Another electric hoist recently installed is that of the Ray Consolidated Mining Company, Ray, Ariz. While it is not intended to hoist from a great depth, it handles a load of 121/2 tons from a depth of 500 feet at a rate of 300 feet per minute.
Surface Haulage.—The evolution of sur face haulage follows closely to that of under ground work as given above, beginning with coolies in China, Indians in Mexico as men of burden, followed by the llama, burro and pack trains, and later by wagons, as represented by the 20-mule-team of a borax company in California. A few years ago 125 horse power traction engines were tried in the West many of which were abandoned on the plains by reason of the fact that they could not carry sufficient fuel and water to run them across the desert country. Steam, compressed-air, gasoline and electric locomotives are in almost universal use in the various mining districts of the United States. The introduction of the motor truck is now quite common in many of the remote dis tricts where railroads have not yet been built.
Wire Rope Trams.—Wire rope trams were first introduced 200 years ago. Cable ways, such as are now used in quarries, were invented and used in 1851. One of the earliest large installations of cable ways was in the Tilly Foster mine, New York, where 600,000 tons of ore was recovered after the removal of an over burden of 300,000 tons. A typical example of the aerial tram is that of the American Nettie mine in Colorado. This tram is 3,400 feet long, the first 500 feet of it sloping 45 degrees. The longest span is 1,800 feet. The ore is carried in buckets each carrying 1,000 pounds of ore. Another example of an aerial tram used in coal mining is one installed at Electric, Mont. The cable is 7,800 feet long, the ele vation of the upper end of which is 1,200 feet above the lower. This type of transportation finds a place in rough inaccessible mountain regions.
Gravity planes are used at some of the mines, as for example, the one now in use at the Boston Consolidated mine in Utah. This plane is 1,900 feet long sloping 22 degrees, and representing a height of 737 feet. Twelve-ton skips are used on this incline and 1,350 tons of ore is handled per eight-hour shift. This is one of the largest incline planes in the United States.
Belt Conveyor.—An example of belt con veyors is that recently installed at Miami, Ariz., where a 30-inch belt conveyor travels 300 feet per minute up an incline of 15 degrees. The capacity of this belt is 2,000 tons of crushed ore daily. Belt conveyors are used largely in ore-dressing plants, cement mills and other sur face plants. Many of these are operated by electric motors.
Endless Rope Haulage.— Endless rope haul age is in use at many mines.
Railway Haulage.—At nearly all large mines, the major part of the surface haulage is on the scale of railroad operations. For example, in the Minnesota iron mines, and copper mines in the West where the mining is done by steam shovels, the ore is loaded direct into 40 or 50 ton steel cars. In the case of the Minnesota iron mines these loaded cars are sent 75 to 100 miles to Duluth to the ore docks, where the cars are dumped automatically into bins from which the ore is drawn into the lake steamers. It requires less than two hours to load one of these steamers with 10,000 tons of ore. In the case of the Western copper mines, the standard gauge cars that are loaded by steam shovel are sent direct to the smelter varying from only a few miles to 100 or more.
Treatment of Ores.—After the ore or min eral has been mined, it is subjected to various metallurgical treatments as the case may require; thus iron ore is sent direct to the blast furnace where it is melted into pig-iron. Copper ores are concentrated and the concentrate sent to the blast furnace where it is smelted in a manner similar to the iron ores, thus producing copper bullion. Gold and silver ores require various treatments depend ing upon the character of the ore, the principal methods being stamp milling, amalgamation, cyaniding, chlorination and lixiviation. (See article on GOLD MINING). Lead ore, after con centration, is smelted in an ordinary blast fur nace, while zinc ore is distilled in retorts and collected in its metallic state known as spelter. Mercury is likewise distilled and condensed in retorts and when cold remains liquid. The treatment of minerals from which such metal as chromium, cobalt, titanium, tungsten and vanadium are obtained is described under the various headings. See COPPER; GOLD; LEAD;