GEOLOGY OF THE NORTHWEST SHORES OF HUDSON BAY.
The following account of the geology of the northwest shores of Hudson bay has been compiled from observations made during the trip of the launch from Winchester inlet to Chesterfield inlet in September, 1903. These are supplemented by the notes made in May, 1904, while making a track survey from Cape Fullerton to the entrance of Chesterfield inlet. The observations to the north of Fullerton were made by Mr. Caldwell, in April and May, 1904, while on his surveying trip to the head of Wager inlet; to these are added observations by the writer made on a boat trip along the coast later in that spring, on the way to and from Southampton island, when the rocks of the mainland were examined as far north as Yellow bluff.
The rocks seen along the shore between Chesterfield and Winchester inlets are largely a flesh-red to pink mica-hornblende granite-gneiss, often only slightly foliated, and varying in texture from medium to coarse-grained. These are associated with broken bands of dark-gray or red gneisses, usually very quartzose, and containing a considerable quantity of mica and hornblende, the latter often partly decomposed to chlorite. These gneisses have evidently been cut and broken by the intrusion of the granite-gneisses. Many veins of pegmatite cut all these rocks; it consists chiefly of red or violet feldspar with much quartz, and in some places large crystals of black hornblende.
The granite-gneisses are also most abundant inland, as was seen along the lower part of Chesterfield inlet and in the country forty miles inland from Winchester inlet.
The granites occupy the shores and islands between Winchester inlet and the west side of Island bay, about half way to Fullerton, when they give place abruptly to a series of dark schists. These schists are largely micaceous, but there are also frequent bands containing considerable quantities of hornblende, and these are more basic than the more common mica-schists, which always contain quartz in varying amounts. These mica-schists appear to have been clastic rocks associated with bands of trap, all having been altered and foliated by the granite intrusion. The schists are very regular, and have a constant strike of N. 10° W. Many of the basic bands contain varying quantities of pyrite, but it was never seen in sufficient abundance to constitute a mine. All the schists carry dark-red garnets, some of which are regular in their crystallization and of good size.
The islands about Fullerton harbour are formed partly of granite and partly of these dark schists. On this eastern contact of the granite with the area of schistose rocks, the latter have been greatly disturbed by the intrusion, being squeezed, contorted and broken by granite masses, as may be seen from the illustration. Areas of coarser basic rocks now occur in the rocks along the coast, usually in the form of coarse gabbro, but often in a more altered condition as coarse hornblende-gneisses. The granites are the prevailing rocks along the coast as far north as the mouth of Wager inlet, and have generally a red or pink colour. Associated with them and evidently altered by their intrusion are patches of gray quartzose gneiss, and less frequently areas of old basic intrusive rocks.
At Whale point, where the rocks were closely examined, the oldest rock was represented by a medium to fine-grained, gray and pink, very quartzose gneiss. This had been cut by a coarse diabase, and both had been foliated and broken by the intrusion of the newer granite. Dikes of a newer diabase cut all the other rocks.
Contorted Gneiss and Granite at Fullerton.
The granites prevail about Wager inlet, but there are more and larger areas of the dark basic rocks about that great bay than to the southward, making it a more promising field for economic minerals, especially as these basic rocks generally carry sulphides, and Rae reported free gold to have been found about the head of the inlet.