. In parts of the formation iron pyrites 

 replaces the magnetite. Almost horizontal, interbanded 

 iron pyrites and silica are seen on the south half of lot 5 in 

 the second concession of Whitney. A sample of banded 

 quartz and iron pyrites gave 40 cents in gold per ton. Iron 

 pyrites occurs in considerable quantity with a sugary quartz 

 on lot 9 in the second concession, and might be worthy of 

 investigation as a source of sulphur. 



