Vol. 4] 



Knopf. — Foothill Copper Belt. 



419 



approximates 100 feet. Within this zone, however, typical augite 

 porphyrites and coarse breccias may occur, as the croppings at 

 the Empire shaft show. The general strike is N. 60° W., and 

 the dip 61° to the northeast. 



Four thousand feet south of the Union shaft (the present 

 hoisting shaft) is found a small gabbro boss, which from the 

 nature of its inclusions, is determined to be intrusive in the green- 

 stones of the footwall country. The gabbro consists essentially 

 of abundant diallage, often altered to actinolite, and basic plagio- 

 clase feldspars, largely converted to aggregate of minute zoisite 

 prisms. Toward the southern end of the boss a more basic modi- 

 fication of the gabbro is met with, which may descriptively be 

 designated a feldspathie hornblendite. A similar rock occurs 

 in small isolated croppings 200 feet southeast of the mill in 

 the hanging wall of the lode, surrounded by schistose augite 

 porphyries. The hornblendite here consists of numerous stout 

 hornblende prisms bound together by a mesostasis of basic plagio- 

 clase feldspars which poikillitically enclose small perfect idiomor- 

 phic hornblendes. This hornblendite is cut by a system of 

 epiartzose biotite granite dykes. The main gabbro boss is intruded 

 by thin albite dykes containing some faintly pink zoisite. At 

 two points on the periphery of the gabbro, and on opposite sides 

 of the boss, are lenses of serpentine, not exceeding 30 feet in 

 thickness. Discrete areas of this serpentine, attaining a maxi- 

 mum width of 60 feet, appear intermittently along the footwall 

 of the lode as far north as the Union shaft. It is occasionally 

 altered to a talc schist. Along the footwall are also limited expos- 

 ures of a deeply decayed rock of granitic habit, which fresher 

 samples from the mine workings show to be a quartz monzonite. 

 The greatest thickness exposed is 50 feet, and the northernmost 

 cropping is -1000 feet north of the Union shaft, or about 8000 

 feet north of the gabbro boss. The mutual relations of the quartz 

 monzonite and the serpentine were not discoverable. The quartz 

 monzonite is intrusive into the chlorite schists of the lode, the 

 actual contact showing a limited degree of fusion and assimila- 

 tion over an inch or two. The quartz monzonite is composed of 

 hornblende and biotite, both entirely chloritized, oligoclase, and 

 orthoclase in equal amounts, and abundant quartz, with accessory 



