18 Iwasaki: 



one mine. In the remaining three, their existence was doubtful. 

 When the ore-deposit is in contact with the volcanic rocks, the 

 deposit becomes thinner and thinner as we descend changing at 

 last into a network or dissemination, and passing by imperceptible 

 changes into the volcanic rock itself. 



Impregnations: — One of the characteristics of the ore-deposits in 

 the Kosaka Province is the abundance of impregnations. This 

 type of ores is perhaps evidence of the intense pressure and the 

 high temperature of the emanations. The emanations form 

 massive deposits by impregnation in the igneous rocks such as 

 quartz-trachyte or andésite ; and sometimes they produce bedded 

 deposits by dissemination in sandstone. When the rocks are 

 traversed by numerous veinlets, the result of emanation is em- 

 bodied in networks. Sometimes whole masses of igneous rock are 

 changed into metasomatic ores. From these deposits gold is 

 usually worked ; copper and iron also are sometimes got from such 

 ores. The vein-stufïs are chiefly quartz and clay; besides, pyrite, 

 hematite, chalcopyrite and barite are found as accessory com- 

 ponents. I shall take the Washinosu Gold Mine as an example 

 of impregnation in the Kosaka Province. 



The Washinosu Gold Mine^^ is situated in the prefecture of 

 Iwaté in the inner zone of North Japan. The largest part of the 

 deposits in this mine consists of impregnations in quartz-trachyte 

 (plagioliparite) erupted through the Tertiär}^ beds; only a small 

 portion belongs to the Tertiary formation. The hill of quartz- 

 trachyte is about 900 feet above the lowest water level in the con- 

 cession. Veinlets traversing the eruptive are usually 1 or 2 inches 

 thick, but sometimes they become as much as one foot in thick- 

 ness, and 300 feet in length. Where the veinlets are ver}^ 

 densely crowded, the impregnations are very rich. In the veinlets, 

 quartz and chalcopyrite are most abundant, while barite and 

 micaceous iron exist in small amounts. Gold is rich in the 

 pyritic quartzose ore, but very poor in the chalcopyrite. 



There are numerous gold deposits like those of Washinosu 

 in the environs of the mine. They are also developed in the 



1^ Nishiwada : The Digest of " Report on Gold and Silver Deposits," 1907. (Japanese) 



