828 



DIAMOND-DEPOSITS OF COPETON, X.S.W. 



eiated with diamond-beariug gravels. These have been mentioned 

 in c-ouuection with the Tertiary deposits at Oakey and Staggy 

 Creeks. A petrologieal description of the rocks, and an analysis 

 from each locality, are given under the section on Petrology. It is 

 evident that the rocks are very similar in chemical and physical 

 characters. The analyses show that they differ considerably, in 

 chemical composition, from the peridotite of the South African 

 mines. The Oakey Creek occurrence (Plate xci.. fig. 1) deserves 

 special mention. The plan (Text-fig. 4) illustrates the position 



0«kev Ck Turjiei 



Text-fig.5. — Section illustrating the dolerite-dyke at Oakey Creek, 

 and known extent of the dolerite-mass at Oakey Creek. The section 

 (Text-fig. 5) shows the relationships of the dyke, granite, river- 

 gravels, and basalt. The linear development and the plane slicken- 

 sided wall, showing in one of the drives, enable the mass to be 

 classed as a dyke. It is 26 feet wide in the main drive, and is a 

 considerable width at a distance of 500 feet to the south of this 

 drive. The width here cannot yet be determined, as the open cut 

 has disclosed only one boundary of the dyke-mass. There is very 

 clear evidence that this dyke was older than the river gravels 

 overlying it, as an exposure in the easterly drive shows the contact 

 of these. Moreover, decomposed boulders of the dyke-mass are 

 abundant in the river-gravels. 



The dyke intrudes the Oakey Creek granite, and the junction is 

 sharp and well defined. Though there is no marginal differentia- 



