352 Proceedings of the Royal Society of Victoria. 



yield of gold to June, 1904, is about IIH tons; worth 

 £11,150,0<S7. Average value of the gold about £\ Is. Ofd. 

 per oz. 



Geological Hlstory. 



In considering the series of events that have combined to 

 produce Mt. Morgan as it stood when mining operations began, 

 the period preceding that at which the Desert Sandstone sea 

 covered the Mount, will not be considered, as these antecedent 

 events can be more accurately and easily followed when the 

 lower workings are further developed. 



At; the time this sea encroached on the top of the Mount, there 

 was a large area of siliceovis ore bounded by igneous rocks, ex- 

 posed at the surface, that had undergone some denudation, as 

 proved by the position of the " overflow " of Dr. Jack, and this 

 ore had no doubt become oxidized to a greater or less extent. 

 Still, it is not probable that oxidization had penetrated 

 to a very great depth. When the water from the sea 

 spread over this ore with unaltered sulphides near the 

 surface a violent set of reactions appears to have been 

 set up in the area now occupied by the secondary ores. 



Why this special area should have been the centre of so much 

 activity is not apparent, unless it represents a portion of the ore 

 mass more highly charged with sulphides than the rest, or with 

 sulphides more easily oxidizable than in the surrounding mass. 

 The effect of this action was to completely disintegrate the 

 siliceous sulphide mass of ore, and to oxidise the sulphides and 

 dissolve the gold and silver contained in the sulphides. Only a 

 violent mechanical auction, the result of fierce chemical reactions, 

 could have torn this ore apart and reduced it to the condition 

 of saiid and argillacous material, such as formed the secondary 

 ore. The extremely iiTegular manner of the deposition also 

 points out that the water it was laid down in was not by any 

 means quiescent. All the materials found in the secondary ore 

 beds are such as would be furnished by the siliceous sulphide 

 ores ; but the whole of the material supplied by the sulphide ore 

 was not laid down again in the area in which the violent re- 

 actions took place. A great deal of it, in suspension as fine mud, 

 was carried further away, and may now be seen at a lower level 



