MINE SITE UNSEEN
Geophysics, science of the doodlebug, scores a triumph in the realm of Canadian mining
DURING last March Canadians interested in this country’s heavy industries were deeply stirred by the official announcement of a discovery of high grade iron ore at Steep Rock Lake,
Ontario. The find, made at a point 135 miles west of Port Arthur, four miles north of the C. N. R. station of Atikokan, shows an ore body estimated on the preliminary investigation work to contain 100,000,000 tons of ore averaging between fifty-five and sixty per cent pure iron.
In average good times Canadian heavy industries consume around 2,000,000 tons of iron ore a year, or more. Since 1915 the Dominion’s production of iron has steadily declined. almost to the vanishing point.
Instead we have imported ore from the United States and Newfoundland.
Much of that ore has been taken from mines on the American side of Lake Superior, almost directly across from the site of the Steep Rock Lake discovery. Mining men have long cherished the dream that the iron deposits across the boundary might extend under Lake Su¡xrior to the Canadian side. Exploration and drilling last winter, leading to the official announcement of March, indicate that the dream may come true.
In time this Steep Rock Lake iron deposit may change the entire picture of heavy industries in Canada, espe daily with regard to steel and steel product«. That remains to be seen.
Its special significance for the purposes of this article lies in the fact that the comparatively new science of geophysics is credited with having played an important part in proving the existence of this immensely valuable iron range.
Geophysics, as a science, is only about ten years old in Canada. Its name is compounded of the two allied sciences which contribute to its manifestations—geology and physics and its operations are described as geophysical exploration. The Steep Rock Lake discovery marks the greatest triumph geophysical exploration has achieved to date.
Long before geophysics was recognized as a true science, numerous ingenious gentry, some plainly rascals, others merely self-deluded, were abroad in the land, claiming extraordinary, often occult powers for this or that fantastic process by which they professed to lx* able to detect the presence, below the visible surface of the earth, of valuable mineral deposits. Ribald mining men pinned the nickname “doodlebug" on these prestidigitators and their gimcrack gadgets alike. The name has stuck, SÍ) that today even the gravest, most scientific geophysical explorer refrains from flinching when his youthfully irreverent assistants gaily announce that they are about to doodlebug a mining property. Steep Rock Lake was most thoroughly doodlebugged.
Reduced to its simplest form the theory of geophysical exploration may be stated so: Various rock substances existing below the surface of the earth, respond in different ways to certain electrical, magnetic, gravitational and seismic influences. By employing on the surface instruments designed to create these influences underground, it is possible, by recording sub-surface reactions, to ascertain with considerable accuracy, the rock or soil conditions existing below the surface at depth. The findings so established supply the mining engineers with information upon which to plan their future operations.
Geophysical exploration methods may be divided roughly into three groups: the gravitational; electric, including electromagnetic; and the seismic methods. Of these the electric and electromagnetic methods are most generally employed in Canadian mining. The work done in the Steep Rock Lake district was electric and electromagnetic. Most spectacular of all geophysical exploration methods is the seismic; but that is of no value in hard-rock prospecting, being employed only to assist the search for oil.
At Steep Rock Lake the presence of iron ore had been indicated by geological surveys for many years, and to some degree proved through diamond drilling operations; but the extent and the actual position of the ore body were unknown. Last winter, Dr. A. Brant of the Physics Department, University of Toronto, with three associates, also from U. of T., J. Britton, R. Clark and F. McDonald, made a complete geophysical survey of the entire area. Their explorations outlined an ore body 4,000 feet long, curving in a great arch in one section of the property. At another ]x)int a mile and a quarter south of this body, preliminary geophysical work indicated the presence of another deposit which hitherto had not been known. Diamond drilling in this latter location showed high grade ore. It was upon the findings of Dr. Brant’s survey, verified by the cores brought to the surface by the drillers, that the owners of the property based their estimate of a probable 100,000,000 tons of high grade iron ore.
Exploration Costs Cut
THIS comparatively youthful science of geophysics has already taken a lot of the guesswork out of mining, will take more in years to come. Its practical value to the mining industry is that it can save many thousands of dollars hitherto spent annually in futile and costly diamond drilling.
Let us avoid error. The geophysicists have not banished the prospector; nor have they evicted the geologist and his little hammer from the outcroppings, or thrown drill crews out of jobs. Their work complements all three. They follow the prospector and the geologist, toil side by side with the driller, indicating to him just where he can bore holes to the best advantage.
