46 Vol. XLIIL, Art. 5.— T. Katô: 



in the former with very irregular boundaries. Chalcopyrite in 

 minute specks is usually intimately admixed with bismuthiaite. 

 It is indicated by their modes of occurrence that native bismuth 

 deposited first and that it had later undergone sulphuration which 

 has advanced gradually toward the interior. Fluorspar in small 

 masses is sometimes found in the ore under consideration. 



On examining this ore under the microscope, the wolframite 

 shows a long needle-shaped cross-section (PI. VIL, Fig. 5) embedded 

 in an aggregate of quartz grains. This mineral is the earliest to 

 crystallize out. It is sometimes altered to a colourless, transparent, 

 strongly double-refracting mineral — probably scheelite, the alteration- 

 product assuming the original platy crystal often in admixture with 

 remnants of wolframite (PI. VIL, Fig. 5). Cassiterite is the next 

 crystallized mineral. It is usually embedded and enclosed in quartz 

 grains in the form of small crystals and grains. It is a notowoi-thy 

 fact that minute crystals and. grains of cassiterite show a tendency 

 to accumulate along the thin plates of wolframite ; in thin sections 

 it is observed that the cassiterite grains and crystals are attached 

 to the slender needle of wolframite like magnetic sands attracted by 

 a magnet. Quartz is mostly of subsequent crystallization to wolf- 

 ramite and cassiterite, and occurs as aggregates of grains enclosing 

 them. But in places well-defined hexagonal prisms of quartz are 

 developed surrounded by grains of the same mineral often showing 

 a zonal structure due to successive growths, and zonally arranged 

 inclusions of fine crystals and grains of cassiterite and others (PL 

 "VIL, Fig. 1). Fluid inclusions are abundant in quartz. 



Occasionally a ring- ore similar to that of the first stage of 

 mineralization is found as a product of this stage. The present 

 writer found a typical one of this category in the Sekiei vein, 

 in which two or three cassiterite -bearing layers are usually present 



