No Silver Bullet, But a Silver Lining

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Once so cheap it was used for pennies, copper is now so valuable that pennies contain almost no copper and they still cost more than one cent to make.

 

Native copper. The USGS studies processes that form copper deposits and reports global production and consumption.
Native copper. The USGS studies processes that form copper deposits and reports global production and consumption.

Once so cheap it was used for pennies, copper is now so valuable that pennies contain almost no copper and they still cost more than one cent to make. And as standards of living rise across the globe, demand for copper and other important metal commodities will likely continue to go up. This means that the number and size of copper mines are going to have to increase as well, and that it is more important than ever to understand the potential environmental effects of mining.

Predicting to Prevent

Much has been written about abandoned mines and their effects on the environment. However, approaches to protecting the environment from mining impacts has undergone a revolution over the past several decades and the sustainability of that revolution relies on an evolving scientific understanding of how mines and their waste products interact with the environment.

This research is important because it can both explain and predict the environmental and health impacts. So how does USGS minerals research play into that?

Starting from the Beginning

Pretend you work as a mine planner. Before you even get a mine started, you need to learn about the area you want to mine. This is known as the pre-mining baseline. When people talk about restoring mined areas to what it was like before, the pre-mining baseline is what they’re referring to.

However, what if no one has that pre-mining baseline? Then you’ve got to do your best to figure what things would have been like if the mine was not there. USGS has evaluated several techniques to figure out that kind of information, and they can be found here.

Now that you know what’s there, it’s possible to identify what might cause problems when you actually start mining. USGS has evaluated tools that can provide insights about the likelihood of metals and other chemicals leaching into water and their potential to generate acid-mine drainage.

It’s the Pits

Iron mine pit lake, Minnesota. Credit: Bob Seal, USGS
Iron mine pit lake, Minnesota. Credit: Bob Seal, USGS

Many of the biggest mines are what are called open-pit mines, which are just what they sound like. Often, these pits will become large enough that they reach the water table, meaning groundwater starts flowing into the mine. This water is pumped out while the mine is active, but once the mine is closed, groundwater, rain, snow, or other precipitation often fills the pit to create a pit lake.

The water in these pit lakes can end up picking up a lot of the metals and other chemicals that were present in the mine. Thus, it’s important to know how these pit lakes form, what’s likely to get in them from the mines, and what the quality of the water is likely to be. SUNY Oneonta, Interralogic, and USGS have new studies explaining just those things.

Flowing with the River

Of course, sometimes the metals and other chemicals from the mines don’t stay in the mines. They can escape into groundwater, surface water, or even in precipitation. The well-known acid mine drainage is one such example.

However, recent USGS and University of Montana science shows that mine drainage is unbelievably complex. Not only do different trace contaminants from mines behave differently in acid waters vs. neutral waters, but some even have daily cycles in concentration level.

USGS research also shows that mine drainage doesn’t come from a single source, but rather a complex interaction between water, air, and micro-organisms like bacteria. In addition, though acid mine drainage is the most familiar type, mine drainage can be basic, neutral, or even high in salts, and each of those types have their own impacts on the environment and their own sets of challenges to address.

Cement Creek, CO. Credit: Briant Kimball, USGS.
Cement Creek, CO. Credit: Briant Kimball, USGS.

Toxic in the Water, Toxic in the Sediments

Many of these metals and other chemicals don’t stay in the water long, though, even when they make it out of the mine. They can bond with the muds and sediments that are in the streams or lakes, or even with the sediments on the river or lakebeds. Once there, out of sight, out of mind, right?

Not so much. They can have a serious impact on invertebrates that live down there, making them sick or killing them. This is not only a big problem for fish who survive on these invertebrates, but also for us because we eat the fish. The food chain isn’t the only concern, though. When we eat fish that have been eating so many compromised invertebrates, our health is at risk too.

As such, in order to maintain the health of the ecosystem and the fisheries it is important to find out which substances are getting into the sediments. USGS has evaluated many of the different sediment-sampling techniques so you can use the right one for the right job. USGS has even looked at a new technique for predicting how toxic certain metals will be in aquatic environments.

 

Martha gold mine, Waihi, New Zealand. Credit: Bob Seal
Martha gold mine, Waihi, New Zealand. Credit: Bob Seal

Cyanide—the Golden Poison

One of the chemicals that is most problematic when it escapes a mine is cyanide. A well-known poison, cyanide is also used to mine gold and silver. In certain cases, cyanide may end up accidentally being spilled into the environment.

Normally, cyanide is safely disposed of when it disperses into the atmosphere under appropriate conditions, where sunlight will break it down to non-toxic chemicals.

USGS research shows that mining operations using cyanide are best-served by building in plenty of time for the cyanide to enter the atmosphere, either directly or after exposure to sunlight.

Looking Ahead

Finally, USGS is helping to prevent future mine impacts by identifying issues in new or advancing mining techniques. Enter slag, the leftovers after mining and smelting. Recently, companies are beginning to turn to previously processed slag to recover valuable minerals that may still be left behind.

But does this make slag a valuable resource, or does processing it threaten the environment? To help best use the slag, USGS and the Geological Survey of Canada reviewed what was known about it. One of the biggest things we observed is that, because slag is the byproduct of mineral processing, its physical and chemical properties depend a lot on what the original mined mineral was.

Their research shows that non-ferrous slag--that is, slag that didn’t come from the processing of iron and steel, but commodities such as copper, zinc, or nickel--may be less attractive for re-use, as it has a higher potential to negatively impact the environment than slag that did come from iron or steel production.

Start with Science

USGS minerals research can thus help identify problems before they become problems, or at the very least, help address the impacts that do exist. See a special issue on just this topic, published in Applied Geochemistry here. Read more about USGS minerals science here, or follow us on Twitter at www.twitter.com/usgsminerals.