Popular Science Monthly/Volume 50/January 1897/A Curious Canadian Iron Mine
|A CURIOUS CANADIAN IRON MINE.|
THE province of Quebec in the Dominion of Canada is sometimes known as French Canada, because of the rights and privileges granted the inhabitants of French origin when Canada passed into the possession of the English crown, and because the majority of the inhabitants are of French ancestry and speak the French language. Time has flown, but in many parts of Quebec language and customs have remained stationary. To-day the student of language or of folklore or of ballads finds large portions of French Canada what old France was a century or more ago; and just as the student of the French language can hear spoken to-day the French tongue as it was spoken a century ago in old France, so the traveler who visits the historic district of Three Rivers may turn back the hand of time, as it were, and see to-day the mining of iron ore, and until recently the smelting also, carried on exactly as in the Old World decades ago.
At Three Rivers, not far from midway between the cities of Montreal and Quebec, the St. Maurice flows from the north into the St. Lawrence. The lower portion of the valley of the St. Maurice is historic ground in the annals of iron-smelting on this continent. The immense deposits of bog ore of this district were objects of attention during the French régime, and as far back as 1668 official examinations of these deposits were made by order of the Government of France. The erection of a furnace was begun by a private company under very favorable arrangements with Louis XV of France in 1737, but it seems that the French Government obtained control of the work, and in 1752 the St. Maurice furnace was blown in, and the old stone stack with Walloon hearth bearing the date 1752 and the insignia of France, the fleur-de-lis, still stands to dispute with that of Principio, in Maryland, the right to be considered the oldest in America. This quaint old furnace was in use until as late as the summer of 1883. It is worthy of note, too, that in 1775, during the American invasion of Canada, one of the lessees of this old furnace aided the Americans and actually cast shot and shell to be used by them against the city of Quebec.
The manufacture of iron is still carried on in this district. A few miles from the old St. Maurice furnace one finds at Radnor the well-equipped modern water-jacket forty-to fifty-ton furnace, the property of the Canada Iron Furnace Company, producing a very superior grade of charcoal iron. This touch of the modern world seems almost out of place in a region in which old France lives again, but, as we proceed still farther up the St. Maurice Valley, the curtain is once more drawn, as it were, over the modern world.
At Lac à la Tortue, twenty-one miles from Three Rivers, we are again in the dim past. We can stand upon the shore of this lake and see a sight that might have been the original for an illustration of iron-ore gathering in Scandinavia one hundred years ago.
This Lac à la Tortue (Turtle Lake) is our curious Canadian iron mine. It is a body of water about four miles long by a mile and a quarter in average width, occupying the center of a large area of swampy land. The surrounding land is largely composed of sand formed by the wearing down of the Archæan rocks by glacial action.
It is well known that decaying vegetable matter yields acids that dissolve the oxide of iron. Evidences of this solvent action of vegetable acids on iron are frequently seen in pieces of slate. The slate is colored by iron, but frequently white or light-colored spots occur. These are points where a leaf or a fragment of bark has been deposited with the fine mud in which form the slate was deposited. The leaf or bark has decayed, the vegetable acids thus formed have dissolved the iron oxide to which the color of the slate was due, and of course a white or colorless patch is formed.
In the sandy area around Lac à la Tortue we find the most favorable conditions for the action of vegetable acids on iron oxide. The sandy land produces a rank vegetation, and its decay furnishes abundance of organic acids. These acids are in solution in the drainage waters, which on their way to the lake percolate through the sand. They thus come into contact with the iron oxide in the finely divided materials, dissolve it, and carry it along to the lake. Here a new chemical action comes into play. The solution of iron in vegetable acid (in which the iron is in what the chemist calls the form of a protosalt) is oxidized by the action of the air on the surface of the lake into a persalt, which is insoluble, and appears on the surface in patches that display the peculiar iridescence characteristic of petroleum floating on water. Indeed, not infrequently these films of peroxide of iron are incorrectly attributed to petroleum. These films become heavy by addition of new particles, they sink through the water, and in this manner, in time, a large amount of the iron ore is deposited on the lake bottom. It must not be supposed that the ore is deposited as a fine mud or sediment. On the contrary, in this lake ore, as it is called, we have an excellent illustration of what is known as concretionary action—that is, the tendency of matter when in a fine state of division to aggregate its particles into masses about some central nucleus, which may be a fragment of sunken wood, a grain of sand, or indeed a preformed small mass of itself. Precipitated in water, as our lake ore is, it of course has great freedom of movement, and we therefore find it in flat concretions, more or less porous and circular in outline; the general appearance amply justifying the term "cake ore," which is locally applied. These concretions vary much in size, some of them being no larger than mustard seeds, others eight or ten or more inches in diameter. Frequently the larger cakes are joined together and form masses looking not unlike batches of a certain kind of bun commonly exposed in the shop window of every confectioner, and made by coiling a strip of dough round and round a piece of itself.
