n8 



grains, and calcite is abundant. Secondary feldspar is 

 present in the form of clear grains. The rock may have 

 been a diabase or basalt, but is now much altered. 



Acidic Rocks. The light-colored, more massive rocks 

 are principally quartz-porphyries and felsite, which in 

 places intrude the more basic rocks. When the porphyry 

 occurs in some volume, as around the Hollinger mine, the 

 name rhyolite has been applied to it. Much of the porphyry 

 has been altered to a sericitic schist, and frequently a rather 

 massive rock can be traced into a very schistose one. This 

 change can be well seen in the porphyry to the southwest of 

 the Dome mine workings. A porphyry from the south half 

 of lot 4 in the first concession of Tisdale, examined in thin 

 section, shows the phenocrysts to be largely plagioclase 

 feldspar, while quartz in rounded grains is also present. 

 The groundmass is made up princiDally of plagioclase feld- 

 spar and quartz. Laths of tourmaline are scattered through 

 the rock. 



The schist at the surface, and at 50 feet in No. 1 shaft 

 of the Hollinger mine, is fine in grain and of a light grey 

 color when fresh. The groundmass consists essentially of 

 sericite (or talc), dolomite, quartz and feldspar. In this 

 occur round and irregular eyes of quartz which may 

 represent phenocrysts in the original rhyolite or quartz- 

 porphyry from which the schist has probably been derived. 

 Cubes of iron pyrites are commonly set in the rock. Other 

 thin sections from the grey schists on the Timmins 

 properties have about the same group of minerals, and most 

 of them effervesce with hydrochloric acid. 



The somewhat massive rhyolite exposed just southeast 

 of Miller lake is made up of a fine-grained matrix of quartz, 

 feldspar and sericite, in which are set small phenocrysts of 

 quartz and feldspar. The rock is much impregnated with 

 dolomite. 



A sample of schistose rock from the 140-foot level of 

 the Bewick-Moreing shaft, east of Pearl lake, shows an 

 abundance of sericite, chlorite and calcite, with numerous 

 quartz grains. The rock is entirely altered, but some of the 

 quartz grains may be remnants of phenocrysts. 



A sample of schistose quartz-porphyry from south of 

 the Dome mine workings shows phenocrysts of cmartz and 

 feldspar in a fine-grained groundmass of these minerals. 



