Butte, America (part 2 - Montana Resources)

When last we left our intrepid explorers, they had seen the eventual outcome of the strip mining of copper, a toxic-water-filled pit.

Today our scene opens on the pit to the east of Berkeley Pit in the creatively named East Pit (or the Continental Pit according to Wikipedia) where copper and molybdenum ore is still being mined, ground, and purified by Montana Resources who were nice enough to host our teacher camp participants for a field trip. Big, big, big thanks to Tad Dale and the folks at Montana Resources. They were great hosts.

Check out their video of the processes at the pit.


Montana Resources module SD from Washington Corporations on Vimeo.

We started toward the end of the process, in the grinding and flotation plant.

Mike McGivern, in yellow, was our tour guide. Here we started our tour outside the flotation plant. Big thanks to Courtney Young (in white), our Montana Tech host.

Be warned, lots of photos after the jump...

The smaller drums in the back are the rod mills where the ore - already crushed from car-sized boulder outside - is crushed into smaller pieces by tumbling with the rods shown to the right of the drum. The near drums, turned 90 degrees, are the ball mills. The crushed stone from the rod mills go into the ball mills for further crushing.

The mills didn't stretch as far as the eye could see, but they did stretch a fair way. From the ball mills, the finely crushed ore goes to the right into the cyclones. Small - dust-sized particles - leave the cyclones for the flotation ponds. Larger pieces return to the ball mills. The ball mills are replenished with steel balls every couple of weeks. The tall hoppers on the far right edge hold steel balls (about three to four inches in diameter) all the way to the ceiling.

Her are replacement rods for the rod mills.

The flotation tanks take copper-rich ore and draw it to the top where it is skimmed off to the side for drying and further processing.

Here the ore from the ball mills heads into the flotation tank with liquid being added.

The purest copper ore comes off in the first flotation bays (the ones nearest where we stood) of each tank. Subsequent bays purified the slurry and return it to the first tank for further purification.

There were quite a few flotation tanks, each with dozens of wheels spinning and churning the slurry.

Quality control has to happen within the plant, and it's good to see that those burette skills can be put to good use.

Chemicals are added to the slurry to bind the molybdenum- and copper-rich ores to the bubbles so that they rise and to make the bubbles more durable so they don't pop before the flotation.

The flotation plant keeps a record of their monthly targets and performance as well as the price of the metals that they are producing. July didn't look like a great month for copper or molybdenum. Mike explained that they were mining the poorest copper ore of any mine in the world. Typically they can get five pounds of copper from a ton of their ore, a 0.25% return.

From the flotation plant we headed into the East Pit. Along the way - driving on the left for safety (that way the truck drivers can look directly down on the berm to their left and - if there is an accident - will be further away from each other) - we passed a couple of trucks loaded with ore on their way to the crusher and the flotation plant.

At the level being worked, we saw the scoop load four or five trucks full or ore that had been blasted the day before. It took three or four scoops to fill a truck completely.

You can see the scoop operator for a sense of scale.

Trucks leave fully loaded...

This one had 243 tons of ore in its bed (see the red 243). As the truck was loaded, the scale registered the weight in the truck. Mike said that the trucks were supposed to be 240-ton trucks but could handle up to 260 tons before the truck automatically sounded an alarm and had to dump their load before driving in anything above 1st gear.

Sometimes the trucks were used to haul around machinery, too.

From the East Pit floor we headed to the reclamation plant. In the foreground is steel piping that had been used to pump tailings into the Yankee Doodle Tailings pond, seen in the top map as the fan stretching out to the left. The tailings pond is behind an earthen dam that is the largest in the world and grows taller every day. The board above showed how much discard is mined. That discard is used to increase the size of the dam.

At the reclamation plant shredded steel cans (the brown piles) have cooper-rich water poured across them. The copper is recovered via single-replacement reaction. Copper recovered here is about 50-65% pure.

The mound to the back holds back Berkeley Pit and is above water level. The green streak in the foreground is water that has leaked through the earthen dam after seeping through the tailings pond and picking up any copper it can dissolve. The leaks through the dam are expected and - in fact - wanted as it prevents pressure from building up behind the dam. It is this water that is used in the reclamation plant.

The dirt in the back is the earthen dam that holds back the tailings pond. The yellow gantry is used to move railcars full of steel cans for the reclamation project.

Berkeley Pit is behind the wall. The water in the mid-ground is from the tailings pond and is bound for the reclamation plant.

We didn't get to tour the post-flotation purification plant where the molybdenum-rich ore from the copper-rich ore. Here the molydenum-rich ore floats in the flotation tanks, and the copper-rich sinks. The copper leaves here and is dried to about 25% pure before being shipped off by railcar for smelting in (mostly) China.

The molybdenum-rich ore is shipped off via semi truck in the large, white bags shown here. Mike said most of it is bound for the steel-making industry.