AUSTRALIAN MINING-FIELDS 119 



process failed, owing to the presence of barite in the ore, and 

 both ore masses were acquired by a Melbourne mining company 

 as a copper-mine, the gold and silver being recovered as by- 

 products. The attempt was encouraged by the discovery of 

 a huge bonanza of rich silver ore below the Iron Blow in a 

 shoot, doubtless formed by the concentration of silver, leached 

 from the hematite above. 



The geological relations of the ore mass were hidden by the 

 dense forest, nourished by the heavy rainfall on the western 

 coast of Tasmania. But the ore mass was seen to be enclosed 

 in schists, and to occur close beside their contact with a series of 

 quartzites and quartz conglomerates. 



The rocks of the field may be classified as follows : 



Pleistocene : Alluvium, glacial clays and moraines. 

 Mesozoic : Diabase of Mount Sedgwick. 



Palccozoic : Fenestella shales of the Linda Valley (carboni- 

 ferous). 

 Devonian quartzites and conglomerates, isolated 

 blocks of which form Mount Lyell, Mount 

 Sedgwick, Mount Owen, etc. 

 Silurian limestones and shales at Zeehan. 

 Silurian or Ordovician. The quartzites and lime- 

 stone of Queenstown. 

 Pre-Silurian : The Mount Lyell schists: a series of intensely 

 {Archcan ?) altered quartz porphyrites and acid volcanic 

 tuffs, with intrusive dykes and masses of diabase 

 porphyrite. Some of these rocks have been 

 well foliated and altered into quartz chlorite 

 schists with masses of margarodite, with no 

 traces of the original minerals or rock 

 structures. 



The schists form the basis of the whole mining-field, and 

 are exposed beneath the Devonian conglomerates, blocks of 

 which form the summits of the West Coast range. On the west 

 the schists are faulted against the Silurian or Ordovician lime- 

 stones and quartzites of Queenstown. The schists have been 

 regarded as of various ages, from the Archean to the upper 

 Devonian or post-Devonian. As to their precise age, there is 

 as yet no final evidence. They are clearly pre-Devonian and 

 pre-Silurian, and they are the oldest rocks in the district. In 



