Articles

Introduction

Metals and minerals produced by terrestrial mining have built our modern economy. Iron is mined to produce steel for bridges, buildings and equipment. Copper power cables enmesh the world, whilst consumer electronics are a fascinating mass of copper, cobalt, lithium, aluminium and many more minerals. Our buildings, houses, planes, trains and automobiles are all the result of mining.

Terrestrial mining activity has tirelessely supplied minerals to meet these demands, and in so doing has become a huge and impactful industry. However, the size of mines, scale of equipment involved, and volumes of waste produced are tremendous, and the public is mostly unaware of the vast scale of this industry.

Despite major improvements in recycling rates, terrestrial mining activity is growing and not abating. An awareness and understanding of the impact of terrestrial mining is important in order to have an informed discussion around deep-sea mining.

How Much Land is Impacted by Terrestrial Mining?

There are huge number of mines worldwide, which cover an astonishing area of land and impact even more.

S&P Global currently tracks around 37,400 mining properties and 7,750 operating mines worldwide. However, it is estimated that there are hundreds of thousands of abandoned mines around the world (Ippolito et al., 2019).

Satellite imagery has been used to measure the total land area involved in mining worldwide, which is estimated at 101,583km² (Maus et al., 2022). This is around 0.07% of total land area. By comparison, urban areas cover around 0.51% of total land area globally.

How is Land Impacted by Terrestrial Mining?

Unfortunately direct mine land usage alone is only a small component of the impact of terrestrial mining. Mining generates large volumes of mine waste, and around 1 million km² of our planet is now covered with this waste (Macklin et al., 2023). This is about 0.67% of the total global land area - about a third more than the total urban area worldwide.

Land usage from mining is primarily for overburden storage and tailings ponds, although there are many other uses of land associated with mining (example, roads, infrastructure, processing facilities, camps etc.):

Overburden (Waste Rock) Storage

Overburden is the soil or rock layer that needs to be removed in order to access the ore being mined, and it is often referred to as spoils. Unlike tailings, overburden does not contain toxic components, and is typically removed from the mine location and stored nearby.

The size of the proposed mine and depth of the ore body determine the volume of overburden to be removed, and often this can be significant. Some of the largest vehicles in the world are associated with removing and transporting overburden, including the Overburden Conveyor Bridge F60 (the world's largest land vehicle by physical dimensions), and the Bagger 293 bucket wheel excavator (the world's tallest terrestrial vehicle).

Tailings and Tailing Dams

Tailings are the waste materials left after the process of separating out the valuable part of the ore. Given that typical ore grades are around 0.5-2%, tailings constitute the vast majority of the volume excavated - for example, tailings are typically 90-98% for Copper ores (see "Minerals Recovery and Processing"), meaning that up to 50 tonnes of tailings may be produced per tonne of Copper.

Processing methods used to separate out the valuable part of the ore from the tailings mean that tailings often contain significant volumes of water, and they are typically stored in an impoundment (lake) contained by a tailings dam. Processing also means that tailings are likely to contain toxic chemicals, including heavy metals, sulphides and radioactive elements, and this leads to challenges in their long-term storage.

Tailings dams are some of the largest engineered structures in the world, and they are used to enclose large lakes of liquid slurry tailings. Given that this slurry is often toxic and potentially radioactive, their integrity is critical. Unfortunately there are a significant number of tailings dam failures each year, with 3 major failures recorded already in 2024. Failures are unfortunately often accompanied by loss of life and destruction of property.

Summary

Worldwide demand for metals and minerals is growing at a tremendous rate, and modern society is literally built upon these resources. Consequently mining is a huge industry, with hundreds of thousands of active and historical mines around the world.

Mining typically doesn't take place in your backyard, and public awareness of the scale and impact of mining is somewhat limited. The areas impacted are huge, the equipment used is often enormous, and unfortunately the impacts of land can be tremendous when incidents occur.

Deep-sea mining is certainly not devoid of impacts, and consequently there is ongoing scientific research into these impacts, as well as active engineering work to find improved solutions.

Given continued development and operations of terrestrial mines, the scale and nature of the impacts of deep-sea mining needs to be weighed against the significant and widespread impacts of terrestrial mining.