Of the five types of FeS 2 distinguished in the early Paleozoic Nairne pyritic formation, one of the two types designated as primary forms about 90 percent of the deposit; it consists of pyrite which is probably sedimentary in origin, occurring as small grains distributed parallel with the bedding or in small veinlets developed during metamorphism. A coarser-grained pyrite, commonly enclosed by altered pyrrhotite, is found together with Ag-Sb minerals in large veins and may be of hydrothermal origin. Iron sulfides of secondary origin are represented by two types of replacement products of pyrrhotite--concentric FeS 2 consisting of nodules of extremely fine-grained pyrite and/or marcasite, and zoned pyrite sometimes enclosing and perhaps formed from concentric FeS 2 -- and a third type which is definitely a product of weathering.

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