Diamond drilling through hard rock is an expensive
business. Average costs run about $1.75 a foot in the nearer mining areas, and may mount to $2.25 or $2.50 a foot in the remoter camps. To put down half a dozen test holes on an ordinary prospect will nick the treasury for $6,000 or $7,000, and that’s not pin money. A geophysical exploration, taking a month or six weeks time, costs from $2,000 to $2,500. That’s not hay, either, but once a mining engineer has those geophysical charts in front of him he knows where he can drill with the best chance of getting results. If the property is nothing but moose pasture, he’ll know it, and he’ll throw no more good money after bad in wasted efforts to discover something that just isn’t there.
To the uninitiated the evolutions of a geophysical exploration party in the field appear to be a bit on the queer side. They smell of witchcraft. A wayfarer from outside, chancing upon the Brant party going about its daily chores in the Steep Rock Lake area last winter, for instance, would have seen a group of young men bearing tripods, bundles of steel rods, and rectangular boxes looking something like portable radios. The boys would have been observed driving the steel rods through the snow deep into the earth, then connecting them up with wires. They’d be fussing around with their boxes, taking voluminous notes. None of this seeming monkey business might be expected to make sense to the casual onlooker. To the trained geophysicist these various operations reveal a clearly charted outline of rock and mineral conditions underground.
Mineral substances and mineralbearing rocks respond in different ways to electricity. Some are highly conductive; others are highly resistant. The electrical method of geophysical exploration measures the degree of conduction or resistance to electrical currents registered by the rock substances existing below the surface within the area explored. The record of that conduction or resistance shows the geophysicist the identity of the underground strata and their locations.
Those steel rods, strategically placed and wired to a battery, carry a measured electric current through the surface earth—called by mining men the overburden—to the rock below, then return it to recording instruments. By charting the quantity of current returning through different sections of the area under survey, there is obtained a reasonably accurate idea of the formations below surface inside that area.
Modern Canadian mining practice uses the electrical exploration method increasingly each year. It is equally effective in the hard-rock gold-mining districts, as it proved itself at Steep Rock Lake. But other, older, and simpler methods are still being employed. The dip needle, which is nothing more than the ordinary magnetic needle the man from the water department uses to locate through a snowdrift the right place to turn on your water supply, has its uses in magnetic survey work and was employed in the early prospecting work at Steep Rock Lake. Just as different ore-bearing bodies respond in different ways to electrical currents, so some ores are highly magnetic, others less so.
When the dip needle is suspended, it takes up a definite known position controlled by the ordinary magnetic forces associated with the earth. Where magnetic ores exist below the surface the needle registers wide variations from this normal position, and the degrees of those variations will tell the geophysicist, to some extent, what lies beneath. At least it will tell him whether the underlying rock formation contains magnetic or nonmagnetic ores.
The electromagnetic method is an elaboration of the simple magnetic process. The dip needle is linked up with an electric current. The measurements of magnetic force obtained by this method have been found more accurate and of wider range than those registered by the dip needle alone.
Of all methods of geophysical exploration, the seismic method, requiring the artificial production of a series of miniature earthquakes, is the most elaborate, most costly, and most mystifying to the layman. Also it has the highest record of efficiency. Although it is of no value in hard-rock territory, it gives to the oil industry a confidence and certainty never before dreamed of.
"POLKS FROM outside who chance to be ^ wandering around the Turner Valley while a seismic survey is in progress, may well find cause for alarm if they happen to come across the spectacle of a group of khaki-clad men apparently engaged in the grim business of blowing up the countryside.
Such suspicious-looking parties travel with three or more motor trucks and a number of fast private cars. The trucks are equipped with numerous strange devices, not usually seen on commercial vehicles. Curious people who trail this peculiar cavalcade will find it halting at a certain spot in the open country not discernibly different from any other spot in the open country. There, men will dig holes, plant various objects in the holes, string wires from the holes to the trucks. Then, obviously because one of these sinister characters has thrown a switch, there will be an explosion. A fountain of mud and water will soar skyward, then fall to earth, while the dull “boom” of a dynamite blast assaults the eardrums.
There is nothing to worry about. The lads in the khaki shirts are merely prospecting for oil, using the spectacular seismic method of geophysical exploration.
