About 30% of the world’s nickel (Ni) comes from magmatic deposits. Despite accounting for a minority of Ni production, magmatic deposits are highly sought-after due to their large tonnage, high grades, and ease of processing relative to Ni laterite deposits. In fact, the world’s most valuable ore body is a magmatic nickel deposit.
Magmatic Nickel Basics
As the name implies, magmatic nickel deposits form directly from molten rock. Mafic-ultramafic (metal-rich, silica-poor) magmas naturally contain higher Ni contents, and when this Ni encounters sulfur the two elements stick together to form droplets of sulfide melt.
This sulfide melt is immiscible with the common silica-rich magma, causing the sulfide droplets to separate like oil from water. Unlike oil, however, sulfide melts are denser than the surrounding magma, causing it to sink to the bottom of the magma chamber where it accumulates to form a deposit of nickel-rich sulfides.
As an added bonus, these droplets act like sponges, absorbing precious metals such as gold (Au) and platinum group elements (PGEs) from the magma as they sink through it, enriching the Ni ore in precious metals.
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