ORIGIN AND MODE OF OCCURRENCE OF GOLD-BEARING VEINS. 129 



Fig. 5 is in Gippsland, at the Crooker River, and had a 

 thickness of abont eighteen inches, and for a depth of 80 feet 

 gave an average yield of over two ounces and a half of gold to 

 the ton. 



Fig. 6 was also about eighteen inches thick, and yielded 1^ 

 ounces to the ton, being very rich in arsenical pyrites. It was in 

 the same locality as Fig. 5. 



Both these examples have been taken from Brough Smyth's 

 work referred to, and have been chosen on account of their being 

 good illustrations of this class of quartz vein. 



The dyke lodes of Victoria are certainly a most peculiar class 

 of auriferous deposit. They consist of dykes, or what appear to 

 be dykes, of either a decomposed igneous rock or a sedimentary 

 one which has been very much altered. In some cases they have 

 much the appearance of decomposed diorite, whilst in others they 

 are described as having a slaty cleavage. The'auriferous portions, 

 however, consist chiefly of narrow nearly horizontal veins of 

 quartz, some of which intersect the dyke at right angles to its 

 dip, while others lie nearly parallel with the walls, occurring in 

 strings or lenticular bunches. 



The horizontal veins are like thin floors of quartz, and some of 

 these pass out of the dyke and for a short distance into the 

 containing walls. 



There can be little doubt that in many cases these belts of 

 decomposed or partially decomposed rock are true dykes of igneous 

 origin, in which the veins of quartz have been subsequently 

 formed. They have often been proved to be very rich, but are 

 seldom continuous to a great depth, being cut off in many cases 

 by a hard undecomposed igneous rock, from which it appears 

 probable that the dykes are offshoots. The Waverly dyke, of 

 which I give a section (Fig. 7), and the Morning Star dyke 

 (Fig. 8), are examples of this class of deposits. 



The pipe veins are also a class worthy of particularizing as 

 being a mode under which quartz veins are sometimes found in 

 Victoria, and it may not be out of place to mention here that 

 many of the quartz reefs both in that and other parts of the 

 colonies, dip on their strike or bearing. Instances and examples 

 of this will be given further on in treating of the New South 

 Wales gold veins. 



One of the most interesting districts in Victoria to the 

 Engineering Mineralogist is that of St. Arnaud. This place 

 contains a perfect net-work of quartz veins intersecting the strata 

 at all angles, and occurring so close together and sometimes of 

 such large dimensions that the question of how they were all 

 formed, and what relation they may bear to each other, is a. 



I-September 7. 1887. 