Most people who read newspapers understand something of the theory upon which the seismograph operates. An ! almost incredibly sensitive instrument, it has been used for many years to register earthquake shocks wherever they may occur, and to record them faithfully as to direction and severity. The recording machinery produces on sensitized paper an I accurate graph of the ’quake’s duration j and violence, as well as its approximate longitude and latitude.
As adapted to oil prospecting, the seismic theory is based upon the subterranean conditions in which oil is usually found. Almost always, oil occurs in conjunction with salt water and gas in sands or porous rock. Limestone, for example, is a common oil carrier.
The seismic method of exploration in territory that is geologically correct for oil, is especially suited because of the peculiar nature of oil-bearing rock formations, which often occur in a series of hills and valleys, domes and basins. Gas and oil, both lighter than water, seek the highest levels. Therefore, where wavy formations exist above porous rock, the gas and oil separate from the water, rise to the peak of the dome, and collect there in pools, imprisoned underground by layers of hard nonporous rock. Such an oil pool becomes an oil well, once it is found and tapped.
A seismographic survey party may consist of anywhere from fifteen to thirty men, with an expert seismologist in charge. There are five units in a full crew, under a party chief—surveying, drilling, shooting, recording and computing. The apparatus —worth about $20,000—and the crew are transported in trucks.
Once on the ground in a location that geological surveys have shown favorable to oil, a series of shallow holes are drilled into the earth. The holes are equally spaced, yards apart, the distance between each hole determined by the area to be explored. Into these holes are set seisphones, delicate little telephonic instruments which carry the shock records through wires to the seismograph on the recording truck. An average seismic exploration shot will employ ten seisphones. Again the number is governed by the size of the area to be tested.
Two more holes are drilled in a line with the seisphone installations. Into one of these goes an instrument called a weathering time indicator, which establishes the depth of the overburden. The final hole is the shot hole. The seisphones are wired to the recording truck, the others to the shooting truck. The two trucks, usually located about a quarter of a mile apart, are connected by telephone, so that the two units are in constant communication. It’s a tricky business, and time is the essence.
At zero hour a man on the shooting truck throws a switch. A small charge of dynamite—about five pounds to the shot hole—is exploded. The shock vibrations travel downward at an angle to the nearest hard-rock layer, from which they are reflected back to the surface and carried through the row of seisphones to the seismograph. At [x)ints where the rock formation is nearest the earth’s crust, the elapsed time between the blast and the returning vibrations will be less than at points where the rock is lower down. Tracing the time variations over a charted area, the expert seismologist can tell where the hills and valleys occur below the surface.
The automatically recorded photographic maps are about four inches wide. They show a wavy line something like a stock-market chart on an active day. Where the line rises, the rock is comparatively close to the surface. Where it falls, the rock is farther down. Between are the valleys in which oil, if present at all, would be likely to accumulate in pools.
Seismographic timing is amazingly accurate. Measurements may be made to within one thousandth of a second. Woi kers on a seismic job must stand still while the shot is being made. If they move, their footsteps would be recorded and the map spoiled. The seismograph is that sensitive.
Oil men get findings at great depth through this method of exploration. Oilproducing structures a mile below the surface have been recorded on the seismograph, and on the Gulf of Mexico the range goes even deeper, to 10,(XX) feet. The method works just as effectively under water as on land.
TT’S AN expensive operation, but the big oil companies have found it worth the price. On a forty-thousand-acre tract of land, a seismic exploration party covering an average of fifteen hundred acres a day would require a month to complete the job. The cost would range between S7.(XX) and $10.(XX) a month, depending ujxin a number of local conditions, location, the amount of explosives required and the degree of difficulty encountered in drilling operations. On the other hand, hit-or-miss drilling on one dry hole might cost ten times ten thousand dollars.
The seismographic method has proved itself to an astonishing degree. Use of the seismograph in oil development work dates back only to the early nineteen-twenties. Fifteen years ago, when drillers for oil had only surface geological indications to guide them, less than three per cent of the test wells drilled brought in oil. Today, with seismic recordings pointing the way, more than ninety jx?r cent of the holes bored show traces of oil. They may not come in right away as paying wells, but nine times out of ten oil is there if the
seismograpli says conditions below the earth are favorable.
