Vol. 4] 



Knopf. — Foothill Copper Belt. 



417 



magnetite dust. A few small magnetite phenocrysts are involved 

 in the convolutions of the flow lines, nmch like the numerous 

 larger quartzes. The flow bands are feebly polarizing mosaics, 

 probably cryptocrystalline quartz and feldspar. Epidote grains 

 are abundant in some, or yellowish chlorite in others, or both 

 together in yet others. 



Numerous augen of glossy quartz in a highly schistose matrix 

 of taleose appearance is the most characteristic feature of the 

 sheared quartz porphyries. The schists from the mine workings 

 are very light colored with a tinge of bluish green. Under the 

 microscope the original bipyramidal character of the quartz is 

 often recognizable. Many of the quartzes have been affected by 

 a process which gives them a frayed appearance : short streamers 

 of quartz have grown out from the main mass of the phenocryst 

 parallel to the schistosity. The matrix consists of quartz and 

 sericite intimately interwoven. Sections cut parallel to the schis- 

 tosity show aggregate polarization of a scaly character. The 

 interference tints are quite low (yellow to gray), which may be 

 due to a compensatory effect of overlapping scales of finely foli- 

 ated sericite. The talc-like mineral fails, however, to react for 

 alkalies, but yields silica, alumina, and water at high tempera- 

 tures. It appears probable that with the sericite a large amount 

 of a hydrous aluminum silicate mineral is present. 



■ The chalcopyrite present in the quartz porphyry schists has 

 been sheared along with the other minerals, appearing now as a 

 plating between the foliation planes. In this section it is seen 

 to occur in long narrow streamers conforming to the schistosity, 

 except where partially replacing quartz phenocrysts. 



At the site of original location (malachite-azurite croppings) 

 some barren lenses of vein quartz, 1 to 2 feet long, occur in the 

 schists. Certain unschistified horses of quartz porphyry have 

 escaped mineralization, but have undergone a profound meta- 

 somatic alteration. The original glassy quartzes of the quartz 

 porphyry now appear as phenocrysts in a cryptocrystalline 

 ground of silica. Under the microscope this ground is shown to 

 be composed of fine granular quartz, portions of which assume a 

 rude form of the "retiform structure" of Spurr. Some minute 

 fibres of white mica can be detected under the highest power. 



