80 



Diorites and Granites of Swift's Greek, 



no great depth from the surface. It may, perhaps, be of 

 some significance that, when the reefs discontinue, the dioritic 

 rocks, as a rule, cease to be decomposed. Some few auriferous 

 reefs have been discovered, and worked within the diorite 

 area ; but in these cases isolated patches of contact schists 

 associated with them prove that the general absence of these 

 rocks is in reality only due to denudation. The occurrence 

 of these quartz veins in the decomposed diorites adjoining 

 sediments is paralleled by the occurrence of auriferous quartz 

 veins in decomposed or mineralised dykes elsewhere. 



At Swift's Creek the auriferous and metalliferous quartz 

 veins are evidently connected with a vast mass of intrusive 

 and often granitic diorite. In other parts of Gippsland 

 auriferous quartz veins are found in connection with dykes 

 of similar mineral character. I take as instance the dyke 

 and reef at Kafhr's Hill, Stockyard Creek, and the dyke and 

 reef at Walhalla. . 



I^ggftl 



Diagram No. 7.— Dyke and Reef at Stockyard Creek. 



(a.) Silurian (upper ?) mudstones. 



(6.) Granitic dyke. 



(c.) Auriferous quartz veins. 



In this instance the auriferous quartz veins pass through 

 the dyke, and penetrate the sediments on each side. The 

 dyke, which is from a few feet to 200 feet in width, is almost 

 completely decomposed ; indeed, so much so as to rapidly 

 crumble away when brought to the surface. The outline of 

 porphyritic felspar crystals in a kaolinised state can be recog- 

 nised in the more granular portion. No hornblende or mica 

 is visible in this rock, nor could I determine whether any 



