Vol. 69.] PETROLOGY OF THE KALGOORLIE GOLDFIELD. 671' 



V. Summary and Conclusions. 



In this paper an attempt has been made to show that, by means 

 of detailed microscopical and chemical study, carried out hand in 

 hand with mapping-, it is possible to unravel the structure of such 

 a district of serpentines, amphibolites, and greenstones as most of 

 the Western Australian goldfields present. The petrographical 

 methods on which most insistence has been placed are the inter- 

 pretation of pseudomorphs of earlier minerals and the recognition 

 of relict-structures revealing the original inter-relationships 

 of these minerals. By these methods a fairly clear picture of the 

 original rocks may be restored, while a knowledge of the chemical 

 composition of the rocks in question gives valuable aid in checking 

 or corroborating the results obtained. It is found that most of the 

 coarse-grained amphibolites of the goldfields of Western Australia 

 were originally pyroxenites, hornblende-dolerites, dolerites or 

 gabbros, and quartz-dolerites or quartz-gabbros, and all these 

 types occur in Kalgoorlie associated with serpentines derived 

 from pyroxene-peridotites. In addition, there is present in Kal- 

 goorlie and elsewhere an older series of fine-grained amphibolites 

 Avithout recognizable relict-structures, but having the chemical 

 composition of basalts. Corresponding to all of the above types of 

 amphibolite there are greenstones consisting mainly of chlorite,, 

 carbonates, and sericite ; but greenstones that were formed from 

 the pyroxenites and hornblende-dolerites are rare and unimportant. 

 In Kalgoorlie a distinctive feature, not recorded elsewhere in the 

 State, is the abundance and importance of albite-bearing greenstones 

 obviously formed by the albitization of quartz-dolerites, and also 

 the presence of dykes of albite-porphyry and albitized porphyrites, 

 which clearly have a close connexion with the albitization. On 

 these grounds it is suggested that the whole series of intrusive rocks- 

 at Kalgoorlie belongs to the spilitic suite, and that the formation 

 of the telluride gold-lodes is due to after-emanations of the spilitic 

 magma. A classification of auriferous deposits according to theii" 

 genetic connexion with magmas of Atlantic, Pacific, or spilitic 

 f acies is a natural corollary of this view. 



While much of the latter part of the paper may be regarded as 

 suggestive rather than conclusive, it furnishes a basis for future- 

 petrological studies in the other goldfields of Western Australia. 

 Such studies will in turn throw light on some of the complexities 

 of Kalgoorlie. 



To Dr. J. M. Maclaren I am indebted for permission to publish 

 those parts of this paper which refer exclusively to Kalgoorlie : for 

 the work was carried out on his behalf, in the preparation of a 

 report on the economic geology of certain groups of mines. The- 

 field-work was carried out in association with him, and the bearing 

 of the petrological results was discussed with him at every turn. 

 But, after the development of the theory of the spilitic suite in 

 Great Britain, certain views as to the relationship of the rocks,. 



