20 Iwasaki : 



Serigano and other gold mines. 



First of all, after the formation of fissures, gold, argentite and 

 pyrite were deposited around andésite horses, at the same time 

 that the quartz veins were formed, after that, secondary enrichment 

 took place, and gold together witli other minerals was formed upon 

 the andésite nucleus in the inner side of the first ring. Thus double 

 rings were produced there. Together with the above-described 

 processes, silicification also took place in the andésite horses, which 

 were all or nearly all changed into quartz. Although such ring 

 ores are also found in the Kosaka Province, they are most frequent 

 in the Satsuma Province. This is perhaps due to the greater basic 

 property of andésite, compared with quartz-trachyte, shale, and 

 sandstone, which are the most important mother rocks in the 

 Kosaka Province. 



The so-called replacement veins of Lindgren^' are also often 

 found in the Satsuma Province, and are, as Emmons"'^ stated, dis- 

 tinguished by their unsymmetrical structure, variable size, complex 

 arrangement of minerals, and the preservation in the ore of the 

 microscopical structure of the original rocks. I have studied the 

 replacement veins in the Okuchi and Kushigino Gold Mines, in 

 the Satsuma Peninsula, southern Kyûsyû, and therefore will state 

 here the results of my observations. 



The andésite, which is the mother rock of the mines, seems 

 to have erupted in the Tertiar,y or the Diluvial epoch, usually 

 forming low undulating hills due to erosion. The rock is grey 

 and compact, with augite and felspar phenocrysts. The former 

 is conspicuous to the naked eye, but the felspar is not so distinct. 

 Under the microscope, the felspar is seen to be very large, usually 

 twinned in the Carlsbad type, enclosing augite and magnetite. 

 The augite is monoclinic, its pleochroism being very strong. 

 Magnetite is so abundant that the ground-mass often seems black 

 and opaque. Brown coloured glass is abundant in the ground- 

 mass containing microlites of felspar and augite in the fluidal- 

 arrangement. The andésite is the pyroxene-andesite, very com- 



1) " The Genesis of Ore De^josits,'' p. 517. 



2) Loc. cit., p. 517. 



