GEOLOGY AND ORE DEPOSITS OF SU-AN 9 



Accessory: Graphitoid, rutile (clayslate- 

 needles), maguesium-tourraaliue, magnetite. 



Macrotexture : Thin-slaty. 



Microtexture : Granoblastic, lepidoblastic. 

 The dark-gray rock has a weak lustre on the perfectly even 

 cleavage-plane which is faintly dotted with non-lustrous black spots. 

 The spots are merely local accumulations of graphitoid. After diges- 

 tion in HCl and ignition, the graphitoid ^^ is entirely removed, and 

 then the section appears to consist entirely of crystalline components — 

 a plexus of long rounded albite (?) arranged in one prevailing direction 

 cemented by xenomorphic quartz which probably crystallized out from 

 colloidal silica. TJie quartz has haggled, concave faces, adapting 

 itself to the interstices of the plagioclase grains, and is blastolepto- 

 morphic. Fibrous-lamellar sericite is present in thin laminœ made 

 dirty by magnetite and coal dusts. Clayslate-needles (PL I. fig. 4) 

 are abundant though small as compared with those of slaty mica-schist 

 (see page 6, and PI. I. fig. 2), and the rudely hemimorphic magnesium- 

 tourmaline (sec fig. 4) is present in a meagre quantity. The blastic 

 series is tourmaline, rutile, albite, sericite, quartz, graphitoid and 

 magnetite. Locality : Tol-hogai ^^ to Tol-tari ^\ 



e) Contact=Metamorphosed Limestones. (PL I. figs. 3, 5, 

 6 ; PL II. figs. 1-4 ; PL III. figs. 1-2.) 



Composition : Calcite, diopside, garnet, muscovite, ilvaite, 



magnetite, chrysotile, bornite, chalcopyrite, 



irou-pyrite. 



Macrotexture : Fine-saccharoidal. 



The country limestone has a tabular structure and light-gray 



color. The specimens at my disposal are the contact-metamorphosed 



1) The black dust to which argilllte usually owes its color, is mainly of graphitoid 

 with very little, if any, of magnetite. 



2) mjL 3) iBm 



