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This story is of a friend of mine, "Bob Ellithorpe" an equipment operator in Colorado. The rock is on display in the Denver Museum of Natural History and I have personally seen it on display!

http://pagosasprings.com/the-summitville-141-oz-gold-boulder/

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That's awesome you know him! It's a part of Colorado mining lore.

One of the first places I tried to metal detect when I first bought a GMT was Summitville after reading about that boulder. It has a guarded perimeter like 10 miles around it though, designated Superfund cleanup site.

I panned in some of the creeks outside the perimeter where they drain into the Alamosa headwaters and they stained my arms red and yellow for a week afterwards!

That place would be pretty cool to detect if they open it up again ever.

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What is the source of the toxicity?

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It was like the largest cyanide spill in the history of the US or something. The water there was particularly nasty but the water in the San Juans in general is often red or yellow though because those mountains are crazy mineralized (and spectacular).

You can see the steepness there and understand why detecting Colorado can be quite a challenge. This pic is not Summitville but another area in the same range I tried detecting (not my photo).

sanjuans.jpg

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22 hours ago, mn90403 said:

What is the source of the toxicity?

With 120 years of extensive mining excavation on the summit the weathering of the exposed minerals is accelerated. This raises the acidity of the water draining from the peaks and affects the pH of the upper Alamosa river basin. The low pH (acid) and the elevated dissolved copper levels are the main concern. The cyanide has combined with the runoff and been neutralized years ago so it's not really a direct concern anymore.

Here's the health assessment from the EPA on the current state of the Summitville recovery project.
 

Quote

 

Human exposure to these contaminants is limited, since no one lives within 2 miles of the site nor uses the immediately surrounding groundwater for drinking. Drinking water wells for San Luis Valley residents living more than 20 miles downstream of Summitville have been sampled on numerous occasions and have never shown elevated metals concentrations associated with the site. In 1997, the Agency for Toxic Substances and Disease Registry (ATSDR) released a Public Health Assessment that classified the Summitville site as no apparent public health hazard.

Ecological impacts from site contaminants are considerable, as the Alamosa River system below Summitville cannot currently support aquatic life. Studies have found potential adverse effects to agriculture and livestock from regular use of Alamosa River water. Preliminary results have indicated some uptake of metals in livestock and some agricultural soil degradation from irrigation. However, in both cases the effects haven't been of a level that affects the viability of local farm products or impacts the food chain.

The upper Alamosa basin has always had a low pH due to the naturally high mineralization in the higher elevations. Natural concentrations of valuable minerals always create an acidic environment but the erosion of the exposed mineral deposits from mining lowers the pH even more than the natural deposits would.

Due to the exposure and break down of the naturally occurring metal/sulfur compounds, in particular the exposed pyrites, this process will continue until the surface exposures reach a natural equilibrium again. Those mountain streams have always been acidic and they will remain so even after the remediation obtains the natural state again.

High acidity can be fairly easily countered by the addition of a limestone filter (usually large pieces of limestone dumped in the waterways draining from the source) the elevated dissolved copper is a little more difficult to recover. That's done at an on-site treatment plant. When the copper and other heavy metals are removed from the Summitville water they are concentrated and redeposited in the pit. The pit then drains back to the limestone beds and treatment plants again - assuring clean up work for years to come!

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