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Tombstone Mills | |||
LocationExact location unknown. In January 1878, the Tombstone Mill and Mining Co. installed and operated 10 stamps at Millville (later Charleston) on the San Pedro river. Later, the Corbin Mill and Mining Co. operated 15 stamps starting January 12, 1880 and by January 31 shipped the first bullion. The Grand Central Mill, 10 miles north on the San Pedro came online shortly thereafter. The TMMC reportedly processed a large amount of low-grade ore first; reason, to “throughly fill all cracks before treating the high-grade ores”. At TMMC, raw ore was fed through a “rock-breaker”, presumably a jaw crusher. This device was of wrought iron (not cast) and had toggles and set screws jibs to minimize breakdowns. The rock-breaker operated at 2 rpm and the crushed product fed a rotary drier through an inclined chute. The discharge from the drier fed the stamps which operated at 100 drops per minute. A double discharge from the stamp mortars led to cars which carried the pulp to four amalgamation pans stirred by revolving mullers. Mercury (called quicksilver then) was kept always in the stamp batteries , plus mercury was shaken in a fine shower from a buckskin bag into the pans. Quantities of coarse salt and sulfate of copper were added to the pans to assist the amalgation by breaking down the base metal combinations with the silver. Below the amalgation pans were two large settlers and the tramway crab-cars which ran the amalgam into the retort room. The usual run was about 15 tons per day on a continuous 24 hour-per-day operation. Two retorts and a melting furnace completed the TMMC Charleston Mill. The retort residue was melted and cast in iron brickmoulds to form solid bars of a silver-gold bullion; one-fifth gold, four-fifths silver. The gold color however, did not show. Quicksilver was very costly and was “never wasted”. Special care was taken to condense and recover all the distilled mercury from the retort.9
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