Copper-lln Vtins of the Akénobô Di3trict. 13 



same period of ii-ruption, they show sometimes conspicuous dif- 

 ferences in character even in different portions of the same mass. 

 The following are the chief types : — 



Gahbroid Dlorite. Near the entrance of the Sekiei 5th adit, 

 a small mass of gabbroid rock is exposed. It is a part of the 

 large dyke-shaped mass which is met with in the main cross-cut 

 between the Nihonmatsu and Sekiei veins, and continues to tho 

 outcrop of a lighter coloured dioritic rock observed on the slopo 

 between the Daisen main adit and the Sekiei 5th adit. 



The rock is usually more or less decomposed. It is medium - 

 grained holocrystalline rock, consisting of w^hite feldspathic and 

 dark green ferromagnesian ingredients, sometimes showing indistinct 

 parallel arrangement of the constituent-minerals due to dynamic 



processes. 



Under the microscope, the rock is composed chiefly of plagio- 

 clase, hornblende and a small quantity of malacolite (PI. IV., Fig. 

 2). The plagioclase is commonly xenomorphic, while the fer- 

 romagnesian minerals are idiomorphic or hypidiomorphic. The 

 plagioclase is usually either altered to kaolin, appearing turbid, cr 

 changed to dense aggregates of clear transparent flakes and fibers 

 of sericite ; sometimes it is altered to saussurite or an aggregate of 

 minute grains and prisms of clinozoisite-epidote minerals. The 

 hornblende forms the predominant constituent of the rock, and 

 occurs in aggregates of hypidiomorphic grains and idiomorphic 

 prismatic crystals, often bent and torn by dynamic processes (PI 

 IV., Fig. 5). It is very light coloured but distinctly pleochroic, 

 li c light green, ± c light yellow to almost colourless. The extmc- 

 tion angle is very small, c:t==ca. 15°. The plagioclase encloses 

 the crystals and grains of hornblende, and fills up the interstices 

 between the latter. A small quantity of colourless malacolite in 



