Platinum (Pt), a rare and dense metal, is highly valued for its exceptional resistance to corrosion and high melting point, classifying it as a noble metal. It is significantly scarcer than gold and silver, occurring in only minute concentrations within the Earth’s crust. This scarcity, combined with its powerful catalytic properties used in industrial applications, establishes its high economic importance.
Geological Formation of Platinum Deposits
Platinum’s presence in the Earth’s crust is largely concentrated in primary magmatic deposits, which result from magmatic differentiation as molten rock cools deep beneath the surface. The most economically significant deposits are hosted within large, layered mafic intrusions, which are immense bodies of igneous rock formed from slowly cooling magma chambers.
The formation process begins with high-temperature, silica-poor magma rich in iron and magnesium. As the magma cools, minerals crystallize and settle out in distinct, horizontal layers, a process known as fractional crystallization. Platinum Group Elements (PGEs) do not easily fit into the crystal structure of common minerals, remaining dissolved in the residual magma.
PGE concentration occurs when the magma becomes saturated with sulfur, forming small, dense droplets of an immiscible sulfide liquid. PGEs have a strong chemical affinity for sulfur and are collected into these sulfide droplets. As these heavy, metal-rich droplets settle, they form thin, continuous layers known as “reefs” within the layered intrusion. Secondary placer deposits also exist where platinum-bearing rocks have eroded and the dense metal grains have accumulated in riverbeds.
Global Concentration of Platinum Resources
Platinum deposits are highly centralized, with the Bushveld Igneous Complex (BIC) in South Africa containing the bulk of the world’s known reserves. This massive formation holds nearly 90% of the world’s known platinum group metal reserves and accounts for the majority of annual global production.
Miners within the Bushveld Complex target specific, metal-rich layers, notably the Merensky Reef and the Upper Group 2 (UG2) Reef. The Merensky Reef is a narrow layer known for its high platinum content, while the UG2 Reef is a chromitite layer that has become a primary source due to its extensive reserves. A third, shallower layer, the Platreef, is also mined in the complex’s northern limb.
Russia is the second-largest global producer, extracting platinum primarily as a coproduct of nickel and copper mining from the Noril’sk-Talnakh deposits in Siberia. This massive deposit is a distinct type of magmatic sulfide body where PGEs are concentrated alongside base metals.
Zimbabwe holds the third-largest reserves within the Great Dyke, an immense linear geological structure similar to the Bushveld Complex. North America contributes a smaller portion of the supply, mainly from the Stillwater Complex in Montana and the Sudbury Basin in Ontario, Canada, where platinum is recovered as a byproduct of palladium and nickel operations.
From Ore to Metal: Mining and Refining
Extracting platinum from the Earth is a challenging and costly process due to the low concentration of the metal within the ore body. In primary deposits like the Bushveld Complex, the narrow, deep reefs necessitate complex deep underground mining techniques, involving drilling, blasting, and hauling rock from great depths. Platinum ore typically contains only about three to six grams of platinum group metals per tonne of rock.
Once the ore is brought to the surface, it is crushed and ground into a fine powder. This powder is subjected to a flotation process, where it is mixed with water and chemical reagents to create a slurry. Air is bubbled through the slurry, causing the PGM-bearing mineral particles to attach to the bubbles and rise to the surface, forming a mineral-rich froth that is skimmed off.
The resulting concentrate is dried and fed into a furnace for smelting at extremely high temperatures exceeding 1,500 degrees Celsius. This heat melts the metal components, separating them from the waste rock and forming a metallic matte. The matte is further treated to remove impurities like iron and sulfur, yielding a purer PGM concentrate.
The final stage is complex chemical refining, which can take several months to complete, as the six platinum group metals must be separated from one another. This is often achieved using hydrometallurgical techniques, such as dissolving the concentrate in a strong acid mixture like aqua regia, followed by a series of precise chemical precipitation and filtration steps. This laborious process is necessary to isolate and purify the platinum to the required commercial grade of 99.95%.