Hard-rock mines that contain sulfide ore are notorious for the toxic drainage that commonly flows from their portals and from the tailings. Oxidation of the sulfide (mostly in the form of pyrite, an iron sulfide) produces a very acidic environment (dilute sulfuric acid), and the acid waters thus produced are capable of dissolving considerable quantities of heavy metals, such as lead, cadmium, arsenic, mercury, and zinc, which can be quite hazardous if concentrated in drinking water. This is not a known problem in the Magnolia region, but well water from down slope of the mines should be periodically checked for heavy metal content. Boulder County will do the tests for a small fee.
Another potential source of contamination is cyanide. In the first decade of the nineteenth century, a technique called heap leaching was developed and was employed at several sites in the Magnolia district. The technique involves dripping or spraying a cyanide solution on ore that is piled on an impermeable surface (a large neoprene mat is used today). Cyanide dissolves gold, so the liquid that drains from the bottom of the pile is collected and processed to extract the gold. From a mining perspective, the advantage of heap leaching over more conventional processes, such as gravitational separation, is that much lower grades of ore can be beneficiated. Around 1905, the Redemption Mines Company built a "cyanide mill" (inferred to employ a process similar to heap leaching) that could process 50 tons of ore at a time. In 1908, the Cash mill also built a cyanide leaching facility. It seems highly likely that at least some of the cyanide escaped into the surrounding soil; even in modern "state-of-the-art" heap leach operations, such as at the now-infamous Summitville Mine in southern Colorado, major spills have occurred. The exact locations of these leach sites in the Magnolia districts is not known, nor is the life span of cyanide in the soil, but these are subjects that should be pursued.
Rocks high in potassium, such as granite and shale, generally contain relatively high amounts of thorium and uranium, both of which consist of several radioactive isotopes. The Boulder Creek granodiorite is anomalously radioactive compared to most other rocks in Colorado due to its relatively high content of uranium and thorium. In addition, some mineralized veins in the Magnolia area also contain significant uranium (and possibly thorium) that was introduced during periods of shearing long after the granodiorite initially cooled.
During the normal radioactive decay of thorium, one of the daughter products is an isotope of radon, a radioactive gas that is heavier than air, with a half life of about three and a half days. The potential exists, therefore, for the accumulation of radon in non-sealed, low areas, such as basements. It would be advisable for those with sunken basements or natural exposures of rock within the house to have the house checked for radon. Radon can also be transferred to the air environment of a house through the water, especially from showers. There are relatively inexpensive home kits that can test the air for radon, and a house's water supply can also be tested for radon for a fee by the County.
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