It is a very old story in rocks too. Oil had bigger money and bigger companies so it got more drive there. Particularly in gravity, which did not lend itself to grid readings as it was slow and delicate, but with the oil biz, the could pretend they were looking for much larger targets, ergo fewer readings, and the field principle of "far away = lower resolution" demanded fewer more widely spaced readings anyway. Also the oil boys primarily used seismic, which the mineral boys had never figured out how to use for their discipline. So it was two solitudes of exploration, instead of co-operation.
But CSAMT (controlled source audio-magnetic tellurics) was started in order to look at mineral bodies, and while the oil boys had been using AMT, its natural cousin, they did not want to use CSAMT because oil was non-conductive and no one had demonstrated the efficacy of the method of electrical sounding to the US industries satisfaction. The Russians were using a version of it for decades and it had even been demoed before the CDN version, so it is suspicious, like much other tech that drifted west, that in fact is was "borrowed". I have other reasons to believe that too. At any rate, someone realized that it was positive for oil, but just worked in reverse and needed a bit of modelling both for 3D and body geometry of the oil or pool, et voila! you knew you had oil down there. With seismic it could be anything. CSAMT was positive, or at least positive in its negativity. Now despite the seeming shallower depth penetration of CSAMT is has become all the rage for oil explo and has vastly expanded the fields of Tennessee, Ohio, and other Appalachian areas as well as Omaha and Texas. 5000 to 10,000 feet is no never mind for this method. Now the geologist in the States can see what prompted the Russians to use it. It lends itself to horizontal conductors and no conductors better, but it could be adapted to vertical plates too. In the early days they were using it to find mineral faults and they did not know how to interpret it. I could see in the graphs what was going on, but was surprised the inventors could not! It needed a 3D resolution geometric system as well as math modelling.
Geofizz for rocks got started with Faraday, believe it or not, who was in Toronto in the 19th century mapping the deviations of the compass. Tesla never got into it, which was too bad as he would have revolutionized it before it got started. Then Edison used to find the mag signature of the Frood in Sudbury, in the 1870's, but they never found the ore. No diamond drill back then. Had not been invented. Renshaw used a primitive form of mag and self potential in 1917? to find the Buchans Mine in Newfoundland in one of the first uses of gephysical electrical methods in Canada. Probably the dip needle had been used before that to map many formations since the 1800's. (A dip needle is just a compass laid on its side, the dip of which maps the changing vertical field of the magnetics. See Faraday, above. It was used in Geraldton to map the formations there in the 1930's) heritage.nf.ca
here they state Guess and Lundberg were the instigators, and omit Renshaw who was a lowly geologist who implemented the method in the field. Somehow fieldmen who make it work never get the credit.
The fluxgate magnetometer had been developed at Wood's Hole by the US Navy to look for submarines during WWII. It was successful but its efficacy was kept a secret. The mehod was adapted by CDN geophysicists who also took a proton counter method and developed the first highly accurate frequency counter to measure audio electrical frequencies which emanate from an induced spin-changing proton mass in a magnetic field They came out with the proton precession magnetometer in the 1950's by using the reverse method of counting the time for each wave zero crossing, for a good length of time, and then averaging. No one had every figured out how to count such low frequencies to such high accuracy necessary to measure the magnetic field. The proton machine could measure accurately to a quarter of a teh thousandths of a gauss, trifield.com BTW this link has it wrong. They are not practicing earth scientists or they are trying to oversimnplify to make sales. There is a very good reason to measure to better than a nanotesla. But that would is for another day. A proton mag can detect a can of beans at 3 metres, an airtight stove at 20 feet, and a railroad train at a distance of one mile. It can see planes flying in the sky. So magnetic ore bodies even 2 miles deep are no never mind. There is a saying in the mining industry, "mags see forever." Now you know why.
Later some idiot who should have kept his mouth shut indicated to some thieves that since many substances were 'paramagnetic', or weakly magnetic whilst not ferrous, that they could be mapped by a magnetometer in the human body, just like a mag maps rocks by Euler deconvolution according to Parasnis' reworking of the Maxwell field equations. These equations define the B (from the mag permeability of the source), the total field strength (which the proton mag maps ignoring direction of the field). This total field is equal to an integration of the X, Y and Z directions of the mag field strength by a formula. By taking 100's of readings at different places and doing some algebra you can map where the sources are in space that give rise to this mag field. The XYZ gradients or directional fall-off of the fields show their relative location, even if many hundreds of these sources overlap each other. Ergo, the MRI machine, which is just a large computer driven mapping magnetometer using an active mag field to light up the paramagnetic substances in your body. It takes science to build one of those things, I won't kid you, but the principle is quite simple.
