February 11th, 2013
Diagnosing a Bedrock Blowout on Gold Rush
In the last episode of Gold Rush (“Bedrock Blowout”), we saw yet another example of how a little incident can cause a big problem.
We watched as the team at Indian River was digging material towards the bottom of their "cut" near bedrock, which was coarser and more "slabby" than what they had been feeding their wash plant previously.
The KPI-JCI conveyors and Cascade screen were designed to handle maximum "lump sizes" (maximum size of rocks) up to about 8" in diameter. Feeding rocks larger than that can cause various components of the equipment to prematurely wear or fail, as well as cause "rock jams" at the transition points of the system.
Since KPI-JCI does build and market heavier-duty equipment, one might be inclined to ask why Team Turin/Hoffman didn't simply put in heavier-duty machinery that could handle the larger feed sizes. There are a couple of good reasons:
- Cost. The cost of mining equipment can climb very rapidly when you use more steel, larger bearings and heavier components. In most cases, the energy cost to operate heavier machinery is also much higher. Therefore the cost-per-ton can rise significantly, cutting into profits.
- Application. The main objective at Indian River is to capture the gold within the sand and gravels. For the most part, the larger stones do not harness any significant quantity of gold, thus it only costs more money to handle larger feed sizes that are really not yielding any higher quantities of gold.
Accordingly, when trying to reject large rocks ahead of a system like the KPI-JCI wash plant, it is common to install "grizzly bars" over the feed hopper. These bars act like a filter to prevent larger particles from entering the system while allowing smaller, desirable material to pass through. The feed hopper, which is feeding the wash plant at Indian River, is equipped with grizzly bars. Typically, these bars will be spaced between 4-6 inches apart, so in theory no matter what the crew has in the loader bucket, the wash system should only see 4-6”-minus material – well within the design specifications of the KPI-JCI equipment operating in the Klondike.
However, as we mentioned earlier, the material at bedrock can be inherently "slabby" in nature, so even a rock that is 12-20” long might be only 4” thick and can can still pass between the grizzly bars and get fed to the processing equipment.
This is exactly what happened in the last episode. Large, slabby material that was too large for the system passed between the grizzly bars and got hung up between the discharge hood of the feed conveyor and the feed box of the Cascade screen. This required that they shut down the plant to dislodge the rock jam; unfortunately, the water feeding the sluices was left on during this incident and as such it is possible that gold was flushed out of the sluices. Fortunately, the team had another 100+ ounce clean-out, and Team Turin/Hoffman is now within real striking distance of achieving their 1,000-ounce goal.
Still, this episode was all too familiar to those of us who are regularly engaged in this kind of equipment. A rock jam can not only lead to costly loss of production, but such a disruption can also have a ripple effect throughout the plant, which can have an impact on profitability and/or quality.
Unfortunately, about the only solutions to prevent the occasional slabby particle from entering a plant are:
- Have the loader operator essentially inspect ever rock that he puts into his loader bucket - in reality, this is impractical;
- Install additional heavy-duty vibrating screening equipment ahead of the rinse screen as an alternative to static grizzly bars, but this would add to the cost-per-ton.
Realistically, given the time-pressure that the Indian River crew is under in order to meet their goal before the weather pushes them out, probably the best solution is also the simplest- simply task someone to keep a very close eye on the plant and react quickly and address problems if and when they do arise. Aggregate producers refer to these employees as “ground guys”…their job is simply to keep the plant up and running. As Dave Turin said in the episode, "Don't step over a dime to pick up a penny." As we saw, if Todd had listened to Dave and kept a closer eye on the plant, he could have potentially gotten more gold. Unfortunately, we'll never know how much gold may have been lost.
Turin told his crew that the rock jam incident "was a wake-up call." I would be surprised if we’ll see many more rock jams from here on out.