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R. J. COLONY 



effects producing the so-called "micropegmatites," which are 

 essentially the consolidated "concentrates" themselves — the "acid" 

 differentiate of the more basic portions of the magma. These rocks 

 consist of alkalic feldspars, biotite and hornblende, engulfed in a 

 matrix composed of a micrographic intergrowth of quartz and alkali 

 feldspar, which sometimes comprises 50 per cent of the rock. 



Ftg. s Fig. 6 



Fig. s. — Photomicrograph of norite from the Sudbury region, near Windy Lake, 

 Ontario. Nicols crossed, magnification 20 diameters. The orthorhombic pyroxene 

 here has been ahnost wholly converted to serpentine (Bastite) (5). A small amount 

 of end-stage quartz (Q), in places mixed with feldspar in micrographic intergrowth (M) 

 is usually associated with, or in proximity to, the serpentinized pyroxene. The feldspars 

 in this facies of the norite have been but very slightly affected by hydrothermal 

 attack, carrying very sparingly distributed small patches of sericite here and there. 

 Fig. 6. — Photomicrograph of norite from the vicinity of the Blezard Mine, Sudbury 

 region, Ontario. Nicols crossed, magnification 20 diameters. Carrying considerable 

 end-stage quartz (Q) and showing albitization margins (A) on some of the feldspar. 

 The orthorhombic pyroxene has been almost wholly converted to pale green actinolitic 

 hornblende, grading into biotite in places, remarkably ragged and patchy, and penetrat- 

 ing the feldspar in many places. 



The biotite has been changed to chlorite, at times spherulitic; 

 the hornblende is actinolitic in character, suggesting derivation 

 from some other original. 



In places the quartz increases in quantity so that it forms large 

 groups of crystals of considerable area, but related nevertheless 

 to the very end-stages of consolidation, judging from its structural 

 relations to the other minerals. The phenomena described may all 



