448 Transactions. — Geology. 



The presence of gold in these reefs appears to depend upon a variety of 

 circumstances which are not yet thorouglily understood ; I may, however, 

 mention a few essentials which have been observed. The first of these is 

 that the reefs should be passing through moderately hard compact country, 

 and where this is traversed by thin black pyritous veins which junction 

 with the reef, the character of the country may be looked upon as more 

 favourable. Where any reefs are found passing through this class of 

 country they are generally more or less auriferous, and this is specially 

 noticeable in the large reefs of the district. There are, however, in addition 

 to the large reefs, innumerable small leaders, from Jg- inch thick up to a 

 few inches, which, while following approximately the same strike as the 

 other reefs, are as a general rule somewhat steeper ; and where these junc- 

 tion with the main reefs in favourable country, very rich deposits of gold 

 are frequently met with. Besides these hanging-wall leaders there are also 

 many droppers from the foot- walls of the reefs in which also rich gold is 

 often found, and they give one the impression of being leaks, if I may use 

 the term, from the main reef, by which some of the gold has escaped. 



The character of these deposits points most conclusively to the fact that 

 the greater quantity of the gold in the reefs was deposited from solution, 

 and the fact of the junctions of different leaders making the gold, leads one 

 to believe that it was only where two streams, carrying the necessary ingre- 

 dients in solution, met and mingled that any precipitation of gold ensued 

 and a deposit of the precious metal was formed. 



There are many other points bearing upon the behaviour of the reefs 

 which are of great interest, but which it is not my province to discuss here. 



That all the gold in these reefs is not derived from the same source, is 

 I think, however, apparent, for that which is crystallized or occurs in 

 dendritic forms, would owe its origin to super-heated steam, in the same 

 manner as the last described set of rocks, and the description of gold with 

 native arsenic from the Kapanga Mine, Coromandel, which will be found 

 under the head of arsenic, offers a very striking illustration of this. 



With regard to alluvial gold but little need be said. The principal 

 alluvial fields are those of Otago and the West Coast, with some smaller but 

 still important ones in the Nelson district, and the alluvial gold partakes 

 of the same characters as that obtained from the reefs. Large nuggets are 

 rare, indeed the largest which has been obtained is one from Eocky Eiver, 

 Collingwood, weighing lOozs., and another from the same locality weighed 

 8 ozs. These are mentioned by Dr. v. Hochstetter, (New Zealand, p. 100.) 



Gold is also obtained from what are known as the Cement workings, 

 at Tuapeka, and elsewhere. These cements consist of heavy gravels which 

 have been consolidated, and are the remains of an old glacier or glacial river. 



