REPORT OF THE DIRECTOR I9II I49 



The gneiss in the hill is typical Grenville and is confidently classed 

 as sedimentary, and thus the ore body lies wholly within sedimentary 

 rocks. Pegmatite, however, is abundant, appearing as irregular 

 masses but more commonly injected in thin sheets parallel to the 

 banding of the gneisses. It is particularly abundant in immediate 

 association with the ore but apparently contains no pyrite. This is 

 so unlike other localities, however, that it is probable pyrite was 

 overlooked. The ore appears to be merely a modification of the 

 ordinary gneiss, containing large, but variable, amounts of pyrite. 

 There is a gradual transition from gneiss to ore, no sharply defined 

 ore body being present. 



More than at any other mine, the pyrite tends to occur in distinct 

 crystals which seem to form quite regardless of surrounding minerals. 

 This is particularly true of a variety of ore consisting of a very fine 

 chloritic aggregate, evidently an alteration product, through which 

 are scattered abundantly quite perfect crystals of pyrite, seldom more 

 than half an inch in diameter, and showing nothing more complex 

 than cube and pyritohedron, as far as noticed (figure 7). This is 

 evidently an extreme case of the tendency shown at all mines for the 

 pyrite to crystallize more perfectly when in a chloritic matrix. As at 

 the Cole mine, graphite is a constant accompaniment of the pyrite, 

 though quite unevenly distributed. A considerable amount of milky 

 white quartz is present, of vein origin and younger than the pyrite 

 crystals, while there has been a still later deposition of calcite in 

 limited amount. 



Thin sections confirm the conclusion drawn from field study that 

 the ore is a part of the Grenville gneiss enriched in pyrite at the 

 expense of the other minerals. The ordinary gneiss on the ridge is a 

 rather fine grained aggregate of quartz, feldspar, both orthoclase 

 and plagioclase, abundant muscovite and a pale brown mica, prob- 

 ably phlogopite. There is a little graphite and an occasional grain 

 of pyrite. A similar rock, close to the ore, is darker in color, very 

 quartzose and micaceous, with more graphite and considerable 

 pyrite. The mica is changing into a greenish, chloritic material of 

 weak or indistinguishable double refraction, and sometimes with a 

 fibrous texture. This same substance also grows in quartz and 

 feldspar, together with small quantities of sericite. There is also 

 present some colorless pyroxene and a dark brown mineral, probably 

 rutile. 



In the sections, as in hand specimens, the pyrite seems to have 

 grown freely into other minerals and only occasionally is molded 

 upon them. Although in somewhat elongated and branching aggrc- 



