ON THE ROCKS OF TIIP] IIAUKAKI GOLD-FIELDS. 2G7 



clently to a land-slip, and tliese veins contained gold.* We can 

 hardly suppose that the thermal springs have brought up gold so 

 near to the surface and at so recent a period, and yet have left no 

 other evidence of their existence. 



The fifth argument is founded on the quality of the gold itself, 

 which is an electrum similar to that found in similar volcanic 

 rocks in Hungary and Nevada, but different from that usually 

 found in older formations. 



I think therefore that we must look to the volcanic rocks 

 themselves for the source of the gold, and with the gold the quartz 

 also ; and that we may dismiss all idea of either of them ha\-ing 

 been brought up by thermal springs. If the quartz of the buck- 

 reefs, which are either barren or do not contain more than lOdwt. 

 of gold per ton, is also due to lateral segregation, as appears 

 probable, then we may suppose that, in these cases, the greater 

 pai't of the gold was deposited from solution in the feeders before 

 reaching the main fissure. It is more probable that the bulk of 

 the gold should have been deposited in the fissures which were 

 fee ling the buck-reef, than that the whole of the gold should have 

 come from the buck-reef aiul the bulk of it should have passed out 

 into the small fissures. The pi^ocess I have suggested seems to 

 have taken place at Coromandel, and at Te Aroha, but Mr. Cox 

 has pointed out that in the Moanataiari Mine an auriferous vein, 

 with clearly defined walls, crosses a buck-reef obliquely, f In this 

 case undoubtedly the buck-reef is the older of the two, but this 

 single fact is not sufficient to form the basis of an induction that 

 all buck-reefs are older than the auriferous viens. 



Sir James Hector is of opinion that " the quartz which forms 

 the veins and infiltrates the auriferous gangue must have been 

 introduced into these rocks subsequent to their original formation, 

 but not derived from their partial decomposition, as the rocks 

 themselves are deficient in silica, considering the felspathic nature." J 

 But my microscopic examination of the rocks has shewn that large 

 quantities of silica have been removed from the bisilicates and 

 from the felspars, only small portions having remained as secondary 

 quartz, and this silica must have gone somewhere. That the 

 rocks are noiv deficient in silica, goes far to disprove the opinion 

 which Sir James Hector would found upon it. 



Indications of favourahh Country-rock. — Mr. Cox says that 

 "the white fairly hard stone is the best country," that "reefs in 

 good ground are remunerative but in hard ground do not pay," 

 that " hard green dioritic belts and jointy or shingly ground am 

 not good for gold," that " moderately hard country tr; 

 small veins and of a pyritous nature near the reefs is tl 



* Reports Geological Explorations, 1868-9, p. 26, fig. 2. 

 t Reports Geological Explorations, 1882, p. 25 

 I Reports Geological Explorations, 1S68-9, p, 27. 



