How rain and rocks can produce pollution

Sidebar by Ed Quillen

Pollution – April 1998 – Colorado Central Magazine

IF MINE DUMPS consist of unprocessed rocks that were already present, albeit underground, how can they contribute to water pollution?

Most mineral deposits hereabouts are either sulfides or sit with sulfides, which are compounds of metals with sulfur. Molybdenite, the stuff that made Climax a profitable industry for several generations, is molybdenum disulfide (MoS2). Galena, the principal ore of lead, is lead sulfide (PbS). Argentite, a silver ore, is silver sulfide (Ag2S). Zinc’s main ore is sphalerite (ZnS). Gold seldom forms sulfides, but it’s often found with pyrite — iron sulfide (FeS2), better known as fool’s gold.

As long as these sulfides sit dry and deep underground, they don’t bother anybody. But they can be exposed to water in several ways:

1) That part of the earth can become elevated when mountains are formed. Overlying layers erode way, putting the sulfides on the surface.

2) Faults in the earth can carry surface water down to the sulfides, and the water will then escape from another fault.

3) Miners can haul the rock to the surface and spread it out in tailing dumps.

As for water, when rain falls through the atmosphere, it encounters carbon dioxide, and the result when it hits the ground is a weak solution of carbonic acid.

That’s fairly harmless stuff (diluted club soda, in essence), but when it encounters those sulfides, it reacts to produce sulfuric acid, which in turn can dissolve some metals. The result is acidic water with many metallic ions — stuff that isn’t good for fish and most other aquatic life.

Note that this can happen naturally, as a result of mineralization, or artificially, as a result of miners bringing the rocks to the surface and digging holes that allow water to penetrate sulfide-rich areas underground.

Since the Leadville district is one of the most mineralized areas on this planet, this inspires a question: Was the uppermost part of the Arkansas ever “pure”? Did it carry fish before the miners arrived, or was it already so acidic and mineralized that it could not support fish?

Trout are quite sensitive to metals, so we should be able to answer the question if we could find out what the Upper Arkansas offered in the way of trout-fishing before 1860.

The earliest known account of the Arkansas headwaters — Juan Bautista de Anza in 1779 — doesn’t mention fishing at all, and Anza didn’t go upriver past Salida, anyway. The next account, from Zebulon Pike in 1806-7, doesn’t mention fishing either, although he commented on the abundance of deer, elk, and buffalo.

Pike ventured no farther north than Hayden Flats, so even if he had encountered cut-throat trout by the bushel, his account wouldn’t tell us whether the uppermost Arkansas held trout before its flow was diluted by tributaries flowing in from less-mineralized zones.

John Charles Frémont came through in 1845, looking for the headwaters of the Arkansas that he had skirted in 1844, and ventured up the river from Bent’s Fort to cross Tennessee Pass.

Although Frémont’s journals are rather detailed, there’s hardly any mention of fish, one way or the other, at any of his stops.

His guide in 1845 was mountain man Bill Williams, who’d been through the territory several times, and Frémont does mention that Williams had a favorite fishing hole along the way: “Williams’ Fishery.” Frémont put it on the Western Slope, along the Eagle River; other old maps put it at Twin Lakes on Arkansas drainage.

But that tantalizing bit of early information, at either site, doesn’t tell us whether there were any fish in the Arkansas above the mouth of Lake Creek.

The same seems to hold for the fur-trappers of the 1820s and 30s — their recollections mention some beaver along the upper Arkansas and its tributaries, but there’s nothing about fish.

Although some pioneer diaries from other mining districts, like the San Juans, sometimes mention creeks teeming with cut-throats, nothing like that has ever turned up for the Leadville area.

Steve Voynick, whose words occasionally grace these pages and whose Leadville: A Miners’ Epic is the definitive history of Cloud City mining, says he has “never found a single mention of fish in the Arkansas above Lake Creek in any old diary or journal.”

He, like many mining engineers and geologists, believes that the uppermost Arkansas could not support fish in geologically recent times. By passing through a highly mineralized zone, the river naturally ran acidic and full of heavy metals until it was diluted by cleaner tributaries like Lake Creek.

So, it may be that there were no fish in the Arkansas above Lake Creek after the glaciers receded a few thousand years ago. At least, there’s no evidence to the contrary — no account has come to light of anyone filling his creel with cut-throats at the mouth of California Gulch in 1854.

If this is the case, it raises an interesting conundrum about modern efforts to clean the upper end of the river. If the Arkansas becomes “clean” enough to support fish, it won’t be “natural,” and if it’s “natural,” it won’t be “clean.”

— Ed Quillen