OCCURRENCE OF GOLD IN AUSTRALIA. 437 



been found in any sedimentary rock of the Mesozoic or Cainozoic 

 groups or in any Plutonic rock erupted through such strata. 



There is therefore no direct evidence to show that in Australia 

 any auriferous vein has been formed later than Palaeozoic times ; or 

 if it has, it has never had the pluck to show its head above Palaeozoic 

 strata. Moreover the dykes which traverse the Mesozoic and 

 Cainozoic rocks in Yictoria do not resemble in any respect the 

 diorite and other auriferous dykes of Gippsland which traverse the 

 upper Palaeozoic rocks ; but all are augitic in character, similar to 

 the Cainozoic lava-sheets with which they are associated. 



It may be, however, that gaseous emanations, highly auriferous, 

 attended with sufficient force to open old lines of reefs, did take 

 place at the close of the Miocene and preceding the Pliocene 

 volcanic activity, unattended with the intrusion of volcanic material ; 

 but these would more likely form the rich " shoots " in the lodes, 

 so constantly met with in Victorian mines, and not have formed 

 enormous reefs, such as those of Clunes and the Black Hill at 

 Ballarat. 



Further careful observation is required to clear up this subject ; 

 but the result of such inquiry would probably confirm the assertion 

 that the majority of auriferous veins in Australia were formed 

 during the Upper-Palaeozoic period, and were afterwards enriched 

 during both the great Cainozoic volcanic epochs. The Mesozoic 

 seems to have been a period of almost entire volcanic quiescence. 



Tn conclusion, it would seem desirable to note the different modes 

 of occurrence of gold in Eastern Australia, for the information of 

 explorers in other countries : — 



1. In joyritous diorites, e. g. Gooroomjam Diggings, Queensland; 

 alluvial drifts from these contain gold in paying quantity. 



2. In joyritous felsite, e. g. Paddy's and Sharper's Gullies, Cape ■ 

 Diggings, Queensland ; the alluvial drifts from these very rich. 



3. In pyritous granite, e. g. the granite of Bowenf els and Hartley, 

 New South Wales. 



4. In alluvial drifts derived from the degradation of serpentine, 

 c. g. Canoona Diggings, Queensland. In neither of these cases has 

 the rock been found to pay for crushing. 



5. In irregular strings and veins of quartz and other matrix, 

 evidently the result of the decomposition of the auriferous pyrites 

 of TsTos. 1, 2, 3, and their redeposit from chemical solution. 



6. In pyritous quartz and calcspar veins in the rocks of Nos. 1, 

 2, 3, 4 (better defined, more permanent, and wider than those of No. 

 5), whose matrix and mineralization has been derived partly from 

 the bounding rocks, but mainly from the hydrothermal action from 

 below, and which have been repeatedly opened for the introduction 

 of fresh material. E. g. Gympie, Upper Cape, Etheridge, and Mount- 

 Wheeler Diggings, Queensland, the Queensland and New- South- 

 Wales diggings generally, and the Gippsland district of Victoria. 



7. In quartz and other veins in Devonian and Upper Silurian 

 strata in immediate proximity to rocks of Nos. 1, 2, 3 types, e. g. 

 Queensland and New-South-Wales diggings generally, and larger 



