Description of the deposits
Magmatic deposits are mineralized deposits formed during the solidification of igneous molten rock (magma) deep in the earth. The most important magmatic deposits are ones derived from Mafic (oceanic crust) and Ultramafic (very old oceanic crust) magma as they tend to be highest in valuable metal minerals most sought after.
The molten liquids can separate – with one resulting liquid containing the heavier metals and the other lighter minerals. The individual magma tend not to remix and would be considered immiscible. The resulting solid magma will have layers, with one or more enriched in a potential valuable mineral/ore.
The resultant ore body is located on the bottom of the magma chamber as the mineral enriched liquids are heavier and “sink”. This type of magmatic deposit is referred to as “liquid immiscibility” with Nickel, Copper with/without cobalt and tend to be massive sulphide in appearance.
Separation and gravity settling
Magmas do not crystallize all at once, it occurs in steps. As certain minerals (Chromium) cools it forms chromite crystals before most others. The chromite is heavier than the remaining magma and sinks to the bottom forming thin layers enriched in chromite on the bottom of the magma chambers.
This is a common ore body for chromite deposits.
A combination of complex immiscibility and separation
Although the process is not well understood, there is a complex reaction series which results in occasional deposition of platinum groups within either deposits listed above.