Copper -Tin Veius of the Àkénobé District. ;>7 



tion of cassiterite-bearing veins witli intermediate rocks is only 

 exceptional.!) \^^ the Akénobé district no granitic or allied acid 

 plutonic rocks have been observed. Dykes of liparitic rocks are 

 rather scarce, although a liparite flow is extensively developed on 

 the ridge between Akénobé and Mikobata. Dykes of porphyrites 

 and andésites are of commoner occurrence. Those dykes commonly 

 <3ut the veins intricately, and are clearly later in generation than 



the latter. 



To the writer, the veins of this district seem to he related to 

 the dioritic rods, particularly to the later offshoots from the main 

 diorite magma. As has been fully stated in a previous chapter, of 

 the parallel veins belonging to the Daisen vein group Daisen and 

 Nihonmatsu are most characteristic as copper-tin veins, Hyakken 

 and Sekiei contain only a small quantity of tin-ore, and the 

 easternmost vein, Shotoku, contains little or no tin-stone. The 

 decreasing tin- ore content toward the east suggests that the ore- 

 brin^er lies nearer to the Daisen vein. The only mighty igneous 

 mass exposed near the Daisen, Nihonmatsu and Sekiei veins is the 

 large dyke-like offshoot of the altered diorite (PI. L). 



In the Higashiyama area, a leucocratic igneous rock, ahenoheite, 

 corresponding in composition to (luartz-monzonite-pegmatite or aphte, 



1) Many tin veins, once supposed to be connected with intermediate rocks, have been 

 proved to have a close relation to acid rocks. For instance, some Bolivian tin veins were 

 thought by Stelzner to be connected genelically with andesitic rocks (A. W. Stelzner, " Die 

 Rilberzinnerzlagerstiitten BoUviens," Zt. der deutsch, geol. Gesellsch., Bd. 49, S. 51-142, 1897), biit 

 AV. E. Kumbald {" The Origin of the Bolivian Tin Peposits," Econ. Geo!., Vol. 4, 1909, pp. 

 :$21-364) and M. Armas (op. cit.) state that the' Bolivian deposits are invariably connected with 

 acid rocks, viz., granitic and liparitic rocks. 



The Suzuyama veins in the province of Satsuma, Japan, were supposed to be connected 

 ^\ith an andésite, but recently it has been proved tbat they occur in connection with a granite- 

 porphyry (T. Iki. " Report on the Suzuyama Mine," Bull. No. -I« (in Japanese), Imp. Geol. 

 Survey of .Tapan, 1914 ; T. Katô, loc. cit.). 



At the present time, most investigators infer that the tin veins are, without exception, 

 genetically connecte.! with acid igneous rocks, i.e., granites, qu.itz-porphyries, rhyolites and 

 others. 



