Metnlloft'ouy of tho Tapanose Islands. ],',7 



contrast witli the indented grains in the old veins. Ronndisi-i 

 pores with narrow connecting passages are very noticeable. Both 

 the pores and passages are lined with brown siderite. These 

 phenomena show that, dining the formation of the veins, the 

 emanations from tlie qnartz-trachyte (liparite) contained very large 

 quantities of gases which were for the greater part carbonic 

 acid remaining as siderite in some interspaces between quartz 

 gi-ains. This is surely one of the most important properties of the 

 ores. '.:^. 



The gold grains from this mine may be divided into two 

 classes, granular and crystallized. Tlie former is covered with 

 siderite, while the surface of the latter is fresh and brilliant. The 

 gold grains are grouped together in colonies (Fig. 5). 



Blach sulphide ores: — Ores of this kind are found in the 

 inner zone of Nortli Japan. They were not investigated until late 

 years, and Hirabayashi, ^^ Geologist to the Mining Bureau, was 

 the first to treat their origin and characteristics in detail. Accord- 

 ing to him, the black sulphide ore is an intimate admixture of 

 galena, zincblende, and barite. It occurs most frequently in the 

 form of replacements, but, in a few cases, as mineral veins or 

 impregnations. Tlie ore-bringers are quartz-trachyte or andésite, 

 the latter being generally altered into propylite. Hirabayashi gave 

 a single example of basalt taking the place of an ore-bringer, but I 

 believe it was only an eruptive succeeding the formation of the 

 deposits, as in the case of the Hol-gol Gold Mine, described by 

 Prof. KoTÔ.'^ 



The occurrence of the black sulphide ores furnishes us with 

 materials for making clear the magmatic theory. According to 

 Hirabayashi, there are 43 mines in Japan, in which these 

 ores are worked. They are all in Tertiary beds, and always 

 associated with younger volcanic rocks. In 14 mines, quartz- 

 trachyte is found, in 10 mines andésite or propylite, and in 14 

 mines both these rocks together. Basalt has been found only in 



1) Hirabayashi: "Report on Black Sulphide Ore-deposiis," I. and IT., Mining Bureau, 

 Tokyo, 1908 and 1910. 



2) Loc.cit. 



