How Deep Is Down?
Sinking a mine shaft in the middle of a lake is only one of the many notable feats of Canada's mining engineers
AGAINST the Northern Ontario skyline, the shaftheads resemble fantastic monuments. They are. Over a mine that has failed, the shafthead is a
Over a mine that has failed, the shafthead is a monument to vain hopes and lost endeavors. Over a new mine it is a monument to faith. Over an established producer, wrenching tons of ore frorh the black depths of the earth, day in and day out, it is a monument to the labor and ingenuity of many men.
Most of all, I like to think, it is a monument to the men who sank the shaft—the drillers and muckers and timbermen who did the dangerous and back-breaking job of gouging and blasting and smashing their way into the solid rock, cutting out that huge rectangular hole, plumb and neat for thousands of feet below the surface.
A salute, then, to the men who sink deep shafts—the men who play their part in changing the answer to the question, “How deep is down?”
Because the answer, you see, is not constant.
There is a limit to the economical depth of a shaft. There is a limit to the depth men can descend into the earth. That limit, however, has not yet been reached. And in thrusting their way deeper and deeper into the hard Pre-Cambrian crust, Canadian mining men have done some fantastic and epic jobs.
A Shaft in a Lake
AT THE Lake Shore Mine, in the Kirkland Lake gold field, they had a problem. A shaft, be it known, is never sunk directly into the ore body. Its location is determined by the pitch and dip of the ore, so that the shaft will be in the “footwall” of solid, valueless rock. Prom the various levels, then, miners will tunnel toward the ore —very long tunnels, perhaps, in the upper levels; shorter, perhaps, at the lower depths where the downward dip of the ore body may be nearer the shaft.
At a new property the location of the permanent shaft will be determined from discoveries made by diamond drilling or the sinking of a small pilot shaft. At a proven mine it will be based on the knowledge engineers and geologists have gleaned from the workings already established. At the Lake Shore, the management had agreed upon the necessity of a new shaft, but they were on two horns of a dilemma when it came to selecting that shaft’s location.
To achieve their desired purpose they could sink the shaft at a point on land which would involve long overhead carriage to the mill with a hundred other vexing problems to solve above ground and below, or they could sink it out in Kirkland Lake.
So they decided to sink the new shaft, planned as an elaborate job with an ultimate depth of 4,000 feet, out in Kirkland Lake.
To sink a shaft in a lake may seem impossible. It isn’t. But it is difficult. Not as difficult, however, as the task of sinking a shaft in a bog. And Kirkland Lake is no shining northern lake. It is a soggy grey swamp of mud—tailings from the mine mills where rock is pulverized, the gold extracted and the waste discarded.
To sink a shaft you have got to dig down to bedrock first. Then you have to drill into the rock; you have to erect a temporary headframe so that workmen and tools and supplies can be lowered, so that muck can be carried up to the surface. You have to build a concrete “collar” for the top of the shaft. It’s a big job in rock. In eighty feet of mill tailings, blue clay and lake-bottom silt, it’s a staggering job.
If they could get that shaft into the rock, if they could get it collared and headframed, the Lake Shore people knew they could drill up from the levels already established below ground and hook up with the work done above. A literal case of starting at the bottom. Sinking a shaft in reverse, as it were.
So they called in an engineering company whose experts designed three caissons. Two were solid, for headframe support. The other, with an outside diameter of forty feet, was six feet thick, made of wood staving bolted to circular trusses It had a steel cutting edge. The big caisson was
set in place and a crew of sandhogs went to work as the caisson was filled with concrete, cutting down into the oozy tailings under its own weight.
It was started as an open caisson, but the construction people made provision for converting it into a pneumatic caisson if they had to. They did. Down fifty feet, the caisson slanted out of plumb because of the hard material overlying bedrock, so from there on the men worked in an airlock under twenty-seven pounds of pressure. This gave better control over the sinking operations.
It took from May to November, but by the time the caisson was down to grade, down through sixty-seven feet of mill tailings and another twentyeight feet of clay, hardpan and rock, it was in alignment, and there was no further danger that the permanent headframe of Lake Shore Number Five would wind up looking like the Leaning Tower of Pisa. When you are lowering and raising skips and cages to depths of 4,000 feet, your shaft has simply got to be straight up and down.
At any rate it wras a big job and a fine job. It cost $120,(XX), and if you visit the Lake Shore now you can go out onto a great concrete platform just a short distance from the shore of the lake, and you’ll see a big, modem shafthouse. The shaft itself is unique in the Western Hemisphere, one of the great shafts of the world, not wholly on account of the fact that it begins in a lake, but because it is completely fireproof.
Most shafts are lined with timber. The forests of British Columbia have contributed heavily to shaft jobs all over the world, for British Columbia fir, treated with zinc chloride, is practically everlasting — great stuff for lining a shaft. They don’t board the whole shaft from top to bottom, of course, but they install “sets” about eight feet high at intervals of about six feet apart, hanging them together by metal rods and resting them at intervals on concrete ledges.
