Watson — Association of Native Gold with Sillimanite. 243 



limited extent with their micro-graphic intergrowths. It is 

 interleaved along cleavage directions with both biotite and 

 muscovite, occasionally extending across the cleavage in frac- 

 tures and sometimes formed along the mineral boundaries, 

 being especially noticeable as partial rims to biotite; between 

 the acicular crystals of sillimanite, sometimes as large and 



Fig. 1. 



Fig. 1. Photomicrograph showing relation of native gold (in black) to 

 quartz and feldspar (white areas), garnet (light-colored mineral of high 

 relief near center of figure), and biotite the intermediate dark mineral, a 

 large shred of which occupies the lower part of the figure. Gold partially 

 rims and fills fractures in the garnet, and lies along the cleavage positions 

 in the biotite. Magnified 60 diameters. 



small irregular areas and sometimes filling distinct fractures in 

 the mineral; and partially rimming and filling microscopic 

 rifts in the garnet. 



These diverse relations of the gold to the rock minerals are 

 shown in figures 1 and 2, which are microphotographs of dif- 

 ferent parts of the thin section. An interesting feature of the 

 rock is the presence of abundant sillimanite and native gold in 

 intimate association, as indicated in fig. 2. Microscopic study 

 discloses the relations of the two minerals to each other to be 

 such as to indicate that the sillimanite formed in advance of 

 the gold. Rifts or microscopic fractures are shown in the 

 sillimanite, garnet, and micas, and the quartz exhibits strain 

 phenomena. Muscovite is not infrequently bent and sheared 

 and sometimes broken across. These structures have devel- 

 oped since the formation of the rock, and since the gold fre- 



