“Dark green eruptive rocks, chiefly diabase, are largely developed in the Huronian, composing a considerable proportion of the rocks of the system. In many cases these rocks have been crushed and sheared, a slaty cleavage or schistose structure has been superinduced, and the original minerals have been broken and altered, both in their shape and composition. In other cases the rock remains massive, or there is developed in it a concretionary or bomblike structure, the bombs, often a foot or two in diameter, being usually separated by somewhat schistose bands, which differ slightly in colour from the rest of the rock.
“On the east side of Hudson bay this rock was found to have, disseminated through it, a large amount of both iron and copper pyrites, while these minerals were often found collected somewhat more closely together in the numerous veins of quartz and calc-spar which almost everywhere traversed the rock. No large deposits of the sulphides were seen, but when they are so freely distributed through the mass of the rock it is not at all improbable that large masses may be found segregated out along the zones where these green schists are in contact with masses of eruptive granite or gneiss. Very little of the vein rock has been collected for assay, but some pieces of vein quartz, picked up by Doctor Rae near the south side of Corbett inlet, were found to
Carry a Small Amount of Gold.
“On Great Fish river, Mr. Pike speaks of the ironstone formation, of dark fissile slates or schists, probably belonging to the Huronian system extending down the river from Musk-Ox lake to Beechey lake, a distance of seventy-five miles.
“The shores of Point lake, one of the expansions of Coppermine river, have been described by Sir John Richardson, who passed through that country in company with Sir John Franklin in 1821, and from his descriptions there is no difficulty in recognising the Huronian rocks. The following is his description of the rocks, slightly condensed:—Greywacke passing into greywacke slate, greywacke with small imbedded crystals of hornblende, dark greenish or blackish grey clay slate. Several of the islands in the lake consist of greenstone. A rock standing apart from the neighboring hills on the border of the lake, having a rounded summit, but bounded on three sides by mural precipices about two hundred feet high, is composed of compact earthy greenstone, containing disseminated iron pyrites, covered with layers of greenstone slate. On the north side of the lake there is a high bluff hill with a precipitous side, which seems to consist principally of a conglomerate. The basis is earthy-clay slate. The embedded masses have an ellipsoidal form and smooth surface, are from one to two feet in diameter and appear to consist of the same material as the basis, but impregnated with much silica, and not showing evident slaty structure. When broken they present an even fine-grained fracture.
“ ‘During our first and second days’ journey down Point lake from the above mentioned encampment, being eleven and one-half miles on a west-northwest course, the rocks we had an opportunity of examining consisted of greenish grey clay-slate, generally having a curved structure, and splitting into slates of very unequal thickness.’
“From these few isolated and widely separated occurrences it may be seen that, as in the Archaean areas of northern and western Ontario, so on the Barren Lands, Huronian rocks occur at more or less frequent intervals, squeezed in between adjacent areas of Laurentian granite and gneiss.
“That these belts of Huronian rocks will eventually prove
Of Great Economic Importance,
there can be no doubt whatever. In Ontario the wonderful general richness of these rocks is just beginning to be recognized, but from them were taken in 1896 gold to the value of one hundred and twenty-one thousand dollars, nickel to the value of one million one hundred and eighty-nine thousand dollars and copper to the value of three hundred and twenty thousand dollars; while in the states adjoining Lake Superior the total production of iron ore in 1895 from these rocks was ten million two hundred and sixty-nine thousand long tons, valued at about twenty million dollars. This was 62·31 per cent. of the total amount of iron produced in the whole United States. The rapid progress with which these mines are being developed is shown by the fact that the Mesabi range was first opened up in 1892, and in 1895 the product of the mines in the range was two million eight hundred thousand tons. Thus you will see that in these rocks there is a prospect of discovering extensive deposits of valuable minerals.