Mineral mining is the process of extracting valuable, non-renewable geological materials from the Earth’s crust. This activity focuses on metallic minerals (such as iron, copper, and gold) and non-metallic minerals (including gypsum, salt, and potash). The resources gained are fundamental to modern society, providing raw materials for everything from construction to advanced electronics. The choice of mining technique depends on the mineral’s location, concentration, and geological structure, leading to four primary methods of extraction.
Excavating Minerals from the Surface
Surface mining is the most common method globally, responsible for extracting over two-thirds of the world’s yearly mineral production. This technique is used when mineral deposits are close to the Earth’s surface, making it economically viable to remove the overlying soil and rock, known as overburden. The two principal forms are open-pit mining and strip mining, which differ based on the deposit’s shape and depth.
Open-pit mining creates a large, deep, funnel-shaped excavation, typically used for massive, block-shaped deposits of materials like copper, iron ore, and diamonds. Excavation proceeds in a series of horizontal steps called benches, allowing equipment to safely descend and haul ore and waste rock. The scale of these operations requires specialized, heavy machinery, including powerful shovels and massive haul trucks, to move the extracted material.
Strip mining targets minerals that lie in flat, horizontal layers near the surface, such as phosphate or certain industrial minerals. Miners remove a long, narrow strip of overburden to expose the mineral seam. Once the resource is extracted, the waste material is often deposited into the previously mined strip. Because the excavation moves horizontally across the landscape, strip mining affects a broader surface area than open-pit operations.
Extracting Minerals Deep Underground
When mineral deposits are too deep to be economically or safely accessed by surface methods, underground mining is necessary. This technique involves constructing a complex infrastructure of vertical shafts, inclined ramps, and horizontal tunnels (adits) to reach the ore body. The process targets hard minerals like gold, copper, and iron, as well as softer deposits like salt and potash.
A common method for extracting relatively flat-lying deposits, such as uranium or iron ore seams, is room-and-pillar mining. This technique involves excavating open areas, or “rooms,” while leaving strategically placed columns of unmined ore, called “pillars,” to support the overlying rock mass. The size and spacing of these pillars are calculated based on rock strength and depth to prevent collapse.
For more irregular or steeply dipping deposits, miners may use cut-and-fill mining, which offers high selectivity for the ore body. In this process, the ore is mined in horizontal slices, and the void created is immediately filled with a stabilizing material, such as waste rock or cement slurry. This backfill serves as a working platform for the next slice of ore, ensuring the structural integrity of the mine as work progresses upward.
Sifting Through Loose Sediments (Placer Mining)
Placer mining involves separating valuable, heavy minerals from loose, unconsolidated sediment, rather than hard rock. These deposits are typically found in riverbeds, beaches, or ancient stream channels where minerals like gold, tin, or diamonds have been naturally concentrated by water flow. The technique relies on the significant density difference between the target mineral and the lighter sand and gravel aggregate.
The separation process frequently uses water and gravity to recover the heavy material. Small-scale operations may use a sluice box—a long, sloping trough with internal barriers (riffles) that trap denser minerals while lighter material washes away. On a larger scale, mechanical dredging operations float on a pond or river, scooping up gravel and processing it through an onboard system of screens and sluices.
Chemical Extraction (In-Situ Mining)
In-situ recovery (ISR), also known as solution mining, is a non-invasive technique that extracts minerals without physically removing rock. This method is applicable only to specific, soluble minerals where the host rock is permeable, such as deposits of uranium, copper, or soluble salts. The process eliminates the need for traditional excavation, significantly reducing surface disturbance and the generation of mine waste.
The method begins by drilling a series of injection and recovery wells into the ore body. A chemical solution, called a lixiviant, is then pumped through the injection wells into the deposit. This solution, which is usually water fortified with an oxidant and a complexing agent (like sulfuric acid or sodium bicarbonate), circulates through the porous rock and chemically dissolves the target mineral.
The mineral-rich liquid is then pumped back to the surface through the recovery wells, completing a closed-loop system. At the surface facility, the dissolved mineral is separated from the solution using processes like ion exchange before the remaining water is treated and recirculated back into the ground. This approach is often considered more environmentally considerate for certain low-grade deposits, particularly for uranium, which accounts for a large percentage of global ISR production.