Copper-Tin Veins o£ the Akénobé District. 5 



underwent poneplanation during tlio ^Nfoi^ozoic continental period of 

 Chiigoku. Daring the latest upwarping period, i.e., the Tertiary 

 age, this district was elevated more than 1000 meters, while the 

 upheaval of the western and central parts of Chiigoku lias been 

 generally from 400 to 500 meters. Thus the elevated peneplain 

 formed at this period had a higher surface in this district, and, 

 consequently, the rejuvenescence of rivers was more conspicuons 

 and erosion more active here than in the other districts. For these 

 reasons, the district in question is full of precipitous mountains, 

 w-hile the other parts of Chugoku still remain an elevated peneplain 

 deeply sculptured hy rejuvenated rivers. It is proved by field 

 observations, however, that faults and other tectonic disturbances 

 have also played not unimportant parts in the formation of the 

 present physiographic features of this district. 



in. General Geology. 



In its geological structure Eastern Chôgoku is very complicated, 

 hteing composed of sedimentary complexes of diverse ages, intricately 

 faulted and folded, and intruded by various igneous rocks. A 

 glance on the general geological map"^^ of this region shows this 

 clearly. The Akénobé mining district, being only a small part of 

 this complicated region, encloses comparatively few rock varieties, 

 consequently the intricate major structure cannot be revealed by 

 the field study of such a limited area as the district in question. 

 Considered petrologically, however, this district affords many in- 

 structive data, especially concerning the alterations of rocks by 

 hydrothermal solutions, to the action of wdiich the formation of 

 most veins of this district is due. 



1) Ikuno Sheet, in scale 1:250,000, publi^ihed by Imp Geol. Survey of Japan. 



