Recently, while researching mining projects, I noticed a very interesting concept—what is the stripping ratio? Simply put, it’s the ratio between the amount of waste rock that needs to be removed during mining and the amount of ore extracted.

It sounds simple, but in reality, there’s a lot involved. First, it’s important to clarify that this ratio considers not only quantity but also the type of material. The costs of moving loose soil and hard rock are vastly different, so the same volume can have completely different difficulty and costs.

How is this ratio calculated? The basic formula is the thickness of the overburden divided by the thickness of the ore. For example, if the overburden is 100 meters and the ore is 50 meters, that’s a 2:1 ratio. In other words, to extract 1 cubic meter of ore, you need to remove 2 cubic meters of waste rock. This number is crucial for assessing project profitability—the lower the ratio, the better, because it indicates lower mining costs.

I’ve observed a pattern: if a deposit’s stripping ratio is particularly high, say well over 5:1, the project usually has limited profit margins. Too much waste rock means costs are too high, making mining potentially unprofitable. Conversely, low-grade deposits may have low ratios but still require removing more material due to poor ore quality. That’s why mining companies carefully calculate this data before development.

Real-world examples illustrate this well. The Candelaria copper-gold-silver mine in Chile operates with a lifecycle ratio of 2.1:1, which is considered quite ideal. Canada’s Copper Mountain project is similar, at 2.77:1. But high-grade deposits are different—Bisha copper mine in Eritrea has a ratio of 5.4:1, and the New Liberty gold mine in Liberia even reaches 15.5:1. These high ratios are sustainable because the ore quality is exceptional.

A particularly interesting case is Western Copper and Gold’s Casino project in Yukon, Canada, which reports a lifecycle ratio of only 0.43:1—truly rare in the industry. Similarly, World Copper’s Zonia project in Arizona reports a low ratio of just 1.1:1. Projects with such low ratios are obviously more attractive to investors.

Overall, the stripping ratio is a key indicator for determining whether open-pit mining projects are worth investing in. Generally, for large low-grade copper deposits, controlling the ratio below 3:1 is considered good. But each deposit is different; high-quality ore can support higher ratios. That’s why mining companies spend a lot of time precisely calculating this data before deciding to proceed with development.