THE DEEPEST MINES

Southland Times, Issue 19172, 16 February 1924, Page 6

THE DEEPEST MINES

MORRO VELHO NEAREST EARTH’S CENTRE. Dr. T. T. Reid, of the United States Bureau of Mines, in a recent address stated that Brazil still contains the mine that goes the deepest below the surface of the earth, although the deepest below sea level and the nearest therefore to the centre of the earth is in the United States. The deepest hole in the earth is a gold mine in the State of Minas Geraes, and is known as the Morro Velho, or St. John del Rey mine. It is owned by St. John del Rey Mining Company, an English corporation, which has been working it almost continuously since 1834. The mine is now 6726 feet below the surface at the top of the shaft through which it is entered. The next deepest mine is in the Kolar goldfield of India, where one shaft descends to 6140 feet. The Village Deep mine in South Africa goes to 6100 feet. The deepest in the United States is Tamarack No. 5, a copper mine in the Lake Superior region, with a depth of 5308 feet. The bottom of this shaft is 4100 feet below the level of the sea, while that of the St. John del Rey is only 3958 feet below sea level, since the mouth of the shaft is in a mountain country 2708 feet above sea level. The Tamarack mine goes nearest to the centre of the earth. The temperature of the rock at the lowest level of the St. John del Rey mine is 117 degrees. The miners work in an air temperature of §8 degrees. The outside air has an average temperature of 68 degrees, but is cooled to 42 degrees before being forced to the lowest levels, from which it is drawn to the surface by powerful fans. On its way to the lowest depths it gains hea| from the rocks and from its own compression, because air at that great depth is ‘ considerably denser than air at sea level. The mine is a dry one, there being no water at the lower levels, and because of the low relative humidity of the air which has been dried before being forced into the mine the men are able to work under satisfactory conditions. The St. John del Rey mine is not only the deepest mine in the world, but is operated by the oldest registered English mining company, organised in 1830, to work a mine at a place some distance from the present workings. This mine proved to be unprofitable, and in 1837 operations were transferred to the present site, where they have since' been carried on almost continuously. The deepest hole in the bedrock foundation of the crust of the earth has been recently reported to have been drilled in South Africa. It is not the deepest from the surface, but the point is that its 5300 feet of depth is all in the pre-Cambrian strata, the underlying rocks which were laid down and finished some hundred million or so years ago. The other deep bores mentioned above are in rocks of more recent formation, or even, especially in the case of the Tamarack shaft, in superimposed sedimentary material.