GEOLOGY AND ORE DEPOSITS OF SU-AN / 



INIacrotexture : Thin-schistose, stretched. 



Microtexture : Porphyroblastic, helicitic, lepidoblastic. 

 The rock is a thin-lamellar, fine-wrinkled, greenish-gray schist, 

 the schistose plane of which is a glistening silver-white owing to the 

 presence of muscovite. It is minutely dotted with ilmenite (magnetic) 

 which is, when seen under the microscope, distended into blade-like 

 shapes, presenting the appearance of skeletal crystals. This bluish-gray, 

 opaque ilmenite is seen at the tJiin edge to consist of a typical sagenitic 

 aggregate of rutile veiled under brownish lamellae. The character- 

 istically bi-axial muscovite has a ragged lamellar form, enclosing 

 sagenitic needles of rutile. Its transverse section is sharply outlined 

 by its base, and the mineral is wrapped in a deep bluish-green, rather 

 thick-lamellar clinochlore. The latter is biaxial with the optical angle 

 2E = 54°, and positive. The absorption is strong in the direction 

 parallel to the lamellœ ; the difference of it between a and h is slight, 

 and the refraction and double-refraction are rather strong. The ground 

 is built up of interdigitate grains of quartz. The muscovite and 

 clinochlore constitute the main bulk of the schist. The light-brown, 

 hemimorphic magnesium-tourmaline occurs in various dimensions. Yel- 

 low and colorless anhedrons of epidote are seen enclosing rutile-needles. 

 A little idiomorphic apatite is also observed. The blastic series is 

 rutile, tourmaline, epidote, apatite, ilmenite, muscovite, clinochlore, 

 and quartz. The rock seems to be primarily derived from an igneous 

 rock. Locality: the Yang-liogai^\ 2 km east oï Sang-uön. 



c) ChIorite=schist. (PL I. fig. 1.) 



Composition: Essential: Quartz, clinochlore, muscovite. 

 Accessory : Magnetite, tourmaline, rutile, 

 apatite. 

 Macrotexture : Thin-schistose, stretched. 

 Microtexture : Porphyroblastic, helicitic, lepidoblastic. 



1) 



