Abstract

In basic magmas the oxides of iron and titanium and in part of chromium, along with volatiles, become enriched in the residual magma, and are the last, or among the last, minerals to crystallize. This heavy residual liquid trickles down through the interstices of early crystallized silicates to form a late gravitative liquid accumulation, which rests upon a floor of early crystallized silicates. The down trickling heavy residual liquid makes room for itself by causing plagioclase crystals to float upward, bending and jostling some of them, to form overlying anorthosite. The residual liquid accumulation undergoes purification by eliminating the remaining silicate constituents; the degree of this purification determines the richness of the resulting ore deposit. If the residual liquid accumulation crystallizes under quiescent conditions a concordant or stratiform deposit results, e.g., Bushveld titanomagnetite layers. If pressure is exerted before final consolidation, the mobile residual liquid accumulation is squirted elsewhere, either along the structure of the host rock or transgressing structure, to form late magmatic injections somewhat similar to, but differing from, filter pressing, e.g., Kiruna and Taberg, Sweden, Adirondacks, Allard Lake, Quebec, platinum pipes of South Africa. Residual liquid accumulation accounts for many purified magnetite and ilmenite deposits, and some chrome deposits, that lie concordantly within the parent rocks where evidence of squeezing is lacking, and for many late magmatic injected deposits.

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