During the past season a prismatic compass and micrometer survey was made of both branches of the Montreal river and all navigable waters adjoining them. This work was done by Messrs. T. Firth, J. R. Marshall and A. B. Moffatt. Most of the small ponds lying some distance from a canoe route were located by rapid chain and compass methods, and in a few instances west of Duncan lake by a compass triangulation from hilltops; the larger ones have been measured by pacing or chaining, the smaller ones sketched. Some of the more prominent hills were located by triangulation, and their heights ascertained by aneroid determinations. The water levels were obtained in the same way, but cannot as yet be referred to sea-level.
The geological work was performed by the writer, assisted by Mr. Firth. Besides a thorough examination of all the surveyed routes, a systematic examination of the intervening country was carried out as closely as the time and varied requirements of the area would permit. As this was the first season spent in the district and a continuation of the work is anticipated, the present results are offered as incomplete and subject to revision.
HISTORY OF DEVELOPMENT.
Since the discovery of silver cobalt ores at Cobalt in 1903, exploration has shown the adjacent country to be locally enriched by mineral veins of the same character and genesis. At the close of 1907 an area 65 miles long in a north and south direction, and about 45 miles wide, extending from Lake Timiskaming and the Ontario-Quebec boundary westward, was known to include at least ten mineralized districts besides the principal one at Cobalt, of which the most recently found lie near the Montreal river. It has also become known gradually that these deposits are closely connected with the post-Huronian quartz diabase of the region. This diabase was known to extend for a very considerable distance farther west, leading to the inference that more discoveries were to be expected in that direction. The spring of 1908 saw interest centred upon the Montreal River finds, and early in the season active exploration had commenced. The Montreal river, up to that time, had not been regarded with special favour, the diabase being considered of no economic importance, but with the new conceptions gained by exploitation of the silver-cobalt district, this formation in the west began to attract attention. At the beginning of the field work, early in July, a considerable number of prospecting parties were on the ground, as far west as Duncan and Pigeon lakes. During July and August this movement, encouraged by the succession of mineral discoveries that were being made near Bloom and Everett lakes, increased steadily, in spite of the scarcity of available topographical and geological information dealing with the region.
Early in August discoveries of native silver were made almost simultaneously by Messrs. Mann and associates, and by Messrs. Crawford and Dobie on the west side of Gowganda lake, but were not made public until the first week in September when the claims were recorded at Elk Lake and specimens were exhibited. Twenty-four hours later the leading canoes of an inrushing body of prospectors had reached the new field, and within two weeks most of the promising country between Gowganda and Elkhorn lakes and northward had been staked, regardless of the mineral discoveries necessary to validate the claims. Since then numerous discoveries have been made, and the news of a new silver field, until recently confined to the Montreal River and Cobalt districts, has spread widely. As a consequence, a mid-winter rush is now in progress, and hundreds of prospectors, regardless of deep snow and severe cold, are entering the country. Much inadvisable staking will be done, no doubt, before spring, but the disappearance of the snow and reopening of river navigation will certainly be followed by an increased rush of prospectors.
SUMMARY AND CONCLUSIONS.
The results obtained from the field work indicate that the Montreal River district does not differ essentially from the Cobalt or other neighbouring districts. The surface has the same rugged monotony of the pre-Cambrian peneplain, relieved somewhat by ridges of Huronian, which stand from 300 to 550 feet above the general level. The country is well watered, and offers exceptional facilities for canoe travel. Pleistocene deposits are thin, and nearly everywhere the rock formations are well exposed.
A basement complex underlies the entire region, either appearing at the surface or hidden beneath areas of Huronian sediments. This basement consists largely of Laurentian biotite and hornblende gneisses, with patches of vertically foliated, Keewatin schists caught up in the former; the intervening contacts forming indefinite zones, in which intrusive action is manifested. In this report, for convenience, this complex will be referred to as the Archæan. The Archæan possessed a peneplanated surface, not greatly different from the present one, which is well preserved where overlain by erosion remnants of Huronian sedimentary rocks, but which at other points has been further denuded. The Lower Huronian rocks are of clastic nature, consisting in ascending order, of conglomerate, greywacke, slate and quartzite, which pass conformably into an upper conglomerate; while a granite-like, arkose member is believed from its similarity to rocks of the same character in the Cobalt area, to be possibly of later, Middle Huronian age. They are remarkably well preserved, and show only slight indication of disturbance. A later intrusion of quartz diabase has developed a system of dikes in the Archæan and large tongue-shaped areas in the Huronian believed to represent sills of several hundred feet thickness, lying in the bedding planes of the Huronian sediments. The diabase magma has been notably differentiated, giving rise to forms ranging from gabbroid to syenitic in composition, and to younger aplite dikes. With the diabase is associated a group of veins containing an association of cobalt and silver ore identical with that of Cobalt and vicinity. The veins cut both diabase and aplite as well as the Huronian, and are therefore younger, but probably not much younger than the aplite, since it contains some of the minerals found in them. The distribution of the veins so far as known is confined to the larger diabase areas, the dikes and smaller bodies being undifferentiated and unmineralized; but the Huronian adjacent to the diabase also contains veins, somewhat more siliceous, yet evidently of the same age as the others. Alteration and impregnation of the country rock has taken place to an unknown, but, presumably, limited extent. Some of the veins are remarkably rich, and many of them occupy persistent, well defined fissures. The cause of these fissures is not yet known, but they appear to be too large and continuous to have resulted from contraction alone.