Sequences of cumulates form concurrently by downdip accretion from a column of liquid layers that are primarily separated by diffusive interfaces. The low cumulates grow in advance of the upper cumulates in accord with their higher crystallization temperatures. An important observation is that mixing of the two parent liquids lowers their crystallization temperatures and, consequently, should produce unsaturated hybrids that could dissolve earlier cumulates. The repetition of cyclic units above the J-M Reef is explained by having periodic additional injections of dense magma beneath the subsiding column of crystallizing liquid layers. Neither the J-M Reef nor the Bushveld ore zones should ever have been continuous across the floor of their respective magma chambers; and, for Bushveld, the circumstances resulted in zones that are actually minable.--Modified journal abstract.

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