Hoisting Works, Shafts, and Mining, Past and Present.
The Comstock Lode crops out along the eastern face of Mount Davidson about 1,200 feet below the summit, and just above the western suburbs of Virginia City. To the northward and southward the vein runs along the east side of other and smaller mountains of the same range. The face of Mount Davidson slopes to the east at an angle of about twenty-five degrees, and the vein dips in the same direction at an average inclination of forty-five degrees. It was at first supposed that the vein dipped to the west (into Mount Davidson), and the first hoisting works were erected on or near the croppings, where shafts were sunk and inclines sent down. For the first 400 to 500 feet the vein did pitch to the west into the mountain. Mount Davidson was then supposed to be the great central magazine, or nucleus, of all the silver found near the surface, and claims located on the slope of the mountain below to the eastward found but little favor in the eyes of mining men and would-be purchasers. Suddenly all this was changed, and there was a general “right-about-face.” It was discovered in the Gould & Curry and the Ophir Mines that at a certain depth the lode became perpendicular, then turned and took a regular dip to the east, of about forty-five degrees, following as a footwall the syenite slope of Mount Davidson. It was then seen that the false dip above was caused by the top of the vein being bent over under the pressure of sliding material on the slope of the mountain at and near the surface.
THE THREE LINES OF HOISTING WORKS.
However, much ore was mined at the first line of works, particularly at the Ophir, Mexican, California, Gould & Curry, Savage, and Hale & Norcross Mines. But, as the dip of the vein was away from these first works, it presently became necessary to move to the eastward about 1,000 feet. As very deep shafts would there be required in order to intersect the lode, larger and much more powerful hoisting works and pumping machinery must be erected. Indeed, the new works required to be first-class in every respect, as the shafts would be far deeper than any yet put down on the lode, and it was by this time known that there would be immense quantities of water to handle.
Accordingly, the second line of fine and powerful first-class works, seen at present, and again in active use, was constructed. The shafts of the new line of works all cut into the heart of the vein, and in several the “bonanzas” found were so large and so rich as to astonish the whole mining world and create a much greater and far more widespread excitement than was seen when silver was first discovered in the croppings of the vein at the Ophir Mine. All the leading mines were soon taking out their tens of millions, but when the “big bonanza” was struck in the Consolidated Virginia and California the yield of gold and silver bullion soon became a matter of scores of millions. It was then that the fame of the Comstock spread to every corner of the world, and the rush of speculators, fortune-seekers, and adventurers of all ages, sexes, and classes was greater than ever before. Though what is called the “Big Bonanza” was struck in the Consolidated Virginia in October, 1873, at a point on the 1,167-foot level, it was not until October, 1874, that the excitement in regard to it reached fever-heat. The main shaft had then reached the 1,500-foot level, and the ore disclosed by drifts and chambers was of such extraordinary and astonishing richness that experts could hardly believe their eyes or assayers their figures.
The Comstock Lode had a width (between the syenite wall on the west and the propylite on the east) of from 1,000 to 1,200 feet at the point where the “Big Bonanza” was struck. The space between the two walls was filled with what is locally termed “vein material” (gangue), and in this was found the ore body or “bonanza,” which was in one place over 300 feet in width. This mass of ore yielded from $100 to $700 per ton, but in places were found masses of pure native silver and spots of ore so rich in black sulphuret and gold that to make assays of it was much like making assays of the pure metals. From the “Bonanza Mines” alone from 1873 up to 1882 were taken $111,975,761.39; but in 1879 the yield began to fall off as the vein was followed downward, and in 1882 the amount of bullion taken out was small, not paying expenses.
In the meantime (while the big bonanza of the Consolidated Virginia and California companies was being worked out) most of the leading companies had exhausted their second bonanzas. Instead of prospecting further in their immediate neighborhood, they all determined to go still farther east, sink a new line of shafts, and tap the vein at a still greater depth. This time they went out about 2,000 feet beyond their second line of hoisting works, or 3,000 feet east of the croppings of the lode. As it would be necessary to sink shafts to a depth of about 3,000 feet to intersect the vein, the hoisting works, hoisting machinery, and all else was made much larger, more powerful, and on a grander scale in every respect, than the second line. The principal works on this third line are those of the Combination shaft, New Yellow Jacket shaft, Osbiston and Union shafts, and the Forman shaft. In sinking these several companies united, the work was prosecuted with the greatest energy, and no expense was spared as regarded machinery and appliances.
THE COMBINATION SHAFT.
Of these shafts, that which attained the greatest vertical depth was the Combination—the joint shaft of the Chollar, Hale & Norcross, and Savage Companies. Before work on it was discontinued it had reached the great depth of 3,250 feet. There is but one deeper vertical shaft in the world. This is the Adalbert Shaft, in the silver mines of Bohemia, which is 3,280 feet deep. There is no record of the time when work on this mine in Bohemia was commenced, though its written history extends back to 1527. The Combination Shaft was sunk at the rate of three feet a day, even in rock as hard as flint. The whole shaft is sunk in very hard rock (andesite), every foot of which had to be blasted. It is thirty feet by ten feet in size and is divided into four compartments for the accommodation of the hoisting and pumping apparatus.
The shaft was sunk to the depth of 2,200 feet before more water was encountered than could be hoisted out in the “skips” with the dirt. Down to the 2,400 level two Cornish pumps were used, each with columns fifteen inches in diameter. A drift run west into the vein tapped more water than the Cornish pumps could handle, when the management introduced hydraulic pumps. These pumps are run by the pressure of water from the surface through a pipe running down from the top of the shaft, whereas the Cornish pumps were run by huge steam engines. The shaft is connected with the Sutro drain tunnel at the depth of 1,600 feet, and to that point it was necessary to pump all the water. At the 3,000 level were placed a pair of hydraulic pumps, the deepest in the world. In Europe the deepest point at which a hydraulic pump has ever been worked is 2,700 feet. This is in the Hartz Mountains, in Germany.