ry<^ Vol. XLIIL, Art. 5.— T. Katô : 



under the microscope. These minerals occur, though rather spar- 

 ingly, in ordinary cassiterite veins, and are most abundantly asso- 

 ciated with hydrothermal tin veins, siderite, particularly, being of 

 deposition, in most tin veins, in the last stage of pneumatolysis, or 

 in pneumato-hydatogenetic or hydrothermal stages.^) 



The occurrence of chalcedony, evidently transformed from an 

 opaline silica, as an important gangue- mineral is most instructive. 

 Tliis mineral is an extremely rare associate of tin- stone. Only a 

 few examples of tin veins containing chalcedony have hitherto been 

 reported,^) and they all belong to the category formed under 

 hydrothermal or allied conditions. As already fully discussed under 

 tlie heading of " the deposition of the main cassiterite ore," the 

 presence of chalcedony in the veins under consideration indicates 

 that they were formed under hydrothermal conditions at a tem- 

 perature below 360° C. 



On the other hand, it must be noted that some minerals 

 regarded as common associates of pneumatolytic deposits, such as 

 fluorspar, wolframite and bismuth ores with sporadic microscopic 

 topaz, are present in the veins. These minerals are, of course, of 

 very common occurrence in the deposits formed at high tempera- 

 tures, but may be deposited either from gaseous solutions or from 

 superlieated aqueous solutions containing soluble or gaseous com- 

 pounds of fluorine, tungsten and bismuth. Typical hydrothermal 

 veins containing scheelite, wolframite, fluorspar, bismuth ores, etc. 

 are numerous even in this country.^) 



1) Ferguson and Bateman, loc. cit., p. 225; T. Katô, opt. cit., p. 161. 



2) The Mexican deposits (Ingalls, loc. cit.) ; Those of Northern Nevada (Knopf, loc. cit. ) 

 etc. 



3) The Kanagasé copper vein of the Ikuno mine, Prov. Tajitna, containing scheelite, wol- 

 framite, rative bismnth, etc.; the gold-silver veins of the Nishizawa mine, Prov. Shimotsuké, 

 eontainirg wolframite, bismnthinite, etc.; the copper veins of the Ashio mine, Prov. Shimotsuké, 

 containing fluorspar, wolfiamite, apatite, etc.; and others. 



