142 



OHSKRYATIOXS ON THE OCCURENCE OF GOLD, ETC. 



from a special enlargement of the vein, or what the miners 

 term " a blow," and consequently it may be expected that the 

 extension, horizontally on either side of the first discovery, will 

 present a narrower but well detined lode of aui-iferous pyrites 

 but that the lode at the point of discovery will continue of con- 

 siderable dimensions to some depth, and that the whole will 

 prove to be a true metalliferous vein of the class 

 which extend downwards beyond the limit of practical mining 

 operations. 



The general geological features of the country are those of a 

 granitic anticlinal axis with thick beds of serpentine rocks and 

 altered slates of the Devonian period resting on the flanks, 

 wdiile horizontal sandstones of mesozoic age are found capping 

 some of the hills and i-anges, but have been largely removed 

 by denudation. 



It is chiefly in the Devonian rocks that metalliferous deposits 

 are found, and more especially where they have to some extent 

 been altered to serpentine, while the existence of veins of 

 magnesian silicates may be considered a favourable indication 

 of auriferous deposits. 



As most of the gold workings in this district, and indeed in 

 Australia, have been in auriferous quartz, with only a propor- 

 tion of auiiferous pyrites, the existence of a large deposit, 

 almost exclusively consisting of auriferous pyrites, is no doubt a 

 novelty to miners accustomed to other conditions ; but in 

 Europe and America pyrites have been worked for more than a 

 hundred years with pi-ofit, even when the gold has been less 

 than one niillioiith part of the ore. 



One important consideration in working gold ores of the 

 character found at Mount Morgan is that the ordinary stamp 

 mills with amalgamated plates and mercury riffles, though they 

 may collect a considerable part of the gold, will fail to save a 

 large percentage of the very fine gold, both on account of the 

 pai'ticles being covered with oxide of iron, and also that the 

 oxide of iron having a higher specific gravity than quartz 

 is more difficult to seperate by washing ; and it will be 

 necessary to subject the whole of the finer part of the tailings 

 to amalgamation in pans or barrels, in contact with mercury 

 and wrought iron. 



Fortunately the surface ore at Mount Morgan is so com- 

 pletely oxidized by atmospheric action that the whole of the 

 sulphur has been dissipated, and only gold, oxide of iron, and 



