THE DEVELOPMENT OF MINING IN AUSTRALASIA. 225 



Attention was then directed to deep leads, or deposits formed 

 by rivers which had flowed during earlier geological times, and 

 which had since been buried up by flows of basalt that had 

 protected them from the denuding action of the fresh streams, and 

 preserved their wealth intact. 



Large sums of money were invested in opening, proving, and 

 working these deep leads, especially in the neighbourhood of 

 Ballaarat, where they have proved exceedingly rich and paid 

 handsome dividends. 



Reefs moreover have received much attention, and in many 

 localities, have yielded very large returns of gold. 



Perhaps the most valuable mine in the colonies has been the 

 " Caledonian " at the Thames, New Zealand, which paid no less 

 than £552,000 in dividends during one year, but many others 

 have been very rich and have paid very well. Even the reefs 

 however, with few exceptions, have not been worked far below 

 tlie water level, for when the stone became pyritous and the 

 proportion of fi'ee gold decreased, the difiiculties and expenses of 

 treatment deterred speculators from undertaking the necessary 

 outlay to carry on the works, and for several years gold mining 

 was by no means so flourishing as heretofore. There were however 

 some mines in which works were carried down to considei-able 

 depths, as for instance on the saddle reefs of Sandhurst, and in 

 other localities, and the working was conducted so judiciously 

 that a very small yield was suflicient to pay working expenses, 

 and dividends were declared on stone yielding only a few penny- 

 weights per ton. 



The discovery of gold in ironstone at Mount Morgan gave a 

 fresh impetus to this branch of mining and necessitated the 

 adaptation of a process which would deal with such fine gold, 

 a proportion of which was coated with a thin film of oxide of iron. 

 The result was that Messrs. Newbery and Vautin patented a 

 chlorination process, which with cei'tain modifications, has been 

 found to be perfectly satisfactory, and this process has since been 

 adapted to the treatment of pyritous ores. 



The reefs which have been worked hitherto are chiefly in 

 Silurian rocks in Victoria, New South Wales, and Queensland, 

 while beds of Devonian age are also traversed by reefs carrying 

 gold. In New Zealand, on the other hand, while reefs have been 

 worked on a small scale in the Silurian rocks of Otago, the most 

 important are those of Reef ton, in slates, etc., of Carbonifei'ous 

 age, and tufaceous beds of probably Cretaceous age at the Thames. 



The copper oi-es which have hitherto been worked in Australia, 

 appear to be always associated with rocks of Silurian age, and 

 very frequently with dykes of diorite. The remarkably rich 

 surface deposits of the Burra Burra mine in South Australia 

 seem to have been formed by a secondary action, the soil, and a 

 limestone which rests unconformably upon the Silurian beds 

 P 



