18 AllT. 12. — B. KOTO : 



san. On the north side of the equatorial dale of Morai-chhi, just 

 mentioned, and just south of the mine, a mass of basalt makes its 

 appearance at the junction of the porphyritic granite and the 

 contact-metamorphosed limestones. The basalt is sometimes quartz- 

 hearing, and at other times agglomeratic, being composed of blocks 

 of the same rock and also of fragments of the porphyritic granite. 

 Minor exposures of the volcanic are seen to occur sporadically in 

 the same valley. 



One interesting fact concerning this effusive rock is that its 

 continuation could be traced farther east for over 1,500 feet in the 

 form of a regular dyke, measuring from one to four feet in breadth, 

 and looking as if it were interbedded in the limestone beds with 

 northerly dips. 



C. Ore-deposits 



The ore-deposit of the Hol-gol gold mine occurs, as shown in 

 the annexed geologic map (PI. IV.), partly around the junction 

 of the limestone with the metamorphics and porphyritic granite, 

 and partly in the lime-silicate-hornfels that comes in direct contact 

 with the porphyritic granite. It does not form any definite lode 

 or fissure-veins by which a boundary line separating it from the 

 surrounding country-rocks could be drawn. By tracing the prob- 

 able limit of the ore-containing portion, the deposit is divisible 

 into two^^ irregularly rounded ore-bodies — the eastern and the 

 western. In these ore-bodies, as well as in the space between 

 them, no definite line could be fixed separating the ore-bearing 

 from the barren portion. 



The ore occurs mainly in lime-silicate-hornfels which is ir- 



l) See the accompanying map, PI. IV. 



