RELATIONS OF PYRRHOTITE AND CHALCOPYRITE. 135 



the country rock may be coated with chalcopyrite, or the latter may lie as 

 a bunch between the rocky fragments, and vice versa as to the other sulphide. 

 There is no uniformity in their mode •of occurrence with regard to one an- 

 other, and they appear to have been introduced among the fragments of 

 broken country rock simultaneously and under the same conditions. The 

 dioritic wall-rocks on either side and also the included bowlders and even the 

 smaller fragments are often thickly impregnated with disseminated grains, 

 spots and patches of all sizes, both of pyrrhotite and chalcopyrite. These 

 spots of ore have usually rounded outlines in cross-section and approach 

 spherical and ovate forms. The two sulphides may occur side by side in the 

 same isolated kernels or amygdules; but just as frequently the latter consist 

 of one or the other alone, although in such cases the same rock-section may 

 contain as many of the one kind as the other and all indiscriminately mingled 

 together. 



Figure 1 represents a fresh section of the brecciated ore, two feet high 

 and a foot and a half wide, as exposed at the northeastern end of the drift 

 from No. 4 shaft, Murray mine, in October, 1890, the shaded part being 

 mostly chalcopyrite (with some pyrrhotite) and the rest fragments of diorite. 

 The shaded spots in one of the latter on the right side are included patches 

 of the ore. Figure 2 represents a section four feet high and three feet wide 

 of the decomposed ore on the southwestern side of the railway cutting through 

 the mass at the' Murray mine. The shaded portion is the gossan with some 

 undecayed pyrrhotite and chalcopyrite, the rest beiag fragments of diorite. 

 Figure 3 represents a hand specimen of the ore from the Stobie mine. It 

 was traced directly from nature and reduced to one-half the linear dimen- 

 sions. The portion shaded horizontally shows pyrrhotite, the vertical shad- 

 ing chalcopyrite and the dotted areas rounded fragments of the silicious 

 country rock. 



Numerous analyses of the ores have shown that the nickel is confined to 

 the pyrrhotite, in which it is present in the proportion of about 1 to 5 per 

 cent.; but it has not been determined whether it replaces a corresponding 

 proportion of iron uniformly throughout the mass or exists in the form of 

 disseminated grains of polydymite. This mineral occurs as crystals, plainly 

 visible in some of the ores from the Worthiiigton mine, in the township of 

 Drury. 



The Genesis of the Ores. 



The ore bodies of the Sudbury district do not appear to have been accumu- 

 lated like ordinary metalliferous veins from mineral matter in aqueous solu- 

 tion, but to have resulted from igneous fusion. The fact that they are always 

 associated with diorite, which has been left in its present positions in a molten 

 state, points in this direction. As the diorite and the sulphides fuse at about 