Before the proton mag the GSC had begun to map Canada aerially with the fluxgate mag, measuring the vertical field of rocks. They were the first country to do so, leading the US and most other countries by 30 years in doing grid surveys. Much of that was due to the higher efficacy of mapping basement archean rocks by this method. We have the highest exposure of such rocks in the world. Half the land mass of Canada is made up of exposed 'basement' rocks. The rest of the world is mostly covered by marine sediments later than 500,000,000 years old and having fossil fish in them. Religious and anti-evolutionary theorists take note.
Just about every Schlumberger invention was adapted by CDN geophysicists since the second world war to map Canada electrically with grid surveys on the ground and in the air. In ontario these methods became known by the government as EM methods 1 through 40 designating the various techniques of electrical measurement used with various coil positions and electrical paramaters and interactions with different types of fields in different ways. IP was pioneered by the way way back in the 1930's in Canada. It induced a very large, up to 200 ampere current, into the ground and listens for the decay echo of the sulfides current dying off after induction shutoff. It had been introduced into Chibgougamau Quebec by a geologist who founded Roxmark Mines, BTW.
Just about 75% of ALL rock-mineral geophysics came out of Canada, reason stated being that the unique exposed rock mass of this country lent itself to this sort of mapping. Also we had no capital gains taxes, so foreign money was pouring into Canada that could support survey-type grass roots exploration. The US investor was 'hiding' his money, so to speak, in CDN mining stocks, which traded more shares in any day than the NYSE. This type of wildcat scientific work was encouraged. So grid type searches, unheard of in the US or other countries, were standard practice here.
Canada, with its unending wilderness seeming to hiding vast treasures just inches below swamp, seemed to demand this sort of relentless combing. And it paid off. Noranda mines geologists who had developed many of these doodble bug coils for searching for sulfides began to find things and othre people copied them. Aerial contractors sprang up and mines began to be found.
But grid geophysics is a shotgun method, creating many false starts and barren enterprise. Investors start to tire unless a discovery or rush is on. Few companies can bear the expense of grass roots searches and the concomittant technological development. It takes a magician to keep the investor going dry hole after dry hole.
Along came Texas Gulf in the 1960's and using a system that they mounted on a helicopter. What they did was take an aeroplane mounted electrical towed bird system called the Canadian Aero system, shrunk it down by using the newly invented transistor, and left out the traditionally used magnetometer which accompanied most such electrical systems. This allowed the "bird" to be towed by a Bell 47, a very small helicopter of the day. They could read whether or not the conductor was magnetic by the in phase and out of phase of the system, so they could ignore magnetite which will often light up such systems. There was no need for a mag. (They were funded for this search, which cost them 6 million a year in today's dollars, by the money the company made selling sulfur. This substance was pumped from he ground with hot water by the Frasch system which Bernard Baruch had got them into after the war.) At the end of a two year search and 64 barren anomalies but technical successes in fact, they found Texas Gulf's massive orebody of copper-zinc in Timmins. But it was on someone else's land. They had to buy it out, and got into a lawsuit over it too. At almost 200 million tons of 5 % metal, the Texas Gulf discovery was the largest and richest discovery of base metal ore by any search method, let alone grass roots gridding. For 7 or more years after Canadian mineral industry expenditures increased by an order of magnitude. Millions were spent in Timmins alone. But amazingly, despite the well known geological fact that these types of orebodies come in clusters, nothing else was ever found in this area of such note! One of the reasons may be that the electrical methods used by most people in the standard way have the fatal weakness of very low intrinsic correlation with ore. They create anomalies that without further back up are essentially meaningless.
This great discovery by a relatively junior company changed not only the mining industry and its methods permamently but also changed the economy of Canada. Indirectly and directly this discovery has led to a change in methods of many companies and the acknowledgement and adoption of electrical geophysics by just about every company in the world who looks for ore.
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