Copper-Tin Veins of the Akénobj District. 4l 



The high-grade ore of this stage is a qiiartzose ore containing 

 abundant cassiterite in clusters, and has a dark gray or dark 

 brown colour. Under the microscope, the cassiterite is always the 

 earliest crystallized mineral and is enclosed in irregular gi*ains or 

 liypidiomorphic crystals of quartz. ' ■ 



The main cassiterite ore is sometimes represented by a n'm/- 

 ore}'^ which is especially well developed in certain parts of the 

 Daisen vein. The ring-ore is formed in places where fragments of 

 the country rock abomid. It is composed of layers of quartz and 

 cassiterite deposited successively along the altered rock- fragment, 

 thus giving rise to an aggregate of concentric banded rings (PI. 

 v.. Figs. 2, 3). As can be observed macroscopically and micros- 

 copically, the rock- fragments forming the nuclei of the rings are 

 extremely silicified and sorrietimes almost entirely altered to an 

 aggregate of minute quartz grains, but they are rarely partially 

 or entirely sideritized. 



The first crust formed on the fragments consists of quartz and 

 cassiterite ; microscopic grains and crystals of cassiterite forming a 

 concentric streak (PL Y., Fig. 2) are enclosed in the quartz crust. 

 Sporadically the rock- fragments are directly surrounded by the 

 cassiterite band which is encrusted with a quartz layer ; this is a 

 special case and under the microscope a certain amount of quartz 

 is always found mingled with cassiterite. The second crust is veiy 

 characteristic. It is composed of chalcedony. On keen observation, 

 we can recognize a concentric layer with a tliickness of 3-5 mm., 

 covering the first quartz-cassiterite layer, and having a luster 

 resembling wax, with a pale blue colour (PI. Y., Fig. 2). Under the 

 microscope, it is essentially a fibrous aggregate showing a radial 

 and concentric structure (PL Y\., Figs. 1, 2, 3). The fiber shows 



1) T. Katô, " The ring-ore from the Akénobé ruine, " loc. cit. 



