Magmatic sulfides, a significant source of valuable metals like platinum, palladium, and chromium, are formed through a fascinating process within Earth’s fiery depths.
The Formation Process
- Mafic and Ultramafic Magmas: These magma types, rich in iron, magnesium, and sulfur, are the foundation for magmatic sulfide deposits.
- Early Crystallization: As these magmas cool, minerals like plagioclase, pyroxene, and olivine crystallize first, leaving behind a melt enriched in sulfur and other minor elements.
- Sulfide Mineral Formation: Eventually, sulfur concentrations reach a point where sulfide minerals, like those containing iron and nickel, begin to crystallize.
- Density and Settling: Sulfides are denser than silicate minerals and the magma itself, causing them to sink towards the bottom of the magma chamber.
- Cumulate Formation: Over time, these dense sulfide minerals accumulate, forming a layer called a cumulate, which can be centimeters or even meters thick. These cumulates are often composed almost entirely of sulfide minerals.
The Metals
Cumulate sulfide minerals include:
- Pentlandite (Fe,Ni)9S8: A key source of nickel.
- Chalcopyrite (CuFeS2): Important for copper production.
- Pyrrhotite (Fe1-xS): Another source of iron and nickel.
- Pyrite (FeS2): A common sulfide mineral containing iron.
Importance of Cumulates
Cumulate sulfide deposits are vital to the global supply of metals:
- Nickel: Almost 60% of the world’s nickel production originates from these deposits.
- Platinum and Palladium: Over 95% of global platinum and palladium production comes from cumulate sulfides.
Why Felsic Magmas Don’t Produce Cumulates?
Felsic magmas, rich in silica, are extremely viscous. They cool and crystallize too quickly to allow dense minerals like sulfides to settle and form cumulates.
Oxides in Cumulates
Besides sulfides, other minerals like oxides can also form cumulates:
- Magnetite (Fe3O4): A major source of iron.
- Ilmenite (FeTiO3): An important source of titanium.
- Chromite (FeCr2O4): A significant source of chromium.
The Bushveld Complex
The Bushveld Complex in South Africa is a prime example of oxide mineral cumulates. It boasts extensive layers of chromite, along with platinum, palladium, and other valuable elements.
Conclusion
Magmatic sulfides and cumulates are a testament to the complex geological processes that create valuable mineral deposits. Understanding these processes is crucial for exploring and mining these resources sustainably, ensuring a steady supply of vital metals for our world.
