(14 
ECONOMIC GEOLOGY 
22 per cent. of Ni); millerite or capillary pyrites (NiS) is 
well known from its hair-like crystals. Nickel also occurs as 
an arsenide, and as a hydrous nickel-magnesium silicate, 
the garnierite of New Caledonia. 
SupBury — THE GeNEsis oF ITs Ores — The most im- 
portant nickel mining field is around Sudbury in Ontario, 
35 miles N. of Lake Huron. The field consists of pre- 
Paleozoic rocks, including a basin of sediments, 36 miles by 
16, surrounded by a ring of igneous rocks, outside which are 
steeply tilted sedimentary rocks with greenstones and still 
older igneous rocks and gneisses. The formation may be 
tabulated as follows :— 
Keewenawan Intrusives— 
ith Quartz - diorite; 3rd Granite; 2nd Micropegmatite ; 
ist Gabbro (Norite).1 
F16. 35 —NIckeL SuLpHIDE ORE 
OF SUDBURY, 
Nickel sulphide ore of Sudbury 
(after T. C. Phemister), The 
sulphides, black, are replac- 
ing the silicates in * norite,” 
The replacement often follows 
the cleavage planes in the 
felspars. 
Animikie. Sandstone, slate, and tuff with the Trout Lake 
Conglomerate at the base. 
Greenstone including pillow-lavas like those of the Keewatin, 
and steeply tilted sediments, conglomerate, and slates 
which are in places altered to schist. 
Granitic gneiss and older schists. 
The nickel ores occur chiefly with pyrrhotite and chalco- 
pyrite. Some mines contain sperrylite, the arsenide of 
platinum (Pt As,). The veinstones are quartz, secondary 
biotite, a felspar-quartz intergrowth, and fragments of the 
countrv rocks. The sulphides occur (Fig. 38) as veins 
I The traditional name is norite ; Prof. Coleman remarked that much 
of it has no rhombic pyroxene, and according to T. C, Phemister the 
oulk is gabbro.