But the spectre of fire haunts every mine manager. When you consider that the Hollinger, for instance, uses about 8,000,000 board feet of timber underground every year, it becomes apparent that there is a lot of wood in a big mine. Even when it gets the zinc chloride treatment, which prevents fungus growth and acts as a fire retardent, it is still a lot of wood. And if a fire broke out, got past the fire doors, with a big 4,000-foot shaft acting
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as a chimney, even if that shaft is dripping moisture
The new Lake Shore shaft is fireproof. Steel isn't satisfactory. It is liable to buckle. The new Number Twenty-six shaft at Hollinger will be practically fireproof when it is finished, made so by the use of copper-bearing, corruga ted-iron firebreaks l>etween the wooden sets. At Lake Shore they lined the shaft with haydite.
Haydite is made at Cooksville. Ontario. Molten shale forms a porous slag used as a medium for casting cement slabs. Mechanical Superintendent D. W. Cramp, who had cliarge of the surface layout, designed the slabs, and now the big new shaft, which exist $1,750,000 and went into operation in February of this year is fireproof from top to bottom. The use of heavy electric cables to serve subshafts at greater depths, was a big factor in influencing the fireproofing decision.
An expensive shaft? Yes, it cost a lot of money. But it will open up at least $15,000.000 worth of ore. That’s the answer.
An Internal Shaft
AND MINING men take off their hats - to their brethren who sank Number Six internal shaft at the Dome, in South Porcupine—another big job recently completed. One of those million-dollar affairs that would be a respectable achievement if carried out from surface in any camp. But this was created in the heart of the earth.
Number Three is the main shaft that serves Dome from surface, its skips carrying 1.500 tons of ore a day. It is more than 2,tXK) feet deep. Number Six is almost identical, with the exception that it begins almost a mile from the bottom of Number Three, is complete and self-contained in the depths of the rock from hoistroom to loading pocket.
General Superintendent Bob Dye saw that I had service plus when I went down to visit Number Six a few weeks ago. At the foot of the main shaft a trolley locomotive was waiting, for it’s a long walk between the two shafts. Over heavy rails the tiny train went roaring down the tunnel. Electric lights gleamed at intervals above. Away ahead, ruby and green lamps glimmered in gloom. A huge door, one of the many that control ventilation of the mine, blocked the tunnel ahead. The locomotive thundered straight toward it, the door split and swung automatically open, closed behind us again when we went tlirough.
Over this 4.600-foot railway, they hauled 400 tons of steel and three quarters of a million feet of lumber for ttye new shaft. Over it will be carried the ore'that will be
brought up from the lower levels served by Number Six. Over it was carried the million cubic feet of rock they excavated and sent over to the Number Three shaft to be taken to surface. Over it was carried the huge drums and massive electrical equipment. 250 tons of it in all, for the hoistrooms. Some of the sections weighed as much as ten tons.
And the hoistrooms, one for the cage hoist and one for the skips, with their enormous ten-foot drums, and their great 700 horsepower motors-those hoistrooms, roofed with haydite slabs, with their concrete floors and whitewashed walls, those immaculate chambers in the heart of the'earth, are the results of monumental organization and labor.
Picked men. the best all-round miners on the payroll, sank the shaft. Eighteen men—twelve drillers and six helpers -would drill holes in the rock. The holes would be filled with explosive and blasted out. The loose rock would be broken up and hauled up the shaft, sent over to Number Three, nearly a mile away, for removal to surface. Nearly five times as much time would be spent in this “mucking” as in drilling.
Men coming on shift would carry on from where the previous shift left off, and in a day they would use from 1,000 to 2,000 sticks of explosive, would average an advance of eight and a half feet.
Every three days they would turn to the job of timbering, installing the big creosoted “sets” of British Columbia fir that were cut on surface and sent down in sections. They would install two or three of these sets at a time, hanging six feet apart, so that always the timbering kept within twenty-five feet of bottom. Government regulations allow a maximum of forty-five feet. A loose piece of rock dropping from the side of an untimbered shaft can cause a lot of damage, although the men work under a big safety shield that follows them downward.
So from August, 1936, to the end of July, 1937, the Dome crews sank the big internal artery. The amazing part of it is that the ordinary day-to-day work of the mine was not disturbed. Dome went on hauling 1.500 tons of ore up Number Three as usual from the upper levels.
Number Six cost about $150 a foot, and it is 2,062 feet deep. And while the shaft was going down, other miners were tunnelling from other workings, tunnelling away down under the shaft-sinkers and cutting out stations. They would tunnel away down and across to the place where their surveys told them the new shaft would hit the 18th level, and they would blast out a big cavern for the station before
the shaft got there. Then, from another working, they would tunnel down and under to the 23rd level, prepare another station. And so on, to the 27th level.
The slightest error in the surveys would have meant a vast waste of time, money and energy, but as the shaft went down it entered station after station—“hitting ’em right on the nose every time,” a workman told me proudly.
For, make no mistake about it, the men are proud of these big jobs. You’ll hear the word “we” used in reference to these accomplishments, oftener than “the management.”
“A Futuristic Cathedral”
AT CREIGHTON MINE, in the Sudbury area, the International Nickel men are particularly proud ot the hoistroom that serves the big Number Five shaft.