In Canada the seismographic method has only recently been introduced, although its use is increasing rapidly. In the vast oil fields of the United States it is now routine practice, involving huge annual expenditures for field crews and research work. Over a considerable perkxi last year one big American oil company alone spent $2,000,(XX) a month on tins branch of its activities, including the cost of laboratory experimentation. This is a startling figure but it comes from an official source, and stands as conclusive evidence of the very real value of seismic exploration to the oil industry.
There is nothing so very new in the abstract theory of geophysical exploration for minerals. Only its present-day efficiency is new. Back before the War. geophysical methods of mining exploration were being tried out in Europe, notably in France, Germany and Sweden. The United States was playing about with geophysics in 1916, and the idea spread to this country in 1920, when we had time to get around to it; but practical demonstrations under scientific test conditions, backed by the authority of the Dominion Government, were first made in this country in 1928 through to 1930, and it is from those experimental explorations that the present important developments stem.
Before the Geological Survey, supreme mining authority of the Dominion, took up its intensive study of the life and habits of the doodlebug, a lot of monkey business was going on. Those were gay and carefree days for the wild-eyed witch doctors and the deliberately conniving confidence men alike. Crooks and conjurers were always bobbing up in mining and oil circles, professing magic powers enabling them to save worried mining engineers a peck of trouble by telling them exactly where they could dig up gold or silver, copper or coal, oil or sulphides.
Among the oil men especially are many legends of old-time doodlebugs, the tales of whose goofy experiments and even more goofy apparatus are good for a laugh wherever, and on whatever occasion, drillers foregather. There was, for example, the madcap enthusiast who developed the unique theory that oil, as a substance, possessed strong feminine characteristics. I le professed to have discovered a sympathetic male liquid, instantly responsive to the presence of oil beneath the earth’s surface, and he walked up and down various oil fields for innumerable miles, carrying oil’s Big Moment in a jug, trying to find new wells. Not one new well was ever brought in by means of this experimenter’s sex appeal methods. Again, there were the two clever young chaps who carried on their shoulders a strange device slung on two poles, and containing some hidden instrument that ticked away industriously like a tin alarm clock. This dingus delivered a strip of paixtr on which was neatly printed the area of the alleged oil field, its depth, specific gravity, geological condition and the approximate number of anticipated barrels. Those bright boys never stopped in any one place long enough to see their findings verified, which was probably just as well.
XJOT SO long ago three impressive gentlemen arrived in the city of Toronto from Pittsburgh, and came close to persuading one of Canada's most astute mining magnates that they had discovered an infallible system for locating goldbearing ores. Their claim was that certain woods were allergic to certain ores; cherry to coal, mahogany to gold, maple to copper; stuff like that. The mining man was sceptical, but he thought enough of the notion to have a series of elaborate tests made, under laboratory conditions, at the University of Toronto.
The tests were fooland tamper-proof. A dozen or so specimens of ore. heavily loaded with as many minerals, were enclosed in identical wooden boxes. The lids were nailed down tightly. When the gold-hunting doodlebugs arrived, the system devised for the test was carefully explained to them. Were they ready to proceed? They were. They were even anxious.
One after another the three solemnly clipped a disc of wood to the tip of a forked piece of steel. They held the two ends of the fork in their hands. The idea was that when the wood responsive to gold was passed over the box containing the gold ore, the point of the fork would dip violently. This same process is used bywater diviners, or “dowsers,” who have a considerable following in some parts of the world, although there exists not the slightest shred of scientific substantiation for their claims.
Once the doodlebug trio had identified a particular box as containing a certain mineral, the box was promptly marked with the name of that ore and locked away in a separate room. After hours of this sort of flummery the test was complete. Every box had been identified through the divining-rod method, and marked. Then the boxes were opened.
Professor Lachlan Gilchrist, of the University of Toronto Physics Department, made that test. It is one of Dr. Gilchrist’s innocent amusements these days to relate this story and ask his listeners to guess what proportion of the marked boxes turned out to be accurately labelled. Most people figure, purely on a percentage basis, that the boys must have had three or four right.
Actually they scored a one-hundred-percent flop. In no single instance did they guess correctly. Every box was wrongly identified. “I don’t think they were crooks,” Dr. Gilchrist says, leniently. “Had they been crooked they would, I think, have refused to go through with the test. Just mental cases.”
