820 DIAMOND-DEPOSITS OP COPETON, N.S.W., 



lead, oil the south, to a spot half a* mile to the north-west of 

 Cope's Creek on the north. Beyond this point, the Tertiary 

 river-system is completely hidden by basalt-flows as far north as 

 Inverell. 



The western lead has not yet been considered. This was a 

 large tributary stream, which flowed from a spot 10 miles west 

 of Copeton, and joined the main stream at the town itself. The 

 course of this lead is nearly parallel to that of the Gwydir, but 

 the fall is in the opposite direction. The continuity of the lead 

 has been destroyed by several creeks, which have worked back 

 from the Gwydir. The effect of this is, that there now exist a 

 number of isolated basalt-areas with a linear arrangement, yet 

 separated by steeply flowing creeks. The extreme western limit 

 of the lead, which has proved diamond-bearing, is at Oakey Creek. 

 Here a north-flowing tributary of the Gwydir has intersected the 

 east-flowing Tertiary lead, leaving the gravels exposed at the 

 surface on each side of its valley. The deposits were worked by 

 means of tunnels, and both diamonds and tinstone recovered 

 from the wash. It was while driving a low-level tunnel in the 

 granite underlying these deposits, that Messrs. Pike and O'Donnel 

 met with a very remarkable occurrence. The tunnel was found 

 to intersect a large body of decomposed igneous rock, and it was 

 noticed that a great deal of this was found in the wash in associ- 

 ation with that part of it which was richest in diamonds. The 

 dyke-rock is a dolerite. Jt does not outcrop on the hill-slope, 

 but is entirely covered by basalt. 



The diamonds found at Oakey Creek are rather smaller than 

 the average Copeton diamonds, ranging from four to five to the 

 carat. About half the stones recovered are white, and most of 

 the remainder straw-coloured. Few octahedra have been found, 

 and there is no record of bort having been discovered. 



The lead continues through the hill forming the watershed 

 between Oakey Creek and Kirk's Creek, and the gravels again 

 outcrop on the eastern slope of this hill. Here another drive, 

 known as Dodd's tunnel, was put in to reach the wash near its 

 bottom-level. This tunnel, like that at Oakey Creek, also inter- 

 sected a dyke, boulders of which were in the adjacent diamond- 

 bearing wash. 



