BURIED TREASURE IN THE EMPIRE

Otago Daily Times, Issue 21431, 4 September 1931, Page 7

BURIED TREASURE IN THE EMPIRE

MODERN METHODS OF FINDING MINERALS NEW FACTS ABOUT GEOPHYSICS (From a Correspondent.) LONDON, July 23. New information which will be of great importance to the mining industry of the whole Empire ie contained in a report issued by the Cambridge University Press on the work of the Imperial Geophysical Experimental Survey, which went to Australia for two years at the joint expense of the Commonwealth Government and the Empire Marketing Board to test under field conditions the most up-to-date methods of prospecting for minerals. The eye of science is beginning to pierce the crust" of the globe, and to see into the earth's interior. The report describes how minerals which lie hidden hundreds of feet below the surface can be accurately located, and even their depths and size determined, without disturbing a grain of earth or chipping a splinter of rock. Almost incredibly sensitive instruments can be placed on the surface, and will show, by the mere quiver of a needle, the presence of ores beneath. THE "DOWSER” TO-DAY^ The geophysicist, as this magician of minerals is called, is the modern descendant of the “ dowser ” who searched for underground water and precious minerals (and even, on occasion, for witches and lost animals) with a hazel twig. But the modern prospector’s findings depend on scientific facts and not on occult powers. For the first time all the different methods of geophysics—there are four distinct systems, each with many variations —have been tried out and compared under varying conditions. The director was Mr A. Broughton Edge and a Canadian, Dr Beiler, was assistant director until his death on active service in Australia. THE EMPIRE’S MINERAL RESERVOIR. Geophysical methods are of particular importance in many parts of the Empire, especially in the tropics and in Northern Canada. In the tropics the original surface of the ground is covered with thick deposits of decayed rocks — often 100 feet deep—which conceal the true nature of the ground. Thick vegetation, too, makes it impossible for the ordinary prospector to explore the rocks beneath. In Canada there are great expanses of country where the polar ice cap has receded during recent geological times, leaving behind vast stretches of glacial deposits. The old prospector, who could only chip off a bit of rock with his hammer where it actually jutted through the ground, has been baffled (even when assisted by the skilled geologist) by these deposits. But the geophysicist—the Sherlock Holmes of the mining industry—can track down the presence of minerals beneath these layers of decomposed matter and vegetation, and can find the buried treasure through great depths of ice and snow.

The four methods of geophysical prospecting which were tested in Australia were the electrical, the • magnetic, the gravimetric, and the seismic. AN ARTIFICIAL EARTHQUAKE.

The seismic method has already been used with striking success in prospecting for oil in the United States. It consists of staging an artificial earthquake. A charge of high explosive ie blown off in the ground, and then the progress of the shock is measured by extremely delicate seismographs. The pace at which the shocks travel depends on the nature of the rock through which the waves have to pass. They will go through granite at 20,000 feet per second, but in sandy soil they only travel at a tenth of that rate. In Texas these methods have found oil down to 7500 feet. Oil itself cannot be directly located, so the practice is to find the “ salt domes ” —deposits of crystal-

Used salts of uncertain origin, near which oil pools are often found.

GEOPHYSICS IN" A.D. 136.

The seismic method is at once the oldest tmd the newest in geoghysics. It is only since the war that it has been used for finding minerals; JMuch of the essential preliminary research was done on the vibrations of the big guns during the war, and seismic methods were actually used to locate positions.) But a seismograph for tracing earthquakes was invented in n.D. 136 by a Chinese called Choko. It consisted of three dragons holding brass balls in their mouths. When there was a shock the balls fell into the open mouths of three frogs squatting beneath.

Electrical methods—there are many—depend on the fact that some metallic ores are better conductors than the rocks surrounding them. Electrical currents are passed into the earth and the paths that they follow underground are traced and charted. This method can be used to find water. One of its advantages is that salt water can be distinguished from fresh, and this is likely to be of great significance in the more arid, parts of the Empire. Electrical surveys in Tasmania located copper-nickel.or.es under swamp country, where no ordinary, prospector could have found minerals; - HOW GOLD IS FOUND.

The magehetic method is the oldest, and can only be used for magnetic ores, which will deflect a needle just as a piece of iron or steel agitates a compass. This method has been used to find gold on a New South Wales field where production had been steadily going down. * Magnetic surveys indicated the most likely spots for boring through the thick lava" on top of the field which prevented profitable working. . . . Gold is distributed in the soil in such small amounts that it can never be fouud directly; but sometimes it can be tracked down by locating another mineral with which it is often associated. Gold mines now working in Sweden have been found by detecting sulphides. _ The main object of the Geophysics Expedition was to test the various methods and then make them available to the world at large. Instruments which have r hitherto been closely guarded secrets are described in the report. Geophysical prospecting is likely jto play a very im*. portant part in opening up new sources of mineral wealth in the Empire : Already mineral production exceeds £1,750,000,000 a year. We can only guess at how much more hidden treasure lies beneath the Empire’s quarter of the earth’s surface.