Arizona weekly journal-miner., 1901-06-12
FUTURE OF DEEP MINING

Some of the plans which are being formed by mining engineers else where for future deep level operations make the development in mining in California look like a very puny affair. The deepest shafts on the coast are only a. little over 5000 feet. Com pared with old time mining ideas 5000 feet seems to be an extraordin- ary depth. But mining engineers in the Transvaal are seriously discussing the exploration of the gold bearing reef of the Rand to depth of 15,0OO feet. This is nearly three miles in a vertical line below the surface of the earth or five times deeper than the deepest workings on the Pacific Coast.
 The deepest shaft at present in America Is that of the Calumet and Hecla, which is down practically 5000 feet. On a neighboring mine a shaft is how being sunk which will cut the conglomerate vein at the the 7500 foot level. It has been sup posed that the vein can be followed from this shaft to a depth of 10000 feet; but the latter level has been re- garded by the most venturesome min ing engineers in this country as the limit of engineering science and me chanical possibilities, as now under stood. The Transvaal mining en- gineers do not, however, discern any impossible engineering problems in reaching a depth 5000 feet lower than the limit to which the Michigan deep copper mines are supposed to be cap able of being carried.
 The most serious obstacles which the Rand engineers seem to antici- pate are those associated with the natural temperature of the formation. There is some fear that the heat limit of human endurance may be reached at 12,OOO feet. If so, operations must be stopped at that depth, unless the heat can be overcome by artifal means, Perhaps this is one of the instances where liquid air will have an important function to perform in future mining. for the lowering of the natural temperature of the earth's crust.
 In the discussion of the great depths to be attained in the future workings of the Rand reef the engi- neers have embraced a suggestion first thrown out by the ''Chronicle," name ly, that the mill for ore crushing must be introduced into the mine. The plan is considered not only feasible but desirable. to save the cost of hoisting. It is even assumed that with such a change in the location of the mill mining may be carried on at a depth of l5,000 feet below the sur
 ace at less cost per ton than it isnow being carried on at 5000 feet with surface mining.
 How shall such great depths be reached is the chief factor in the problem of future mining operations It is supposed that 1000 feet is the limit of vertical shaft hoist. The Rand engineers, therefore, favor an incline following the dip of the reef which will admit of dividing the hoist into sections without material increase in the expense. To pierce the Rand reef with either incline or shaft to q depth of 15,0O0 feet will expose gold bearing mineral which will take many centuries to exhaust at the present rate of working when all the mines are in full operation. The prize is therefore, worth the effort. The same may be said of all our California veins, for every thousand feet ac- quired in the depth adds at least hall a century to the life of the mine. We may, therefore, truly say that the deepest gold quartz mine in the State has, as yet, only scratched the surface of the lode ald that our career in deep mining Is only beginning. Sal Francisco Chronicle.