REPORT OF THE DIRECTOR igi2 99 



6 Years ago an attempt was made to mine the garnets which 

 occur in the coarse, feldspar, biotite, garnet, Grenville gneiss two 

 and three-fourths miles north of North Creek, but this locality is 

 of no special interest. 



7 At the Hooper mine the garnets occur as crystals (dodeca- 

 hedral) often with good crystal boundaries, up to an inch or a 

 little more in diameter. They are thickly scattered through a 

 medium to moderately coarse grained, dark to light gray, very 

 gneissoid, hornblendic rock which has the composition of a basic 

 syenite or an acidic diorite. It is important to note that these 

 garnets never show the rims of hornblende. In fact the garnets 

 n:ay sometimes be almost surrounded by feldspar. This type of 

 occurrence has not been observed on a large scale at any of the 

 other localities within the county, though a rock almost exactly 

 like it occurs at the Rogers mine as a distinct zone (wall rock) 

 intermediate between the typical garnet-bearing gneiss and the 

 country rock of syenite, where the garnet rock grades perfectly 

 into the syenite. The significance of this fact will be explained 

 below. 



The deposit is an extensive one and a very large mine pit has 

 been opened up. After blasting out the rock, it is somewhat re- 

 duced by sledge hammers, then taken on cars to the mill where 

 it is crushed. By the use of an ingenious method, involving the 

 use of jigs, the garnet (almandite) is almost perfectly separated 

 from the rest of the crushed rock which is of lower specific |?^'av- 

 ity than the garnet. 



ORIGIN OF THE GARNETS 



All modes of occurrence of garnets observed by the writer on 

 the North Creek and Thirteenth Lake sheets are summarized as 

 follows : 



1 As crystals or grains in various Grenville rocks, for example, 

 the garnet-pyroxene gneiss ; the hornblende-garnet gneiss ; bio- 

 tite-garnet gneisses, etc. 



2 As distinct crystals frequently occurring in all types of in- 

 trusive rocks — syenite, granite, granite porphyry, and gabbro — 

 except the diabase. 



3 As large more or less rounded masses with distinct horn- 

 blende rims in the long, lenslike inclusions of Grenville horn- 

 blende gneiss in syenite or granite. 



4 



