Describes the main phase of crystallization within a cooling magma body, occurring before the late-stage pegmatitic or hydrothermal phases. During this stage, the bulk of the silicate minerals precipitate out of the melt to form the primary igneous rock. Economic geologists look for orthomagmatic deposits where heavy metals like nickel, copper, and platinum group elements settle out of the melt early in the cooling process.
Heard on the job
The platinum group elements here are concentrated in an orthomagmatic deposit near the base of the intrusion.