Platinum (Pt) is a noble, transition metal distinguished by its high density, corrosion resistance, and high melting point. It is one of six elements collectively known as the Platinum Group Metals (PGMs). These elements share similar physical and chemical characteristics and are generally found together in nature, often concentrated in the same mineral deposits. Platinum is exceptionally rare. The metal occurs naturally either in its pure, native form, or alloyed with other PGMs and metals like iron, forming platinum-iron alloys.
Primary Geological Settings
The vast majority of the world’s platinum reserves originate from a geological process called magmatic segregation within large, layered, mafic-ultramafic igneous intrusions. These massive rock formations crystallized slowly from cooling magma chambers deep within the Earth’s crust. The key to concentrating platinum is the formation of an immiscible sulfide liquid within the cooling silicate magma. This sulfur-rich liquid phase separates from the main silicate melt, acting like a solvent that effectively scavenges and collects the Platinum Group Elements from the surrounding magma.
This sulfide liquid, dense with concentrated platinum, settles under gravity and crystallizes into distinct, continuous layers known by miners as “reefs” or tabular orebodies. These platinum-rich layers are confined to specific stratigraphic horizons within the larger igneous body. The host rocks for these reefs are typically ultramafic varieties like pyroxenites or chromitites. The concentration of PGMs in these reefs is much greater than in the surrounding host rock, making them economically viable to mine.
Secondary and Accessory Deposits
Platinum is also recovered from deposits formed after the initial magmatic crystallization or as a byproduct of mining other major metals. One type, known as placer deposits, forms when weathering and erosion break down the primary igneous host rock. The liberated platinum particles, which are dense and resistant to corrosion, are transported by water and physically concentrated in riverbeds, stream channels, and alluvial fans. These secondary deposits contain native platinum or platinum-iron alloys and can be found in both active streams and ancient river systems.
Platinum is an important accessory metal recovered from large nickel-copper sulfide deposits. While nickel and copper are the primary economic commodities, the PGMs are intimately associated with the sulfide mineralization. Although the concentration of platinum is lower than in magmatic reefs, the enormous scale of base metal mining means they still represent a significant source of global supply. The platinum is typically found chemically bound within the sulfide minerals or as microscopic inclusions.
Global Distribution of Platinum Reserves
The geographic distribution of platinum reserves is highly concentrated, with a few major complexes dominating the world’s supply. The most important region globally is South Africa, which holds the largest-known reserves and accounts for the majority of production. This immense wealth is contained within the Bushveld Igneous Complex, a colossal layered intrusion. Mining within the Bushveld focuses on three primary layers: the Merensky Reef, the Upper Group 2 (UG2) Reef, and the Platreef.
Russia is the second-largest global producer, with a major source being the Noril’sk-Talnakh region in Siberia. Here, platinum is predominantly recovered as a byproduct from massive nickel-copper sulfide deposits associated with the Siberian Traps flood basalts. Another significant source is the Great Dyke in Zimbabwe, which is a narrow, linear layered intrusion and the second-largest PGM reserve after the Bushveld Complex.
The North American continent also contains important reserves. These include the Stillwater Complex in Montana, United States, a geologically similar layered intrusion to the Bushveld. Additionally, platinum is recovered in Canada, primarily as a byproduct from the nickel-copper sulfide ores of the Sudbury Basin in Ontario.