The distribution, and occurrence, of sulphides and opaque oxides as normal accessory minerals or minor constituents in the common igneous rocks has received little detailed attention, although the subject has an important bearing on both petrogenesis and ore genesis.

Variations in the species of sulphide and oxide minerals, in their contained metals, and in their different positions in the crystallization sequence of the rock silicates are present and should have a significant bearing on the time and manner of possible metal departure from a magmatic source.

The correlation of these variations with different rock types and rock occurrence has given some interesting and unexpected results.

Normal igneous rocks, with a considerable range in composition and texture and from many widely scattered localities, were studied in polished sections, supplemented, in a few cases, by thin-section study. The study was intended to outline and generally survey the field rather than to . . .

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