FiNLAYSON. — Geology of Quartz Veins of Otago Goldfields. 



73 



east and west, and standing almost vertically. These are well shown on 

 the plan, and it will be seen that there is also a subordinate series of diagonal 

 veins crossinsr them. 



The lode-matter consists of crushed and altered schist, impregnated 

 with pyrites and traversed by defined and continuous seams of quartz, 

 which may run on either or both walls, occasionally occupying the whole 

 width of the vein, with frequent splits and branch stringers. The quartz 

 seams often show a very fine comb-structure. 



In the upper levels the ore was oxidized, and extraordinary values 

 were frequently obtained from small patches near the surface. In depth' 

 the ore is reported to be refractory, and sulphides — pyrite, galena, and 

 blende — become prominent. 



The individual veins have been described in detail in Bulletin No. 5, 

 N.Z. Geological Survey. The group also includes the Alta scheelite-vein, 

 which lies about three miles to the east of the main grouj). This seems 

 another instance of the segregation of ores. 



^'^ct.^ O* 



BENDIGO VEINS 



Surveys by G. F. Hosking 



Si-u/f o/ Chains. 



Bee Vein 



Hit or Miss Vein 



The Si/stem of Fissures. — The Bendigo group illustrates the sheeting of 

 rock by fissures, discussed many years ago by Emmons in his " Structural 

 Relations of Ore-deposits.''* It is also noteworthy that the best ore was 

 largely obtained from the neighbourhood of intersections wath the cross- 

 fissiires — an instance of ore-shoots at intersections. The minor cross-veins, 

 in fact, besides being payably auriferous, served as reliable indicators. At 

 the intersections a mutual displacement frequently occurred — a phenomenon 

 characteristic of crossing fissures, even when formed simultaneously. 



The cross-veins are doubtless the result of shearing stresses set up in the 

 rock at the time of formation of the main fissures, the compound fissure- 

 lines being opened in such directions as would best relieve the strain. 



* Enimous, " ScructuvAl Relations of Ore-depo iits," Trans. Amer. Inst. Min. Eng., 

 vol. xvi, p. 821. 



