Fi'SLAYSON. ^Geology of Quartz Veins of Otago Goldfields. 



69 



The lode-formation varies in width from 8 ft. to 20 ft., and has generally 

 defined walls with tough clay casings. The value of quartz varies from 

 5 dwt. to 20 dwt. per ton. The gold is fine, hackly, and free, the extraction 

 being about 80 per cent, by mill amalgamation. The pyrite is auriferous, 

 but not by any means rich enough to warrant the treatment of the pyritic 

 lode-formation, as some promoters would have us believe. 



In places, more especially near the surface, the lode-formation contains 

 bands of a soapy yellowish-grey rock, especially near quartz, and devoid of 

 pyrites. 



The following analyses indicate the normal mode of alteration : — 



H.O 



SiOa 

 Al.Os 



Fe^Os 

 FeO 



CaO 



MgO 



KgO 



Na.,0 

 Mnb 

 TiO, 

 CO., 



FeS., 



100-01 



100-88 



86-43 



+ 



Unaltered country rock. 

 Altered lode-formation. 



4-64 

 18-22 



-13-58 



Altered lode-formation, recalculated on a basis of constant alumina. 

 Gains and losses of altered rock. 

 These figures show — (1) that a good deal of replacement has occurred 

 injconnection mth the segregation of quartz ; (2) that the type of rock- 

 alteration may be regarded as partial sericitization. ■ 



The following analyses indicate the nature of the yellowish altered rock : — 



