Vol. 69.] PETROLOGY OF THE KALGOORLIE GOLDFIELD. 667 



district, such as Ravensthorpe, in which the albite-granites are 

 developed, should help to throw light on these questions. At 

 present, our knowledge of the albite-granites does not materially 

 affect the discussion of the phenomena at Kalgoorlie. 



Quartz-dolerites are also admitted by Mr. Dewey & Dr. Flett 

 among the rocks of the spilite suite : both because of their 

 occurrence along with the Cornish spilifes and albite-dolerites. 

 and because of their occasional (but incomplete) albitization in 

 Scotland, to which may be added also, because of their association, 

 as at St. David's Head, with soda-aplites. It is clear, however, 

 that all quartz-dolerites cannot find a place here. Those of the 

 Tertiary igneous series of Britain, for instance, are associated with 

 rocks of distinctly Pacific type, such as granophyres, and not with 

 soda-felsites or soda-granites. Quartz-dolerites appear, therefore, 

 to be ' diphiletic rocks,' l and it would be interesting to know 

 Avhether any constant raineralogical or chemical peculiarities 

 (such, for instance, as the presence of enstatite-augite) are found 

 in those associated with the spilites. 



At Kalgoorlie, the absence of granophyres, the association of the 

 albite- porphyries with the quartz-dolerites, and the albitization of 

 the quartz-dolerites, are sufficient grounds for the classification of 

 the latter rocks in the spilitic suite, and for concluding that the 

 porphyries and porphyrites belong to the same series of intrusions 

 as the quartz-dolerites. Nevertheless, the analogies with the con- 

 ditions in Britain are not complete, for the albitization appears to 

 have been effected in a somewhat different manner. Mr. Dewey & 

 Dr. Flett remark : 



' Clearly, then, the albitization is a process intimately connected with the 

 nature of the individual rock ; the spilites and quartz-free diabases show it, 



but the quartz-diabases do not The albitization is not characteristic of 



the whole suite, but is especially frequent in certain members of it, such as the 

 spilites and diabases, while others like the quartz-diabases are less liable to this 

 change. It is not due to weathering or shearing. Good evidence exists to 

 prove that the albitization took place soon after the rocks had solidified, and 

 consequently it may be grouped among the post-volcanic or juvenile changes of 

 rock-masses.' (Geol. Mag. dec. 5, vol. viii, 1911, pp. 207 & 246.) 



At Kalgoorlie the albitization has affected quartz-dolerites, but 

 it does not appear to have been caused by solutions emanating from 

 the actual magma that consolidated relatively near the surface as 

 quartz-dolerite. Before discussing this phase of the subject, it is 

 necessary to consider whether the albitization preceded or succeeded 

 the uralitization of the quartz-dolerites. It is just here that the 

 greatest difficulty in the petrography of Kalgoorlie presents itself. 

 Some specimens collected near the boundary of the arnphibolites 

 and the greenstones certainly seem to indicate that the albitization 

 has been effected on the arnphibolites ; but, on the other hand, the 

 perfect preservation of the felspar-prisms in many of the green- 

 stones and bleached greenstones is difficult to account for, if these 



1 See J. A. Thomson, ' On Rock-Specimens from Central & Western 

 Australia ' Journ. & Proc. Roy. Soc. N.S.W. vol. xlv (1911-12) p. 316. 



