Mercury mining in the Phoenix Mountains

This story comes from the archives of the Arizona Department of Mines and Mineral Resources which has now been absorbed into the Arizona Geological SurveySee full paper here.

“In December of 1916, Sam Hughes, a Phoenix resident, discovered cinnabar deposits in the area now known as Dreamy Draw. Cinnabar, a mercury sulfide, had been discovered earlier that year in the area. Near his largest deposit, the Rico Mine, Sam Hughes erected a retort furnace, built a cabin, and sunk a main shaft and water well. Hughes, working alone, would fill an ore bucket, climb 100 feet of ladder to the surface and then hoist the ore bucket using a hand windless. In 1925 the U.S. Bureau of Mines reported that, “the bottom of the mine is damp, the temperature in the face of the drift is high, and the ventilation is poor.”  Approximate location is at the “A.”


Total production from the mine is reported to be 65 flasks (4,972 pounds).

“Mercury, also known as quicksilver, is the only metal that is liquid at ordinary temperatures. Its chief uses are in drugs and chemicals. It is also

used in mercury-vapor lamps, power-control switches, thermometers, barometers, and in dental preparations. Mercury is found in only a few minerals; most commonly, cinnabar, a mercuric sulfide (HgS). The color of cinnabar generally is vermilion-red. Mercury in the Phoenix Mountains was in the form of cinnabar.”

An appendix to the main report has some environmental and health information about mercury.

“The two types of mercury most likely to be found in the Dreamy Draw area are elemental mercury, (the “quicksilver” most of us have seen in thermometers and thermostats), and mercuric sulfide, also known as cinnabar. Elemental mercury may have been deposited in the Dreamy Draw area as a result of the refining and transport process during the early part of the 20th century. These deposits were probably short lived due to elemental mercury’s propensity to evaporate at temperatures greater than 77 degrees Fahrenheit. Elemental mercury also readily forms alloys (amalgamates) with most metals except for iron and readily combines with sulfur at room temperature. Elemental mercury combined in this manner forms a tight bond and is essentially immobile in the landscape and biologically unavailable. If ingested in the unamalgamated, elemental form, mercury is poorly absorbed (<0.01%)  in the stomach and intestinal tract. Once ingested, elemental mercury also has a relatively short half life of 60 days and is eliminated in the urine, feces and by exhalation. Cinnabar is even less biologically available and environmentally mobile than elemental mercury, due largely to it’s low solubility in water.”


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