58 J. A. Dunn : • 



(c) Secondary Minerals. — Quartz is the chief secondary- 

 mineral. Practically all the Bendigo rocks are silicified to a 

 greater or less extent. This secondary silica occurs either in the 

 ground-mass, or at times it forms small angular grains of quartz- 

 which have grown from definite points by force of crystallisa- 

 tion ; this often gives the appearance of a sandstone to what was 

 originally a slate. At other times the quartz acts as a border 

 to secondary cubes of pyrite, generally bordering the quartz, 

 only in the direction of the cleavage of the slates. - 



Chlorite is an important secondary mineral. In part this ap- 

 pears to have been brought in with the secondary siliceous solu- 

 tions, but occasionally it is secondary to muscovite, biotite and 

 tourmaline. 



Mineral carbonates, probably ankerite, are common as second- 

 ary minerals, generally replacing the ground-mass of both slates 

 and sandstones, and occasionally replacing grains of felspar. 

 These carbonate's also appear to have accompanied the secondary- 

 siliceous solutions. 



Pyrite, pyrrhotite, arsenopyrite, sphalerite, and galena occur 

 distributed throughout the whole series. They occur 

 both irregularly, and with definite crystal boundaries, and are- 

 probably contemporaneous with the siliceous solutions. 



Leucoxene is secondary after ilmenite. The greater part of 

 the sericite is also secondary, particularly in the slates and' 

 ground-mass of the sandstones — it is evidently the alteration-, 

 product of the clayey material of the original sediments. 



Heavy* Liquid Sepapation of Minerals. 



By means of heavy liquids, the minerals occurring in small 

 quantity in a sample of sandstone were isolated and examined, 

 as grains under the microscope. A typical sandstone from the 

 2400 feet level of the Sea Mine was crushed, then ground in 

 a disc crusher, and passed first through an 80-mesh sieve, then 

 part through a 100-mesh, thus giving two grades of fineness.. 

 These were then weighed : — 



2817 grams through 100-mesh. 

 438 grams through 80 mesh, and over 100-mesh. 



3255 grams total. 



These grades were each panned oflf separately to ensure cleaner- 

 panning. Residues were panned three times to have a minimuirt 



