REPORT OF THE DIRECTOR IQII 163 



mines. Even where, at the lower end of the island, the pyrite has 

 gabbro on both sides, the ore still occurs in the strongly laminated 

 rusty gneiss rather than in the gabbro itself. As a matter of fact, 

 very little pyrite occurs in definitely recognizable gabbro, and when 

 present at all appears plainly to be a secondary infiltration, as illus- 

 trated by figure 28. 



For these reasons, together with others to be mentioned later, it 

 seems to be a necessary conclusion that the ore is not, even when 

 closely associated with gabbro, a direct product of magmatic dif- 

 ferentiation. On the other hand it is possible that solutions and 

 vapors given off from the gabbro magma may have played a part in 

 forming the ore deposits, although no positive evidence bearing 

 upon the question is at present available and its further consideration 

 is, therefore, best deferred till more extended data can be obtained. 



A specimen of ore from the bed of the river consists of a very 

 fine-grained, dark green, chloritic aggregate, with abundant graphite 

 and rather evenly disseminated, irregular masses of pyrite. The thin 

 section shows a quartz-feldspar-mica aggregate, with kataclastic 

 structure, containing an abundance of graphite, light green chlorite 

 and pyrite. The pyrite shows some skeletal structure with inter- 

 spaces filled with chlorite. Though in itself of somewhat doubtful 

 nature, the section closely resembles several from other localities 

 v\'hich were, from the evidence given by the intermediate stages, 

 regarded as formed by the alteration and replacement of Grenville 

 mica gneisses. The dark color of the hand specimen might suggest 

 a pyritiferous phase of the gabbro, but the microscope does not 

 support this view and indicates that the color is due to the chlorite 

 and the graphite. Another and very similar specimen, though 

 almost as dark in color, is shown in a thin section to be very 

 quartzose, but at the same time exceedingly rich in graphite together 

 with a good deal of deep green chlorite. The quartz is much 

 crushed and the chlorite has replaced it largely. The pyrite, in fairly 

 large masses, shows few fractures and must have been deposited or 

 recrystallized subsequent to the crushing. The original rock appears 

 to have been a quartz schist. 



A specimen from the dump differs from the above in being coarser 

 grained and lighter colored, showing much quartz and mica and little 

 graphite. Pyrite is abundant, evenly distributed and often in dis- 

 tinct crystals. The thin section shows very large areas of pyrite, 

 green chlorite and bleached mica. The pyrite is somewhat cracked 

 and recemented by secondary quartz. Indeed, it is quite possible 

 that all of the quartz is of this origin. A single grain of plagioclase 



