Finlayson. — Schists of Central Otago. 11 



is composed of altered olivine rock, and sections show the 

 characteristic mesh structure of serpentine derived from -olivine* 

 Where least altered, it is a black serpentine rock, showing occa- 

 sional good cleavage-surfaces of hypersthene. The serpentine- 

 in more-altered portions graduates into talc, and the rock is 

 traversed by veins of calcite and chrysotile asbestos. 



The surrounding rock is a fine-grained mica-schist with a 

 band of fine chlorite-schist. For a distance of 6 ft. from the 

 contact the mica-schist has been altered into a highly quartzose 

 schist, with a striking development of biotite blades arranged 

 across the foliation - planes. The chlorite - schist shows, as a 

 result of the intrusion, numerous actinolite needles. This 

 development of the magnesia minerals, biotite and actinolite, 

 is a characteristic contact- effect of magnesian intrusions. 



Moke Creek Dijke. 



This occurs on the right bank of Bushy Creek, 300 yards 

 above its junction with Moke Creek, between Kilpatrick and 

 Moke Lakes. It lies on approximately the same line of strike 

 as the Moke Creek copper lode, and is, like the other, a serpent- 

 inked olivine rock. The outcrop is very obscure, and highly 

 weathered into a talcose serpentine, with remnants of massive 

 dark-green serpentine. 



This dyke is particularly interesting, in that an analysis- 

 of the serpentine showed it to contain 0-075 per cent, of copper. 

 Copper - ores are frequently associated with magnesian rocks, 

 and. this proximity of a copper - bearing dyke to a copper lode 

 strongly suggests that the ore in the lode has been formed from 

 a previous concentration of the ore in an ultrabasic magma 

 beneath. 



5. On the Presence of Segregated Gold in the Schist. 



The majority of writers — notably Hector,* Ulrich,f McKay,}: 

 and Rickard§ — in order to account for the vast amount of alluvial 

 gold in Otago, claim that the schists carry gold segregated in 

 the quartz laminae. In the first place, the contention is un- 

 necessary, as is evident from a careful study of the lodes 

 in Otago. In the second place, only two examples have 



* Sir J. Hector, " Outline of New Zealand Geology " (Wellington, 

 1886), p. 83. 



t Hntton and Ulrich, " Geology of Otago " (Dunedin, 1875), p. 157. 



J A. McKay, "Gold-deposits of New Zealand" (Wellingtcn, 1903), 

 p. 68. 



§ T. A. Rickard, " Goldfields of Otago," Trans. Am. Inst. Min. Eng., 

 vol. xxi, p. 442. 



