Copper-Tin Veins of (he Akénobé District. 55 



terlstic of pneumatolytlc processes have been observed even under the 

 microscope, though the diopsidization, a characteristic contact- alteration^ 

 is found rather rarehj in the slate near, or at the contacts toith, the 



dioritic rocks. 



The chloritization, silicification and sideritization, which the 

 country rock underwent very intensely and extensively, are charact- 

 eristic of hydrothermal processes. 



vni. auARTzosE Veinlets Cutting the Country 

 ROCK Adjacent to the veins. 



The country rock adjacent to the veins is commonly traversed 

 by minute quartzose veinlets, sometimes showing a netted structure. 

 Occasionally they contain cassiterite in association with muscovite 

 and chlorite. In the following paragraphs are described those 

 cassiterite-bearing veinlets found in the wall-rocks of the Daisen 



vein (PL VIL, Fig. 3). 



They are commonly less than 2 mm. in width, and cannofc 

 be distinguished with the naked eye from those of barren quartz. 

 Cassiterite occurs in minute prismatic crystals, often rounded, and is 

 the earliest crystallized mineral. Quartz occurs in idiomorphic and 

 hypidiomorphic hexagonal prisms, its crystallization being hindered 

 only by cassiterite crystals, which are usually embedded in it. 

 Chlorite is the last deposited mineral and fills up the interstices be- 

 tween the crystals of cassiterite and quartz ; it is the most abundant 

 constituent. The chlorite is pale green in colour, fibrous to flaky 

 radial in structure, showing a cross-bar between crossed niçois. It 

 shows very weak double refraction, indicated by a gray interference 

 colour. In close association with the chlorite, particularly along 

 the selvages of the veinlets, a mineral in radiated fibers and flakes 



