Vol. 4] 



Knopf. 



.—Foothill Copper Belt. 



421 



The appearance of the typical ore is adequately expressed by 

 its local designation: "black pyritous slate." From the slaty 

 forms the transition to the chlorite schists is not great. Under 

 the microscope the typical ore presents a uniform deep green 

 color with little or no individualization of the chlorite into dis- 

 tinct flakes. Between crossed nicols a few rude shadowy crosses 

 become apparent, and a general streaked effect, expressed in low 

 blue gray colors, indicates the trend of the flow cleavage. The 

 chalcopyrite is distributed in small stringers parallel to the cleav- 

 age, and is often accompanied by a fringe of epidote grains. 

 Some of the large granules of chalcopyrite are associated with 

 a little quartz and chalcedony. A very small amount of chalcocite 

 was noted, some of which was peripheral upon the chalcopyrite. 

 The quantity of secondary sulphide, however, is nearly insig- 

 nificant. 



The chlorite schist ore differs from the preceding only in the 

 fact that the chlorite is in well-developed plates, many of which 

 show evidence of internal movements. Some grains of titanite 

 occur. 



Ore rock taken from near the footwall of Level 4 shows a 

 few additional features. In sections cut normal to the schistosity 

 the rock is seen to be composed almost exclusively of chlorite, 

 often in minute spherulites, and a few "porphyritic" plates of 

 clinochlore. The discrimination, clinoehlore, is made on account 

 of its superior birefringence and deeper pleochroism. In certain 

 plates chalcocite can be seen replacing the clinochlore parallel 

 to the cleavage lines. The amount, however, is inconsiderable. 

 A few rectangular sections of andalusite occur. Grains of 

 titanite, sometimes partially idiomorphic, are rather abundant. 

 Splendid rutile prisms, surrounded by strongly pleochroic halos 

 of deep olive green color, constitute a characteristic feature of 

 this variety of chlorite schist. 



The andalusite may indicate contact metamorphism by the 

 quartz monzonite intrusive, and lends weight to the probability 

 suggested by the petrographic and stratigraphic data that the 

 Copperopolis chlorite schists represent argillaceous andesite tuffs 

 dynamically metamorphosed. 



Since the deposition of the ore much movement has taken 