The ore is not found over the whole lake bottom; it occurs along the whole margin, and also well out from shore where streams enter the lake, the distance of the ore deposit from shore depending, of course, upon the volume of water carried by the streams and the velocity with which it enters the lake. Certain strips of ore occur at a considerable distance from the shore and in as much as sixteen feet of water. These deep-water, mid-lake deposits denote probably the courses of former streams which are now nonexistent, owing to some change of level.
Not only is this lake an iron mine, it is more; it is something like the widow's cruse of oil of which we read in Holy Writ—the supply is being constantly renewed. Vast amounts of iron still exist in the surrounding sands. Vegetable acids are formed from the decay of each year's vegetation, and each year the drainage carries into the lake and deposits there a large amount of iron. This is no mere theory: one can actually see the deposition of the ore along the margin, and, moreover, it is found in actual working; if a certain spot be worked out, it will in a few years again yield ore in paying quantity.
Lake ores are abundant in northern Europe, but, so far as the writer's knowledge extends, Lac à la Tortue and a neighboring lake are the only instances of the kind in North America. The ore is extracted from our lake mine by hand and by power. The shallow margin is divided into sections and allotted to suitable parties who may desire to work them and who are paid at a specified rate per ton of ore raised. Two men generally work in company. Their implements are a shovel, a strong circular sieve, and a rough hand barrow. When work is to be begun the workmen remove shoes and stockings and use their feet in searching for ore which lies imbedded in the soft sand, nothing coarser than sand, except ore cakes, being found in the lake. Guided by their feet, the workmen put down their shovels and bring to the surface a quantity of ore and sand which they throw into their circular sieve. This is then held below the surface of the water and made to rotate to and fro until the soft sand is washed away from the ore, which is then thrown on a scow provided for the purpose or carried to shore. When a sufficient quantity has been collected it is carted to the railway near at hand and loaded on cars.
From the deeper parts of the lake the ore is raised by means of a steam dredge. The captain of the dredge moves over the lake, and, putting down a pole and working it about on the bottom, can easily learn where there is a body of ore suitable for dredging. The dredge is then moved to the desired spot and work is begun. The ore and sand are brought up in buckets on an endless chain and thrown into a long, revolving screen, adjusted and inclined so as to deliver it upon scows moored to the dredge. In its course down the screen the mixture of ore and mud is acted upon by water which is thrown upon it with considerable force.
By this means the mud and sand are washed out of the screen and the clean ore is deposited on the scows. These are towed by a steamer to the landing at the head of the lake, and the ore is transferred to cars to be conveyed to the furnace, ten miles distant.
The plant on the lake consists of the dredge, a number of scows, and a small tug, the latter being used in moving the dredge from place to place, in towing the scows, and in carrying supplies, for the crew live on the dredge from Sunday night until Saturday night, and work overtime, in order that a year's supply of ore may be raised during the summer.
The ore obtained from this lake is essentially a brown hematite—that is, hydrated peroxide of iron, with which is associated more or less organic matter. The writer has made numerous analyses of the ore, and the following is that of a sample representing a large quantity:
|Loss on ignition||16·84|
This lake ore, mixed with carefully selected bog ore from the adjacent district and with a certain percentage of magnetic ore, is smelted with charcoal in the Canada Iron Furnace Company's furnace at Radnor, and produces a charcoal iron (brand "C.I.F.") far superior to the iron from the Lake Superior charcoal furnaces. It brings a high price, and is largely used in the manufacture of mill rolls and car wheels. Indeed, its superior qualities are so marked that it is used by various manufacturers in the United States in cases where great strength combined with wearing and, in the higher grades, chilling quality is of first importance.
As an evidence of the splendid quality of this iron the writer gives the following extract from a letter written a short time ago by a leading American manufacturer, viz.:
"Desiring to make a casting which should combine great strength with a tough wearing surface, we have lately been experimenting with the Canada Iron Furnace Company's metal, and by using it we have raised the transverse strength of our test bars from 2,300 and 2,500 to from 3,900 to 4,000, the test being with one-inch-square bars twelve inches long. We have never been able to accomplish any such results with any other iron we have used, and in addition to this greatly increased strength we find an added toughness which makes the casting work almost like a piece of steel."
- Very interesting details concerning the ores are found in Percy's Metallurgy.