Mount Morgan Gold Mine. 353 



on the sides of the Mount, covering the rocks and surface as 

 exposed before the Desert Sandstone was laid down. This bulk 

 of " overflow " should, roughly, represent the space left in the 

 secondary ore, and subsequently filled in by a plug of Desert 

 Sandstone, plus, perhaps, some of the material subsequently 

 leached (uit from the sulphides at lower levels. 



The sand of the secondary ore came from the siliceous com- 

 ponent of the ore, the aluminous material from the kaolinised 

 dykes, etc.. and perhaps from portions of the ore either in the 

 form of solution or suspensin, or both ; the limonite was sup- 

 plied by the decomposition of iron pyi'ites. As solvents of gold, 

 supposing the Avaters were sea water's, there would be chlorine, 

 bromine, iodine, etc. 



When the more violent conditions ceased, the materials filling 

 a basin shaped cavity began to re-arrange themseh^es, and first 

 the heavy iron solutions and the coarse sandy particles were 

 laid down, and with these much of the gold in solution was 

 deposited, but not the silver ; and this would imply that con- 

 ditions prevailed favouring the deposition of gold, but not 

 silver, from the solutions. In this way the gold was so com- 

 pletely parted that it approached chemical purity. 



Although an area above described was subject to powerful 

 action, by which the ore was completely disintegrated, the rest 

 of the area of sulphide ore exposed to the same action was not 

 disintegrated, but the sulphides were merely oxidised and 

 leached away, leaving the siliceous skeleton standing at the 

 surface ; this was usually nearly black from manganese oxide. 



Just as the disintegiuted portion of the ore only extended 

 on the surface over a certain area, so downwards the disintegra- 

 tion was also limited. The deepest point was about 150 feet 

 from the surface, but over much of the area the depth was 

 much less than this. So that beyond the limits of the disin- 

 tegrating forces the chemical reactions appear to have been less 

 active ; perhaps they were slower, and possibly the sulphides 

 were less plentiful or of a different composition. 



Still, oxidization and leaching of the sulphides continued long 

 after the disinte^Tating forces ceased to act. and may ha 

 continued down even to the present time. 



