[TYRRELL] PRE-CAMBRIAN GOLDFIELDS OF CENTRAL CANADA 105 



mineral is absent. In one vein the pyrrhotite was replaced by Arsenopy- 

 rite. Chalcopyrite, galena and sphalerite were also recognized. Gold 

 occuis both in the clear quartz, and in the darker bands, where the 

 pyrite or pyrrhotite is usually most abundant, and I also found a few 

 small flakes of gold in a quartz-porphyry which formed the wall rock 

 of one of the veins. 



Of the rocks more or less closely associated with the gold-bearing 

 veins, that which is considered to be the oldest is a fine-grained green- 

 stone of Keewatin age, often showing ellipsoidal structure, and with 

 the component minerals very much decomposed. The more massive 

 varieties gradually pass into green chloritic schists high in calcite or 

 ankerite. 



Associated with the greenstones and schists are extensive bodies 

 of quartz porphyries with phenocrysts of quartz, orthoclase and plagio- 

 clase, the latter often predominating. These porphyries are altered 

 in many places to a thinly foliated sericite schist. 



They are called by ^Dr. Coleman Wawa Tuffs, and with the under- 

 lying greenstones and some overlying patches of Iron Formation are 

 included by him in the Keewatin Complex, though it is not improbable, 

 as he points out, that some of the porphyries and acid schists are 

 younger than the Keewatin. 



Overlying these schists, etc., are highly altered and squeezed 

 conglomerates called by Dr. Coleman Doré Conglomerates, and con- 

 sidered by him as the equivalents of the Temiskamian Series. 



There are also granites of at least two different and distinct ages, 

 some of which are stated by Dr. Coleman to be in eruptive contact 

 with the Doré Conglomerates, in which case these latter would corre- 

 spond with similar rocks of Algoman age in other parts of Canada. 



Of basic intrusives a coarse quartz-diorite that occurs at Mackay 

 Point on the south side of Wawa Lake is older than the gold veins. 

 A Mica lamprophyre rich in olivine occurs on a number of properties 

 associated with the veins, but whether it is older or younger than them 

 it was impossible for me to determine in the time at my disposal. A 

 fine-grained diabase also occurs as dykes on a number of mining claims. 

 None of these diabase dykes were seen to intersect veins on the surface 

 on any of the properties examined ; and all the shafts were full of water 

 at the time of my visit, so that it was impossible for me to inspect them 

 where they had been encountered underground, nevertheless I was 

 credibly informed that these dykes cut off the veins, and consequently 

 are younger than them. 



1 A. P. Coleman and A. B. Willmott, Michipicoten Iron Region. 11th Rep. 

 Ont. Bur. Min. 1902, pp. 152-185 and Map. 



