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Pebble is different from other Alaska mines

August 12th, 2011 | Kendra Zamzow Print this article   Email this article  

Alaska's history is rich with mining, and every mine is different. Gold, copper, lead. But when it comes to the risk of contamination, differences in geology and hydrology - rocks and water - drive the risk. Pebble is different from other Alaska mines because of rocks and water.

Much of the mineral wealth at Pebble is encased in or tied to sulfide rocks. Miners won't be extracting veins of copper, they'll be crushing chalcopyrite - a mineral that is copper, iron, and sulfide all bonded together. Pyrites turn into sulfuric acid - battery acid. Some rock will go acid quickly, while Pebble Partnership geochemists predict some will take up to 40-60 years to go acid. This "acid drainage", once it starts, can continue for hundreds, even thousands, of years.

That acid, in turn, dissolves trace metals - copper, zinc, lead, and so on - that are also present in the same rock. While the mining company will be doing their best to extract the copper, gold, and molybdenum, they won't get all of it. What remains, along with trace amounts of other metals, are available for acid to dissolve and wash into the waterways. Additionally, very little of the rock in the area actually contains any valuable minerals - it's more like a few specks of glitter in a handful of dirt than the veins of copper and gold miners of old followed. This means there will be a lot of waste rock. Much of it with sulfides like iron sulfide that will go acid.

Mitigation efforts, like putting the "problem rock" under water can limit the process that turns solid rock into sulfuric acid. At Pebble, there will be billions of tons of waste rock - a monumental task to sort out "problem rock" and vast areas dedicated to keeping the rock underwater. Forever.

Pebble dwarfs all the mines in Alaska put together. Mountains of waste rock will have snowmelt, rain, fog, and wind etching away at them, starting the acid reaction if the rock wasn't sorted correctly, eroding particles with trace metals, washing out toxic elements like arsenic that don't need acid to mobilize. Miles of tailings ponds containing the milling waste - a slurry of finely ground mineralized rock and processing chemicals - that will leach down into permeable gravels. Hopefully the contaminants will leach slowly enough that groundwater dilutes them, but that is an awful risk -groundwater feeds salmon spawning habitat.

Groundwater and surface water d ance intimately in this area. Surface water goes underground and pops back up, groundwater travels under hills and from one watershed to another. Water is the bus those acid-dissolved contaminants are going to hitch a ride on.

It only takes tiny amounts of increased copper - parts per billion - to affect salmon, to lose their sense of smell which they use to identify predators, prey, mates, and their home stream. The future could be a slow decline, overlaid on the natural cyclical ups and downs of population returns.

The Fort Knox gold mine has beautiful rock, with lots of buffering capacity. Pebble is nothing like Fort Knox.

At Red Dog, waste rock was sorted - and rock that was supposedly neutral went acid after 17 years. At Pebble, it could be 60 years - possibly after the mine has closed - before anyone knows a mistake was made.

The Red Dog mine is on permafrost. Surface water and groundwater don't mix. If acid dissolves contaminants, they will stay in the surface water, making them easier to detect. Pebble is nothing like Red Dog.

The Kennecott Copper mine on the Copper River had sulfides, but also neutralizing rock. High grade copper veins - 13 percent copper compared to Pebble's 0.34 per cent - meant there was little waste. It would take over 2,000 Kennecott-sized mines to produce the same ore tonnage that is projected for Pebble. The Kennecott mine was high in the mountains, and salmon never used the Nizina and Chitina rivers near the Kennecott mine for spawning or rearing. Pebble is nothing like Kennecott.

The image of the Alaska miner is still that of a man with a gold pan, or a burro and a pickaxe. But industrial mining is different. Pebble is not your grandfather's mine. It's also like nothing you've ever seen in Alaska.

Kendra Zamzow, a resident of Chickaloon, is an environmental chemist and the Alaska representative for the Center for Science in Public Participation. She has a doctorate in environmental chemistry from the University of Nevada, Reno and a bachelor's degree in molecular and cellular biology from Humboldt State University, California.


Kendra Zamzow can be reached at, or by phone at 907-348-2449

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