Copper-Tin Veins of the Akénobé District. 4^ 



sulphides being evidently of later deposition than zincblende. 

 Pyrrhotite occurs also as an early precipitation in this stage» 

 sometimes enveloping cassiterite. 



The ring- structure in the ore of the first stage of mineraHzation 

 is often obliterated and rendered obscure by later impregnation of 

 chalcopyrite and other sulphides of the third stage of mineraliza- 

 tion. The ore of this stage, showing no ring- structure and consisting 

 of massive quartz with abundant cassiterite, is not infrequently 

 cut by innumerable veinlets and streaks of chalcopyrite, and is 

 heavily impregnated with the same mineral belonging to the third 

 stage of mineralization, giving rise to a massive siliceous chalco- 

 pyrite -cassiterite ore (Fig. 9). 



Toward the end of this stage, small quantities of siderite, 

 fluorspar, scheelite, and again some sulphides such as pyrite and 

 chalcopyrite were precipitated. It has already been stated that 

 in the ring-ore, siderite, fluorspar and scheelite occur as linings of 

 the drusy cavities. Moreover, siderite in irregular specks occurs^ 

 as a filling of the interstices between quartz grains. Pyrite and 

 chalcopyrite occurring as impregnation in quartz in close association 

 with siderite belong also to this stage. 



The products of the first stage of mineralization, particularly 

 the chalcedony 1) in the ring- ore, afford very instructive data as to 

 the genesis of the Akénobé veins. Though the temperature limits 

 in which chalcedony is formed are not yet experimentally deter- 

 mined, it is certain that this mineral has never been found in 

 pneumatolytic deposits characterized by high temperature gangue 

 minerals. J. Koni^rberçrer and W. J. Miiller^^ observed that gelati- 



1) It w-fis told by a mining engineer that in a part of the Daisen vein a similar chalcedony- 

 was once found as cruslified layers along the selvages. Bvit such an occurrence is of extreme- 

 rarity. 



2) Königberger und Müller, " Versuch über die Bildung von Quarz und Süiltaten," Centrbl. 

 f. Mineralogie usw., 19(JG, S. 371. 