It is an industrial poem. Big as a skating rink, all black and white tile, housing huge sleek black motors and two Gargantuan black drums that are the biggest machines of their kind in North America, it looks like a futuristic cathedral for the worship of Power. Here the drums of the cage hoist are fourteen feet in diameter, and raise and lower the six-ton cage that can carry tifty-four men. Here, too, is the skip hoist, twenty-five feet in diameter at the large end, operating the two live-ton skips, each with a capacity of nine tons, at a top speed of 3,000 feet a minute.
Identical with the huge Number Three shaft at Frood Mine, also operated by International Nickel, the big Number P'ive job at Creighton goes to a depth of 4,075 feet, which explains the mammoth hoisting equipment. There are deeper mines in Canada, but there are no deeper shafts. Its companion, the old Number Three, is one of the most interesting jobs in the country in that it is one of the few inclined shafts in the country that is, it was sunk at an angle of fifty-five degrees, and the skips and cages, accordingly, run on rails.
A trip down Number Three at Creighton has bobsledding beaten. You sit on a wooden bench at the slanting back of the great cage, with its grilled window in the door. And when the hoistman lowers away and that four-ton car goes roaring down the tracks into the interior of the earth, the sensation can’t lye equalled by any rollercoaster ride in the world.
You don’t travel as fast as in a vertical shaft—no more than 1,100 feet a minutebut the deafening uproar of your journey down that steep incline, the flash-flash of the station lights swooping past the grill, combine to create the impression that you are shooting down the slippery slide to Avernus at a breakneck gait.
Down below, you can walk through the subterranean tunnels over to Number Five shaft country —they refer to men working in such-and-such a “country” at Creighton, as if a big mine is a world in itself, which is true enough. Then you can continue your journey down Number Five to bottom, where it is definitely very warm and very wet. But to attempt any comprehensive description of Creighton and Frood mines, those enormous networks of burrows with the ultimate in modern equipment, would require an entire copy of Maclean s, and we are merely trying to learn how deep is down.
The Ultimate Depth
ARTHUR A. COLE, mining engineer ■ of the T. & N. O. Railway, has actually made a hobby of this subject. The study of deep mining has fascinated him for years, and he told me that the deeper he digs into the matter the more there is to learn. Which seems appropriate enough.
Problems of heat and humidity at depth, for instance. In South African mines, the temperature rises one degree for every 220 feet of added depth. In Canada the temperature rises more quickly, one degree for 200 feet. But this holds true only to a certain stage. At great depths it gets hotter faster, as men approach ever so
little closer to the white-hot core of the globe.
In the depths of the deepest Canadian mines, workmen are given salt tablets to j counteract the effects of humidity. At 8.000-foot depths in South Africa, the natives can work only for a few hours at a time, in a welter of perspiration. Experimental work with great refrigerating devices has been in progress for some time now, but it may be several years before conclusive reports can be made. Perhaps by the time Canadian mines get to similar depths, improvements in ventilation and refrigeration may have solved some of the problems of staying down.
Problems of getting down, however, have been handled with high success, as exemplified by the notable shaft jobs described in this article, by the achievements of Teck-Hughes in reaching the record Canadian depth of 6,142 feet. Shaftsinking is a wet, dangerous job. demanding the very best all-round miners and the very finest organization if speed is to be achieved. Canadian miners have shown that they can sink tremendous shafts with speed and safety. There was only one fatality on the Lake Shore job, only one at the Dome internal, and each was from an accident unconnected with the actual sinking.
But deep-mining problems are economic rather than physical. The tremendous rock pressure necessitates more extensive means of support for the workings. Costs of mining, hoisting, pumping and ventilation all go up as the mine goes down. The use of alloys, permitting lighter cages and cables, may increase the present economic depth of 4,000 feet for a shaft. And then, too, Canadian mines are fortunate in that the rock is hard and comparatively easy to work in. But the value of the gold must repay the cost of mining it.
As to that, it appears that in the major Canadian gold camps, miners will find gold ! as deep as they can go under present conditions. Whether they will be able to go as deep as the gold persists that is something else again. At depth, Canadian gold mines of the first rank show no appreciable diminution of value or change in type of mineralization.
In the Witwatersrand, in South Africa, where the Robinson Deep plunges to 8,(XX) feet, there is very little notable change in the average grade of the ore. All deep mining in the world is done in Pre-Cambrian rock—in the Transvaal and Witwatersrand, in India, in Brazil, and in the deep copper mines of Michigan —and Canadian gold mines are likewise in Pre-Cambrian.
So it appears that the gold will go deep.
At Kirkland Lake, for instance, the ore bodies are in the proportion of one foot vertical to four feet horizontal. The main ore shoot of the camp, from the TeckHughes Mine on the west, through the I^ake Shore property to the WrightHargreaves on the east, is more than 3,(XX) feet in length. If the ratio holds good, there will be ore at a depth of 12,000 feet - and the Teck-Hughes is Canada's deepI est mine at half that distance.
How deep, then, is down?
As deep, so far, as it pays to go.