810 DIAMOND DEPOSITS OF COPETOX, N.S.W., 



flattened and waterworn. It is evident that they have travelled 

 a considerable distance, having probably been derived from 

 jasperoid bands in the slate-formation. At Benson's farm, 

 better known, perhaps, as the Old Farm, the wasli is unusually 

 coarse, boulders up to 20 cm. in diameter being very common. 



In some places, the wash has undergone secondary change, as 

 at Kirk's Hill, and the Banca mines. Here, a very common 

 feature is what is locally known as the iron-band. This is a 

 layer of wash which has been cemented by the infiltration of 

 iron-bearing waters. It so happened that the wash, thus altered, 

 was rich in diamonds, and a considerable quantity of it has been 

 profitably mined. It w^as found that the band was too hard to 

 be crushed without risk of fracturing the diamonds. This diffi- 

 culty was overcome by heating the material on iron. plates, care 

 being taken not to raise the temperature to the combustion-point 

 of the diamond. The differential expansion of the diamond and 

 its host caused the stones to become freed by this method. 



The second zone of the deep lead deposits— ^Ae drift— con- 

 stitutes by far the greatest bulk of the material. The sands 

 comprising this possess a grain-size of about 2 to 3 mm., and 

 frequently enclose one or more subsidiary layers of wash. The 

 maximum thickness observed was about 35 feet at the Round 

 Mount. Some of the grains are waterworn, while others are 

 angular, but there is nothing very distinctive about the main 

 mass of the material. It is not found to contain diamonds in 

 payable quantities, even where the gems are most abundant, 

 though occasional stones have been recovered from it. 



The third zone — comprising fine mud and clay — occurs only 

 at a few places on this field. At Rider's lead, the most notice- 

 able feature is the presence of a large body of pipeclay, which 

 overlies the gravels of the diamond-bearing wash. This portion 

 of the lead has been worked for nearly a mile, and the bed of 

 pipeclay has been found practically continuous throughout that 

 distance. The clay is a soft, white material, almost pure kaolin, 

 and has an average thickness of about 2 feet. Below it, lies the 

 drift, and below this, again, is a bed of wash, from a few inches 

 up to a foot in thickness. The whole series is covered by a con- 



