Which of the following is NOT typically associated with magmatic segregation deposits?

• A. Quartz and calcite veins
• B. Quartz and calcite veins
• C. Carbonatites, chromite, pentlandite
• D. Nickel-copper sulfide rich zones

Answer: (C)

Magmatic segregation deposits form when a sulfide liquid separates from a silicate magma as it crystallizes, concentrating sulfide minerals such as nickel-iron sulfides (like pentlandite and pyrrhotite) and copper sulfides (like chalcopyrite) in labeled zones or layers. In many mafic to ultramafic intrusions, you also encounter chromite-rich horizons formed from cumulate processes, which are commonly linked to this magmatic segregation style.

Quartz and calcite veins, by contrast, are classic products of hydrothermal fluids moving through rock after emplacement. They form vein networks rather than disseminated sulfide deposits and aren’t indicative of the sulfide-liquid segregation process inside a crystallizing magma.

Carbonatites are carbonate-rich magmas that create a distinct class of intrusions with their own suite of ore associations (often Nb, REE, and phosphate minerals). They do not represent the sulfide liquid segregation style that defines magmatic segregation deposits, even though they can coexist in the broader igneous milieu.

Nickel-copper sulfide rich zones are a hallmark of magmatic segregation, arising directly from the immiscible sulfide liquids in the crystallizing magma.

Putting that together, the combination that does not fit the typical magmatic segregation deposits is carbonatites with chromite and pentlandite, since carbonatites belong to a different ore-genesis style and are not a standard part of magmatic sulfide segregation systems.