Copper-Tin Veins of the Akénobé District. 57 



-chalcopyrite and zincblende in tlie form of small specks. They 

 -correspond probably to the barren quartz of the last stage of 

 jûineralization. 



IX. Summary and Conclusions. 



At the present time, it is generally accepted that tin veins can 

 be deposited from pnenmatolytic as well as hydrothermal solutions,^) 

 although those of pnenmatolytic origin, containing characteristic 

 pneamatolytic minerals such as fluorite, topaz, tourmaline, apatite 

 and other fluorine and boron-bearing minerals, and accompanied by 

 typical pnenmatolytic alterations of the country rock, are of com- 

 moner occurrence. 



That the veins under consideration were not formed under 

 pure pnenmatolytic conditions is indicated by the absence of 

 ■characteristic pnenmatolytic alterations of the wall-rocks. The slaty 

 rocks in which the veins are enclosed are often intensely chloritized, 

 silicified, epidotized and sideritized,^^ while no characteristic pnenma- 

 tolytic minerals have been observed in them even under the 

 microscope. These alterations are regarded to be characteristic of 

 hydrothermal processes. Moreover, the veins themselves contain 

 usually more or less siderite and chlorite, as can easily be revealed 



1) The tin veins of hydrothermal origin have been reported by many investigators, the 

 following being some typical examples: — 



The tin-bearing veins of the transmetamorphic zone in the Zeehan Field of Tasmania (W. 

 H. Twelvetrees and L. K. Ward, " The ore bodies of the Zeehan field," Tasm. Geol. Surv. Bull. 

 8, laiOj. 



The tin deposits of Mexico, in rhyolite surface flow and accompanied by topaz, quartz, 

 chalcedony and opal, wolframite and bismuth ores (W. E. Ingalls, " The tin deposits of Durango, 

 Mexico," Trans. Am. I. M. E., Vol. 25 (181)5), pp. 146^163). 



The tin veins of Northern Nevada, containing exclusively wood-tin as tin mineral, in as- 

 sociation with opal, chalcedony, lussatite, tridymite, hematite, etc. (A. Ivnopf, "Wood tin in the 

 Tertiary rhyolite of Northern Nevada," Ec. Geol., Vol. XI, 1916, pp. 652-661). 



The cassiterite veins of the Snzuyama mine, Satsuma Province, Japan (T. Katö, loc. cit.). 



2) Compare with the altered country rock of the Suzuyama veins (T. K.atô, opt. cit., p. 119 

 ■et seq.). 



