Abstracted from a paper read before the General Mining Association of Quebec,
by L. A. Klein, M.E., 1892
Until 1879, Italy supplied nearly all the fibrous asbestos required by the world, but in that year a number of companies were formed to work the veins known to exist near Thetford and Black Lake, in the Province of Quebec, Canada. Since then, owing to the constantly extending use of woven asbestos, the working of this mineral has become of considerable importance. According to the official statistics of the Canadian geological survey, the value of the asbestos in Canada in 1891, was $1,000,000, being exceeded only by that of coal, nickel, copper and petroleum.
This industry is now in the hands of thirteen incorporated companies, having an authorized capital of about three and a half million dollars of which two and a quarter million, according to Mr. Klein, are invested in the industry in Canada.
To prepare the asbestos for market, two operations are necessary namely, the mining proper and cobbing, or separation of the asbestos from the adhering serpentine. At most of the mines the drilling is done by steam or compressed air, 45 feet of hole per day of 10 hours. In the former case and 50 to 55 feet in the latter being considered a fair days work, at an average cost of seven to eight cents per foot of hole drilled. At present there are in use seven compressors, with a total capacity of 44 drills, and there are 44 steam drills.
The average cost of drilling amounts to three and one-half cents per ton of rock broken. Dualin, which contains 85 per cent nitro-glycerine, and costs 20 cents per pound, is the explosive used; it is fired by electricity. The expense for explosives is about 8 cents per ton of rock. The broken rock is roughly sorted in the pit, the waste rock being sent to the dump by wheelbarrows, or in the larger mines by derricks and the crude asbestos to the cobbing sheds. The cost of this averages 25 cents per ton of rock.
The second and most important part of the work is the dressing or cobbing of the asbestos and then grading it. This grading is generally done by hand by boys. Some of the mines have, however, partially or entirely adopted machinery for this purpose, in order to avoid the loss of asbestos contained in the so-called cobbing stone, i.e., large pieces of rock with a vein of asbestos in it, which did not separate by the blast, and which can only be separated by heavy sledge hammers or by crushing.
The first to try to solve this problem was the Scottish-Canadian Asbestos Company. Their plant consisted of a Blake crusher, traveling picking tables, Cornish rolls, revolving screens, elevators, chokers and blowers.
The mines of this company were closed during 1888, and it was not until the winter of 1890-91 that the American Asbestos Company started to experiment in this direction, the main object being to do away with what is known as grade No. 2. At this plant the crude asbestos is conveyed by an inclined railway, and automatically dumped in front of a Blake crusher, the jaws of which are set at 1-1/2 inches. The crushed ore drops on an inclined sieve in shaking motion, which separates all the loose fiber and the dust from the larger pieces of rock and asbestos veins, the former going directly to the cleaning or grading machines, the latter dropping on a revolving picking table, where the barren rock is removed by hand to one side of the table, the asbestos veins being left on the other. At the end of the table is a receiving chute which is divided into two compartments, and into which rock and asbestos are discharged respectively. The rock drops from the chute directly into a larry and is wheeled to the dumps, while the asbestos is conveyed either to the kilns, necessary in winter time or rainy weather, or to the fine crushers for further treatment. These latter are of unique construction, of which the object is to allow particles of a certain size and loosened fiber to go through, without being further crushed, as thereby the asbestos fiber is likely to be injured. This so reduced stuff is brought to the cleaning and grading machines, consisting mainly of a set of inclined sieves in rapid shaking motion in connection with blowers, fans etc., while the remaining unbroken stone and unloosened fiber goes back to a set of still finer crushers to undergo the process again.
The plant at King Brothers mines in Thetford, which was principally erected for the extracting of asbestos out of large pieces of rock on the old dumps, which some years ago did not warrant the expenses for block-holing and further handling, consists of a Blake crusher, from which the stuff is conveyed on a set of Cornish rolls, with the intention of having all stone reduced to powder, from there to a revolving screen, of which the object was to screen out all the dust and leave the clean fiber. This object, however, has not been fully realized, owing to the failure of the rolls to break up the rock entirely, and an additional blowing and screening plant has been put in, which produces now a very clean product of one grade.
The Anglo-Canadian also runs a crusher and a set of sieves, and the Johnson company has recently put in a couple of crushers to overwork the old dumps. None of the processes at their present state, however, may as yet be considered complete, the main difficulties being two:
1. That, if asbestos is crushed with a considerable amount of stone, until the latter is reduced to powder- the long and most valuable asbestos is partially destroyed.
2. If the stone is not entirely reduced before grading, it is nearly impossible to free the fiber from the stone, and a large amount of waste is the result.
The cost of cobbing, according to Mr. Klein, varies considerably, according to the quality of material. While some asbestos will break from the stone very easily, other requires considerable labor; then larger veins will sooner be gathered than small ones. He places it, including the breaking of the cobbing stones, at $7 per ton at the leading mines.
The asbestos after being graded, which is, however, in the entire discretion of every particular mine, is put in bags of 100 pounds each. Cost of bags are from 5 to 6 cents each; cost of bagging, 20 to 25 cents per ton. The cost for transport to cars and loading, varies from 10 to 60 cents a ton according to distance from railroad.
In estimating the cost per ton of asbestos Mr.Klein says: On this subject the opinions of the asbestos quarrymen are very different, and while some claim to mine only 50 or 60 tons of rock to the ton of asbestos, others go as high as 150. I am of the opinion that as a rule the quantity of rock mined to the ton of asbestos is greatly underestimated. Basing, on the capacity and actual work of our machinery appliances, the known quantity of larry loads removed from a mine during a year, and the known average weight of each load, in relation to the totals of asbestos produced, I hold that one ton of asbestos to 100 tons of rock is a fair average.
If we accept this the cost of production of asbestos may be set down as follows: drilling, 3-1/2 cents; blasting, 3 cents; labor for removing rock and gathering asbestos in the pits, 25 cents, making a total of 31-1/2 cents to the ton of rock, or $31.50 to the ton of asbestos; $7 for cobbing; $1.50 for bags and bagging; 50 cents for loading; $5.50 for supplies, which includes fuel, tools, iron, steel, timber, other materials and repairs; $6 for general business expenses, such as management, insurance, offices, marketing and others; $3.55, 10 per cent wear and tear, calculated on a total of $355,000 in plant, making a total of $55.55 to produce one ton of asbestos. If we calculate now that we have to pay interest on a total invested capital of about two and one-quarter millions of dollars, for which at least 10 per cent must be expected, we have in our sales to average a price of at least $80 per ton of asbestos.
The output of asbestos in 1880 was but 380 tons, valued at $24,700. Since then, the industry has steadily increased, with the only exception of 1888, and reached in 1890, 8,860 tons with a value of $1,200,240. During the period between 1880 and 1890, the increase has been nearly 2,600 per cent in tonnage and 5,100 per cent in value. Since 1880, the prices have been as follows: 1880, $65; 1881, $65; 1882, $65; 1883, $72; 1884, $65; 1885, $58; 1886, $59.75; 1887, $49; 1888, $60; 1889, $69.75; 1890, $127; 1891, $111. During this time the imports of asbestos by the United States have increased from $9,786 in 1880 to $254,935 in 1890.