REPORT OF THE DIRECTOR IQII I 47 



entirely incloses adjacent areas of quartz in perfect optical con- 

 tinuity, thus clearly showing a replacement of quartz with no 

 mechanical disturbance. Two large grains of pyrite with small 

 branches attached suggest very strongly an older generation with a 

 younger growing upon it. This phenomenon is worthy of special 

 note in this case since it is very exceptional in the material examined. 



That the pyrite has crystallized after the other minerals is obvious 

 and there can be no doubt that it has replaced an equivalent amount, 

 not only of chlorite, but of the much more stable and resistant 

 quartz. 



■ A similar rock, but rather more massive, contains a much larger 

 amount of pyrite in large bunches connected by stringers and vein- 

 lets. Thus to the unaided eye the pyrite appears to be secondary, 

 while as there is nothing to suggest preexistant cavities other than 

 minute cracks it seems equally clear that it must be a replacement. 

 In thin sections the rock is similar to the last but has little tour- 

 malin, is decidedly kataclastic and has more chloritic alteration. 

 Pyrite is much more abundant in scattered grains, rods and branch- 

 ing aggregates, commonly in association with chlorite, while the sec- 

 tion is traversed by a vein of chlorite in which the abundant pyrite 

 ranges from large solid masses to rods and shreds that might almost 

 be called fibrous (figure 2). 



The greenish chloritic alteration runs all through the section in the 

 spaces between cracked quartz grains, at whose expense it seems to 

 have developed. Considerable sericite is present, appearing as tufts 

 and shreds in quartz and chlorite, after which it is secondary. It 

 also forms narrow veins around, and fills cracks in, many of the 

 pyrite masses, indicating that the sericite is at least in part younger 

 than the pyrite. Thus the microscopic evidence agrees with that 

 obtained by the naked eye in pointing to a secondary origin for the 

 pyrite, replacing the original minerals which also show pronounced 

 chloritization. 



A specimen of rich ore very similar to ores at other mines is 

 a medium grained, dark rock with abundant pyrite unevenly 

 disseminated through it in crystals and irregular grains and some- 

 times in large masses, like those in the preceding specimens. The 

 dark color of the rock is largely due to fine scales of graphite, which 

 are exceedingly abundant. A thin section shows a large amount of 

 quartz, little orthoclase and no plagioclase. Muscovite, in part at 

 least secondary, is fairly abundant. There is much pale green, 

 nearly or quite isotropic chloritic alteration product, and abundant 

 graphite. The roughly equidimensional grains of pyrite give little 



