803 



THE DIAMOND-DEPOSITS OF COPETON, NEW SOUTH 



WALES. 



By L. a. Cotton, B.A., B.Sc, formerly Linnean Macleay 

 Fellow of the Society in Geology. 



(Plates xc.-xcii.) 



CONTENTS. 



PAGE 



i. Introduction 803 



ii. The Natdre of the Leads — The Tertiary gravels — The wash — 



The drift—The clays— The lignite deposits 804 



iii. Physiography — Present course of Gwydir — Prebasaltic course of 



Gwydir... ... ... ... ... ... ... ... ... 811 



iv. Distribution of Diamond-Leads— The Rider's Lead — Deep Shaft 



Lead -The Oakey Creek — Soldier Hill Lead 815 



V, Geology — The clay-slates — The granites — Basalt-flows, Dykes — 



Relation of these rocks to the distribution of the diamonds — 



Oakey Creek and Staggy Creek dolerites ... ... ... 825 



vi. Petrology — Oakey Creek granite ; quartz-dolerite from Oakey 



Creek and Staggy Creek — Analyses ... ... ... ... 830 



vii. Summary 835 



i. Introduction. 

 The Copeton diamond-field has its centre of activity at Copeton, 

 a small township on Cope's Creek, about two miles above its 

 junction with the Gwydir River. It is thus on the western edge 

 of the New England tableland. The present paper is the result 

 of observations made during June, 1909, May, 1910, and January, 

 1913. A number of investigators had previously given some 

 attention to the field, and several papers have been published in 

 connection with it. The earliest report which I have been able 

 to trace, is that of Mr. C. S. Wilkinson(lO) to the Surveyor- 

 General, in July, 1873. In this report, he refers to the opera- 

 tions of the Borah Tin and Diamond Mining Company on the 

 alluvial drift, which, he suggests, has been derived from the 

 denudation of the deep leads. It is now known that this sugges- 

 tion is the correct one. Other reports have been furnished from 



