Vol. 69.] PETROLOGY OF THE KALGOORLIE GOLDFIELD. 629 



■only a few specimens of the more obscure greenstones. Dr. L. J. 

 Spencer 1 cast some doubt on the derivation of the lode-matter from 

 ■an amphibolite, being deceived by the thorough-going chemical 

 alteration which the bleached greenstones and ores have undergone. 



' No hornblende was detected on any -of the British Museum specimens [of 

 ■telluride-ores], and in published analyses (Simpson, 1902) of these rocks the 

 •small amount of magnesia in the portion of the rock insoluble in hydrochloric 

 acid indicates that not much, if any, hornblende can be present. Bands of 

 hornblende-schist are no doiibt sometimes present in the sericite-schist. Much 

 •confusion between observed fact and theory has been occasioned by 'the 

 attempts of various authors to explain the origin of these schists.' {Op. cit. 

 p. 281, footnote.) 



During 1.909-10, while Dr. Maclaren and myself were engaged 

 in mapping the field, geological work was also being carried on by 

 Mr. C. 0. G. Larcombe, of the Kalgoorlie School of Mines, and 

 Mr. C. G. Gibson, of the Western Australian Geological Survey. 

 A limited exchange of views took place, and the resulting classi- 

 fications 2 show, in consequence, some approximation to each other 

 (see Table, pp. 626-27). Mr. Gibson has not yet presented the 

 petrographical details that led to his conclusions, but it may be 

 noted that he failed to recognize the original rocks from which the 

 amphibolites were derived, while correctly assigning the greenstones 

 to quartz-diabase. Mr. Larcombe dealt mainly with the rocks of 

 '* The Mile,' and, in consequence, has failed to realize the intrusive 

 nature of the quartz-dolerite, which he terms ' quartz-andesite.' 

 Neither of these writers has recognized the albitization of the 

 greenstones, nor the close relationship between the albite-porphyries 

 and the quartz-dolerites. 



III. Descriptive Petrography. 

 Through the kindness of Mr. A. Gibb Maitland, Director of the 

 Geological Survey of the State, all the rock-specimens and micro- 

 scopic sections of Kalgoorlie rocks in the Survey collections were 

 placed at my disposal. By this means it has been possible to 

 identify the rocks of which analyses had previously been published, 

 and to use these analyses in connexion with the classification here 

 adopted. Including the Survey collection, about 500 thin sections 

 have been examined in the preparation of this paper, this apparently 

 excessive number being necessitated by the great variations which 

 the metasomatized quartz-dolerites and peridotites display, and by 

 the lithological resemblances between altered rocks of very different 

 origin. Obviously, for purposes of brevity and clearness, only the 

 more conspicuous types can be described here, and preference 



i ' Mineralogical Notes on Western Australian Tellurides: the Non-Existence 

 of " Kalgoorlite" & " Coolgardite" as Mineral Species' Min. Mag. vol. xiii 

 (1902-1903) pp. 268-90. 



2 O. Gr. Gibson, ' Notes on the Principal Geological Features of the Kalgoorlie 

 Goldfield ' Ann. Rep. Geol. Surv. W. Austral, for 1910 (in Ann. Rep. Dept. 

 Mines, W.A., published 1911) pp. 115-23 and map ; C. O. G. Larcombe, 'The 

 •Geology of Kalgoorlie (Western Australia) with special reference to the Ore- 

 Deposits' Proc. Austral. Inst. M. E. vol. v, No. 2 (1911) pp. 1-312. 



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