36 Vol. XLIir., Art. 5.-T. Kato : 



structure showing the same order of mineral depositions as in the 

 Hyakken vein (Fig. 7) is sometimes recognizable in them. 



21ie Fiijii Vein, wliich lies about 700 meters southwest of the- 

 Daiju mine on the upper course of the same valley, belongs to the 

 same vein group, striking N. 60" W. and dipping southward very 

 steeply. It is a small vein varying in widtli up to 1 meter or 

 so, and was once worked for copper ore. It is noteworthy that 

 abundant gelena is associated with chalcopyrite in this vein, while 

 no tin- stone is recognized. 



From the foregoing deserlption, it is clear that the veins of 

 the Akénobê district are alt consanguineous, and all gradations exist 

 hetween the copper veins containing little or no cassiterite and the 

 copper-tin veins containing much of the same mineral. The scope 

 of the present paper is to investigate fully the origin of the 

 copper-tin veins of this district. 



V. The Ore-Bringer. 



The ore-bringer for the copper and copper-tin veins of the 

 Akénobé district has long remained problematic.^) It is generally 

 accepted that tin veins are usually associated with intrusive acid 

 igneous rocks such as granites, quartz-porphyries and others,^) but 

 rarely with extrusive acid rocks such as liparites.^) The associa- 



1) In the previous paper (" The Eiug-Ore from the Akénobé Mine," loc. cit., p. 36), the 

 ■writer has suggested that '• the veins seem to be related to the liparitic rocks, though not 

 proved," but this has been disproved by later reconnaissances. 



2) Summarized by H. G. Ferguson and A. M. Bateman, " Geologic Features of Tin-Deposits," 

 Econ. Geo!., Vol. VIL, 1912, p. 209 et seq.; J. T. Singewald, jr., " Some Genetic Relations of Tin- 

 Deposits," Econ. Geol., Vol. "STI, 1912, pp. 263-279 ; and R. H. East.all, " The Genesis of Tungsten 

 Ores," Geol. Magaz., No VIII., 1918, p. 368. 



3) Certain tin veins in Mexico are associated with Tertiary rhyolites and rhyolitic tuffs 

 (W. R. Ingalls, "The Tin-Deposits of Durango, Mexico," Trans. Am. I. M. E., Vol. XXV., 1895, 

 pp. 146-163). 



A few of (he Bolivian tin veins are also related to rhyolites (M. Armas, " Genesis of IJoliviau 

 Tin DeposiLs," Eng. and Min. .Tourn., Vol. 92, 1911, pp. 311-311. 



