Copper-Tin Veins of the Akénobé District. 25 



Near the deposit of the Minamidani mine, a porphyrite is 

 exposed as a dyke through the phyllitic slates. It is extremely 

 altered and has become light brown in colour, but porphyritic 

 feldspar is abundantly recognizable. Under the microscope, the 

 groundmass is composed of lathy crystals and irregular grains of 

 feldspar, mingled with abundant scales and flakes of brownish 

 green chlorite. No glass-base is present ; it has probably been 

 entirely devitrified. ]Minute apatite needles are common as an 

 accessory mineral. Plagioclase as phenocrysts, sometimes attaining 

 a length of 5 mm., is usually exceedingly altered, although the 

 characteristic polysynthetic twin- lamellae are indistinctly recogniz- 

 able. It is always kaolinized to a considerable extent. Clusters 

 of prisms and ill-defined crystals of clinozoisite and epidote are 

 often developed in the altered plagioclase. Phenocrysts of fer- 

 romagnesian minerals are entirely decomposed to greenish brown 

 chlorite with rather irregular outlines, and the identification of the 

 original minerals is hardly possible ; occasionally, however, the 

 outlines resembling hornblende crystals are observed. 



A dull-lustered green porphyrite is exposed along the highway 

 about 1/2 km. north of the village of Akénobé. It is intrusive 

 in the green slates. As can be seen under the microscope, the 

 rock is extremely altered. The groundmass is difficult to resolve 

 even under high magnification, but it is clearly observed that a 

 secondary feldspathic substance in irregular grains is its chief 

 component, and it is admixed with abundant kaohn and fine fibers 

 and scales of sericite. Apatite needles remain unaltered in the 

 groundmass. The original feldspar phenocrysts are entirely altered 

 to saussurite. Sometimes they are represented by a confused 

 aggregate of grains and prisms of clinozoisite only, and sometimes 

 by an irregular aggregate of grains of newly developed feldspar in 



