Comstock Lode - Early Mining and Milling

Early Mining and Milling

The ore was first extracted through surface diggings, but these were quickly exhausted and miners had to tunnel underground to reach ore bodies. Unlike most silver ore deposits, which occur in long thin veins, those of the Comstock Lode occurred in discrete masses often hundreds of feet thick. The ore was so soft it could be removed by shovel. Although this allowed the ore to be easily excavated, the weakness of the surrounding material resulted in frequent and deadly cave-ins. The excavations were carried to depths of more than 3,200 feet (1,000 m).

The cave-in problem was solved by the method of square-set timbering invented by Philip Deidesheimer, a German who had been appointed superintendent of the Ophir mine. Previously timber sets consisting of vertical members on either side of the diggings capped by a third horizontal member used to support the excavation. However, the Comstock ore bodies were too large for this method. Instead, as ore was removed it was replaced by timbers set as a cube six feet on a side. Thus, the ore body would be progressively replaced with a timber lattice. Often these voids would be re-filled with waste rock from other diggings after ore removal was complete. By this method of building up squares of framed timbers, an ore vein of any width may be safely worked to any height or depth.

Early in the history of Comstock mining, there were heavy flows of water to contend with. This called for pumping machinery and apparatus, and as greater depth was attained, larger pumps were demanded. All the inventive genius of the Pacific Coast was called into play, and this resulted in construction of some of the most powerful and effective steam and hydraulic pumping equipment to be found anywhere in the world. Initially, the water was cold, but the deeper workings cut into parts of the vein where there were heavy flows of hot water. This water was hot enough to cook an egg or scald a man to death almost instantly. Lives were lost by falling into sumps of this water hot from the vein. The hot water called for fans, blowers and various kinds of ventilation apparatus, as miners working in heated drifts had to have a supply of cool air.

Compressed air for running power drills and for driving fans and small hoisting engines was adopted in the Comstock mines. Diamond drills for drilling long distances through solid rock were also in general use, but were discarded for prospecting purposes, being found unreliable. Several new forms of explosives for blasting were also developed.

Great improvements were also made in the hoisting cages used to extract ore and transport the miners to their work. As the depth of the diggings increased, the hemp ropes used to haul ore to the surface became impractical, as their self-weight became a significant fraction of their breaking load. After hemp rope, iron chains began to become more common. However, fracture was quick, at around half a millisecond. In 1829 Wilhelm Albert had studied and reported on the failure of the iron chains and began creating a twisted metal cabling known as Albert rope. This wire rope went on to be used in San Francisco's famous cable cars. In 1857 A. S. Hallidie manufactured wire rope and was heavily involved in building early cable bridges.

In 1859 the Americans knew nothing about silver mining. In the California placer mines there were a number of Mexicans who had worked silver mines in their own country. Initially, the Comstock miners endeavored to partner with Mexicans, or at least hire a Mexican foreman to take charge of the mine. The Mexicans adopted their methods of arastras, the patio process and adobe smelting furnaces to process silver ore. These methods proved to be too slow for the Americans and could not process the quantities of ore being extracted. The Americans introduced stamp mills for crushing the ore, and pans to hasten the process of amalgamation. Some of the German miners, who had been educated at the mining academy of Freiberg, were regarded as the best then existing to work with argentiferous ores. They introduced the barrel process of amalgamation and the roasting of ores. While the barrel process was an improvement on the patio, it was found not to be well adapted to the rapid working of the Comstock ores as pan amalgamation. The Comstock eventually developed the Washoe process of using steam-heated iron pans, which reduced the days required by the patio process to hours.

In the early days of pan processing of ores, there were tremendous losses in precious metals and quicksilver (mercury). Almost every millman was experimenting with some secret process for the amalgamation of ore. They tried all manner of trash, both mineral and vegetable, including concoctions of cedar bark and sagebrush tea. At that time, untold millions in gold, silver and quicksilver were swept away into the rivers with the tailings. Although many patterns and forms of amalgamating pans were invented and patented, there was much room for improvement. Improvements were made from time to time, resulting in reductions in losses of metals, but none of the apparatus in use on the Comstock was perfect.