Plan B: Reasons to change your mining method from the obvious choice
June 02, 2021
June 02, 2021
Why would you want to change your preferred mining method? Here’s how factors external to a mine’s ore body can inspire a different approach.
When evaluating a mineral resource, mining engineers decide what mining method to employ early in the process. Will it be open pit or underground? My team works with an “ore body out” philosophy in mine design that starts with understanding the characteristics of the ore body that could influence the selection—things like depth, grade distribution, and thickness.
Each mining method has its own strengths and weaknesses, but sometimes the obvious strategy can’t be selected—and it may have nothing to do with the ore body itself. Thankfully, your mining project can likely still move forward. It’s important to know there are options and how to best switch to an alternative technique. Here are some situations that might cause you to change your mining approach.
Open pit often makes the most sense financially for near-surface ore body discoveries, but it can pose challenges if the proposed pit encroaches on a meaningful area for a community like a religious site, burial ground, or national park. As a backup approach, going underground in these situations generally leads to less surface disruption.
In one such case, my team was asked to assess a near-surface deposit located beneath a religious site. Our team noted that the ore body had a higher-grade core, which made it good for underground mining techniques, and we recommended that approach. Though the underground option would return lower financial results, it was more likely to be approved by community stakeholders because the surface disruption wouldn’t be as large. The underground option provided flexibility on locating the surface infrastructure—reducing the footprint and protecting a cherished piece of the community.
Mining technology is always improving, and an update in equipment or change in technology may inspire you to shift mining methods. Recently, my team has assessed several historical producers—some going back to the 1800s! Many of these historical underground mines are good candidates for reassessment as an open pit mine. Precious metal mines that focused on the underground extraction of high-grade veins—while ignoring lower grade adjacent minerals—are good open pit candidates.
Past producers don’t even have to be that old. Though ultra-class haul trucks—with a payload capacity of 270 long tons or more—seem commonplace in many operations now, these trucks are still relative newcomers to the mining world. The emergence of these ultra-class trucks in the past 10 or 15 years has unlocked additional efficiencies for projects last assessed when smaller haul trucks were dominant. And recent battery technology improvements are improving underground mine economics, mostly due to the reduced need for ventilation. In some cases, the savings from different equipment and reduced energy use weren’t options even 5 years ago.
It’s important to know there are options and how to best switch to an alternative technique.
Mother nature—and the desire to protect environmentally sensitive areas—can also lead you to change. The presence of surface water, or even glacial ice, can push mine designers to examine underground alternatives for mines that are initially good candidates for open pit. You encounter the same situation with proposed open pit operations that may impact important water sources—like recreational lakes and rivers. Switching to underground often makes the most sense.
Here’s something else to consider if you need to pivot from open pit to underground because of the landscape. A long hole stoping method with backfill can be a viable alternative to an open pit but without the surface disruption or subsidence that other bulk methods can create.
You might find other situations where the surrounding landscape forces you to be open-minded. There are projects that have limitations on waste dump heights to fit the prevailing terrain of the deposits area—something that under the right circumstances could push an open pit mine to consider alternative ways to lessen the footprint.
The obvious choice for your mining method may also not be possible because of local government rules. Mining regulations and cultural attitudes toward mining are different around the world, and it’s important to know this when approaching a project. Sometimes government stances can change even over a few years. Recently, some jurisdictions have banned open pit mining, leaving underground as the only alternative.
My team was recently involved in producing an underground design for a deposit that was a better candidate for open pit. The client was concerned about ambiguous government regulations about mining adjacent to a water body, so they asked for a preliminary underground study to be completed as a back-up plan should the government decline the permit application. Ultimately, the government declined the open pit application.
It’s fascinating to look at how to pivot when the obvious mining method isn’t available. There’s often another solution that may not be obvious during the first assessment of the deposit. What’s important is finding the right solution—one that satisfies stakeholders, local governments, community members, and the project team.