While this sort of buffoonery was cropping up from time to time in the mining industry, some genuine geophysical exploration was being carried out during the middle twenties by commercial companies, some of them reputable, others not entirely above suspicion. A meeting of the Canadian Mining and Metallurgical Institute, held at Quebec in February, 1928, asked the Geological Survey to undertake a series of experiments designed to demonstrate the value, or otherwise, of geophysical exploration. The late Dr. W. H. Collins was then Director of the Geological Survey. He appointed Dr. James B. Mawdsley. of the Survey staff, to serve on a committee of two to carry out the investigation. Needing a physicist to complete his team, Dr. Collins asked Dr. Lachlan Gilchrist to tackle the job. During 1928 and 1929 a series of field tests were made of various methods of geophysical exploration, on the six-hundredacre property of the Abana Mine in Desmeloizes Township, Quebec.
Five of the commercial companies operating in Canada at the time were invited to participate. Three ç>( them— Radiore Company, Limited, of Montreal; Schlumberger Electrical Prospecting Company, of Toronto and New York; and the Swedish-American Prospecting Company, of Toronto—-went through with the tests successfully. The other two companies declined for various reasons.
Other similar geophysical investigations were carried out jointly by the Geological Survey of Canada and the United States Bureau of Mines during 1929 and 1930, in widely separated areas in both countries where known conditions were favorable to scientific research. As a result the conclusion was reached in 1931 that there was merit in geophysical exploration, with the reservation that there was room for considerable improvement in the practices developed up to that time.
"L-TAVING gone so far, the Geological Survey withdrew from further activities. Research work, as well as actual
geophysical exploration in recent years, has been carried on by two or three commercial companies and by parties of students from the University of Toronto and McGill, who. headed by Dr. Gilchrist and Dr. Brant of Varsity, and Dr. A. S. Eve and Dr. D. A. Keys, of McGill, work out a large slice of their summer vacations on doodlebug surveys. Dr. Brant’s Steep Rock Lake exploration was a winter proposition, but the bulk of the work done by the college crews is done during the warm weather months, for two reasons. The task is less formidable when the snow is off the ground, and the summer surveys afford valuable field experience for senior students of geophysics. The collegeconducted surveys are financed by mining companies desiring to know just what their chances are of uncovering another Hollinger.
The company pays the wages of the assistants for one month in the field, pays also for the necessary preliminary tests in the laboratory and for the preparation of maps and reports, which become the company’s property. These basic expenses are more than covered by a lump sum payment—$2,000 for a magnetic survey, $2,500 for an electrical or electromagnetic exploration. The balance of this amount goes to the University of Toronto, earmarked for geophysical research work under Dr. Gilchrist's direction. If members are added to the party, their transportation and wages are paid out of the lump sum. The company pays their maintenance in the field.
Every geophysical exploration job of this type requires a certain amount of advance laboratory preparation. This is done in the basement of the Physics Building, where a wooden box, waist high from the floor, has been filled with what looks like a gargantuan and singularly unattractive mud pie. Actually it is possible in this box of clay to reproduce closely the conditions known to exist within the area to be explored. By mixing in rock and other geological components in the correct proportions, using miniature electrodes and regulating the current accordingly, a series of small-scale tests are made which give a fair idea of the sort of reactions the party may expect to find in the field.
Geophysical explorations have been made in gold-mining areas, wdth satisfactory results. Mining companies have received scientific rejxirts on conditions, while Dr. Gilchrist and his assistants have learned many new things about geophysics, leading to improvements in methods and instruments.
So far, electrical methods of geophysical exploration for gold have not been able to equal the success record of the seismic method for searching out oil dejiosits. Electrical exploration has its limitations and is not as effective at great depth as the seismic method. Nevertheless, it has proved valuable not only in the mining districts, but in connection with public works. In the Tennessee power development, American and Canadian geophysicists, of whom Dr. Gilchrist was one, were able, through electrical exploration, to locate definitely for the engineers the position of a series of limestone caves occurring at depth on various sites for which great dams were planned. Their findings saved time and money for the enterprise.
The Bureau of Statistics at Ottawa lists seven metallic, nine nonmetallic, and four fuel minerals as produced commercially in the Dominion of Canada during 1937, the latest year for which complete statistics are available at this writing. Their combined value is given as $457,359,092. Any scientific advance calculated to assist so large an industry is a matter of importance to Canada and to every Canadian citizen. Geophysical exploration, following the trail of the pick-and-shovel prospector and the rock-sampling geologist, is doing just that. See what happened at Steep Rock Lake.